MODERN STUDIO TECHNIQUE See Page 460 · You are trained right in modern, daylight shops on Radio, Sound and Television equip- ment under the personal supervision of expert instructors

Milestones in Broadcasting - Making a High -Fidelity Broadcast Receiver How to Make a "Free Reference Point" Analyzer -War -Time Uses of Radio

February 25 Cents in United Sf.ta

and C.n.1.

HUGO GERNSBACK Editor

MODERN STUDIO TECHNIQUE

See Page 460

OUTST IILZATURE

89 DELUXE TUBE TESTER

Mr. Serviceman. 1936 is your big year of opportunity. More p power than at any time in the last six years. A Presidential elec lions of additional listening he urs will be added to the wear and Your service equipment must 1 pep as up -to -date as the newest radio se

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(THE eC S` DIAGRAMMED }

RADIO -CRAFT for FEBRUARY, 1936 449

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CONTENTS -FEB., 1936, ISSUE Volume VII Number 8

Editorial: Needed Broadcast Reforms -.H go Gernsback 453

The Radio Month In Review. 454

Milestones in Broadcasting W. E. Schrage 456

Radio Pictorial 458

Modern Studio Technique W. Palmer 460

Making a 12 -Tube High -Fidelity Broac cast Receiver Part I M. H. Gernsback 461

How to Make a "Free- Reference -Point' Set Analyzer W. C. Bellheimer 462

2 New Metal Tubes F.. M. Purinton 463

Testing Metal -Tube Sets with Present Equipment F. L. Sprayberry 463

Make this "Radio" Motor- Nathan I. Hall 464 A Novel, Self- Matching Output Transformer

C. E. DeHorn 464 Readers' Department - 465

International Radio Review 466

War -Time Uses of Radio - E. W. Slope 467

The Renode -A New Gridless Tube Svend Aker- Rasmussen 468

New Developments in All -Wave Receiver Design. . 469

New German Television Receivers Manfred von ArcLnne 470

HUGO GERNSBACK, Editor -in -Chief C. W. PALMER H. G. McENTEE Associate Editor Associate Editor

R. D. WASHBURNE, Technical Editor

Outstanding Merits of Metal Tubes Herbert M. Neustadt 470

Operating Notes 471

A $30,000 "Radio" Installation._ __ _Russell D. Lanning 472 The Listening Post for All -Wave DX -ers

Charles A. Morrison 473 Oscilloscope Servicing of All -Wave Sets E. E. Sayre 474 New Metal -Tube Chassis Simplifies "Modernizing"

Old Sets Tobe Deutschmann 474 Servicing Theatre Sound Systems -Part III..._A. V. Ditty 475 Short -Cuts in Radio 476 A Beginner's A.C.-D.C. Super. "2 "....R. D. Washburne 477 The Latest Radio Equipment 478 ORSMA Members' Forum 480

A School -Type Broadcast Studio 481

A Broadcast P.A. Unit for Musicians Charles R. Shaw 481

RADIO SERVICE DATA SHEETS: No. 155 -General Electric Models A82 and A87 8 -Metal Tube All -Wave A.C. Superhets - 482 No. 156- Stromberg -Carlson Model 62 and 63 8 -Tube High -Fidelity Chassis; RCA Model 103 4- Tube A.C. Compact Superheterodyne ...- __ _. 484

Technicians' Data Service .. _ 485 Book Review 503

(ANNUAL) BEGINNER:;' NUMBER Radio has so many subdivisions th st the "beginner in

radio" may be more nearly describec as a beginner spe- cializing in public address, electronic short waves, auto radio, television, servicing, etc. For this reason the forth- coming specialized issue of RADIO -C 2AFT devoted main- ly to the beginner in radio will contain not only informa- tion concerning radio receivers but i Iso valuable articles on many related subjects. All of these articles will be pre-

pared in easily understandable form so that the average person will be able to learn "what it's all about" without acquiring indigestion over a lot of heavy technical explana- tions. Expert technicians have prepared easily understand- able articles on all the topics mentioned above. Also, the radio set builder has not been forgotten- easily -built radio devices are described in detail for his benefit.

Don't miss the special RADIO BEGINNERS' NUMBER of Radio -Craft, on the newsstands January I.

HUGO GERNSBACK, President I. S.

Published by Continental Publications, Inc. N. Wesley Ave., Mount Morris, Illinois. E

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450

RADIO -CRAFT for FEBRUARY, 1936 451

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Partial Contents of this Great Book PART 1- CIRCUIT THEORY AND ANALYSIS

R.F. Fundamentals; Superheterodyne Receiver Theory ; A.V.C. and Tuning In- dicator Circuits; A.F. Fundamentals; Pow- er Supply Theory and Circuits; Speakers, Reproducers and Pick -Ups; Commercial Receiver Circuits of All Types, How to Analyze.

PART 2- MODERN SERVICING AND TEST EQUIPMENT

Fundamentals of Metering and Test Equipment Standard Servicing Instru- rnents; The Cathode Ray Oscillograph and Associate Instrumenta; How to Build Es. sential Servicing Test Instruments.

PART 3- PRACTICAL SHORT -CUTS IN TROUBLE SHOOTING AND REPAIRING

Localizing Trouble by Inspection Meth - ads; Short -Cuts with Test Instruments; How to Quickly and Properly Perform All Types of Repairs; Unusual Servicing Ex- periences; Tube Troubles and Character - Litics.

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SEND ME IMMEDIATELY TILE CONTEST BLANK FOR ENTRY IN TILE I 91,800 PRIZE CONTEST.

PART 4- SPECIALIZED RECEIVER AND INSTALLATION DATA

All -Wave and High Fidelity Receiver Servicing and Installation Data; Auto Ra- dio Receiver and Installation; Specialized Servicing and Installation (Remote Tuning Controls, Home Recording. Automatic Rec- ord Changers, Apartment House An- tennas, etc., etc.) ; Eliminating Noise In- terference.

PART 5- MODERNIZATION AND CONVERSION DATA

Modernizing and Improving Methods for All Types of Receivers; Converting A.C. Receivers for D.C. Operation and Vice Versa.

PART 6- SOCIAL AND ECONOMIC PROBLEMS OF THE SERVICE MAN

Improving Knowledge and Technique; Social Problems -How to Organize. Li-t - ing of Servicemen's Organizations; The Future of the Servicing Profession.

PART 7- OPERATING NOTES AND PRACTICAL DATA LISTINGS

Operating Notes on Over 1,000 Receivers; LF. Peaks of Approximately 3.000 Receiv- ers; Voltage Dividers for 800 Receivers. Speaker Field Listing; Radio Mathematics and Measurements.

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To -date we hav: issued the following publications of vital

importance to sE:rvice men:

1931 Official Radio Service Manual

193:1 Official Radio Service Manual

193: Official Radio Service Manual

193 Official Radio Service Manual

193 5 Official Radio Service Manual

Official to -Radio Service Manual (Vol. No. 1)

Official A to -Radio Service Manual (Vol. No. 2)

Every Service Mari, in order to be properly equipped to service the

older sets, which n

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I now own the following manuals (check the one you now have).

1931 Official Radio Service 1932 Official Radio Service 1933 Official Radio Service 1934 Official Radio Service 1935 Official Radio Service

Manual Manual Manual Manual Manual

Official Auto -Radio Service Manual (Vol. No. 1)

Official Auto -Radio Service Manual (Vol. No. 2)

Will you kindly mail me a special proposition whereby I

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"Takes the Resistance out of Radio"

Editorial Offices 99 Hudson St., New York, N.Y. HUGO GERNSBACK, Editor Vcl. VII, No. 8, February, 1936

NEEDED BROADCAST REFORMS An Editorial by HUGO GERNSBACK

EVER SINCE broadcasting became in itself a great in- dustry- growing up like Topsy as it were -it has as- sumed a quite detached existence from the remainder of the radio industry as a whole.

With very few exceptions -such as the handful of broad- cast stations controlled by radio manufacturing companies -broadcasting has chosen to travel á road which is diamet- rically opposite to the one taken by the remainder of the industry. The broadcast industry today of course is in business, first, to make money; and second, to furnish enter- tainment to the American public. As a money- making in- strumentality some of the larger stations have been quite successful, but from the standpoint of entertainment the success has not been so great.

Even our key stations, affiliated with the national chain networks have often found it necessary for financial con- siderations to accept highly questionable business, the sort of business that first class newspapers or magazines would certainly never take. By this means, the broadcast indus- try has been able to get great financial rewards, but un- fortunately at the expense of the public.

It is true, of course, that there are notable exceptions to the above. There are a number of first -class stations which transmit excellent programs year in and year out, and which do not offer questionable merchandise and patent medicines over their stations. However, such stations are the excep- tion.

Wherever a person discusses radio broadcasting today he finds a great deal of dissatisfaction among the listening pub- lic as to the quality of programs. For every good feature broadcast by a network, there are ten mediocre -or even downright poor, programs which clutter the air at practical- ly all times.

It would seem that all broadcasters must reali -e that to hold their audiences the first requisite is worthwhile pro- grams, but this truth appears never to have dawned on the majority of broadcasters. They still go out to grab every- thing in sight when it comes to business, accepting the most blatant and untruthful advertising, which is dinned into an unwilling public's ears, and which, nine times out of ten, causes listeners to tune out the offending station!

It is true that if the stations are to continue in opera- tion they must have business -that is, their programs must have sponsors. There is no question of this under our pres- ent American broadcast system, and that this system is sound has been demonstrated during the past decade. But it also has been demonstrated that the advertiser will still get his share and will still be benefited if the listener's intel- ligence and sensibilities are not shocked in the way they so often are today.

The public instinctively knows that it owes a debt to the broadcast stations for the free entertainment, but the broad- casters do little to get the good will of the public and keep it.

It is a curious fact that some of the most successful adver- tisers over the air are those who do not revert to trick sell- ing, who do not offend their listeners, but use their adver- tising "blurbs" inoffensively and discreetly. And to this,

the public does not object. The great trouble with business concerns wishing to go

on the air is that they expect to get results over night; unless they get such results they often are unwilling to go ahead with their sponsorship. This is the crux of the whole business, and explains why short- sighted broadcasters in desperation are allowing the sponsors to broadcast the huge quantity of offensive advertising that nowadays goes on the air. Successful sponsors, on the contrary, have found that results cannot be had over night; and that it takes months and sometimes years before the expense warrants the business derived -but in the end, it always pays.

Your patent or proprietary medicine manufacturer how- ever does not seem to be interested in the long pull, and in the good will of the public. He wants immediate results - he wants to move merchandise.

To the disgrace of the American broadcasting industry it must be stated that, with practically no exceptions, all pat- ent and proprietary medicines hawked over the air today are worse than useless and a menace to the health of the American public. If you doubt this, read such books as "100,000,000 Guinea Pigs," or the new book recently pub- lished by the same authors, "Eat, Drink and Be Wary."

The huge number of fake patent medicines and other ques- tionable food products ballyhooed over the air is a mute testimony to the gullibility of the American public. It is doubtful that there are a half -dozen medical and food prod- ucts now being advertised by radio which would pass the test of the American Medical Association. At any rate, few of the articles would be acceptable to that discriminating body.

It is to be hoped that the Federal Communications Com- mission will some day step into the picture and rule that any medical, proprietary or food article must first have the en- dorsem*nt of the American Medical Association before it can be advertised over the air. While it is true that if this plan was put into effect few such articles would be adver- tised over the air, it is even more to the point that such a ruling is warranted if public interest -the health of the American people, is at stake.

Naturally this raises a question as to the entertainment value of the programs themselves. It is the consensus of opinion that programs in the United States have not greatly improved. If you use as standards of comparisons the pro- grams offered by the largest and networks -key stations, the remaining, smaller stations seem to put out worse programs as time goes on. In practically all cases we still have medi- ocre music and mediocre talent. The few good programs sent out by the smaller stations invariably are "electrically transcribed" (that is, they are phonograph records). In fact, nine times out of ten their only decent programs are these same "transcriptions" or phonograph records. And, of course, the sponsored programs of these small stations are, as a rule, highly offensive to the listeners due to the blatant sort of advertising that is broadcast day in and day out.

This observer has noted little change toward improvement of radio programs during the last five years; at this rate the future does not look very bright.

453

THE RADIO MONTH ELECTRIC PARTICLES HURLED PROM

O RDER SECNND Inl1.000 MILES

ATMSS ONEAS f,.DRT.CIRCUITIND ADHO WAVES ON LIGHTED SIDE

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r.D`:TIÖ SWEEPS LI SEARCNLIS

:roioñó á '

EARTH TRAVEL,

HOUR I V IOPP, N

The effect of the solar cycle on short-wave Zorn munication is shown.

RADIO FADING LINKIED WITH SUN'S ROTATION

FADING of radio sigr als, espeEially on short w eve - lengths, has long ba filed

scientists, and though various theE ries have been presented from time to ime purported to explain this phenome ion, they have lacked scientific proof.

Last month, however, Dr. J. H. Del- linger, chief of the radio section of the Bureau of Standards, presented evi- dence that fading periods are pre lict- able on the basis of the rotation periods of the sun, and that sharp fading c :.cles of 15 minutes duration occur at iter- vals of two rotations of the sun (54 days).

Following this. Dr. H. R. Mimno of Harvard University, in an article pub- lished in Science went a step furthE r by presenting records tending to show that the fading cycle noted by Dr. Dellinger occurs every sun rotation of 27 days!

At the same time, Dr. Mimno "took a crack" at the Federal Communications Commission for holding up research progress. He said -"During the past sixteen months the F.C.C. has repeated- ly postponed the re- phrasing of certain obsolete regulations limiting the use of automatic apparatus, which effectively block the continuation of fundamental research ... Already an important part of the sun -spot cycle has been com- pletely lost by governmental decree."

INDIAN RULER TO BUY 20,000 SETS

LAST month, news came from far off India that His Exalted Highness

the Nizan of Hyderabad is buying 20,000 radio receivers, one for each of his 20; 000 villages. These will be used to al- low his 15 million or so subjects to lis- ten to the jubilee, Feb. 1936, in honor of his 25th year of reign.

He is also going to install 4 modern broadcast stations. Transmissions will be in English, Hindustani, Telgu, Marahti and Canarese native dialects.

454

s of the fleet of P. A. trucks sent throughout Italy are shown above.

ITALIAN P.A. TRUCKS FIGHT SANCTIONS!

ANEW use for sound trucks was originated in Italy, last month,

when a fleet of these cars was sent on a tour throughout the country to in- struct the people in the art of passive resistance to the sanctions applied by the League of Nations.

Addresses were made at each wayside town, the entire population gathering around the truck.

Another interesting high -light of the Italo- Ethiopian conflict is the situation in international broadcasting. First, when Baron Pompeo Aloisi, chief Ital- ian delegate to the League of Nations attempted to broadcast a speech to the U. S. via a British Broadcasting Co. relay (a standing agreement between American and European stations) the B.B.C. refused to complete the relay. This necessitated setting up a relay from France and disrupted the long- standing international program ex- change agreement.

Later, when Guglielmo Marconi made arrangements to broadcast f om Eng- land, the B.B.C. again stepped in and refused permission. Marconi broadcast to the U.S. twice, recently, directly from Italy.

ELECTRON MULTIPLIER DISSENTION

THE introduction, recent- ly, of the Zworykin elec- tron multiplier tube (see

Radio- Craft, Jan. 1936, page 391) start- ed what promised to be a grand and glorious court battle.

Last month, Philo T. Farnsworth, who is well known for his television ex- periments and the invention of his "mul- tipactor" tubes, gave a talk before the Washington chapter of the I.R.E. on the various types of electron tubes de- veloped in his laboratory.

Since Zworykin's tubes work on simi- lar principles, dissention is expected. There is little doubt but that court action will be taken by one or the other!

METAL VS. GLASS TUBE FIGHT- CONTINUED

TH E f i e r y accusations which Philco has been flinging at G.E. and its

licensees for introducing the metal tubes, which the former claims are not yet ready for the market, brought forth a retaliation, last month, when 47 manu- facturers of metal tube sets (at the in- stigation of G.E., no doubt) banded to- gether and placed a full -page ad. in the New York Times and other papers throughout the country. The names of all manufacturers were listed and the page was ended with the slogan "Be modern -get a radio set with Metal Tubes."

Well, there's one thing certain -the newspapers are not going to complain, however long the fight lasts!

RADIO SET FIGURES AND FACTS

THE United States has lost slightly on its tre- mendous lead in the pos-

session of radio receivers among the countries of the world, but the lead is still far from being threatened. Out of 56,221,784 sets in the world, Uncle Sam has 25,551,569. Not so long ago, the U. S. had more than half the sets.

Statistics published last month by the Electrical Division of the Bureau of Foreign and Domestic Commerce show the United Kingdom runs far behind in second place with 7,055,464 radio - equipped homes. Actually, it has more sets than that because additional sets may be operated with only one permit.

Germany comes third with 6,516,732; France has 2,763,123; Russia, 2,000,000; and Canada 812,335.

The distribution continents follows:

of radio sets by

North America 25,632,981 South America 1,088,374 Europe 22,897,981 Europe -Asia 2,010,000 Asia 2,553,396 Oceania 829,851 Africa 209,201

The distribution of radio sets in the world can be seen at a glance from this map.

TM EAIDar OF 711C WORLD

WI COUNTRIES

RADIO -CRAFT for FEBRUARY, I 9 3 6

IN REVIEW HEARING -AID SALE RULED ILLEGAL!

THE State Board of Med- ical Examiners of New Jersey in reporting cases

in which the Medical Practice Act was enforced included, last month, a case of interest to many radio men.

The case which was described in Medical News stated that: "Cleon E.

`' Shields, Newark, pleaded guilty to prac- ticing without a license and paid the penalty. Shields claimed to improve impaired hearing by the use of a de- vice which he said measures the ca- pacity to hear and furnishes in correct volume the tones that are 'blocked out' by the .impairment."

If individuals and companies selling hearing aids are thus prosecuted for practicing medicine without a license, a large number of radio men and com- panies will be liable!

AMOS 'N' ANDY MISS FIRST BROADCAST

LAST month was an out- standing one with radio listeners in the eastern

states as the first time in over eight years that Amos 'N' Andy missed their nightly broadcast. The two blackface comedians were on a wild turkey hunt near Hanco*ck, Md. -the hunting was good!

SECRET FACSIMILE TRANSMISSION

AMETHOD of secret fac- s i m i l e transmission for telephone lines

and radio was announced last month by the famous French television pioneer - Edouard Belin.

Monsieur Belin, who presented his in- vention to the French War Department guarantees that messages, even though they are intercepted by wire tapping or

It radio reception will be so garbled that they will be absolutely incomprehensi- ble. It is expected that this system will prevent the leakage of messages in case of war.

Below, Belin's apparatus for secret. facsimile trans- mission; inset -actual transcript.

RADIO -CRAFT for

Radio is now such a vast and diversified art it becomes nec-

essary to make a general survey of important monthly de- velopments. RADIO -CRAFT analyzes these developments and presents a review of those items which interest all.

The portable transmitter on the S.S. Manhattan.

NEW PORTABLE TRANSMITTER USED BY WOR

STATION WOR made use of a new portable 7 -met- er short-wave transmit-

ter for the first time last month, at the home -coming of New York's Jimmy Walker.

The tiny portable unit was installed aboard the S.S. Manhattan and with- in 10 minutes was in communication with the receiving point. The latter was located on one of the down -town skyscrapers.

The use of this portable short -wave transmitter not only facilitated the broadcast pick -up but also aided news- paper reporters who were able to relay messages to their city desks.

RCA SECRETLY PREPARES TELEVISION APPARATUS

FOLLOWING the plan outlined severs 1 months ago in Radio -Craft, RCA

and NBC engineers were reported last month to be dismantling the old tele- vision equipment in the tower of the Empire State Building, preparatory to installing new and modern equipment.

The work, however, is being carried out in utmost secrecy and no definite date could be ascertained when the transmitters would be ready for oper- ation. From unofficial sources, we learn that the transmitter will be com- pleted sometime in January.

It is understood that the plan calls for the manufacture of some 500 re- ceivers of four different designs which will be placed in research outposts and the homes of observers to facilitate a complete check on the system. It is ex- pected that one of the four designs will be chosen for manufacturing purposes.

The images will be sent out over a 15 kw. transmitter on a wavelength of about 6 meters. The images will meas- ure about 9 by 10 ins. and are said to be very clear.

FEBRUARY, 1936

Enoch Light and his orchestra are shown above with the sound measuring apparatus.

N. Y. ORCHESTRAS COOPERATE WITH ANTI -NOISE COMMITTEE

pROGRESS was reported last month in New York's anti -noise campaign due

to the voluntary cooperation of "Tin - Pan- Alley." Practically all the metro- politan hotel orchestras under the lead- ership of Enoch Light, well -known ba- ton wielder, offered to cooperate; and, subsequently db. meters (noise level in- dicators) were used to determine the most comfortable hearing levels for playing popular tunes in the ball rooms and restaurants of the respective hotels.

This was done not only to keep the volume at the lowest convenient level for sleeping hotel guests' comfort, but also to prevent the hotel entertainment from increasing the street -sound level, especially in summer.

It was announced that during the first month of the anti -noise campaign, the noise level at Times Square dropped an appreciable amount.

F.C.C. PLANS STATION SHIFT

THE Federal Communica- tions Commission an- nounced last month that

they are working on a plan to eliminate the duplication of network programs, throughout the U.S.

This will involve a proposed reduc- tion in the number of clear channels from forty to twenty -five and the re- quirement that these stations maintain an output of 500,000 watts instead of the 50,000 watts now required. It will be remembered that there is only one 500,000 -watt station now operating - W LW.

The purpose of this re- allocation is to better serve dwellers in rural districts, who are fast becoming a most impor- tant part of the listening public!

455

WF. ARE now in the 16th year of American Broadcasting. The daring idea of youthful David Sarnoff in 1919 when

he predicted the future of broadcasting has grown into a vast industry with many millions of dollars invested and providing thousands of workers with jobs which did not exist before broad- casting started.

No one knows what the directors of RCA thought of this prediction which was included in a report from David Sarnoff -who had just been appointed commercial manager of the company - but it is not hard to guess that they did not consider it seriously or with much confidence.

However, despite this fact, only one year later, on Nov. 2, 1920, Dr. Frank Conrad and his staff of Westinghouse engineers broadcast over KDKA returns of the Harding -Cox presidential elec- tion -and thus staged what was perhaps the birth of American broadcasting.

Since that time broadcasting has con- tinued to grow by leaps and bounds and is at present an important factor in the progress of all civilized nations.

David Sarnoff has also grown. This former telegraph boy who had a weekly income of $5.50 at the age of 15 became, in 1930, when only 39 years old, the pres- ident of RCA. Now, however, after hav- ing so much experience with radio and broadcasting, he is quite tight -lipped with regard to the future of radio, and recently- during an interview with Mr. Orrin E. Dunlap of the New York Times, said the very meaningful words: ". . . Those of today cannot foresee the radio of a generation hence!" And no one can blame him for his attitude, be- cause of tremendous strides made in the first 15 years of American broadcasting.

Fig. 3. Radio sets in public reduce sales resistance.

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456

MILESTONES In this article the author presents a cross - section of radio broadcasting from 1919 to date. The 25 million radio receivers now in

use are analyzed from all angles, and con- clusions drawn concerning the probable trend of the industry. Everyone interested in radio should read this valuable article. (Other references are given at right.) Dr. Conrad and associates starting the Ameri- can broadcast industry on Nov. 2, 1920!

KDKA sent Harding -cos election returns.

OVER 25 MILLION SETS IN USE

To give a simple picture of broad- casting today we may start with the plain fact that on the first of January of this year (1935)* there were about 22,000,000 home radio receivers in use, and about 2,400,000 auto sets in use in the U. S. ( *See page 454. Editor.)

What the figure of 22,000,000 home radio receivers involves may be seen from the fact that it was 50 years be- fore 10 million telephones were in use in America. Let's take these 22 mil- lion home sets and pile them up.

But this trick of statisticians in- volves difficulties where radio sets are concerned, because within the last 15 years about 10,000 different receiver models have been put on the market. There are large consoles and tiny midgets, and table models of medium and large size. Although it is difficult to agree on an average size, by care- ful estimations the average size has been found to be about 24x16x9 ins.

With these figures as average dimen- sions, all 22 million radio receivers piled one on top of the other will give a pillar towering about 8,000 miles!

If this colossal number of radio re- ceivers now operating in American homes is pictorially represented, as in Fig. 1A, by dividing the 44,000,000 ft. pillar into 500 single ones having base dimensions of 24x16x9 ins., each pillar would be about three times as high as Mount Everest (highest moun- tain in the world, which towers about 30,000 ft. into the air.

Now let us group these 500 single pil- lars to form a tower having base di- mensions of about 30x16 ft. deep. Then, taking $50 as an average value per set, this tower would represent $1,100,000; 000. Since the president of the U. S. receives a yearly salary of $75,000, the value represented by these radio sets would be sufficient to pay the salaries of all American presidents for the next 14,666 years!

LISTENERS ARE THE FINANCIAL POWER OF BROADCASTING

That the main part of American broadcasting has been financed by the radio listener is shown impressively by Fig. 1B. The value of all American

broadcast stations including equipment and goodwill is only $60,000,000. The value of all commercial stations in- cluding radio investment on American ships is estimated at about $40,000,000. Radio factories are valued at about $80; 000,000, and the value of American radio retail and wholesale houses may be quoted as being about $50,000,000.

These 4 branches of radio repre- sent a total investment of about $230; 000,000 which is a little more than i/s the value of all radio receivers in use at present in American homes.

There are, as Fig. 1D shows, about 581 broadcast stations in operation in America. More than 31 of them have a power output at the antenna of about 50 kw. One station, WLW, Cincinnati, the world's largest broadcast station, has an antenna power of 500 kw.! But these 581 stations representing a value of about $60,000,000 produce an annual gross revenue of about $90,000,000 which is certainly a worthwhile business for the owners of these stations.

Very interesting also are the rela- tions between the estimated value of the American radio factories and their yearly turnover. In the year 1934, American radio manufacturers sold ap- proximately 4,696,000 radio receivers (this figure includes the export sales of about 612,000 sets), having a total retail value of about $250,390,000. The figures for 1935 amounted to 5,500,000 units (including export) representing a retail sales value of about $300,000; 000. This increase is due to a greater demand for consoles in 1935, and also to the higher average prices for these different types of receivers. (See also Fig. 1C.)

As Fig. lE indicates, the radio lis- teners spend yearly for operating ex- pense about 2.2 times as much as the payroll figure for the manufacturing and distributing side of the broadcast industry. That is, the yearly bill for the 800,000,000 "kilowatt- hours" used to operate radio receivers amounts to a sum which easily surpasses the yearly payroll of all American broadcast sta- tions. Also, the total kw.-hour energy used by radio receivers is greater than the total of kw.-hours used by each of the domestic home appliances represent- ed in Table I.

RADIO -CRAFT for FEBRUARY, 1936

IN BROADCASTING Radio- Craft, in presenting this comprehensive review of the latest facts

and figures concerning the radio "business," supplements the valuable data contained in the following, previously -published industrial reviews.

"The Broadcast Industry," and "A Modern Picture of Broadcasting," Feb. '35; "A Modern Picture of Television," April and May '35; "The Growth of Public Address," May '35; "The Present Status of Automotive Radio," June '35; "The Radio Service Industry," and "The Radio Service Business," July '35; "World -Wide Television," Aug. '35; "Some Facts About Radio As a Career," and "New Opportunities in Radio," Nov. '35; "Tele- vision in the Theatre," Nov. and Dec. '35; and, "Television and Ultra -Short Waves," Jan. 36. (Radio Month in Review items contain additional data.)

TABLE I Estimated total amount of energy used

by domestic electrical appliances

Appliance Kilowatt -hours Radio Receivers 800,000,000 Flatirons 673,000,000 Vacuum Cleaners 235,600,000 Washing Machines 131,000,000 Toasters 152,000,000 Percolators 106,000,000 Heaters 48,000,000

LISTENER INFLUENCE ON PROGRAMS

Because of these important financial relations it would be usual to expect that the radio listener has a tremend- ous, direct influence upon the program planning. However, this is not the case! Despite the fact that the Ameri- can broadcast stations receive yearly about 5,000,000 letters (which are care- fully filed, as far as the networks are concerned), the direct influence of in- dividual listeners upon the program planning is about ZERO! There are, of course, some women's organizations in America which have quite a bit of influence on the kind of programs pre- sented, but even their power is restrict- ed, since program sponsors have the last word in this respect!

However the indirect influence of the radio listeners as a whole on the kind of radiated programs (which are about equally proportioned, as shown by Fig. 2A) is about 100 per cent. A survey made by The Psychological Corpora- tion, New York, by order of the NBC, unveiled many interesting facts as to just how the public is influenced by radio. By means of a very interesting method (which is described with all de tails in a booklet- prepared by Dr. Henry C. Link -entitled, "A Study of

Fig. 4. Increased revenue by "commercials" may be attributed to more effective use of radio as an adve using and publicity medium, as this figure

illustrates.

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1929 1930 1931 1932 1933 1934 199f

RADIO -CRAFT for

WILHELM E. SCHRAGE

the Relative Effectiveness of Major Ad- vertising Media) a great many retail dealers have been asked how far they believe radio broadcasting is a fitting vehicle for advertising messages. This was done because it is realized that the radio broadcasting lacks the great im- or explain the advertising forces which influence his preferences. Since the dealer is actually the clearing house of customers' reactions, this survey (the results of which are shown in Fig. 3) is highly interesting.

It shows that the public en masse has about 100 per cent control of the pro- grams presented, because only programs which suit the public taste will find listeners. Since there are only a few program sponsors who would dare to present to prospective customers a per- formance which did not produce popular satisfaction, the broad mass of radio listeners really has a very effective con- trol of American broadcasting.

Inversely, the great influence of radio broadcasting has had a great effect upon listeners; this buying public (see Fig. 3) has greatly effected the amount of advertising appearing in national news- papers- According to Radio Today (which compiled the diagram shown in Fig. 4), many newspapers and maga- zines had a decrease in advertising be- cause of radio broadcasting. Accord- ing to the above -mentioned magazine a quarrel is going on between the news- papers and broadcast stations, and as always in such cases, both sides are fighting for the patronage of the manu- facturers of nationally advertised brands,

METAL CONTRA GLASS TUBES

But this quarrel in the evolution of radio broadcasting lacks the great im- portance of another combat which has its battlefields directly among the Amer- ican radio manufacturers. This fight which is drawing much attention in the broadcast industry, is the one of metal versus glass tubes.

According to the defenders of the metal tube, 47 manufacturers are using metal tubes in their sets. This fact pub- lished as full -page advertisem*nts in many daily newspapers proves nothing, because there are other facts which en- ter the picture. (Continued on page 489)

FEBRUARY, 1936

STEVENS. ANDERSON - 90 00 0 CT 1935

74.000 FT -t- 60000 T - ;Ii F

MOUNT EVEREST 291002 FT)

30.000 FT - Fl

L 30.6 -í: = + \ -A

FT '

VALUE OF AMERICAN

BROADCASTING STATION

EQUIPMENT AND

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RADIO INDUSTRY

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TELEGRAPH. TELEPHONE INCLUDING SHIP STATIONS

$ 40, 000.000 , -.

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MANUFACTURERS $ 80, 000.000 -8

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LISTENERS STATIONS MANUFACTURING & DISTRIBUTION

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STATIONS

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CEIVERS IN USE

590,000.000 ANNUAL GROSS

REVENUE

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5300000000 RETAIL VALUE OF RADIO

SETSSOLD IN 1935

$ 32,000000 .

$100,000,000 ANNUAL PAYROLL

Boo,000,000 KILOWATT HOURS USED YEARLY FOR OPERATING RADIO

RECEIVERS

S 30,000,000 ANNUAL

PAYROLL -E-

Fig. I, above, and Fig. 2, below. These illustra- tions visualize some modern facts concerning radio.

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457

RADIO PICTORIAL Recorded sound effects for radio broadcast work; short -wave car -relays; novel sets.

INSTANTANEOUS SE- LECTION OF SOUND,

I EFFECTS. This device enables a studio techni- '

cian to select any one of a group of sound ef- fects on a single record- ing. The pickup arms are set by turning a

graduated dial to the number of the required effect. Then, when a I

button is pushed, the arm swings to the exact spot required and the needle drops smoothly onto the record. Two turntables are used so

that the operator may always have the required sound ready. The view

below (right) shows a close -up of dial and tone arm. (Halbran Photos)

Mr. Sinfon is seen adjusting the mechanism of his apparatus which selects the desired groove of the record for repro- duction. The knobs on the for- ward side of the machine are the various volume controls.

The sound effect apparatus (developed by sound. effects specialist Al Sinton, and built by Ans- ley Labs.) has replaced old- fashioned equip- ment, and the results are better than with the old, cumbersome gadgets. An auxiliary, manually -operated tone arm may be seen be- tween the two turntables. This is used on either turntable for additional pick -up, as required.

"GE" TO SO. AMERICA VIA CAR RADIO!), This radio -equipped car was used by Henry Ford, visiting the G.E. plant at Schenectady, N. Y., in talking via short -wave relays to his Buenos Aires plant manager!

TRANSPORTABLE SET. This set by EKCO of England has

a built -in twin -loop aerial, but can be used with the conventional antenna. It in- cludes all the latest im- provements, such as de- layed A.V.C., noise sup- pression, tone control, tone compensated volume con- trol, shadow tuning indica- tor. The dial is uptilted for ease of reading, and has printed on it the names and wavelengths of the various large stations. The cabinet is of moulded bakelite with the handles an integral part.

ON REAR) OF SET

458

"TWO- FACED" SET. This novelty set, housed in a case of the finest woods, has a speaker grille on both sides. The receiver was de- signed for the recent Radio Show (N.Y.C.). The chassis is a 6 -tube A.C. -D.C. superhetero- dyne with 3 ranges which cover all the pop- ular bands in use at present. Both sides of the set are visible when the set is centered on the table. One side carries an electric clock. Since both sides of the set have a speaker grille the set will sound as well from either side.

RADIO -CRAFT for FEBRUARY, 1936

4LIFEBOAT RADIO. This lifeboat is one of the first fo be so equip- ped under the new F.C.C. law. The set and a searchlight are run by a group of storage batteries. Operation is possible even though the set be drenched with water!

(World Wide Photo.)

RADIO , < ATIO

GERMAN BROADCASTER. The transmit- ting room dispenses with the usual panels, using plain glass instead. The metal - framed glass serves only to keep the high power isolated.

}

WAVETRAP. German device has a verrier for exact elimination of signals.

(81'3)

CAUTERY OUTFIT. This medical de- vice shows us 't hat other trades besides the radio in- dustry make use of this style of design. At first glance this ap- pears to be only a midget radio set.

(Compres)

GERMAN 2- TUBER. The speaker is placed along- side the chassis to eliminate cabinet resonance.

ll i'3) MICKEY MOUSE RIVAL. A British concern will make cartoon films of "Sam" and his musket. The operator is examining a film sound track and making a sound chart.

CONVERTER. Addition for the "Peoples Receiver" converts this popular set into a modern (German) superheterodyne.

11Cus.+rhburh

AIRPLANE BEACON ON THE AIR ROAD TO CHINA. Stations are being built to guide the "China Clipper" Trans -Pacific passenger plane on the new airline to the Orient. The Mokapu (near Hon- olulu) station is illustrated. SEASONING RACK. Apparatus at the right enables efficient mass production of Raytheon metal tubes. All tubes of one type are aged alike by the use of this ap- paratus. "Load lamps" for elements connected to the caps are above the drum; others are located inside.

4 . -riy. F

*,1- i. `s-+e-.-.. --.-

RADIO -CRAFT for FEBRUARY, 19 3 6

RADIO TUBE EXAMINATION. De- vice which enables the inspecter to examine the completed tube "mount" before it is sealed in the glass bulb. Notice the great degree of en- largement possible in the projected image of the bioscope. (11P3)

459

LIGHTING AND CURTAIN CONTROL

4 BOOTH

GLASS ENCLOSED BAL ONY BROADCAST

ONTROL BOOTH

-1

NYONE WHO has visited one of the modern broadcast studios has no doubt been struck with the "apparent' simplicity of

the room compared to those used a few years ago. The word apparent is used because, as we will learn later, they are far from being as simple as they seem. The heavy drapes and carpets found in the old -time studios are missing and the announcer is no longer expected to be a Houdini, handling the production of the pro- gram as well as announce, act as mas- ter of ceremonies, and usher for the artists and studio audience!

The studio of today is a well- appoint- ed room, plainly furnished -but usual- ly rich in coloring and lighting.

Yet, under the quiet, dignified ap- pearance of this modern studio lies all the ingenuity of the electrical, acousti- cal and mechanical engineer. Take for example the corner of the studio shown

Fig. B. A corner of a modern broadcast studio.

460

MODERN STUDIO TECHNIQUE A few of the high -lights of building and op- erating a modern broadcast studio show how very complex this apparently simple work has become in perfecting the nation- wide distribution of r a di o programs.

C. W. PALMER

in Fig. B in which Ray Kelly, chief of the NBC Sound -Effects Department is shown with a few of his latest gadgets for producing the background noises and incidental sounds required with every broadcast. The walls of this studio in Radio City are lined with rock - wool blankets, varying in thickness ac- cording to the requirements of the room, and the wall finish, instead of being hard plaster of the usual type, is con- structed of panels of a material known as transite. This transite is perforated on the upper part of the wall, while the wainscot is made of the same material in a solid form. Rockwoot is chosen as the padding because of its characterist- ic of absorbing medium and low tones more readily than high ones. This gives the desired effect of a "dead" space for the medium and low tones and a "live" space for the high ones.

The floors of this studio are also treated in a very special way. There are 5 steps in this treatment. First, the solid concrete building floor is equipped with steel flooring channels which rest on hair -felt- covered spring clips, properly spaced to carry the antic- ipated load. The space between the channels, which are laid parallel the full length of the room, is covered with loose rockwool. Next a layer of heavy, black, building paper is placed over the entire floor, over which a wire mesh is then placed. Finally, a layer of con- crete is poured and the finished floor is ready for linoleum. Some of these steps in floor and wall acoustic treat-

ment are sein In Fig. C. By this method, the drapes are elim-

inated and the studio has better char- acteristics for broadcast purposes.

An idea of the multiplicity of studios used for operating a national chain can be obtained from an examination of Fig. 1. This shows a plan view of the 8th floor of the NBC studios in Radio City. Note the differently -sized studios, each of which is used for a different type of program. There is the large auditori- um studio at the right which is 132 ft. long and 78 ft. wide. This is used for large orchestras and for exceptionally popular programs where large studio audiences always congregate. To the left of this mammoth room which is two floors high and has a large balcony for the studio audience are the various smaller studios, each with its control room, from which the program is moni- tored. Note also the special studios for speakers and (Continued on page 498)

Fig. C. Details in acoustical treatment of studios.

Fig. D. A few of the studio hand signals used to inform the announcer and artists of the progress of a studio program.

RADIO -CRAFT for FEBRUARY, 1936

MAKING A 12 -TUBE

HIGH - FIDELITY BROADCAST RECEIVER Here is a real high -fidelity set solely for superior reception of local stations on the broadcast band.

M. H. GERNSBACK PART I -THE TUNER

IT HAS LONG BEEN the author's desire to possess a receiver which would give really fine reproduction of local stations. It was felt that

great selectivity, high sensitivity and high- quality reproduction did not make good bedfellows so a T.R.F. receiver with "poor" selectivity (as compared with the average modern set) and only sufficient sensitivity to adequately pick up the important locals was designed.

Briefly, the set comprises 2 T.R.F. amplifier stages followed by a diode de- tector. This in turn feeds into a 2- stage A.F. amplifier, with both stages in push -pull. High -quality transformer coupling is employed between the driver

Fig. B, above. Underside view.

and power stages. A separate 2 -stage amplifier with both stages in push -pull is used as a "bass booster" stage to in- sure adequate bass response when the receiver is operated at low volume lev- els. (A 1 -stage preamplifier with mike input transformer is also included al- though this may be left out if the build- er does not plan to make use of it.)

Two type 6D6 tubes are used in the R.F. amplifier and a 76 with plate and cathode tied together serves as detector. A pair of 76s are used in the first A.F. stage and are followed by two 6A3s in the power stage. The bass booster cir- cuit employs two 6F7s and the pream- plifier makes use of an 85 tube. The new type 6E5 cathode -ray tuning in- dicator tube (or "magic eye ") is em- ployed to insure that stations will be properly tuned.

CIRCUIT DETAILS

The T.R.F. amplifier follows conven- tional design with the exception that no attempt has been made to secure sharp tuning. The band -width is of the order of 30 to 40 kc.

The T.R.F. coils make use of a corn-

bination of capacitative and inductive coupling to equalize response over the whole tuning range. (The secondaries of these coils are wound with solid cop- per wire rather than litz, as solid cop- per wire in this place prevents too much selectivity.) The tuning range with a 3 -gang, 365 mmf. tuning condenser is 530 to 1,700 kc.

It should be noted that the plates of the R.F. tubes are supplied with 100 V. instead of the usual 250. With 100 V. the impedance of the 6D6 tubes is greatly reduced and makes possible a better impedance match between the tubes and R.F. coils. The loss in am- plification is not enough to be of any concern, while the selectivity curve is flattened somewhat more by this pro- cedure.

Automatic volume control is employed on both R.F. tubes. It was originally planned to avoid A.V.C. and operate the R.F. tubes at a fixed bias in order to overcome distortion caused by oper- ating the R.F. tubes on a curved por- tion of their characteristic curve. (This condition occurs when the bias on a tube, even a (Continued on page 486)

Fig. I, below. Circuit diagram of the high -fidelity R.F. tuner chassis.

MIKE PRE AMPLIFIER T1 85 T2

.02 MF. Y

1. MEG.

BA3$ 0005rER 30 HT .15- .25 BASS BOOSTER .255-? EG. AMP 02- CN. MF MEO. LMP 6F7, MF rMir9r. 6F71 . OHMS /

0.5 MEG.

MF SOCKET

SOCKET

OHMS

15- MF

-30 HT. CN 25'

MEG

F Ll

50,000 OHMS

.02-MF 05-MEd. DUAL POT 005-

3- 365 MMF (GANGED)

lg.R.F 25P.R.F.

Í 606

MF.

PHONO. 0.1 haF

DIODE DE i A V.C. 76

T3 P

6A3

300 -- OHMS

O. .MEG MF

1.MEG (EACH) W04 AROET

5 6E5

A V9 X

fTe L MEGH) . (EACH

(EAC

O.5.MEG DUAL PO

150 HT. A.F.OI.

-PW R. A.F.

6A3

MO/ LIGHT FOSE X VICI X

PLUG-.

VII 250V /

20000 010,5. 1 WATT. 30.000 OHM

POT. (EACH)

25.000 OHMS (WITH SLIDERS)

RADIO -CRAFT for FEBRUARY, 1936 461

HOW TO MAKE A "FREE- REFERENCE -POINT"

MULTI -PURPOSE SET ANALYZER

Fig. A. The unit in its wooden case.

Fig. B. The "works" -note the cable wiring.

TIIIS TESTING instrument con- sists, essentially, of a universal volt -milliammeter, Fig. 2, and a free -reference -point unit, Fig. 1.

Three sockets are available for current readings of all modern tubes.

Voltage scales, A.C. and D.C. of 10, 100, 500 and 1,000 are selected, as shown in Fig. 2, by means of a rotary selector- switch, Sw.6. Rotating the same switch in the reverse direction, selects current scales of 10, 100, 500

The amateur who is in need of a set analyzer and tube tester which will accommodate the latest set as well as the

oldest will find this unit unusually flexible.

W. C. BELLHEIMER and 1,000 ma. Setting the toggle switch Sw.10, cuts a 10 -A. shunt di- rectly across the meter.

Jack switch Sw.4 selects current or voltage; Sw.5, A.C. or D.C.

Resistors R5 and R10 convert the meter to a 0 -5 voltmeter; R6 then completes the total resistance for the 10 -V. scale.

(Carbon resistors having a 5 per cent tolerance were found accurate enough for ordinary service work.)

The current shunts, with the excep- tion of the 10 -A. shunt, are hand - calibrated from wire -wound resistors, for a 5 -V. meter. The 10 -ma., 550 - ohm shunts are obtained by moving the clips of a standard, 500 -ohm size, bare- wire -wound resistor closer to the ends. The extra value of 50 ohms is readily obtainable.

The 10 -A. shunt is a stock size for this meter. The 10 -ma. shunts are connected in the plate leads between the socket selector switches. To make current readings on this scale with the test leads, it is necessary to set the socket -selector switches across one of these shunts.

Switch Sw.7, in Fig. 1, is in posi- tive lead, and Sw.8 the negative. To measure plate voltage from the cable, Sw.7 should be set at P, or, according to the RMA socket numbering system

Fig. I, below. The circuit of the free -reference -point unit.

Fig. 2, right. The analyzer volt- milliammeter unit.

Fig. 3, lower right. The adapters for permitting 4-, 5 -, 6 -, 7 -, or octal -prong tubes to be tested and connected to the unit.

TEST 5W 1

- 0 Q

TEST

TC Tw0 TC )ACe5

TOGETwER

Sur 2

4 _4.5 53

""CLIP CABLE

(aro) rC

1 7

3 4 / 5w8 5

-6 TO MN JACKS - (LEADS)

462

to 3, while the Sw.8 is set at K or II (or 7 or 8), depending on the type of tube. To measure plate current of the same tube, both switches should be set at P, the jack switches thrown to their proper position, and the correct scale selected.

Several dead points remain on the socket selector switches for future tubes, and on the scale selector for other scales.

All types of tubes may be tested in the analyzer, using the grid -shift method. For tubes with the grid at the socket pin, Sw.1 is thrown to "TEST." When the control -grid is at the top cap, Sw.2 is thrown to S. -G. (Toggle switch "NOR" on the panel is an "extra" for future use.)

The 5Z4 rectifier tube, having one different filament post, need cause no worry, because the cable feeds straight through, so that the filament posts in the set under test will occupy the same pins in the analyzer socket. To read the filament voltage of the 5Z4, set Sw.7 at 2, and Sw.8 at 8.

Current shunts are connected in leads 3 and 4. This may be extended to include all the leads, or toggle switches may be connected in several leads, and opened for current readings, the shunt then being connected to the scale -selector (Continued on page 488)

R5 -1 _LNK R111 10 AMP

{ CLOSED

`o C Sw.9

R2 5W.6

/ ti0 100

RS 500 T

R4 , 00

100

y 500

1,000

` SW3

. RC

O O

119

tt 0

LEÓÓS O.C. SW 5 A

7 704 7105

O' ],

s ...-i0 _e.

s0 6

ó/

7106 7107

.s.

51 2 a.' 'D-

i., i

7708

. s ` 6.0 42

2)r.0

t,,=5.

C-

. .l

-E-

1 s 1 _A_

RADIO -CRAFT for FEBRUARY, 19 3 6

2 NEW METAL TUBES! Here are two new additions to the metal -tube line. One is

a (first metal multi- purpose!) "improved equivalent of the 75 tube; the other is a full- fledged metal tube (it is a gas - filled filamentless rectifier), but glass -lined inside!

R. M. PURINTON

THE 6Q7 DUO -DIODE TRIODE This tube has circuit applications corresponding to those

used with the type 75 glass tube. Reference to the charac- teristics of the new 6Q7 shows noteworthy changes in the triode section. The amplification factor is 70 and the plate resistance 59,000 ohms -both lower than in the 75. The mutual conductance of the 6Q7 is slightly higher.

The result of these changes is a definite improvement in the signal -handling capability of the 6Q7. This tube is of the uni-potential cathode type; ype; heater rating is 0.3 -A. at 6.3V. Additional characteristics are as follows.

Triode- Section Class A Amplifier (Operating Conditions and Characteristics)

(Shell tied to Cathode) Plate voltage 250 100 Grid voltage -3 -1.5 Amplification

factor 70 67 Plate resistance,

ohms 58,000 84,000 Mutual conduct-

ance, mmhos. 1,200 800 Plate current, ma. 1.2 0.4

(Continued on page 492)

Base connections of

THE OZ4 RECTIFIER Since this tube operates through the ionization of a gas

contained in a glass inner bulb, it does not require a fila- ment. In basic principles the OZ4 is closely related to the gas rectifier. (This is a type of tube which Raytheon pioneered in 1922, and continued developing to date; sev- eral exclusive patents on this gas -type rectifier are held.) The cathode of the new rectifier operates at an emitting temperature thus permitting values of rectifier efficiency and voltage drop comparable to those found in a mercury - vapor tube, equipped with a filament.

The OZ4 was developed primarily for use in vibrator - type "B" supply units for automobile -radio receivers. It has the typical characteristics of all gas -filled rectifiers -

as regards (a) a constant volt - the 697 and 0Z4. age drop; (b) ability to han-

dle peak currents; and, (c) a tendency to generate R.F. noise. The R.F. noise (c) may be eliminated by proper filter- ing and by connecting the met- al shell to the point giving the best shielding. The shielding

(Continued on page 492)

+ OUTPUT

INTERRUPTED D C SOURCE

(BATTERY AND VIBRATOR)

The author compares the TESTING METAL -TUBE SETS testing of metal and glass tubes in radio receivers. WITH PRESENT EQUIPMENT

F. L. SPRAYBERRY

4ANY

SERVICE MEN are of the opinion that the metal tubes are entirely different from

their older glass cousins. Physically, there is a difference -electrically, how- ever, the principle of operation is the same in both types. It is not abso- lutely necessary to purchase new test equipment in order to test receiver cir- cuits using metal -type tubes.

Changes have been made, but they are not as radical as many believe.

The first thing that seems to worry

the Service Man is the fact that these new tubes have 8 prongs -one more than on any tube manufactured before. However, none of the new tubes have more elements than the former 7 -prong tubes. The 8th prong is connected to the metal envelope of the tube. This is done to give the metal envelope a good ground so that it will act effec- tively as a shield.

A ground or chassis connection on an analyzer is very useful (we advocated it long before metal tubes were intro-

duced), and it has been provided in many analyzers.

Since the new tubes do not actually have any more elements than glass tubes, they may be tested in much the same way.

Of course, an adapter and additional sockets must be used to make connec- tions between test equipment, tubes and the receiver. However, this will not present a serious difficulty if cer- tain fundamentals are kept in mind.

(Continued on page 492)

Fig. I. Circuit connections of the metal tubes and their adapters.

TOP VIEW (BOTTOM VIEW) 4 \ SCREEN

3 l PLATE

HEATER

1 SHELL

CATHODE

5 OSC. GRID

6 OSC. DIATE \7

HEATER

-C-

To I.F. PLATE.

2ND. DET, 6H6

2 ND. DET. XA.V. C. 6N6 _

-B/ OF (

KEY LL SOCKET

tL 1

TO FEED

FEED UNE

o Ipw A.V.0

UNE TO AUDIO

GRID -F-

m ©1 .-A-

TO AUDIO

Too VIEW OFSOCKET

GRID AV.C. 6H6 3 (BOTTOM VIEW)

PLATE O /

HEATER I 1.

B SHELL

CATHODE

GRID

7 HEATER

*(1 G 61L7 \ L d

OF V2

_ -E

ü o

TO IN E'C.

C TO CATHODE S.F. TUBE

a, °

,, OW (y)e °' m

CA wDE V

OF B +, ` -B

RADIO -CRAFT for FEBRUARY, 1936 463

MAKE THIS "RADIO" MOTOR This novel radio -operated device, shown for the first time at the New York Radio Show is easily constructed.

NATHAN I. HALL The crystal -operated motor made for the

N.Y. Show.

AN electric motor can be built using materials usually found in the radio fan's junk box which will run on radio power received from stations some miles

away. The construction of the motor is not at all diffi- cult and the average radio fan will find it both an inter- esting and instructive diversion from his usual radio ac- tivities. (This "motor," essentially, is a galvanometer pro- vided with bearings and a commutator that allow con- tinuous rotation in one direction. Editor)

As might be expected, such a motor cannot be used to drive any mechanism as all of the power developed is used in overcoming friction in the motor itself. The motor built by the writer will run on an input of one ten - millionth of a watt (armature current 7 microamperes and armature resistance 2,000 ohms) and can be truthfully called a "flea -power motor."

The major parts necessary for its construction are: a crystal receiver, a horseshoe magnet, a short piece of iron rod and some small enameled wire from an A.F. trans- former secondary or a Ford coil secondary.

As this motor operates on D.C. only, the purpose of the crystal receiver is to tune in the desired station and to change the R.F. current induced in the antenna into D.C.

A signal loud enough to be easily heard will be sufficient to operate the motor.

It is necessary that the current through the armature winding be reversed at the end of each half -revolution of the motor. On weak signals this must be done with a hand switch but on powerful signals it may be accom- plished with a mercury or metal -segment commutator.

Figure IA shows top and (Continued on page 488)

Fig. I. Details of the motor which will enable anyone to construct one from parts found in the junk box.

ADJUSTING BEARING BRASS AND LOCK NUT

PIVOT =op -/6

NARD WEBER

To - DET

BRACKET

-A-

COMMUTATOR

BRUSH

PET.

CYLINDER

PAPER COIL FORM

METAL SHAFT PIVOT

-D-

I BEARING

INSULATION SLEEVE

COMMUTATOR

NO OF STARTWF COIL ''.r COING ND-

MAGNET PIVOT 11 CYLINDER

BEARING

2,000 TURNS NR 40 ENAM. COPPER WIRE

-C-

IRON CYLINDER

FASTEN- ING

NUTS

UNIVERSAL OUTPUT TRANSFORMER

(PRIA--}

-TESTING -FOR VOICE COIL RESISTANCE-

4L1111'4\

15V CELL

0-1.5A METER

1-OHM.

RESISTOR

Testing voice -coil resistance for impedance matching.

THERE is on the market a "universal output" trans- former so designed that it enables the Service Man to service a large number of radio sets with a single unit

in the event of output transformer failure. Original per- formance is restored, and in some cases better than origi- nal performance is obtained.

The novel feature of the transformer is that although the primary is untapped, it matches almost any single tube or push -pull output stage. For push -pull operation, cor- rect primary matching is obtained when 71A, 45, 50, or 43 type tubes are used. For single tube output using the total primary, correct matching will be obtained with the 33, 47, 41, 42, or 2A5 tubes. One -half of the primary can be used to match to a single 48 tube.

Various secondary matching impedances are obtained by a tapped secondary. The taps are arranged to accom- plish the most uniform variation of impedances with a

464

A NOVEL

SELF-MATCHING OUTPUT TRANSFORMER Description of a novel transformer that is

matched to universal outputs by means of secondary taps, used in combination.

C. E. DeHORN minimum number of terminals. The range of load imped- ances is from 1 to 30 ohms. The various load impedances and their respective terminal connections are given below:

Impedance (ohms)

Terminal numbers

Impedance (ohms)

1 4-5 14 2 4-6 16 3 3-4 or 22

2-3 4 1 -3 25 8 3 -5 28

12 3 -6 30

Terminal numbers

2 -4 1 -4 2 -5

1 -5 2 -6 1 -6

Two other terminal combinations are possible but load impedances for these combina- (Continued on page 488)

The circuit of the transformer, left, and low -resistance ohmmeter, right.

P.p 45,714,47 OR

5NGLE 42, 2A5 OR 47 TUBE

PRI

SINGLE 48 TUBE

SEC

54 17. 3

OHM!

0-1.5 A..

5.5V (DRY CELL),

R, 1.0 OMM,

-8-

RADIO -CRAFT for FEBRUARY, 1936

A department in which the reader

may exchange thoughts and ideas

with other readers of RADIO -CRAFT.

READERS' DEPARTMENT

AMERICAN SET MAKERS PLEASE NOTE! London, W 1, England:

Some time ago I purchased from a radio dealer in London (England), a "Belmont" radio set and took it out to India. It worked splendidly for about six weeks, picking up most of the Continental stations, but then it developed faults -probably the insulation broke down -which could not be located. My dealer supplied no address of the man- ufacturer or its London agent, but I was able to ascertain the Chicago address and wrote accordingly -but no reply ever came. So the set was practically useless and no assistance could be obtained from the dealer.

I am in London, again looking over several portable American sets. There are several -such as "Sparton," "Kylectron" -but my difficulty, after previous experience, is the same -the dealers are unwilling to disclose the agents' or manufacturers' addresses, and no technical data, drawings or information are available on these sets. My personal experience of American manufacturers is that their products are above suspicion and so are their business dealings, and the only conclusion I can draw is that small dealers here, in order to obtain perhaps high percentage of profits and, fearing one might write directly to America, are adopting such practices. It would, I feel, be a greater advantage to American manufacturers if they issued their names and addresses together with those of their local agents with necessary technical details, which would create confidence in the purchase of their sets, as it is admitted here that in small portable radio sets no country in the world can compete with the U.S.A. (Thank you, Mr. Nissar.)

Perhaps it may be of equal interest to the manufactur- ers of "Kylectron" sets if I state my experience that for inquiry of their sets I called at the "Radio Center," 53/54 Haymarket, London, S.W. /1, an agency which is always too willing to assist and advise on matters relating to radio sets, and they gave me to understand that some one left a "Kylectron" set with them for demonstration, but they were unable to either trace the dealer or determine to whom to return the set nor had they any technical infor- mation on hand that would enable them to give any views on the set.

American enterprise in advertisem*nt is par excellence but this takes the cake in lack of proper advertisem*nt.

I am calling the attention of the American Chamber of Commerce here and would also appreciate your courtesy if you can recommend to me a small 5 or 6 valve (tube) portable set (the best on the market), and also ask the makers to send me details, as I would prefer to purchase directly from the States.

Is there any publication in the U.S.A. that will give full particulars on portable American sets or their parts to make up or assemble at home? Your journal does not supply necessary information on this matter.

A. R. NISSAR, % Thomas Cook & Son, Berkeley St.

Here, indeed, is an interesting expression of personal experiences, and one which it would be well for the manu- facturer with an eye to business expansion abroad to give consideration.

There are no publications that furnish construction de- tails for the home construction of factory -built sets, but there are several magazines, including Radio -Craft, that publish complete details, including an itemized List of Parts, for building up radio receivers of all sorts and kinds, from "1 tube -ers" to 10 and 12 tube jobs that do every- thing but wash and dry the dishes. However, unlike some of the English magazines, for instance, which devote a

RADIO -CRAFT for FEBRUARY. I 9 3 6

large portion of their editorial space to the construction of kit sets, American radio magazines seldom describe, in a single issue, the building of more than 2 or 3 radio sets of assorted types, since space must also be available for describing public address amplifiers, test equipment of all kinds, etc. (Except for imported units, tube checkers and set analyzers are an almost unknown quantity in Europe -it is probable that the lack of standardization in tube characteristics, prong and socket connections, etc., are fac- tors that deter even the most adventurous of manufactur- ers.) Several of the American "trade" magazines carry advertisem*nts by the foremost set makers, and the edito- rial columns of these publications include illustrations and reviews of the outstanding features of all makes of radio receivers. The more outstanding designs are discussed, in the Radio -Craft "Data Sheets."

A NEW RACKET? Long Beach, Calif.:

You have had many fine articles on the design and con- struction of P.A. equipment. Also articles on getting business along this line.

However, I have yet to see any mention of "The Authors & Composers Association." Personally I feel this is one of the biggest rackets in the radio -P.A. line. I know that all the radio and P.A. men in this district of California feel as I do on this matter, and I believe that you will find the feeling is the same wherever you go.

What is this association and what right have they to charge us to play popular music on our systems? Don't we pay for the records and sheet music and does not the price we pay include the royalties and cuts for making the records and composing the music? Why then, in order to play records or radio, or to pick up an orchestra playing popular music with our microphones, do we have to pay an additional royalty of $7.50 per day for a port- able amplifier or $300.00 per year for a permanent instal- lation? Haven't the artists or composers already gotten their cut on every record or piece of sheet music?

If the fee was $1.00 or $2.00 a day instead of $7.50, I believe that Service Men' would pay and say nothing, even if they felt it was an imposition. I do know that there are many Service Men (Continued on page 489)

The noted comedian. Milton Berle, had a seat away on the outskirts of the Baer -Louis fight where he could neither see nor hear the progress of the great battle, so he equipped himself with a small portable set and enjoyed

the fight! (We wonder, therefor, whether this "Berled" his neighbors!)

465

INTERNATIONAL RADIO REVIEW

Fig. A. An alkaline' 'B" unit popular in Australi .

Fig. I. An experimental aerial for reducing noise.

Fig. 8. A radio table of English design.

Fig. C. A tuning dial like the automatic phone.

RADIO -CRAFT receives hundreds of magazines from all parts of the world. Since the cost of sub- scribing to each of these would be prohibitive for most radio men, we have arranged with technical translators to prepare reviews for our readers.

A NEW ALKALINE "B" BATTERY THE percentage of "rural" (battery -

operated) sets in Australia is quite high, as many of the outlying towns have small power plants which cannot be depended upon for radio receiver power supply because of the wide vari- ations in supply voltage with varying loads. Also, many of the sets in use are located on farms and ranches where no electric power is available.

Thus, batteries are still a very im- portant item in radio reception "down and under."

Radio Review of Australia (Sydney) recently printed a description of a new "B" battery of the nickel- cadmium type, similar to the Edison battery. This unit contains small cells arranged in groups of 4, which, in conjunction with a unique built -in switching ar- rangement changes the wiring from a straight- forward series circuit to a series -parallel unit having 4 cells in each series group (see Fig. A). By this system, the battery can be charged from any 6 V. battery charger, wind - driven generator or similar arrange- ment.

NOISE -FREE ANTENNA AERIAL systems designed to reduce

the annoyances of man -made static have been sold, now, for some time - since the advent of the all -wave receiv- er. Various types, each having cer- tain advantages, have been made.

Another type, different in mechanical construction from the types available in the U.S. was described in Radio Magazine (Paris) recently. As shown in Fig. 1, it consists of a wire about 30 ft. long suspended between insula- tors and completely surrounded by a cage aerial, slightly shorter than the single wire and completely insulated from it.

The cage is grounded through a con- denser of 500 mmf. maximum capacity and a variable resistor of 5,000 ohms which are connected in series and each equipped with a shorting switch.

By correct adjustment of the re- sistor and condenser, it is claimed that local man -made static noises can be completely eliminated by the shielding effect and (Continued on page 489)

Fig. D. A receiver disguised as a group of books for use on a library table.

Fig. E. A hi- fidelity set of German design.

Fig. Fig.

F. A hexagonal- shaped radio -phono. cabinet. G. A cylindrical -shaped radio and automatic

phonograph turntable and pickup.

466 RADIO -CRAFT for FEBRUARY, 1936

WAR -TIME USES OF RADIO Radio is now used in all branches of warfare; but then, "wireless" communication was essential even in 1 184 B.C.!

E. W. SLOPE ETHIOPIA and Italy at war pre-

sent factors of greater political and economical importance, and more tactical interest than any

that have arisen in other conflicts within the last 30 years. A highly mod- ernized army, equipped with all the de- vices science can provide, fights against an enemy army which is (despite the fact that some modern weapons are available to the Ethiopians) of ancient organization. Our interest in this struggle is not only in the strategical value of the application of modern ma- chine guns. airplanes and tanks in a country of wilderness, but in the test of the communication system utilized in this war.

It is an old strategical axiom that "an army is as good as its communica- tion system," and tactical dogma that "an army without a properly function- ing communication system has about the same value as a chain with some disconnected links." What may be the nature of the communication system does not matter as long as it fulfils its purpose, and effectively parallels the system utilized by the enemy.

"WIRELESS TELEGRAPHY"

IN THE YEAR 1184 B.C.!

The efficacy attained with an old - fashion communication system in war- time is described by Aeschylos, in his famous "Agamemnon" (verses 274- 309), in which he reports how the Greeks (in the year 1184 B.C.) after their victory over Troy, in Asia Minor, telegraphed their jubilant message to

Greece in a surprisingly short time, by means of 9 relay fires kindled at the tops of high mountains, and bridging by this first -known example of "wire- less telegraphy" in history, a distance of about 320 miles.

In more recent times, the importance to victory, of a well -functioning com- munication system, was impressively demonstrated in 1914, by the famous Marne victory of General Joffre UV 'r the Germans. This victory was mace possible not only because the Germans had over extended themselves and had also a defective transportation system, but due also to their communication system which at this time did not func- tion efficiently. The Ethiopians try to copy General Joffre's tactics, permit- ting the Italians (as did Joffre) to oc- cupy important points, even going so far as to cut the unique Djibuti -Addis Ababa railway. But it seems the Ital- ians also have learned from the Marne battle and are careful not to be strung out without immediately setting up an extensive communication net w o r k , which in November, 1935, saved them from defeat in northern Ethiopia.

"SWS" AN ENGLISH SECRET

Still other World War battles were won -and lost, via the communication - system route. The great North Sea battle off Dogger Bank started, to the dismay of the Germans, by the inter- ception of important messages. As a result of messages picked up by the se- cret "SWS interception stations" on the east coast of England, the German High Sea Fleet (Continued on page 490)

RADIO -CRAFT for FEBRUARY, 1936

Newest British "pocket" submarine (e xtreme left); note radio an-

tenna.

Left, another "mystery ray" machine which has its power supply in the large box (which is the carrying case for this entire. demounted Ger-

man "station ").

Right, newest English tank; note aerial. The set works on 9.23 meters

with 2 W. power.

P dal -powered I W. portable station which may be u ed for fone or C.W. work. This German field

radio is depicted ready for operation.

U.S. Coast Guard planes equipped with a loop antenna enclosed in a bakelite "egg" gain 5

m.p.h. more speed!

Two -way radio equipment in the co*ckpit of a U.S.A. Curtis Raven light bomber. Note that the

apparatus is entirely covered.

adio operators of the Italian Army in action. These sets are of the loop type and the batteries are in

the lower boxes.

467

FIRST PUBLISHED DESCRIPTION! In this exclusive article RADIO -CRAFT presents the first description in America of the radically new cathode -ray type of detector, amplifier and oscillator tube. According to available data it apparently results in more selective, sen- sitive, and noiseless performance than present grid -type tubes! It appears to rank in importance with the recently - announced (Jan. 1936 issue) Zworykin electron -multiplier "ray' -type tube.

Fig. B. The appearance of the tube elements.

468

THE RENODE- ANEW GRIDLESS TUBE A revolutionary Danish radio receiving tube of "cathode -ray" type is announced in this

exclusive story by our Danish correspondent.

SVEND ANKER -RASMUSSEN

Fig. A. The internal structure of the tube

showing the cathode sur-

rounded by a shield hav-

ing a slot cut parallel to

its axis; an "intensifier" to speed up the elec-

trons; two "deflectors" to control the electron

stream; and a plate.

GRIDLESS vacuum tubes, in a new series, have just been in- troduced in Denmark! Due to a peculiar patent set -up, Den-

mark has been subjected to excessive licensing fees, and it is this situation which the new tubes have been designed to circumvent.

The following technical and political explanation outlines the characteristics and conditions under which the Renode, as the new tube is called, has been in- troduued.

OPERATES ON CATHODE -RAY PRINCIPLE

In principle, the Renode has some resemblance to the Braun tube, the workings of the former being founded upon deflection of cathode rays (first utilized in the latter).

The interior arrangement of the elec- trodes in the Renode is shown in Fig. lA. The circle indicates a cross - section view of heater; and cathode, K Element C is a metal screen or shield (hereinafter called the concentrator) ;

it surrounds the cathode, and has a slit across it parallel with the length of the filament. Electrode I is an aux- iliary plate termed the intensifier; it is plate- shaped and has in the middle of it a slot of exactly the same size and position as the one in the cathode screen. Plates Dl and D2 are called deflectors. The ordinary plate or "anode" is identi- fied as P.

Now let us proceed to see how this arrangement works, by referring to Fig. 1B. Potentials are applied to the elec- trodes as shown; cathode, and deflect- ing electrodes D1 and 2 are at zero vol- tage; the intensifier, I, and ordinary plate, P, under a certain positive po- tential; and the concentrator, C, at a suitable negative potential (as indicat- ed by [- - -])

Under such conditions a concentrat- ed, straight -line electron beam, the out- lines of which are defined by the aper- tures of the concentrator and intensifier electrodes, will flow across to plate.

CONTROLLING THE BEAM

Now, if the numerical value of the concentrator potential is decreased (as indicated by [ - - ], in Fig. 1C), the beam will spread itself out in the mid- dle between the deflectors. A further decrease of the concentrator potential ([ -], in Fig. 1D) will result in some of the electrons touching the deflectors, which are thus compelled to receive a certain number of electrons.

When the value of concentrator po- tential required to bring the tube func- tions into the state illustrated at Fig. 1D is found, the goal of "ordering the cathode ray" to suit a purpose has been reached. If R.F. currents are now ap- plied to the deflectors, as shown in Fig. 2A, the beam will be deflected alternate- ly towards either of the opposite de- flector elec- (Continued on page 493)

Fig. I. The tuba action in detail.

CONCENTRATOR INTENSIFIER

CATHODE IOI (K PLATE

(p) (

(DI DEFLECTORS -A-

-B- + O +

--- -C- + o +

o . -- il I

-D- + 0 + CycE o

Fig. 2. The circuit for detector action.

RADIO -CRAFT for FEBRUARY, 1936

NEW DEVELOPMENTS IN

ALL -WAVE RECEIVER DESIGN With the number of tubes in some of the new sets running to 20 and more, users wonder if all of them are needed.

THE NEWEST all -wave sets are becoming more and more compli- cated with each succeeding model, until the long- suffering consumer

begins to wonder if he couldn't get along just as well with a lot fewer tubes. We shall try to explain herein some of the uses of this multiplicity of tubes as well as some of the other complications of one example of the latest in phono.- radio combinations.

In the first place, the general trend at present seems to be toward the cover- age of a wider band of frequencies, in order to include more of the interest- ing types of transmission on the air. The set illustrated diagrammatically be- low has a range of 140 to 410 kc. and 540 to 60,000 kc., the space being left, as usual, because of the I.F. amplifier which is tuned to 460 kc. (at which

I.F. an R.F. "dead spot" is produced). The use of metal tubes is becoming

more widespread all the time, and de- spite arguments of the relative worth of metal and glass tubes, the fact re- mains that there are several entirely new types in the metal line which have been found exceptionally useful and efficient. One of these is the 6L7, 2 of which are used in the circuit below; one as a 1st -detector or converter, and the other as an "expander" tube, which latter will later be explained in more detail.

The 6E5 cathode -ray tuning tube naturally cannot be made of metal since the tuning indication must be viewed on the elements of the tube. It is one of the latest types though and counts as "1" in the surprisingly high total of 22 tubes!

The use of a separate A.V.C. ampli- fier and rectifier tube is quite wide- spread nowadays. At first glance this seems to be merely another method used to swell the already large number of tubes. However, the use of these separate tubes provides a much better control of output than if the A.V.C. duty was loaded onto the 2nd -detector.

The push -pull audio stages are used to obtain greater power and better tone quality than would be the case if single -tube stages were used. The out- put stage of the circuit pictured is rated at 25 W. While this is away above that needed for the average use, it in- sures that when a loud low note comes through, there will be sufficient power to reproduce it without distortion.

The output of 25 W. may not be needed so (Continued on page 505)

Fig. I. Circuit of one of the newest all -wave radio -phono. set -the RCA model D 22 -I. The phono. section includes an "expander" in its amplifier.

RADIO -CRAFT for FEBRUARY, 1936 469

NEW GERMAN TELEVISION RECEIVERS Two new television receivers are described -one a reason- ably priced instrument and the other a super -set.

MANFRED VON ARDENNE

TELEVISION technique is now 50 years old- therefore, it is much older than even the earliest types

of radio telegraphy, not to mention radio broadcast transmission. Still, de- spite its antiquity the technical devel- opment of television is still far from its final goal. Each month brings tre- mendous strides towards perfection of image reception. Today, the drawing board and pencil are tools that permit the research laboratory worker to pre- sent a graphical fixation of his ideas much more rapidly than can a corps of dexterous artisans convert the ideas born in the laboratory into devices for practical application.

An impressive demonstration of the progress in German television technique was given at the recent Berlin Radio Show. One of the displays included the inexpensive television receiver shown in Fig. A. This model, devel- oped in my laboratory, is produced in a series of small models by the firm of C. Lorenz, A. G.

A television receiver having much greater dramatic appeal is shown in Fig. B. This set was designed accord- ing to my own latest ideas, and was built by C. Lorenz solely on a quality basis -that is, without regard to cost, just to show what could be done, and also to point (Continued on page 505)

Fig. C. The wide -range amplifier discussed.

OUTSTANDING MERITS OF METAL TUBES A comparison of the dimensions and operating character- istics of glass and metal tubes.

HERBERT M. NEUSTADT

that the metal tube is much shorter than the glass tube. In Fig. C it can be seen that the smaller size of the metal tube is not due to any reduction in the size of the electrodes. The all-

metal tube, as a package, contains just as much vacuum tube but wraps it up with less waste space.

The compact structure of the all - metal tubes (Continued on page 503)

Fig. B. Tube -sits comparison. Fig. C. Comparison of elements. Fig. D. Comparison of leads.

I ; Ij á

_ _ :)

---..

` _

f ,,.,,

------

j __ t

} U' +'

±.t

Fig. B, above. Von Ardenne with the deluxe set.

Fig. A, below. An inexpensive television set.

Fig. A, G.E. (experimental( metal tube No. I!

NW THAT the all -metal tubes O are in everyday use, it is becom-

ing more and more evident that they have several outstanding merits. These merits seem increasingly impor- tant as set designers and Service Men continue to acquire experience in work- ing with these tubes.

In the first place, all -metal tubes are compact. Small size is one of the quali- ties that impresses you immediately when you inspect an all -metal tube. It is mainly because of this small size and because they require no shield cans that some of the new sets are so compact. This compactness of the all -metal tubes is illustrated in Figs. B and C where a 6K7 is compared with its correspond- ing glass tube. You can see in Fig. B

470 RADIO -CRAFT for FEBRUARY. 1936

ANALYSES of RADIO RECEIVER SYMPTOMS OPERATING NOTES

LYRIC MODEL S -8 HE customer complained of noisy reception saying that the set would sometimes play

well for 5 minutes or so then go noisy again. A shorted condenser, Cl, Fig. lA, was found and replaced but the noise continued. Finally the A.F. input transformer was replaced and this cured the trouble. This transformer had checked OK on a resistance test.

CROSLEY MODEL 102 AUTO RADIO WHEN circuit o.cillatea and load: up, test

the 6117 second -detector tube. which will usually be found to have low emission.

When this same set goes entirely dead, the 0.1 -mf. condenser across the power transformer secondary, Fig. 1B, will often be found shorted.

J. H. PARKER

GENERAL ELECTRIC K -64 ON EVERY General Electric model K -64

radio receiver we have received, we have had the trouble of reception cutting off and on as the tuning dial was rotated. As soon as the chassis was removed from the cabinet, the trouble would correct itself.

We have found the cause to lie in a bare wire that connects the stator plates of the condenser gang to the wave -band switch, and which runs close to another bare and grounded wire. The condenser gang is mov- able, inasmuch as it resta on rubber cushions. Now, when the chassis is inserted in the cab- inet, downward pressure is put on the con- denser by way of the shaft that protrudes through the hole in the cabinet and which rube against the upper side of it. This forces the two wires very close together and the least movement of the condenser gang will short them entirely. To correct this trouble, simply separate the wires about twice the distance they were originally.

GENERAL ELECTRIC K -52 AND K -53 HAVE been called to service several

General Electric models K -52 and K -58 radio receivers in which there was considerable hum present. The receivers were operating without a ground connection, and the simple procedure of affixing a ground stopped the hum, whereas other methods had failed.

A.C. -D.C. SETS IN THE small universal A.C. -D.C. radio sets

of several different makes we have increased the sensitivity by taking a short piece of wire (insulated) and attaching it to the stator plates of one section of the condenser gang and making about 4 or 5 turns about the wire leading to the second- section stator plates.

JAMES G. SHELLER. JR.

ATWATER KENT MODEL 45 TROUBLE: volume very weak. Cause: no detector plate voltage. Effect: detector plate

voltage dropping resistor in power pack was found to be open. Inspection of the resistor disclosed a loose metal cap at one end. (This

particular resistor is constructed of a carbon element enclosed in a glass tube with metal caps at each end sealed with solder.) By heating the loose cap with a soldering iron, the old solder was cleaned out and fresh solder applied to re- seal the cap.

The repaired resistor showed no change in value when tested and when placed back in the power pack, the receiver was restored to full volume.

WM. PAUL SPORKA

PHILCO AUTO SET THIS set was installed in a Dodge car and the 1 complaint was intermittent operation. The

trouble seemed to indicate a bad tube but upon checking them, none was found defective. A hard jar would cause the radio to play tempo- rarily. All parts checked perfectly and no loose wires could be found. Eventually the trouble was found in the I.F. coil. Two small nuts on the top were slightly loose. and when tightened the set gave no further trouble.

GAROLD F. SIiRr HARD

PHILCO MIDGET IHAVE often found when servicing this re-

ceiver that the 75 tube is microphonic. These tubes usually teat OK in a tube tester, but when the receiver is jarred or struck sharply, noises are most often traced to this source.

RCA -VICTOR R -17

BY REPLACING the .004 -mf. condenser, con-

nected across the primary of the output or speaker transformer, with a .01 -mf. condenser of the tubular variety, the tone quality is greatly improved.

EMERSON "MICKEY MOUSE" MODEL

THIS receiver is a very small compact midget that sometimes develops an annoying hum

when in service for a short time. This hum can be greatly reduced, if not entirely elimi- nated, by connecting a condenser of high capac- ity, between one side of the line and the chassis. Another method to reduce this hum is by changing the position of the 100 mmf. coupling condenser. The best position for this condenser can only be ascertained while the receiver is in operation.

RICHARD B. GRAF

CROSLEY 58 COMPLAINT: Switch had to be thrown a

half -dozen times before set would play, although tubes and pilot would light. With the "innards" exposed, the placing of the test prods on any part of the "B" voltage system would start the set.

All condensers and resistors. on a separate test, showed OK. I then placed the voltmeter across each condenser with the set off, and then snapped it on. After a few trials, the trouble was found in the condenser bypassing the detector grid -bias resistor. This con- denser was shorted but the least change of voltage would clear it up.

Fig. IA. Noisy reception in a Lyric 5.8.

PLATE é MMC o C2

DET1ti CI

This CON- DENSER SDORrEO

C4 600ROINMS

Cs 30.000 ONMS R2

27 OSC

-A-

RADIO -CRAFT for FEBRUARY, 1936

MAJESTIC 70 THIS set would play for about 5 minutes and

then die away. A snap of the switch. off and on again, would bring the signal back again but it would die out in about a minute. After a great deal of "fusain' around" the fault was located in the filament winding of the type 26 tubes. The voltage would show 1.3 V. when first turned on, then would gradu- ally drop to 0.6 -V.

MAJESTIC 130 -A OSCILLATION from 900 kc. to 550 kc. Bal-

ancing did no good: voltages were OK: condensers tested OK. Poking among the wires in the bottom of the set, I moved the ground lead of the .04 -mf. condenser in the grid circuit of the first R.F. tube and noticed a change in the pitch of the oscillation. I disconnected the lead and the oscillation dis- appeared. A new condenser was tried and the oscillation returned. After trying a couple more with no better results, I returned the set, minus the condensers. Calling around

few days later. I was informed that the set worked better than ever before. (The writer has no explanation to offer for the cause of this fault, or its cure.)

SILVER -MARSHALL MODEL A

THIS set was found with 3 resistors so

changed in value that the voltages were all "haywire." Replacement cleared this up but the receiver didn't have the kick a set of this type should have. A study of the diagram re- vealed an 0.1 -mf. condenser across the 47 -tube bias resistor. I tried a 10 -mf., 25 V. electro- lytic condenser across this resistor and the volume increased considerably, and the tone quality was improved.

SILVERTONE 117 AND COLONIAL 36 A.C.

THESE sets have the same circuit and chassis. In table cabinets the dial must be turned

to the arrow before the chassis can be removed from the cabinet.

RADIOLA 60 IF THIS set acts as though the variable con-

densers were shorting to each other, ex- amine the pilot light bracket. It may have dropped down against the drum dial.

JAMES J. WALTERS

CHAMPIONETTE 5 -TUBE MIDGET

THE receiver. after being turned on, would

bring in a station as soon as the tubes were warmed up and then would fade away com- pletely and remain "dead." All voltages checked OK except that of the detector tube screen -grid, which read 150 V. (a value which was too high). Everything else checked OK so I meas- ured the carbon resistor which is connected be- tween the high -voltage lead and the screen -grid of the detector tube. This resistor. which ac- cording to the color code should have been 25,000 ohms measured only 8,000 ohms. Upon replacing that resistor with a new one of 25,000 ohms. the radio set worked normally.

(Continued on page 487)

Fig. 18. Trouble in power supply of Crosley Model 102.

This CONDENSER SNORTS

I --- 01-MF F 11 600v. DROWN B+ `r FUSE

YELIOw M.A. i,iiat,rA aY R.CCN. .)

/ MF 1

1U1111.1 O.1-MF (EKN) bNiFLDA-----_ GrID_ -J SvNCN40NOUe_VieRATOiL

471

Soundproof box containing the record changer.

"Master control" box located in owner's room.

,f'- lu, I! i l l AL_,

, s;9. f\ (

F.!i: >Jí1t+sìaRSROIFsss»_:-- .._. .

One of the many loudspeaker installations.

The actual apparatus installation.

iWC[ on so.. too 2r 56.5+, re sDDOn URED c bCS t44.

p".5

J ai4)J(wER /

21AF l T2 óF

3.000 HT C O.EPR

rR.wlOf C OR RES.i- roes Os 0 t-rEG (EACH,

4Ce.DC IF C USED Ow AMA Cv RESISTOR WITH CENTER ORO

200 V

472

A $30,000 "RADIO" INSTALLATION First published description, exclusive to Radio -Craft, of a

millionaire's "radio" system conte ning features of interest to the home constructor; uses Hiler- patent A.F. system.

RUSSELL D. LANNING

SEVER.% years ago the writer was first called in by a millionaire in upstate New York to install a "radio" system that would be the

finest available in reproducing radio and phonograph programs. Continuous de- velopment from this starting point has resulted in the superlative installation here illustrated and described for the first time in any publication.

Costing over $30,000, to date, the sys- tem incorporates many new and novel features, some of which are patented. Many of these interesting items are here highlighted as being of interest not only to the technician but also to other home owners appreciative of unusually good voice and music reproduction, and of equipment installed in a manner as befits a luxuriously- appointed home.

The installation pictured here uses as many as 8 speakers in one room! Each reproducer placement is equipped with speakers designed for a special band of frequencies and with an adjustable fil- ter network in each voice coil, as shown in Fig. 1. In the library, two speakers ar3 designed for covering the frequency range from 30 to 400 cycles, two from 200 to 1,500, two from 200 to 3,500, and two tweeters from 2,000 cycles to the upper limits of present -day reception.

Although the sound system is superb, the method of control is still more novel and about the neatest system ever con- ceived.

A FINE REMOTE- CONTROL SYSTEM

Each master control box is equipped with a gold telephone dial, a station - registering dial calibrated in kilocycles, 2 pilot lights, phonograph switch, rec- ord- reject button, on -off switch for A.V.C., radio set volume control, phono. volume control, manual tuning key, mas- ter lock -out switch, speaker mute and on -off switch.

Any one of several favorite pre -tuned stations is selected by a flick of the dial

Fig. I, right. Block drawing of the A.F. out- put system showing how the many speakers are all connected to the

audio rack.

Fig. 2, left. Details of the patented push -puI detector circuit used in this outstanding instal-

lation.

(each hole in the dial corresponding to a station). At the instant of moving the dial, the reproducers are silenced, a red pilot glows, and when the station is tuned -in the light goes out and sound is heard. The method of driving the radio tuner is so precise that pre -selected sta- tions tune to resonance on a tuning meter from either direction, and because of the fact that all master boxes are equipped with indicator dials the move- ment of the tuner is noted in any room equipped with a master box.

Some rooms are equipped with minia- ture boxes which do not include the sta- tion indicator or manual tuning keys.

The cables which go from the control boxes are no thicker than a lead pencil and all are run through galvanized iron pipes to distribution points.

The master of the house may always be assured of non -interference because of his favorite room being equipped with a lock -out switch. This permits others elsewhere in the house to listen, but only he may tune or operate the outfit.

The automatic record changer is a standard instrument equipped with a specially- designed 200 -ohm pickup and a matching T -pad volume control. This mechanism is mounted in an almost sound -proof room.

A "NOISELESS" INSTALLATION

A "standard" installation of the equipment resulted in annoying sounds as the records changed, even though the doors to the cabinet were closed. In order to overcome this disturbance, it was necessary to line the cabinet com- pletely with celotex and felt, and mount the turntable and motor on a felt -insu- lated board resting on sponge rubber. Upon closing the doors when this was done not a sound could be heard.

A hum frequency from the reproduc- ers was another difficult problem, for, whereas a very slight hum cannot be heard in an (Continued on page 494)

500 0.-S

vuo. _ ! -;,Rr..oS à u .. !,frn .,,. ro

0 M> ,00,. 0 . KO.

s-. El. 500

oo,,,wr o. eH

RADIO -CRAFT for FEBRUARY, 1936

C. A. MORRISON THE LISTENING POST FOR ALL -WAVE DX -ERS

A well -known short-wave DX- er -Mr. Irv- ing Goodeve of Kalamazoo, Mich.

IT IS the "unexpected" element in DX reception that makes it interesting. Radio will some day be a Science; at present, however, much about it is unknown. It is these mysterious elements, these unknown equations that

fascinate DX -ers. There are many factors about DX recep- tion that are inconsistent. Often the slightest change in weather, location, or aerial will bring amazing changes in our DX reception possibilities. Strangely enough some of our best DX -ers are located in busy city districts, sur- rounded by all kinds of interference.

My own reception location is far from ideal, as I am located on the corner of two busy streets with plenty of automobile traffic, and other sources of static to contend with, and yet by patient effort, I have managed to cap- ture quite a number of elusive DX goals on the short waves. On the other hand I seem to be in a dead spot as far as broadcast band foreign DX reception is concerned.

During the season of 1931 -1932 I lived on the same street, but two blocks distant, and yet my carefully -kept log shows I received as high as 18 or 20 trans -Pacific broadcast stations on some nights at that location. Since moving to my present location, despite improved aerials, more powerful transmitting stations, and more sensitive receivers I just can't seem to tune them in here! EFFECT OF LOCATION ON DX

RECEPTION

A slight difference in geographical location often makes a great difference in short -wave reception also. Recently I had the thrill of picking up TFJ, Reykjavik, Iceland (12.23mc.) direct, on the occasion of their broadcasting a program for North America. They were heard quite plainly, and with a good signal. A friend of mine with similar equipment, and in a much less noisy location at the edge of town was unable to even pick up the carrier wave of TFJ on this broadcast, although I let him listen to them over the phone from my own receiver! On the other hand this same DX -er tunes in the Japanese, Java- nese, and Philippine phone circuits ev- ery night with good intelligibility while it is only rarely I am able to receive them here.

An even stranger experience occurred one night last winter when we were tuning -in the 7 mc. amateur channels for a certain Buenos Aires amateur. Two idr ntical receivers had been set up in the same room in order that both ends of the conversation might be heard. On one receiver the Spanish ham was received with a good R8 signal, while on the other receiver the station could not be found at all, even after repeated attempts!

IMPORTANCE OF THE ANTENNA

There is little doubt that aerials play a very important role in DX -ing, especially in short -wave DX -ing. Give

Broadcast stations have recently been erected in both Iceland and Greenland for supply- ing the natives with programs of their own music. The picture fo the right shows a group of Greenland folks broad- casting native songs over the stations of the Danish Broadcasting

Co.

RADIO -CRAFT for FEBRUARY, 1936

The Monte Ceneri IS kw. broadcaster lo catad in a remote part of the Swiss Alps.

me a fair receiver with a good aerial array, rather than an extra good receiver, and a poor aerial layout. The great importance of aerials is clearly demonstrated in the re- markably fine standard of program perfection that is at- tained in our network relays from foreign countries, which are picked up at Riverhead, Long Island or some other commercial receiving station preparatory to being fed to the chains. Often when we are barely able to hear the station which they are picking up, the same program on the broadcast -band relay is very excellent. The answer to this is, highly efficient directional receiving antennas plus battery receivers, and a quiet location. The tiny 8 -W. trans- mitter of the Army Air Corps stratosphere balloon, W1OXFH, which tested daily on 13.05mcs., came in very well here -but only on one antenna. W1OXFH could not even be heard on any of the other aerials! In this case the successful antenna was an underground one!

LSN3, Buenos Aires was heard here on their inaugural broadcast with very good signal strength, and audibility, with a 2 -hour program, in which frequent announcements were made in English. I naturally thought every one DX- ing that evening would run across this station, and yet after 2 weeks not a single DX-er had reported reception of this broadcast. Can you account for this?

One morning nearly 3 years ago RNE, Moscow, was heard the first time and with a tremendous loudspeaker signal. Never since that time has RNE ever been heard with anything like this record volume. Apparently every condition for perfect transmission was present at that time.

NIPPONESE BROADCASTERS

Although up to this date foreign broadcast -band recep- tion might be termed a wash -out this season, the Japanese broadcasting stations continue to roll in, for those DX -ers located in the western states. At this time of the year chance are best for receiving (Coo lion ed on onge 496)

473

The author examining the output of a receiver with the aid of the oscilloscope e won in Radio -Craft's recen contest! An oscillator and frequency modulato

are essential. Fig. I, below, Simplified block diagram of the units in the set -up

UN MODULATED R. F OUTPUT

OSCILLATOR 4.

f MOD. SYNC. VOLTAGE

FREQUENCY J ,

MODUL ATOR.

TO 2ND DET 1 OUTPUT

D ANT

I GND

VERTICAL

O PLATES

1 - EST. SYNC. -

:11 . ,ice -.:: CATNOOE -RAY OSCILLOSCOPE

OSCILLOSCOPE SERVICING OF ALL -WAVE SETS

The I st -prize (oscilloscope) winner in Radio - Craft's recent service contest tells interest- ing facts about oscilloscope servicing.

E. E. SAYRE

AIGNMENT of all -wave receivers by the cathode -ray oscilloscope method brings to light some interesting facts that are not usually noticeable in ordinary

broadcast receivers. One of the most interesting observations that can be

made with the oscilloscope is in seeing the changes in the shape of the sensitivity curve of a receiver that take place as the set heats up after it is turned on.

To observe this phenomenon it is only necessary to connect the oscilloscope and its associated equipment to the receiver under observation as shown in Fig. 1, remembering of course that in making an experiment of this kind it is necessary to use a service oscillator and frequency modulator of known stability. SET MUST REACH "OPERATING HEAT"

The receiver first should be allowed to run for a half -hour or so until it has been thoroughly heated, just as it would if it were in actual service, before beginning the alignment procedure.

Carefully align the receiver so (Continued on page 497)

NEW METAL -TUBE CHASSIS SIMPLIFIES "MODERNIZING" OLD SETS A metal -tube modernization chassis permits owner to re-

tain an old, expensive radio cabinet -and speaker set -up.

TOBE DEUTSCHMANN

STATISTICS show that one out of every 3 receivers sold during the last half- decade has gone to re-

place an antiquated receiver rather than equip a new radio home. However, it is estimated that there still are close to 8,000,000 out -dated receivers in opera- tion. The reason for this is the fact that most of these receivers were pur- chased during a period when the aver- age price of a radio receiver was about

Fig. C, a "modernization chassis" with metal tube ,

474

$170.00, and the owners naturally are loath to junk what represents an in- vestment of this nature. Also, many of these receivers are housed in expen- sive cabinets which have been especial- ly selected to harmonize with some par- ticular scheme of decoration.

However, the advantages of modern radio reception may be had by complete modernization of the old receiver; and it is possible to accomplish this at a cost considerably under that of a new re- ceiver giving comparable results. In this system (to be described) the cabi- net and often much of the old receiver are retained, thus safe -guarding the original investment. THE MECHANICS OF MODERNIZATION

There is no place in this article for detailed concern with the technical con- siderations associated with moderniza- tion. It is assumed that the Service Man is an ex- (Continued on page 509)

Above, Fig. A, a rebuilt set housed in an owner's original R.C.A. REI7, cabinet. A new panel ha been made. Below, Fig. B, a comparison of the old

and new panels.

RADIO -CRAFT for FEBRUARY, 1936

SERVICING THEATRE SOUND SYSTEMS

PART I I I

In this (concluding) part, high -fidelity, speaker installation and placement, and screens are discussed.

A. V. DITTY

DYNAMIC SPEAKER field sup- plies for A.C. use a transform- er and either an 80 -type tube with condenser filter or a dry -

disc rectifier with condenser filter for the D.C. voltage. Units used with air - column horns have a field supply of the latter type. The chief source of trouble is in the rectifier, causing hum and low voltage to the field and consequently low volume from the inefficiency of the field. Leaking or open- circuited con- densers will cause considerable hum in the speaker unit. CORRECTING FAULTY REPRODUCERS

Rattling or rasping sound from the speaker units might be caused by metal filings or other foreign particles be- tween the voice coil and the field core or housing. Loose or torn diaphragms or cones, warped voice -coil cores rub- bing against the field core, or loose voice -coil windings will also cause fuz- ziness. Use either thin shellac or flexi- ble collodion for repairing the cones or voice coils. A magnetized needle or other small- pointed object and a pipe cleaner will usually get the filings out. After cones or diaphragms get old or warped they may have a resonant point other than their natural resonating point, at which a "tinny" or "rattling" sound will be heard. The best thing to do in this event is to replace the cone and diaphragm. Voice coils may be centered by cutting an ordinary calling card into strips about a quarter -inch wide and inserting them, properly spaced, between the voice coil and the field core. Remove strips after tighten- ing the centering lock screws. Use the above procedure for servicing both types of units. Sometimes grounding

Fig. 9. Details of speaker placement and

the speaker unit and field- supply case will help to lower the A.C. hum level.

The number of reproducers required and the proper placement of them will be controlled by the size and shape of the auditorium, and limited by the power output of the amplifier. An item of much importance in speaker installations is the speaker efficiency, that is, the ratio of the amount of electrical output of the amplifier to the amount of acoustical power delivered by the reproducer (or, the amount of electrical energy of the amplifier trans- ferred to acoustical energy by the speaker or reproducer).

Table I Contents No. of

Cubic Feet Seats 75,000 500

200,000 1400 600,000 2500

1,100,000 4000

Undistorted Power Output

5 Watts 10 Watts 20 Watts 40 Watts

DETERMINING REQUISITE REPRODUCERS

With the cone -type dynamic units, the efficiency ranges from 3 to 10 per cent with the later reproducers, while the air -column horns or exponential horns are rated at 40 to 50 per cent efficient. The latter are favored in long and comparatively narrow houses, while the former are used with flat baffles or directional horns to suit the wider houses or for special placement. In the very wide houses and houses with balconies, banks and rows of speakers on flat, adjustable baffles or in adjustable, directional horns, provide for proper sound distribution.

The purpose of the exponential horn (or air -column horn) is to isolate a column of air and to set up sound vi-

elevation. for correcting sound distribution.

-FLOOR PLAN- /- SCREEN

BAFFLE AXIS

-SIDE ELEVATION.. .- SCREEN

ONE SPEAKER BAFFLE

L L

AXIS

-B-

S REEN/ -FLOOR PLAN-

/SEATS /BAFFLE AXES / ANGLES BISECTED /

ONE SPEAKER

-A-

TWO SPEAKERS \ SIDE BY SIDE HOUSE

C I L

-SIDE ELEVATION- SCREEN

TWO SPEAKERS - SIDE BY SIDE \. BAFFLE

WIDE HC J 5E

3 L I D-

-SIDE ELEVATION- SCREEN

TWO SPEAKERS-ONE ABOVE THE OTHER.

-..... BAFFLE AXES il LONG HOUSE

L J L 2 -E-

-SIDE ELEVATION - SCREEN BALCONY 1

TWO SPEAKERS -ONE - - ABOVE THE OTHER -' -..-

ANGLE TRISECTED

Y Th-----__ ss BAFFLE AXES

F L ' L- I f~ -. RADIO -CRAFT for FEBRUARY, 1936

Fig. E. An exponential horn with a cone-type dy- namic unit. Note the angle for proper sound

distribution.

Fig. F. Twin exponential horns mounted on a movable tower for correcting defective distribution.

brations therein. The exponential horn itself is not an amplifier of sound waves as is commonly supposed, but is a device to match the high impedance of the speaker unit to the low imped- ance of the isolated column of air. The horns should be placed nearest the center of picture voice action, that is, about two- thirds of the way up and in back of the screen. Speakers should be mounted with the imaginary sound beam center lines directed as in Fig. 9A to F. All drawings are self ex- planatory. SOMETHING ABOUT BAFFLES

Baffles for cone -type dynamic repro- ducers should not be less than 4 ft. square, with a maximum of 10 ft. square. The baffle board should be of some soft, non -resonating material such as s -in. celotex or masonite and should be placed 2 or 3 ins. from the back of the screen. Baffles should be painted a dull black so as to not reflect any light from the picture source. (Using wood for baffles defeats the purpose of a baffle by making a sound- ing board out of it and giving increased amplitude to the particular frequencies at which the wood will resonate. This will give peaks on the sound curve, while the object is to keep the curve as nearly flat as possible.) If the theatre is too reverberant, use a small baffle, as this is intended to slightly attenuate the lows, thus minimizing any boomi- ness in the sound without any appre- ciable loss in quality.

When the speaker cone moves in and out to make the sound vibrations it causes a slight vacuum behind the speaker diaphragm. Without a baffle board the air from the front goes

(Continued on page 495)

475

SHORT -CUTS IN RADIO

ILL WAVE RECEIVER - Fig. I. Antenna tester.

iMlóM GISC VR.

BARELITE BAR y4 -SD 3y2 ' LONG

CORI DI AND

CEMENT WIR NIDI

FINE IRON FILINGS

APPROK 24 PIECES OP

BRISTOL BOARD '' WIDE BY l- TO 172" LONG

WHEN DR, SERAPE EDGES TO AVOID

CONTACT BETWEEN LAVERS

4111111117

Fig. 2. Home -made tuning wand.

RIMER "DAMPERS

ART/AWE COIL

RUBBER MOT DAMPER

MAGNET

NEEDLE HOLDER

NEEDLE

WEBER DAMPER PROM INNER TUBE

RUINER PIVOT DAMPERS CUT FROM CLEAWNWSINO NIPPLE - - --

BSS DAMPER

OLDER

004 TO

DD6.IN RANCE

AR E

SLOT TOR ARM- ATLRE BLADE

Fig. 3. Repairing a defective pickup

Fig. 4, above. Quick speaker test.

Fig. 5, below. 32 V. power supply.

476

FIRST PRIZE -$10.00 ANTENNA TESTER. After in-

stalling an all -wave antenna the Service Man is never sure that it is a perfect job. The device shown enables a test to be made immediately !

It consists of a model T Ford spark coil and a single dry cell. These may be mounted compactly (see Fig. 1), so that they can be put in the tool kit. The apparatus is simply placed near the receiver or lead -in and turned on. Discon- nect one lead of a transposed feed- er system, use the other as the an- tenna, and the noise will come in strong, but, if a good job has been done on the antenna, the regular doublet connection will give a mini- mum of noise.

A. WARD HOwE

SECOND PRIZE -$5.00 TUNING WAND. This handy

piece of equipment muy be made by reference to Fig. 2. An alumi- num disc 1 in. in dia. is fastened at one end of a bakelite rod. At the other end is a core made of iron filings glued to cardboard strips. The edges of the completed core must be scraped to insure that there will be no contact between adjacent layers of iron filings.

C. P. WILLOUGHBY

THIRD PRIZE -$5.00 PICKUP REPAIR. Other than actual burn-out. trouble in pick-

ups is usually caused by drying up of the rubber armature dampers. Repairs can easily be made with rubber from an inner tube which still has good resiliency. and bits from a (transparent) rubber nurs- ing nipple. Use care, when taking the assembly apart as the fine wires from the coil break off with the slightest pull.

RALPH BILLS

HONORABLE MENTION SPEAKER TESTER. Many Widget

sets which can barely be heard with the volume full -on, will be found to have a faulty reproducer. A rapid test for this condition is shown in Fig. 4. It merely con- sists of a 2 mf. paper condenser in series with a small magnetic speak- er and a set of test prods. With the set turned on and tuned to a

local station, touch all the terminals on the speaker with one of the prods, the other being grounded. If the set is in good condition other- wise, a signal will be heard in the magnetic speaker.

HARRY E. WESSEL

Fig. 6. Soldering -iron kink.

SOLDERING. SOLDERING IRON HEAD TIP

SMALL PIECE OF METAL ROO, FILLS SPACE

BELINO TIP, ANO IS INTENDED TO LENGTHEN THE SOLDERING TIP.

FIRST PRIZE $1 0.00 SECOND PRIZE 5.00 THIRD PRIZE _ 5.00 Honorable Mention EXPERIMENTERS: Three cash prizes will be awarded for time- and money -saving ideas. Honorable mention will be given for all other published items. Send in your best I' kinks'!

HONORABLE MENTION "32 V. POWER SUPPLY. Many Service Men are at a loss when

called upon to test, or do work in their shops on, 32 V. radio sets. Ample power for the purpose may be secured from the arrangement shown in Fig. 5. The old Majestic "A" eliminators deliver between 12

and 15 V. when the chokes are re- moved. Hooked in series with one or two 6 V. storage batteries, a handy 32 V. power supply is avail- able.

HERBERT MAI VIS

HONORABLE MENTION sOLDERING IRON HIFTT. A

small length of copper rod the same diameter as the tip is inserted in the space behind the tip. This insures that the tip will remain tight in the seat. Simple as this idea may seem, it is very effective. See Fig. 6.

EUGENE. KENraE:v

HONORABLE MENTION SrRATCH REMOVER. This idea,

shown in Fig. 7, is a remover that will eradicate the worst scratch, yet costs only a few cents to make. Grind up about a dozen pecan kernels, taken fresh from the shells and rub them into a piece of cheese cloth. You now have one of the finest scratch removers it is possible to make. The cloth will last for a year or more before needing renew. al of the pecan oil. Simply rub the cloth over the scratch, let the oil dry a few moments, and polish with a clean. dry cloth.

MORRIS DORSEY

HONORABLE MENTION FILAMENT RESISTOR. The fila- r ment resistor shown in Fig. 8

van be made very cheaply and will not burn out or cause other trouble. In addition it is very handy, since it is adjustable. The insulator which is used as the base can be obtained in several lengths, thus several different ranges of resist- ance can be made. No wire smaller than No. 14 should be used.

The wire is wound on the form first. and then the enamel is scratch- ed off along a narrow line to allow contact with the slider.

L. H. GF.ORGER

(Continued on paye 497)

Fig. 7. Scratch remover.

GRIND PECAN

P1 DOZEN PUB THE GROUND PARTICLES / INTO INC CHEESE CIDTH

(NEESE CLOTH NOCE INTp A POACH P SCLA.C.

RADIO -CRAFT

Fig. 13. Novel tone control.

REmpiE ONE 'VAN OF WIRE FROM VOICE COIL ANO FOR. A COIL AS SHOWN

Fig. 12. Dynamic speaker repair.

Fig. II. Installation help.

PUTTV- SEAIED SPLICE i/

LAVERS O TAPE

ON Purr(

Fig. 10. A weather -tight joint.

CONNECTION MADE HERE

TINNED COPPER

4E SYS- LONG LOOPED AROUND FLANGE ON

RENO AS SHOWN

/Mt

O I ST COPPER S I TRIP C

COPPER ST

SOLDERED HERE

TIP JACK

WiSHÉÄSG

AFTER WIRE IS BENT 10 SHAPE SPREAD SOLDER

ON IT TO MAKE IT S1FF

WITH PHONE TIP IN JACK, CIRCUIT SHOULD BE BROKEN BETWEEN JAR ANO WIRE.

Fig. 9, above. Re- making a tip jack.

Fig. 8, below. Filament resistor.

PORCELAIN TUBE

3 /2 IoNG ETI I. rE ,ERE ONLY

INDENTATION FOR CONTACT

Stl\Illllll 1111 a' 1'Rl' 4 14 0C ENAMELE

COPPER 1,55 `AC'J5'ABLE

SLIDER

FRACTIONAL, 212 OA 6r REGULATION

for FEBRUARY. 1936

ANT

L 4 L1 PRI tic 3-

TICKLER C8

0.1 -MF

R3 DErl.osc 6F7 2 MEGS b DET.2

MMF

/ EXT = ONO

C5, 0.1-MF. REGEN CONI N4

50000 ONUS

CID, MMF

R4 2 MEGS

REGEN CONT NE 2

SHAPED -. r FOR

C2 456 KC., I.F

R FC BSMHY

111

(II 12A71A F 1 8 RECT.

/ TIi.

R6 1MEG

^ 'BROWN

I/1 L2(O5C) J R7

- ' 2.5000NMS

(R1 & 5W. ARE GANGED)

12, 01- MF

R8 7,500 ONMS

(I3 35 MF (Eau)

CH , (ö M5)

C14.)

R9 ME

1.100 OHMS

C15 8MF

(7 .005 MF

REU

) MAGNETIC

REPRODUCER

RIO -346 OHMS (IN PWR CORD)

110 V, AC-DC

FUSES

AN A.C.-D.C. BEGINNER'S SUPER. "2"

R. D. WASHBURNE

ELECTRIFYING the "1- tube" superhet, described in the December, 1935, issue of Radio-Craft, is the most con- venient way in which the beginner in radio can learn his first principles of superheterodyne design, and the

operation of "electric" sets of this type. The circuit as presented here incorporates in 2 multi-pur-

pose tubes, the following 5 functions: (1) First -detector; (2) Oscillator; (3) Second- detector (Operations 1, 2 and 3 take place its

VI.); (4) A.F. amplifier; (5) Power rectifier (Operations 4 and 5 occur in V2.).

DOUBLE REGENERATION

Both detectors are regenerative -the first- detector at R.F. (signal frequency), and the second -detector at I.F. (the in- termediate or "beat" frequency). By "sensitizing" both of these circuits with regeneration the utmost sensitivity is achieved.

It is interesting that regeneration in the second -detector circuit is practically constant, since the tuning of its circuit remains unchanged at the "I.F." (inter- mediate frequency) to which it is aligned.

First -detector regeneration stability is below that secured in the second -de- tector circuit, but an excellent charac- teristic in this respect has been secured by utilizing the pentode -section screen - grid circuit of V1. First -detector regen- eration is controlled by potentiometer R1; and that of the second- detector, by R2.

THE A.C.-D.C. CIRCUIT

Although the original 1 -tube circuit appeared in Fank Magazine (Berlin), it was adapted by the writer to utilize an American tube. It has been still further modified in this new "A.C.-D.C." version -a design which greatly enhances its effectiveness as a portable or home set. It will operate wherever a 110 -V. A.C. or D.C. power line is available.

Except for the power- supply wiring, the diagram is nearly the same as the one in the preceding article. The addi- tional components that permit the con- structor to get away from batteries are

Here is an interesting "double regenera- tive" superheterodyne circuit that embodies the fundamental operations of most radio sets. Two tubes do the work of 5.

as follows: type 12A7 tube (combined pentode A.F. ampli- fier, and half -wave rectifier) ; low- resistance filter choke; a magnetic reproducer; power cord (incorporating a resist- ance of 346 ohms) ; and a few resistors and condensers. Having acquired these components, you're now ready to work on the job of electrification. CONSTRUCTION DETAILS

The first step is to remount all the parts, placing them as shown in the photograph. The low- resistance filter choke measures only 1 /x1 /x% -in. thick; these exceptionally small dimensions permit it to slide underneath the repro- ducer. Filter condensers C14 and C15 constitute a dual 8 mf. electrolytic; its small dimensions of 31x1%x11.-in. thick en- able it to fit nicely on the small wooden baseboard.

The two control resistors, R1 -Sw., and R2, may be mounted on a bakelitc, aluminum or wooden panel; the writer used the latter, recessing one end of the panel into the edge of the baseboard. When mounting the components that align along the front edge of the baseboard, keep in mind that the only item which should project beyond this front edge is the cardboard ring, 1/2-in. thick, (Continued on gage 506)

RADIO -CRAFT for FEBRUARY, 1936 477

THE LATEST RADIO EQUIPMENT

Latest metal -tu be set. (895)

Wind- driven battery charger. (896)

6E5 501,C

e5 tom.TÓ'+é CC%4ECTi0Rl

6F5 CATHODE TVMd6 TQBE

Adapter for 6E5 tuning tube. (897

Aboie, new tube tester. (898)

Below, crystal microphone. (899)

NEW ALL -WAVE RECEIVER (895)

(RCA Manufacturing Co., Inc.) T11E MAGIC EYE tuning tube is used in this new chassis which

incorporates 15 tubes. Five bands are used covering a tuning range of 140 to 60,000 kc. The undistorted output is 10 W., and the set draws 145 W. from the power line. Pro- vision is made for the use of a phono. pickup and a switch changes the set from phono. to radio. All the tubes are of the new metal type, except the rectifier and the cathode - ray tuning tube.

WIND CHARGER (896)

A6 -VOLT charger is illustrated which is designed for use in lo-

calities where there is no available line power for battery charging. The storage battery is kept charged au- tomatically, and the apparatus shuts down when charging is complete. The generator and propeller tilt au- tomatically to keep the charging rate constant regardless of wind speed. A meter indicates current output.

CATHODE -RAY- INDICATOR ADAPTER

(897)

OWNERS of any radio set that

has A.V.C. may now equip their set with the latest develop- ment -the cathode -ray indicator - through the use of this adapter.

PRECISION TUBE TESTER (898)

(Precision Apparatus Co.) OVER 300 tube types are fully

tested by this instrument; all dual -type tubes are given individual section tests. All tubes are tested under rated load. Has neon con- denser leakage test: and hot -cathode leakage and inter- element short tests between any elements. Line voltage checks on main meter. Avail- able in portable, panel and counter types.

UNI -DIRECTIONAL MICROPHONE

(899) (Brush Development Co.)

UNI- DIRECTIONAL microphones are of special value to the P.A.

technician who is troubled with

All -wave oscillator. (900)

New style A.C. -D.C. set. (901)

Laboratory -type oscilloscope. (902)

Recording reactive. (903)

Above, portable superhet. (904)

Below, A.F. amplifier. (905)

acoustic feedback. The crystal mi- crophone illustrated is "dead" at the back; at front, field extends over 180 degrees. By a switching system in the preamplifier, this in- strument can be changed instantly to a completely non -directional unit!

ALL -WAVE OSCILLATOR (900)

AFREQUENCY range of 90 kc. to 60 mc. is covered by this in-

strument. A direct full -vision dial is used with a transparent pointer to eliminate parallax. A modulator tube provides about 35 per cent modulation. Incorporates batteries. Case is of steel, deeply etched and copper plated brass panel. The oscil- lator is calibrated at the factory from crystal standards over all bands.

NEW COMPACT RECEIVER

(901) SIX TUBES are used in this new

set. It is of the superhet. type and has 2 bands, 550 to 1,600 ke. and 70 to 185 meters. A full- vision dial is used, the dual pointers being illuminated. The power cord runs cool since the resistor is in the form of a tube. A dynamic speaker is used. The cabinet measures 13%x 936 ins. deep and the set weighs 8 lbs.

OSCILLOSCOPE (902)

MANY NEW and exclusive fea- tures are claimed for this in-

strument. Either the 3 or 5 in. tube may be employed. A new sweep cir- cuit is used as well as a new coup- ling circuit for the input. Two am- plifiers are provided, which may be used separately or in cascade. The 5 in. tube is supplied with a cali- brated scale. A 6- position gang switch shifts the input so that dif- ferent connections are secured.

PORTABLE SOUND RECORDER

(903) (Sound Apparatus Co.)

THIS MACHINE can be operated by the most inexperienced person,

for recording and reproducing voice or other sounds. Furnished with crystal microphone, crystal pickup,

(Continued on page 499)

Counter -type tube tester. (906)

Name and address of any manufacturer will be sent on receipt of a self- addressed, stamped envelope. Kindly give (number) in above description of device

478 RADIO -CRAFT for FEBRUARY, 1936

Enterst i nment system. (913)

ENTERTAINMENT SYSTEM (913)

(Wholesale Radio Service Co.) SERVICE MEN will find that

there is a large field installing entertainment outfits, such as that illustrated above. Many prospective customers refuse to install an am- plifier a receiver, or a phono, outfit, because they are not complete. This new unit contains all these in a handsome cabinet, and the 20 W., high -fidelity output is sufficient for most requirements.

Radio tuner and amplifier each have their own chassis, the ampli- fier chassis power supply being used to supply the receiver as well.

The T.R.F. radio tuner has a pre - selector providing the necessary se- lectivity to completely cut out strong local stations. The detector is of the diode type and its output is fed into the audio system through a volume control.

The audio system utilizes resistance coupling throughout, except, of course in the final stage where transformers are required. Various leads or taps are provided on the output transformers to enable con- nection to any line or speaker. The input of the amplifier is arranged to use 2 microphones or other sources. such as phono. pickuis -s A separate volume control is provided for each input channel as well as for the radio input.

Specifications are: peak output. 35 W.; gain, 108 db.; hum level, 60 db.: power consumption from

(Continued on pave 500)

FARM RECEIVER (914)

(Allied Radio Corp.) ALTHOUGH this set is called a

"Farm Set," it is designed for use whereeer power lines are not available.

The receiver is a 6 -tube super- heterodyne built to have the lowest possible current drain consistent with practical standards of opera- tion. As a result it draws a total of only 1.25 A. from a 6 V. battery. No other batteries are needed. All the latest features, such as A.V.C., all -wave operation (17 to 565 met- ers). airplane dial and rubber - mounted tuning condenser are in- cluded. Tubes required are: 1 -106, 1-34, 1 -33, 1 -32, 2 -30s. The high volt-

Low drain superhet. (914)

RADIO CRAFT for

Wind battery charger. (914)

age power supply is of the self -rec- tifying, full -wave type, mounted on the set chassis. Either a console or table model may be had.

The recommended method of charging the battery in outlying districts is by means of the wind - charger pictured above. This unit has an automatic governing mech- anism, which functions to keep the charging rate at a substantially con- stant value. regardless of the wind velocity. Thus the battery will not be harmed if the wind reaches a speed of 65 m.p.h. or more. The speed is kept constant by a mechan- ism which tilts the propeller and generator as the wind increases. This action does not start until the wind velocity reaches 20 m.p.h. The

(Continued on page 500)

Self- contained set. (915)

BANDSPREAD RECEIVER KIT (915)

(Eilen Radio Labs.) MANY features are included in

this kit, which enable the builder to construct a fine all -wave receiver. It is intended for all types of usage, such as amateur, S.-W. broadcast and all other types of re- ception.

There are 5 tubes used, and either metal or the newer glass tubes may be employed. The tubes are used as tuned R.F., regenerative detector, 2- stage A.F. amplifier, and rectifier. The set is completely self -contained, the power supply and speaker are mounted in the same case as the receiver proper. The old reliable and highly efficient plug -in coils are used. The case is of heavy steel. fin- ished in black crackle lacquer.

The dial is of the dual pointer variety, and is illuminated. There are two speeds for tuning, the slow speed being used for bandspread. By the use of this system the S. -W.

(Colitinacd on pope 500)

Circuit of the short -wave 5 -tu

Beat oscillator. (916)

MULTI -PURPOSE OSCIL- LATOR (916)

AVARIETY of uses are served by this compact unit. Some of the

uses for which it has already been employed are:

A beat -note oscillator to read code C.W. signals on a receiver which is not equipped with such an oscillator. It will make virtually any superhet. receiver capable of bringing in unmodulated S.-W. sig- nals.

As a beat oscillator for locating weak carriers when hunting for DX. This is accomplished by the so- culled "whistle method." As an oscillator to broadcast phonograph music or voice to your radio re- ceiver. By this same means you can use any ordinary broadcast set as a P.A. system, with a coverage only limited by the capabilities of the A.F. system of the receiver. This type of P.A. system is very versa- tile since the receiver does not need to be tampered with in any way and the entire amplification is used. By providing a modulated signal to the input terminals of the beat os- cillator, the intermediate frequency stages of the superheterodyne may be lined up to peak efficiency.

Many other uses will probably be found, but these are the outstanding ones conceived, in most cases, by the originator of this particular unit.

Most present -day superhets. use an intermediate frequency of be- tween 430 and 500 kc. When the beat oscillator is once adjusted to the intermediate frequency of your particular set, it will not have to be touched again, unless of course the intermediate amplifier is re- aligned. The only operation needed is that of turning the oscillator switch on or off, as needed.

To tune the unit to your particu- lar receiver it is only necessary to tune in a weak signal on the set, then turn on the oscillator and turn the tuning control until a whistle is heard in the speaker. This whistle will then appear at every station tuned in, as long as the beat ascfl- lator is on. It will be noticed that each station produces two distinct whistles, very close together, with a quiet point between the two which is called the zero -beat point. It is to this cero beat that the station is tuned, when the oscillator is used as a station finder. When the cen- ter of the two whistles is found the oscillator is turned off and the sta- tion will be found to be tuned in exactly right.

be set using tuned R.F. (915) - - - a+.W an ems J er svrc 4 0[

r ,a6C61r JKi h i.> 6W WY on'.l srn / \ E. ee

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FEBRUARY, 1 9 3 6

Beat- oscillator circuit. (916)

For use with a microphone. a

mike transformer and battery are needed, and a potentiometer to reg- ulate the volume is helpful, al- though not absolutely necessary. When as phono. pickup is used. the output may be connected directly to the input terminals, providing the ordinary high- impedance type of pickup is employed.

Only one tube is used with this unit, the power being supplied from the set it is used with, by means of an adapter which is placed in the socket of the power tube. The tube is a pentagrid converter (6A7 or 2A7) which is used both as modula- tor and oscillator. The so- called anode grid is not used in this cir- cuit as it was found that its omis- sion enabled a higher percentage of modulation to be obtained. Be- sides the power tube adapter, two other connections are made to the set -the clip which goes to the chas- sis, and the other lead (signal wire) which is wrapped on the I.F. amplifier control -grid lead.

Compact tube tester. (917)

SELECTIVE ANALYZER; AND TUBE TESTER

(9 17) (Tefft Radio Co.)

WO very useful servicing unit, I companions to each other, have

just been announced. The Tube Tester

Illustrated above is this new unit, which is very simple in construction and in operation, yet it will test over 150 tubes including the com- plete new metal line. There is only one adjustment to make before testing any tube this being the set- ting of the filament voltage switch.

The meter is of the zero adjust- ment type and is protected from ac- cidental overload by n fuse which may be readily replaced without tools. (Coatis urd ou pnpc 500)

A convenient set analyzer. (917)

479

MEMBERS' FORUM SERVICE MEN'S

A department devoted to members and those

interested in the Official Radio Service Men's Association. It is the medium for exchanging ideas, kinks, gossip and notes of interest to Service Men, or others interested in servicing.

IN RE "THE TRAVELING SERVICE MAN" RADIO -CRAFT, ORSMA Department:

As a regular reader of Radio -Craft we have noticed from time to time, descriptions and pictures of P.A. equip- ment, which you have printed.

We submit a picture of our truck, with the equipment that is carried. We have been in P.A. work for some time and find it a great financial help in conjunction with radio re- pairs. We will not take any of your valuable space to de- scribe our apparatus, as it is mostly standard.

We employ a W.E. microphone in the truck with a simple device for changing from records to speech equipment (de- signed by the writer). Ordinarily a switch is used for this purpose. In our case a 5 -wire microphone cable is used in place of the 3 -wire cable generally used. On the base of the microphone is a push- button which is connected to a relay. This arrangement is very convenient because the announcer can pick up the microphone at any time and with the button, control both microphone and speech. A few diffi- culties were encountered, such as the loud click which would occur when the relay changed from one position to the oth- er, with the mike current on. All problems finally were solved and the system works perfectly, now.

(If anyone interested in this control system will write us, we will be glad to give them all the "dope. ")

NILS E. SECERDAHL, East Northport, L.I.

Our July 1935 Radio -Craft theoretical cover subject, "The Traveling Service Man," comes to life in this profitable sound and service truck of Mr. Segerdahl!

ANY SUGGESTIONS? RADIO- CRAFT, ORS MA Department:

For the first time, since I've become a member of the ORSMA, I feel I need some helpful suggestions.

My job was to eliminate noise in a Philco Transitone in- stalled in a 1934 Ford sedan. The set worked fine when the car was standing still, whether the motor was running or not (over- looking some noise from the "B" motor -generator).

480

Starting to drive: everything was OK until the clutch started to grip, the noise stopping when the clutch was en- gaged. (At this time I thought it might be static electricity generated by the friction of the clutch.) Driving on, the noise was not noticed when slipping the clutch in shifting to second and third. Some rough roads were tried, but caused little, if any noise.

When the brake was applied the noise was there again. I found that the clutch pedal rubbed against the ungrounded metal floor piece; grounding this however made no difference.

With the motor off, I had someone push the car and al- most every time I pushed the brake pedal the noise was there again!

The owner also claimed that noise was noticeable when he accelerated, especially when he was going up hills, but it wouldn't work that way for me.

I grounded the brake rods, dash control rods, pedals, etc., but to no avail.

(Note: I did not install the set, but it was equipped with plug suppressors, generator condenser, and roof antenna, but no distributor suppressor.)

(I have just learned that the noise has been evident only since the V8 motor was changed.)

Would greatly appreciate any suggestions. WM. MESSERSCH MIDI, Rutledge, Penna.

Mr. Messerschmidt, an experienced radio man, has en- countered a tough one. If grounding car motor to car frame does not do the trick, refer to "Obscure Sources of Car -Radio Noise," June, 1935 issue, page 729, etc.; also, "Front -wheel Static," page 738; and, "Short -Cuts in Car -Radio Service Work," page 742.

AN ORSMA BOOST RADIO- CRAFT, ORSMA Department:

As a member of the ORSMA, I wish to express my ap- preciation concerning your interest in this organization and I am very glad to see Radio -Craft has devoted space in its pages for the development of it.

I have received my first issue of Radio -Craft and as soon as my subscription expires (to the ORSMA Bulletin) I assure you I will become a regular subscriber to Radio - Cra f t.

ROBERT L. CASPER, Box 36, Lloyd, New York.

This fine sound truck and equipment is owned by a progressive radio and P.A. man on Long Island. A unique control system is used for operating the phono. pickup and mi- crophone from a re- mote position. A re- lay is used, and the result is very flexible.

1141111 II

CONTI NUING-"DEFECTIVE VIBRATORS"

RADIO- CRAFT, ORSMA Dept.: Referring to Mr. Jesse Smith's let-

ter in the Member's Forum of the Janu- ary 1935 issue of Radio -Craft, regard. ing the defects in various makes of vi- brators for (Continued on page 501)

RADIO -CRAFT for FEBRUARY, 1936

A SCHOOL -TYPE BROADCAST STUDIO Here prospective artists and technicians are trained com- pletely in the technique of radio program broadcasting.

THE PRESENT high standard of modern broadcasting t e c h n i q u e makes it imperative for the owners

of broadcast stations to employ moni- toring men, operators, and varied other station technicians who are thoroughly experienced in the operation and main- tenance of the equipment used for this purpose.

Conditions being such, it is obvious that if a radio student intends ultimate- ly to attain a position as a technician in a broadcast station, he must in some manner receive his preliminary training and experience on the same type of equipment as used for broadcasting and to have the opportunity to work under the same conditions and environment as found in the better class of broadcast stations.

To make this possible, a West Coast school has developed a highly successful plan.

In addition to conducting a technical radio school they also operate in the same building a school of broadcasting,

Above, the new amplifier in use as an amplifier for a guitar. A "crystal cell' is required for faithf 1

rendition; its easily attached to any instrument.

the purpose of which is to train talented individuals in the arts of singing, dra- matics, announcing, continuity writing, etc. The members of the faculty in this division of the school are all eminent radio stars of the Pacific Coast who have had years of experience before the microphone and are, therefore, capable of supplying students with a most valu- able form of instruction.

An artist's cut -away section of the studios appears in Fig. B and it is here that the classes in broadcasting are con- ducted. These studios are of the most modern design from a technical stand- point, as well as being of architectural attractiveness and furnished according to professional practice.

While the students of the broadcast school use the studios to their particu- lar advantage, yet this equipment is of mutual benefit to the radio students of the technical school who are privileged to act in the capacity of studio and sta- tion technicians, in addition to gaining the most valu- (Cm/tinned on page 501)

Fig. A. Students operate entire station. Fig. B, below. Cutaway view of the diversified equ pment available.

LRCE.\'D A M.a.w.Ji.; R -Studio R: C-- .1y.Ji. C; D - Stadia D: Ie- Trl.w.ion d; R-có"- 1d R..- A; C-. Canna! Ram R: II-A sal ilia x It..: I-D.r.r

Ram; J- R.r.,a,.o Ream , ..4alr,v

A BROADCAST P.A. UNIT FOR MUSICIANS A new field has opened in the P.A. line -that of supplying musicians with sound -amplifying systems such as this one.

CHAS. R. SHAW AND M. RECHT

WITHIN THE last few years progress in A.F. amplification has gone forward with leaps

and bounds. It is only within recent months, however, that the layman has had his interest awakened in this field. The popularity of sound systems has in-

Below, circuit of amplifier; only high fidelity will satisfy musicians' unions. Note use of 2 input channels.

JACK FOR CRYSTAL MIKE 3

MEG&

eo s

S6F5

3000) 6F5 OHMS

MEG

L10V A.0

,25- GI- DUAL MEG (MF 0.5- i MEG

iMF

11_

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6A6 50.000 8 OHMS `MF.

rW DUAL x V3 x

// as.

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8MF. 175v.

( j 8MF

025 / MEG 25000 x v

OHMS

- r. o.L I-IH* MF l

RECT. 83

00000

Sp00 20W-.

oßo

685

L:7

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Lo7 6B5, ONM$ j

)V, l 360V

CH. 200 0HM5

Wag s

FUT

FIELD COIL

2.500 8 MF Z,

BMF.

RADIO -CRAFT for FEBRUARY, 1936

creased to such an extent as to invade the portals of firms which have previ- ously had no particular interest in any- thing electrical. Music concerns, inter- ested only in manufacturing and selling musical instruments, have gone into the field of audio amplification to satisfy the demand for it created by orchestras and singers. Manufacturers of guitars and other string instruments have had am- plifiers and microphonic devices built especially for these instruments so as to increase their tonal volume. People in all walks of life, as well as musicians, have found sound systems valuable ad- juncts for their own personal use.

The result of this popularity has been to create new standards for sound systems. Permanent installations are not suitable for personal use. The out- fits used by sound engineers are too com- plicated for the average layman and are too clumsy to carry about. Portable systems are often lacking in power and quality. Musicians, the most critical of any group of (Continued on page 502)

481

155 Radio Service Data Sheet

GENERAL ELECTRIC MODELS A82 AND A87. 8- METAL -TUBE ALL -WAVE A.C. SUPERHET. (All metal tubes; extended long -wave band; dual -ratio tuning drive; 7 W. maximum output; 10 in. reproducer; sentry box; "perma-

liner" trimmers.)

Above, the sentry box is on the left.

The "sentry box" is the outstanding feature of this set. It contains all coils, the band switch, the R.F. tube VI, the let 1 and osc. tube V2. and all compon- ents of the circuit associated with these units.

Before starting any adjustments on the set, it is advisable to make certain that they are needed, and the use of a "service wand" is the quickest way to do this. Holes are provided in the coil shields to admit the wand without disturbing any parts of the set, so that the test is made under normal operating conditions. (The wand consists of a rod of insulating ma- terial having a ring of non -magnetic metal attached to one end, and a small core of finely- divided iron at the other.) The fol- lowing table shows what circuit adjust- ments are needed for various indications when using the wand.

End Signal Trimmer Adj. Metal ring Decrease None Iron filings Decrease None Metal ring Increase Decrease Capacity Iron filings Decrease Decrease Capacity Metal ring Decrease Increase Capacity Iron filings Increase Increase Capacity

Holes are provided in the coil shields for insertion of the wand in any Ant. or R.F. coil. No provision is made for its

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80770M VIEW Ill OF CMA5515 g) D D

use in any of the oscillator coils since these may be checked by noting the dial calibration.

On all the "permaliner" trimmers used in this set, clockwise rotation of the ad- justing screw decreases capacity while counter -clockwise rotation increase it.

Note that the full available A.V.C. volt- age is applied to the R.F. tube. while re- duced voltage is used on the converter and the I.F. stage.

The volume control used in this set is of the dual type, but both sections are not used for actual control of volume, since R22 is used as a tone compensator by in- creasing the low- frequency response as the volume is reduced. The regular tone control, R23, may be used independently.

Alignment of the set is accomplished by the usual routine. An oscillator with frequencies of 140 kc., 410 kc. (Band A); 465 kc. (I.F.); 680 kc., 1,740 kc. (Band B); 6,000 kc. (Band C); and 18,000 kc. (Band D), is needed for proper alignment, and an output meter must be used for proper results.

The sentry box assembly may be dis- mounted as a complete unit by removing the side -fastening bolts, unscrewing the dial -mechanism fastening nut and unsold- ering the leads to the chassis from the terminal strip.

Circuit diagram. The dashed

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In order to remove the coil shield cans it is necessary to remove the band -switch shaft. With the sentry box removed from the chassis the dial gears may be disen- gaged and the shaft removed merely by lifting the reduction drive and of the dial assembly, allowing the switch shaft gear to pass the dial scale cap shaft. With the sentry box mounted in place, removal of the switch shaft requires removing the dial scale gear and cap shaft.

Three transformers are available for use with different power supplies. Type A is for use on 105 to 130 V., 50 -60 cycles, A.C. Type C is used on the same voltage but 26 to 60 cycles. Type V may be used on 105 -250 V., and 40 -60 cycles. The connections of the various types are shown on the circuit diagram. Types A and C are similar to the transformer con- nected in the circuit, while Type V is il- lustrated at the lower right.

Permaliner trimmers may be replaced by merely removing their particular shield can. It is an easy matter, however, to remove each complete bracket assembly by taking out the mounting bolts and un- soldering the braid connection to the tun- ing condenser. In the case of the oscil- lator and R.F. units it will also be neces- sary to remove the connections to the respec- tive terminal boards of these units.

enclosure at left encompasses the circuits of the sentry box. KC

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482 RADIO -CRAFT for FEBRUARY. 1936

RADIC -CRAFT for FEBRUARY, 1936 483

INSTRUMENTS COULD T

a x ."9 :a 16P1^,

TWIN Instrument Standard Combination No. 120 (Same dial as used in Triplett Model 1200 Master VoltOhm -Mill lam meter.)

Model 321 O -1D.C.

You could easily find out why each Triplett instrument is guaranteed to maintain accuracy within 2%. (Some are guaranteed to maintain accuracy within 1 %). First the design -Tried and checked from every angle. Then the selection of material -The finest without reservation. The construction and assembly- Master craftsmen and factory workers with years of instrument manufacturing training. Final inspection- Checked by experts. Each step shouts Triplett Quality.

Precision Without Extravagance

T117N Instrtt men t

Dealer Net Price. 510.:1:1 The Twin is furnished In any combination of standard 3" A.C. or D.C. movements. Both are included in the special rectangular molded case that requires a minimum of space for special installation. Simultaneous readings can be taken on both instruments when connected in same or separate circuits. Prices on special combinations given on request.

Model 52I- Poll -Ohm -Millisnl nu ter Dealer Net Price. $7.00 Beautiful in Appearance, yet Accurate to 1 °.. Body 41. ". Flange 5 . Body depth. 11x ". scale length 3',o ". Knife edge pointers. molded Bakelite Case. F lush Mounting. An extra large Foundation Instrument. Has long visible scale. An instrument that stands out on your test panel. Can be used to handle practically any values by using proper shunts and multipliers. Available also in projec- tion mounting.

Model 321 -0-1 D. C.- Milliammeter Dealer Net l'riee. $ 1.07 3','x in diameter. Flush Mounting. Bakelite Case. Avail. able also in projection mounting. Triplett offers a com- plete line of r. 3 ". 4' and s in-froments.

WRITE FOR CATALOGUE -SEE YOUR JOBBER

1;7 F1mE7 pes" ELECTRICAL INSTRUMENTS

Model 521

MAIL COUPON NOW! Triplett Electrical Instrument Co. 162 Harmon Drive Bluffton, Ohio

Please rush your new 1936 Catalog

I area particularly interested in

Name....

Address

City State

Please Say That You Saw It in RADIO-CRAFT

Radio Service Data Sheet 156

STROMBERG -CARLSON NOS. 62 AND 63, 8 -TUBE HIGH -FIDELITY CHASSIS

(All -wave, 0.54- to 18 mc.; metal tubes; variable -width intermediate; antenna wavetrap; tuning meter [on No. 6311.

T E Tube Cap

1 2 Type Conn. VI 0 V2 0 V3 0 V4 - V5 0 V6 - V7 - V8 - 42 Spk. - 26

I I M I N A L S

3 4 5 6 7 8

- 230 96 - 235 95 - 230 95 - 0 0 - 25 35 O 250 260 O 250 260

405 405 428 400 430 430

3 - - 3 0 150 - 3 3.5 - - 3.5 o - 1.6 - 1.6 O - 16 O - 16

260 260

o o

All voltage readings are measured be- tween chassis and ground with a 1,000 ohms- per -volt meter. The line voltage is 120 V. for this table. All filament voltages are 6.3, except for tube V8, which is 4.85 V. The set should be tuned to 1,000 kc. with no signal. The numbers over the columns correspond to the socket term-

OSCILLATOR 5-SAND

SERIES ALIGNER.

OSCILLATOR A - BAND

ALIRIES

GNER

0 0

I '

ANTENNA) TRANS

A BAND SHUNT

ALIGNER

B -BAND

ALIGNER

C- BAND SHUNT

ALIGNER

I.F.T l I.F.T.2 1

ALOE

R F INTERS AGE - OSCILLATOR

TRANS TRANS

final numbers which are shown on the bottom chassis drawing. Note that there will be no high voltage in the circuit when the speaker plug is removed. The tuning meter is used only on the No. 63 chassis, but the two are otherwise exactly alike. The variable intermediate transformer is used as a band widener for high fidelity.

3e 4 SPEAKER 2

SOCKET 5 10 06

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LOOKING AT INSIDE BOTTOM OF CHASSIS

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°i FRONT

RCA MODEL 103, 4 -TUBE A.C. COMPACT DUAL -WAVE SUPERHETERODYNE (Two bands, 540 to 1,500 kc., and 1,600 to 3,500 kc.; 6 -tube performance.)

All necessary voltage information is given on the chassis layout diagram. The I.F. amplifier is aligned by connecting the leads of a service oscillator from cap of V1 to chassis. Tune C11 and C12 for best output. Then teed a 1,400 kc. signal to antenna and ground, set receiver dial to 1,400 kc. and adjust C24 and C25 for highest output. Set oscillator at 600 kc. and align trimmer at rear of chassis. Dial reading of set should fall fairly close to G 10 he. The short -wave band will need

18á1o` MMF.

(40)

( L00) .0015-

MF.

(24 5-40 MMF

DET.1 4 OSC. 647;

no adjustment. On the latter band the same oscillator coil is employed, a har- monic being used for actual reception. Power transformera are available for either 25- or 60 -cycle use. The power output is 1.9W. (undistorted), and 3W. (max.). The power input is 40W. at 115V. Filament circuit is novel in that the pilot light and V8 are connected to one winding, while all the other tubes are in series on another section. (Coil resistances, in parenthesis.) Two of the tubes are of multi -purpose type.

I.F.T. OET.24LP. R8,0.174MEG- C17

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110V, A C.

484 RADIO -CRAFT for FEBRUARY, 1936

RADIO -CRAFT for FEBRUARY, 1936

TECHNICIANS' DATA SERVICE NEW JOSEPH CALCATERRA DIRECTOR

A special arrangement between RADIO - CRAFT magazine and the publishers of this lit- erature. which permite bulk mailings to inter- ested RADIO -CRAFT readers. eliminates the trouble and expense of writing to each individual organization represented in this department.

2. HAMMARLUND 1936 CATALOG. Contains 12 pages of specifications. illustrations and prices on the new line of Hammarlund variable. mid- get. band -spread and adjustable condensers; trimming and padding condensers; R.F. and I.F. transformers. coils and coil forms: sockets, shields, chokes and miscellaneous parts for ultra - short-wave, short -wave and broadcast operation.

3. HOW TO GET A HAMMARLUND 1936 SHORT- WAVE MANUAL. A circular containing a list of contents and description of the new 16 -page Hammarlund Short -Wave Manual, which con- tains construction details, wiring diagrams, and list of parts of 12 of the most popular short- wave receivers of the year.

4. THE "COMET PRO" SHORT-WAVE SUPER - HETERODYNES. Describes the outstanding fea- tures of the standard and crystal -type Hammer - lund "Comet Pro" short -wave superheterodynes designed to meet the exacting demands of pro- fessional operators and advanced amateurs for a 15 to 250 meter code and phone receiver, but which can be adapted by anyone for laboratory, newspaper, police, airport and steamship use.

5. ELECTRAD 1936 VOLUME CONTROL AND RE- SISTOR CATALOG. Contains 12 pages of data on Electrad standard and replacement volume con- trols. Truvolt adjustable resistors, vitreous wire - wound fixed and adjustable resistors and volt- age dividers, precision wire -wound non inductive esistors, center- tapped filament resistors, high -

quality attentuators, power (50- and 150 -watt) rhwntats and other Electrad resistor specialties

Radio -Craft Technicians' Data Service 99 Hudson Street. New York City, N.Y. RC -236

Please send to me, without charge or obligation, the catalog, booklets, etc. the numbers of which I have circled be- low.

2 3 4 5 57 62 64 67 73 74 75 76 77

My radio connection is checked below: ( ) Service Man operating own business. ( ) Service Man for manufacturer. ( ) Service Man for jobber. ( ) Service Man for dealer. ( ) Service Man for servicing company. ( ) Dealer. ( ) Jobber. ( ) Experimenter. ( ) Professional Set Builder. ( ) Amateur Set Builder. ( ) Short Wave Work. ( ) Licensed Amateur. ( ) Station Operator. ( ) Radio Engineer. ( ) Laboratory Technician. ( ) Public Address Worker. ( ) Manufacturer's Executive. ( ) Student. ( )

I am a: ( ) Subscriber ( ) Newsstand reader

I buy approximately of radio material a month. (Please answer with- out exaggeration or not at all.)

Name

Address

City State (Please print name and address)

Avoid delay. The catalogs and booklets listed are now in stock and will be sent promptly as long as the supply lasts. Please use this coupon in ordering. The use of a letter causes confusion and de- lay.

57. RIBBON MICROPHONES AND How TO USE THEM. Describes the principles and operating characteristics of the Amperite velocity micro- phones. Also gives a diagram of an excellent humless A.C. and battery- operated preamplifier.

62. SPItAYBERRY VOLTAGE TABLES. A folder and sample pages giving details of a new 300 - page book, containing 1,500 "Voltage Tables" covering receivers manufactured from 1927 to date. published by Frank L. Sprayberry to simplify radio servicing.

64. SUPREME No. 885 AUTOMATIC TESTER. A technical bulletin giving details, circuits and features covering this new Supreme develop; ment designed to simplify radio servicing. In addition to the popular features of Supreme analyzers and tube testers it contains many direct -reading features which eliminate guess- work or necessity of referring to charts or tables.

67. PRACTICAL. MECHANICS OF RADIO SERVICE. Information, including cost, features and outline of lessons of the Frank L. Sprayberry course in Radio Servicing, and list of Sprayberry Data Sheets for modernizing old radio equipment.

73. How TO ELIMINATE. RADIO INTERFERENCE_ A handy folder which gives very complete infor- mation on how to determine and locate the sources of radio noise by means of the Sprague Interference Analyzer. A description of the analyzer and method of using it is included. to- gether with data on how to eliminate interfer- ence of various kinds once the source is located.

74. SPRAGUE. 1936 ELECTROLYTIC AND PAPER CONDENSER CATALOG. Gives specifications, with list and net prices on a complete line of wet and dry electrolytic. and paper condensers made by the Sprague Products Co. for radio Service Men. set builders, experimenters and engineers. In- formation on the Sprague Capacity Indicator, for making capacity tests on condensers and in servicing receivers, is included.

75. SPRAGUE TEL -U -How CONDENSF.R GUIDE. A valuable chart, compiled by the Sprague Prod- ucts Co. which tells the proper types, capacity values and voltages of condensers required in the various circuits of radio receivers and am- plifiers, and how to locate radio troubles due to defective condensers. Includes data on condenser calculations.

76. FACTS You SHOULD KNOW ABOUT CON- DENSERS. A folder, prepared by the Sprague Products Co., which explains the importance of various characteristics of condensers, such as power -factor, leakage, capacity and voltage in determining the efficiency or suitability of a given condenser to provide maximum filtering and safety in operation.

77. SUPREME 391 P.A. ANALYZER. This book- let describes the features and use of the new Supreme 391 P.A. Analyzer, designed to equip the radio Service Men to cash in on the con- stantly growing opportunities for service in the sound equipment and public address systems used in movie theatres, schools, churches, audi- toriums, etc.

A MULTI -TUBE ADAPTER (Correction)

We are in receipt of a correction from the author, Hermie D. Vogel. concerning Fig. 1E of the above article which appeared in July. 1935 page 16. The wire shown dotted should be omitted.

05 4 -5 -6 PRONG TUBE

G2 SOCKET \ \

®p Pl G2

7 PRONG TUBE BASE

141 142

r CUT OFF EAR

H2 H

CUT OFF EAR

INNER CONNECTIONS OF 4- 5- 6PRONG

ADAPTER

Picase Say That You Saw It in RADIO -CRAFT

485

R E A D R I T E

ALL -WAVE SIGNAL

GENERATOR

Five Plug -in Coils cover 5 fre- quency bands from 100 to 20,- 000 Kc. All frequencies funda- mentals and stabilized. Com- plete with batteries and two

No. 30 tubes.

P R ICE ONLY $14.40 Model 554 -A. The new Readrite All - Wave Signal Generator includes all im- provements of present -day engineering. The use of plug -in coils permits any new frequency band to be added by a new coil. Extra wide scale permits accurate fre- quency settings from the large calibra- tion curves supplied. Besides having all frequencies funda- mentals, this new Signal Generator is complete shielded and tube modulated. Model 554 -A, complete with batteries, two No. 30 tubes and installed in leather- ette covered portable case with remov- able cover.

Dealer Net $14.40 Price ... SEE YOUR JOBBER

Readrite manufactures all types of testers used for servicing Radio Sets, including Set Testers, Tube Testers, Resistance, Continuity and Capacity Testers, Point -to-Point Testers and inexpensive Indicating Meters.

1 THIS COUPON BRINGS FACTS

READRITE METER WORKS, 216 College Drive, Bluffton Ohio

Please send me full Information on Model 554 -A Re:Write All-Wave Signal Generator

Catalogue

Name

Address

Cllr........._......_...._._._ State... L

486

NEW!

áiwthvz. WEBSTER

ChicaciD ACHIEVEMENT! A 4- Position 17 -Watt Amplifier

SERVICE MEN! Dealers! Public Address En- gineers! You should know all about this latest development of WEBSTER -Chicago engineers. Its the FOUR -POSITION 17 -WATT AMPLIFIER. It is suitable for four crystal microphones or three

.crystal microphones and one phono input.

Completely Enclosed Unit This unit is self -contained. Its entire mechanism is in one unit. No pre -amplifier is required. High gain. Output impedance is tapped from 2 to 500 ohms. For multiple microphone and public ad- dress systems.

Write today for complete details on the WEBSTER-CHICAGO 4- Position 17 -Walt Amplifier ... also other P. A. Equipment.

THE WEBSTER COMPANY 31125 West Lake Street Chicago, Illinois

There's Only ONE WEBSTER- CHICAGO. Its in Chicago!

EBY uáihj

Binding Posts Tip Jacks Male Plugs

Female Plugs Low -Loss Sockets

A -C Switches Tap Switches

Terminal Strips Short Wave Switches

Moulded Sockets Electric Eyes

Write for Latest Bulletin

HUGH H. EBY Inc. 066 HunFinq Park Ave.

PHILADELPHIA, PENNA.

RADIO -CRAFT for FEBRUARY, 1936

MAKING A I2 -TUBE HIGH- FIDELITY BROADCAST

RECEIVER (Continued from Pope 461)

variable -mu tube, is increased much beyond its normal minimum.) However. it was found that some locals were so powerful that they simply "swamped" the first R.F. tube unless a volume control was placed in the antenna circuit. This was deemed to be an unnecessary complication, so A.V.C. was resorted to as a compromise.

The negative bias voltage applied to each R.F. tube does not exceed 8 or 9 volts on any but stations within a mile or so of the receiver. At this low figure of bias, the amount of distortion in the R.F. amplifier is negligible. The A.V.C. also serves to maintain the B.F. voltage applied to the detector at a nearly constant figure for

, all local stations. This is important as a diode detector only gives linear rectification when the applied signal is within certain rather narrow limits dictated by the design of the detector circuit. Too low a signal input as well as too great an input to the diode will cause severe distortion.

The output of the diode employs the "split - tapped" load resistor arrangement which allows a pair of push -pull grids to be coupled to the diode without the need of a coupling transformer or phase- inverting tube. The first A.F. stage was connected in push -pull in order to keep second- harmonic distortion at a very low value and also to insure sufficient undistorted power for the grids of the power stage. The inter - stage A.F. transformer is a precision device and will give a response flat within 1-db. from 30 to 16.000 cycles.

The power stage employs two 6A3s in class A (not A prime). with a fixed bias source supplied by a separate bias rectifier circuit in the power supply.

The values of bias and plate voltage for the 6A3s in push -pull class A are different from the usual values. The bias is approximately 45 V. The plate voltage is 250. The plate current of each tube should be carefully adjusted so that both tubes balance at 60 ma. per tube. Adjust- ing the grid bias potentiometers mounted under the chassis serves to balance the plate current of the 6A3s.

The output transformer employed has a prim ary impedance of 8.000 ohms, plate -to- plate. The secondaries are arranged to feed a 500 -ohm device or the voice coil of any speaker from 1.75 to 15 ohms. (Taps are provided on the low -impedance winding to give an exact imped- ance match to any particular speaker.) The output transformer has a frequency response flat within 1 db. from 30 to 15.000 cycles. The primary winding should be made to carry 60 ma. per leg continuously.

The undistorted output of the amplifier is approximately 10 W. lower than with the "A prime" arrangement but producing much less distortion than the "A prime" system. An out- put of 10 W. is adequate for ordinary home use: and the lowered distortion makes the drop in power output well worth while in a high - fidelity set.

THE "BASS BOOSTER"

The bass booster is a 2 -stage A.F. amplifier which has a peaked frequency response. It is sharply resonant in the neighborhood of 70 cycles. When turned "up" the result is that the bass register is amplified much more than the other frequencies. This device is only for use when the set is playing at low- volume level.

When operated under this condition there is with any receiver not compensated for the effect. a lack of bass response. Reproduction sounds "tinny." The bass booster however restores to a considerable extent the missing bass. It does this by means of an A.V.C. system connected to the power stage. On loud signals the A.V.C. action overbiases the bass booster and there is little amplification. The response of the set is then governed only by the regular amplifier, and substantially flat response is obtained. When volume is turned down to a low level the A.V.C. action decreases the bias on the bass booster and its gain increases. feeding the boosted bass into the regular amplifier and mix- ing the two to give a frequency response with the bass predominating and thus neutralizing to a considerable degree the low -volume thinness of reproduction.

The mike preamplifier is conventional and needs no discussion. The two transformers in the preamplifier do not have to have as good frequency response as those of the main ampli- fier unless the use of a high- fidelity microphone for musical pick -up is contemplated. The diodes of the 85 preamplifier tube are used to supply the rectified A.V.C. voltage for the "bass booster."

A concluding article will describe the power supply unit and also give information on the adjustment of the T.R.F. circuits and the "bass booster ": the details concerning the high - fidelity reproducer system, utilizing woofer and tweeter units, also will be given.

LIST OF PARTS

One I.R.C. resistor. 3,350 ohms, a -W.; Two I.R.C. resistors, 50,000 ohms, a -W.; Four I.R.C. resistors, 0.5 -meg., Ya -W.: Five I.R.C. resistors, 1.0 meg.. Two I.R.C. resistors, .25 -meg., 1/2-W.: Three I.R.C. resistors, 0.1 -mee., Two I.R.C. resistors, 300 ohms, i/z -W.: Two I.R.C. resistors, 20,000 ohms. Two I.R.C. resistors, 10.000 ohms. !_. -W.; Two I.R.C. resistors, 2 meas.: a -W.:

The chassis layout of the tuner showing positions of parts.

150 MT.

A r CM.

(CO OPT)

05 -MEG DUAL POT.

(00 on)

PNd+O.-QAtKO'.

O Sw

0.5 -0.iEO Oum. POT

!GANG TIMING CONOENSR

PMONO. -TACK

SPG xE0. stKAET

2s'

MIKE SOCKET

TII

pioto

MAT ' /K CA ALUMINUM OA CPEa PLAYED mmmrl

Please Say That You Saw It in RADIO-CRAFT

RADIO -CRAFT for FEBRUARY,

One I.R.C. resistor. 2,500 ohms. 34 -W.; One I.R.C. resistor. 20,000 ohms. 1.0 W.; One I.R.C. resistor. 15,000 ohms, % -W.; One Electrad resistor, with slider, 20,000 ohms,

25 W.; One Electrad resistor, with slider, 5.000 ohms,

25 W.: Two Electrad potentiometers. 50,000 ohms; Two Electrad dual potentiometers, 0.5-meg.; One Electrad dual potentiometer, .25 -meg. ;

One Cornell -Dubilier electrolytic condenser, 25 mf., 25 V.;

Three Cornell -Dubilier paper condensers. 1.0 mf., 400 V.;

Four Cornell -Dubilier paper condensers, .02 -mf., 400 V.;

Eleven Cornell -Dubilier paper condensers. 1.5 mf.. 200 V.;

Fourteen Cornell -Dubilier paper condensers. 0.1 -mf., 400 V.;

Two Cornell- Dubilier paper condensers. .16 -mf.. 200 V.:

One Cornell -Dubilier paper condenser. 2 mf.. 400 V.;

One Cornell -Dubilier paper condenser, .05 -mf., 400 V.:

Three Cornell -Dubilier mica condensers, 100 mmf.;

* Three T.R.F. coils. 1,750 to 530 ke.; One 3 -gang tuning

section; Three Hammarlund air -dielectric trimmer con-

densers, 50 mmf.: Two A.F. chokes, 30 hy., 30 ma.: 'One A.F. choke. 50 hy., 10 ma.: ' One A.F. transformer (push -pull plates to push -

pull grids). T3; 'One output transformer (plate -to- plate -8,000

ohms). T4; ' One A.F. transformer (single plate to push -pull grids), '1 ?;

"'One transformer (tapped primary -500 ohms - to single -grid). Ti;

One Na -AId 6 -prong special socket (for 6E5) ;

Three Eby 6 -prong wafer sockets; Four Eby 7 -prong small wafer sockets; Four Eby 6 -prong wafer sockets: Two Eby 4 -prong wafer sockets; One Raytheon, Sylvania or RCA type 85 tube; Two Raytheon, Sylvania or RCA type 6F'7 tubes; Two Raytheon, Sylvania or RCA tube 6D6 tubes; Three Raytheon, Sylvania or RCA type 76 tubes; Two Raytheon, Sylvania or RCA type 6A3 tubes; One Raytheon, Sylvania or RCA type 6E5

cathode -ray tube; One chassis; One tuning dial. (*Names of manufacturers will he sent upon

request.)

condenser, 365 mmf. per

OPERATING NOTES (Continued from page 471)

RCA M -34 THIS receiver is an automotive radio set and

this particular instrument was "dead" as far as signals were concerned, only vibrator noise being heard in the loudspeaker. Upon checking the receiver out of the car, tubes and everything checked OK, and stations could be tuned in when a finger was placed upon the aerial plug of the receiver. We decided to put the radio set back in the car and upon doing so found that it was again dead. The aerial plug was then disconnected from its socket, which is fastened to the aerial lead -in, and a finger was placed on the plug after which stations came in fine. The trouble had been in the poor connection be- tween the plug and socket which connect the aerial to the receiver. After this connection was repaired by cleaning the contacts and pressing them tightly together, and then tight- ening the band which holds the two parta to- gether, the receiver worked like new.

KENNEDY 20B THE complaint in this set was "distortion

and no volume." Upon checking all voltages with the analyzer, I found 275 V. on the plates of the push -pull 45s, the other voltages being normal. Removing the chassis, I checked the voltage divider (which has each section marked in ohms). The 755 -ohm section at one end of the voltage divider was open and upon replacing it with a new 750 -ohm, 10 W. enameled resistor, the voltage on the 45s be- came 250 V. and the radio set worked fine.

WAYNE STORCH

1936

This N E W Type of RADIO TRAINING

487

ACTUALLY SETS YOU UP IN BUSIUE55 ...

In the Fastest Moving Industry in the World . . e

Here, at last, is a NEW and DIFFER- ENT type of Training that not only teaches you all phases of Radio Service Engineering work -but which equips you for an actual start in business. No matter what kind of Radio training you may take, you will require such mate- rials before you actually enter business. Sprayberry Training gives them to you- -teaches you to work with them under actual Service conditions.

Nor is that all. Never for- get that there are too

many men of only mediocre

ability in ALL lines of business. That is why average wages are low -why many men are out of work. Radio is no exception. But there is al- ways room -there is good pay-at the top of the ladder -and this is where Sprayberry Training is specifically de- signed to put you. It is for men who take Radio seriously -for those willing to work along sound, intensely practical lines to win a real future in a fascinat- ing industry with vast opportunities for future development.

NO PREVIOUS EXPERIENCE REQUIRED -LEARN AT HOME IN SPARE TIME Sprayberry Training is really two courses in one.

Besides the necessary fundamental teaching it in- cludes the famous Sprayberry Practical Mechan-

ics of Radio Service formerly sold ONLY to men already in 'Radio-many of whom had

found their previous training inadequate for modern Radio needs.

Sprayberry Training has been honestly, conscientiously developed to fit you for

a truly worthwhile place in Radio -a place well above the average. It is dif-

ferent from almost any other course you might consider. It is complete - modern- practical. Upon comple- tion, you have both the knowledge

SERVICE ENGINEERING EQUIPMENT Is Yours! This Complete and equipment to enter business then and there for full or part time profits-or to start out in any one of Radio's specialized fields such as sound, broadcasting. etc. Cer- tainly you owe it to your future to investigate- TODAY!

SPRAYBERRY ACADEMY OF RADIO 2548 University Pl., N.W., WASHINGTON. D.C.

Without cost or obligation on my part please rush complete details of your new type of training and the book- let "My FUTURE IN RADIO."

Name.

Address.

SÏÊNTORIAN RC 2/36

SOUND AMPLIFIER NUCLEUS R EM EM REIt' -- guild your Amplifier: STENTORIAN way-for

l foc

l e a volume at IOW cost. For sta- diums, call s y s t e m s , Indces. h a n - ouets. advertis- Ina, ear.

N1'CLEi'S Includes 'Tull- Push" transformer. chokes, audios. outputs and lettered chassis. 6.10 -15 -30 watt amplifiers. A. AR power. 2.5. 6.3 v. tubes. Also for mike Pre- AmplIfiers: and battery amplifier.

!.$ ` l i

FREE:_Send for fun details and illus. bulle- tin- STENTORIAN Amplifier Nuclei and name of your distributor.

General Transformer Corp. 504 S. Throop St., Chicago

--Manufacturers of Replacement Units. Please Say That You So ;a Jt in RADIO -CRAFT

OIL MICA

PAPER ELECTROLYTIC

The finest guaranteed con- densers money can buy.

Write for descrip- tive catalog

No. 128.

CORNELL-DUBILIER CORPORATION

1347 BRONX BOULEVARD NEW YORK

488

CfflTRALAB Every serviceman from coast to coast knows Centralah .. everybody's his friend and the worst thing his enemies can say is that he's a mighty smooth article. Yes .... he's smooth all -right .... and it's that famous non -rubbing contact that makes him "that way." . . a tip from cam - paign headquarters: a mere handful will serv- ice practically any set ever made . . "better than ever before."

Rake Serrin nw«wuw..,rw,f,a,

.1w+.s..ar

MILWAUKEE WIS. RADIOHMS SUPPRESSORS FIXED RESISTORS

AMPERITE HIGH LEVEL YELDEITY Operates WITHOUT PRE -AMP HIGH IMPEDANCE -2000 OHMS

THIS MICROPHONE IS HIGH ENOUGH IN IMPEDANCE TO OPERATE DIRECTLY INTO GRID ... BUT NOT HIGH ENOUGH (ONLY 2000 OHMS) TO INTRODUCE SERIOUS LOSSES IN LINE UP TO 20P.

Per:nces condenser and crystal mites. No changes necessary. E mmates input transformer and its losses. Eliminates hum

trcuble and feedback

IV/POSITIVE -MID- 5M0 OTH-RCT1011 sTAnos

ELIMINATES HUM TROUBLE

MODEL RB -H. for speech and music. MIST $42.00 with coup- ling. MODEL RS -H. Inr gw.ch. but can also be used ter music. LIST 5$2.00 ith coupling. wm. for Ballotin .

Positive, non- sliding. ball-bear- ing clutch) Will never wear out

. never require adjustment. WILL NOT "CREEP". Tightens with only I/e turn of clutch. Mike can be rotated without loosening clutch. SMOOTH. PNEUMATIC - LIKE ACTION up and down. A model for every purpose. WRITE FOR ILLUSTRATED BULLETIN S.

AMPERITE am an toi Moaow.r MW rae

AMPERITE MICROPHONE

if you are interested in servicing electric refrigerators, turn to page 605 of this issue and read the advertisem*nt on the second vol- ume of the OFFICIAL REFRIGERATION SERVICE MANUAL.

RADIO -C

MAKE THIS "RADIO" MOTOR (Continued from page 464)

side views of the motor. The dimensions of the various parts are not at all critical and will be determined by the size of the permanent mag- net available. The iron core for the rotor consists of a piece of iron rod mounted between the magnet poles. The diameter of this iron cylinder should be from

Imo-

to % -in. less than the distance between the magnet poles. (A good length for it is half the length of the magnet). Contrary to the usual motor, this core does not rotate but is fixed and the winding rotates around it. (See Fig. 113)

The only part of the motor where special care must be taken is in the construction of the rotor coil form. A good design for this form is shown in Fig. 1C. It is made of stiff, light cardboard or fibre and care must be taken to see that it is symmetrical. The coil form should clear the iron core by about sss -in. on all sides. It will be seen in Fig. IA that the core is held in place by a pivot which must pass through the bottom of the form. The hole through which this pivot passes should be ap- proximately twice the diameter of the rod.

To the top of the coil form is glued a short length of hard -rubber rod. This rod supports a phonograph needle which serves as the motor shaft. The needle protrudes through the coil form and its point rests in a center -punch mark in the top of the iron cylinder. The top of the hard- rubber rod is hollowed out slightly so that it will hold a few drops of mercury, or it is pivoted at the top with a second phonograph needle as shown in the details of Fig. L

The last step in the construction is the wind- ing of the rotor. The more wire used. the bet- ter will be the results. The writer used 2.000 turns of A.F. transformer wire. half of it be- ing wound on each side of the hard- rubber rod. One end of the coil is soldered to the phonograph needle and the other end makes contact with the commutator. One of the motor input wires connects to the pivot and the other lightly touches the commutator. The two sections of the coil must be separated on the bottom of the coil form so as not to obstruct the core sup- porting screw hole. A thin (for lightness) coat of glue on the finished winding will stiffen the whole rotor and make the coil less susceptible to damage.

Figure 2A shows the circuit diagram using a S.P.S.T. switch for making and breaking the current. Figure 2H shows the method of connecting a D.P.D.T. switch which reverses the current at every half -revolution of the rotor and giving twice the power of the method shown in Fig. 2A. With a little ingenuity the builder can design a switch which can be thrown ssCth a very small movement of the hand. If n powerful station is close by. the switch may be eliminated and a commutator built on the hard -rubber rod so that a wire brush makes and breaks contact at the desired time as shown in Figs. lA and D.

The motor built by the writer has been oper- ated on stations many miles away using the hand commutation method.

(Mr. Hall is connected with the Physics De- partment of West Virginia Un,versity. Morgan- town, W. Va.- Editor)

Connections for the cry tal motor with single -pole and double -pole switch.

RAFT for FEBRUARY, 1936

per cent greater than the D.C. resistance. Then to determine the impedance of a voice coil, it is merely necessary to measure the D.C. resist- ance and multiply this value by 1.3.

A resistance bridge is not necessary for measuring the D.C. resistance of a voice coil. A low -range ohmmeter is sufficient to give the necessary accuracy. The essential parts of such an ohmmeter are: a single dry cell, a 0 -1.5A. D.C. ammeter, and a 1-ohm, 3 -W. resistor.

For example, let us suppose that a certain voice coil gives a reading of 0.55 -A. on the ohmmeter mentioned. The D.C. resistance is then equal to (1.5 -1) or 1.73 ohms. Mul-

0.55 tiplying 1.73 by 1.3, the impedance is 2.25 ohms. Terminals 4 and 6, from the chart, would then be the correct terminals to which the voice coil should be connected.

In addition to being universal electrically. this output transformer is also universal from a mounting standpoint. It can be mounted on either of two bases, one occupying a space of 1 %x2% ins. on the chassis and the other, a apace of 1 %x2% ins. Screw hole mounting centers in the former case vary from 1 ¡sx? -in. to 14x13's ins. and in the latter from 1 Pax %-in. to ltexl% ins.

Many Service Men have found it to their ad- vantage to carry in their stock one of these versatile transformers because of its adaptabil- ity to a large proportion of the radio receivers in use.

A NOVEL SELF -MATCHING OUTPUT TRANSFORMER

- (Continued from page 464)

tions are fractions of an ohm. Use of these combinations is not recommended since the re- sistance of the secondary winding would enter in to such a great extent that the efficiency of the transformer would be very lose (about 60

per cent ). The. Service Man usually does not have the

facilities for direct measurement of the voice -

coil impedance of a speaker. For all practical purposes the impedance of a voice coil is 30

Please Say That You Saw It in RADIO -CRAFT

L by

This article has been prepared front data supplied courtesy of General Transformer Corp.

MULTI -PURPOSE SET ANALYZER

(Continued front palle 462)

switch. The R -C tip jacks are used for resistance and

capacity measurements. Throwing Sw.5 to D.C. gives a scale of 0 -1. ma. at these posts.

A small battery and a variable resistor may then be used as an ohmmeter adapter. (The writer is developing a "free- reference -point" Resistance- Capacity Analyzer, which will be de- scribed in an early issue.) Five adapters are required, and should be connected exactly as shown in the diagram, so that the pin connec- tions will be the same as the analyzer sockets. They may be made by bolting adapter sockets on tube buses or adapter bases.

LIST OF PARTS

One Jewell No. 88, 0 -1 ma. meter; One Na -Add No. 456E composite socket 4 -5 -6

prong, Si: One Na -Add No. 477E socket 7 -7 prong, S3; One Na -AId socket 8 prong, S2: Two Yaxley No. 422 tip jacks, TC; Two Yaxley No. 422 tip jacks. test leads; Two Yaxley No. 422 tip jacks, R -C leads; Your S.P.D.T. toggle switches, Sw.1, Sw.2, Sw.0,

Sw.10: One D.P.D.T. toggle switch, Sw.3; One Yaxley No. 762 jack switch, Sw.4; One Yaxley No. 763 jack switch. Sw.6; Two Readrite No. 27 rotary switches, Sw.7,

Sw.8: One Readrite No. 34 rotary switch, Sw.6: Two Electrad meter shunts, 600 ohms, RI; One Electrad meter shunt. 55 ohms. R2; One Electrad meter shunt. 10 ohms, 113; One Electrad meter shunt, 5 ohms, R4: One Weston 10 -A. meter shunt. R11; One Shallcross multiplier resistor, 4,970 ohms

(unwind 30 ohms from 5,000 ohm precision resistor), R5:

One Continental Carbon multiplier resistor, 5,000 ohms. R6;

One Continental Carbon multiplier resistor, 90,000 ohms, R7;

One Continental Carbon multiplier resistor, 0.4 -meg.. R8:

One Continental Carbon multiplier resistor. 0.5 -meg.. R9:

One Aerovox multiplier resistor, 4.500 ohms (un- wind 500 ohms from 5,000 ohm precision resistor). R10:

One Taurex meter rectifier, RX ;

One bakelite panel. 7 x 9 ins.; One analyzer cable. 9 wires: One dual S.G. cap ami lead: Three Radio City 1sá -in. pointer knobs: Five 7 -hole 4- 5 -6 -7S and S -prong adapter

sockets: Five 4 -, 5 -, 6 -. 7S- and S -prong adapter bases.

RADIO -CRAFT for FEBRUARY, 1936

MILESTONES IN BROAD- CASTING

(Continued from papa 457)

According to Radio Retailing. however, 57 per cent of all receivers now offered use regu- lar glass tubes. About 16 per cent of all sets at present on the market are equipped with glass tubes, but having a metal -tube socket, an- other 16 per cent use both metal and glass tubes in the same chassis, and 11 per cent exclusively use metal tubes.

Since the public quite definitely is "sold" on metal tubes these statistics may change tre- mendously; after all, public opinion is a power- ful force that no manufacturer dare ignore if he wants to stay in business. Although many radio dealers interviewed by the author report a heavy demand for metal tubes, some of these dealers -and, especially, those who had sold metal -tube sets equipped with early models of the new tube -because of the trouble with their customers concerning radio receivers which did not work satisfactorily, are quite biased against metal tubes. But this by no means indicates a permanent antagonism toward metal tubes.

METAL TUBES MUST GET OLDER

It took about 20 years to develop the glass tube into the precise operating devices we know today, and the metal tubes, even if we include the two or three years of experimenting before they were introduced. still are quite young products, and have plenty of time to be im- proved before reaching the age of glass tubes. Then again, 90 per cent more types of tubes are now available in glass than in metal; and of all those most instable yet economical and highly -perfected of tubes -the "multi -purpose" type. only one model, the new 6Q7, is so far available in metal. However, the tube situa- tion changes daily in favor of the metal tubes, as may be seen from another diagram published recently by Radio Retailing (see Figs. 2B and C).

In the diagram Figs. 2B and C, only 39 radio set manufacturers are mentioned as users of metal tubes against 47 claimed in the advertising described above; this is due to selection of only the more important concerns among the 115 American radio set manufacturers. A still better view of the actual situation is given by the fol- lowing, Table II, published recently by the mag- azine Fortune, which indicates how the leading manufacturers ranked in 1934 with respect to set sales.

TABLE II Proportion of units produced by manufacturers. Philco 1,250.000 RCA 500,000 Crosley 300,000 General Household Utilities 300.000

(mostly automobile radio sets) Colonial - 300,000

(mostly for Sears, Roebuck) Wells -Gardner 200,000

(mostly for Montgomery Ward) Emerson . 200,000

(mostly midget) G.E. 200,000

(made by RCA) Atwater Kent 100,000 Zenith 100.000 Bosch 100.000

Total accounted for 3,550.000

During the year 1934 there have been produced and sold ( including 612,000 radio receivers ex- ported),- 4.696,000 radio Bete. Since the per- centage of sales made by the different manu- facturers during 1935 probably is about equal to their percentage of sales during 1934, the advertisem*nt which printed the names of 47 different manufacturers, and disregards their yearly output appears in quite a different light.

READERS' DEPARTMENT (Continued from page 465)

playing their outfits and hoping the Association will not catch up with them. Even these would pay if the fee were more reasonable.

I hope you will print this so that other Service Men will send in their views.

W. R. LUSTIN.

Thanks very mush for your comment, Mr. Lustin, a little Publirlly n gaol jag ihla situation may help.

INTERNATIONAL RADIO RE- VIEW

(Continued from page 466)

waveform distortion introduced by the shielding cage. This aerial offers possibilities for the ex- perimentally- inclined fans.

A NEW TABLE -MODEL SET THE EXPRESSION table made( has become

firmly associated with small sets designed to rest on a table. but in the true sense of the word a table -model set would be one with the set mounted in a table I

Such a set was described in an issue of Wire- less World (London) a short time ago. As shown in Fig. B, the set (a superheterodyne) is housed within a drawer of the table, with the speaker (mounted behind the chassis) facing forward and downward in such a way that closing the drawer does not affect the sound. The piece resembles a serving table with two wings which fold down flat against the sides.

THE TELEPHONE -DIAL SET ANEW German set which made its appear-

ance at the Berlin Radio Show is equipped with a novel type of tuning dial, in the form of a revolving dial disc similar to the dials used in automatic telephone systems. Tuning in this set (Pig. C) which was described in Radio - Handler (Berlin) is accomplished by dialing to a predetermined number. For example, London -74, Berlin -42, Rome -29, etc. Thus, to tune in London the listener turns the dial first to 7, then to 4.

A BOOK -CASE SET NOTHER novelty in set design is made to

imitate a group of books which can be set on a table between bookends. This set, shown in Fig. D, is of French origin.

A glance at the photo shows that the speaker "horn" is located below the tuning controls. When the set is opened for use, the front drop - panel forms a horn -type projector for the small - size speaker.

A HIGH -FIDELITY PHONO: RADIO ANEW German receiver of odd appearance

was introduced recently and is shown in the photo here (see Fig. E).

The receiver is a 5 -tube superheterodyne which has a variable band -width adjustment for fidel- ity control. The set uses 2 dynamic speakers. one for the bass and middle register and the other, a tweeter, for high -frequency response.

A phonograph pickup and turntable are mounted just below the tuning controls. within the "control compartment" at the back of the desk.

(This set sells for about 2260.1

AN UNUSUAL FRENCH SET ARECENT issue of La T.S.P. Pour Toua

(Paris) contained a photo of a peculiarly - shaped cabinet which will interest many Amer- ican radio enthusiasts.

As shown in Fig. F, the cabinet has an irregular, hexagonal shape with the tuning dial on the front facet. On this side also are mounted a tuning indicator. a volume control and tone control. On the adjacent facets, to left and right, are 2 speaker grilles, behind which are mounted the 2 speakers. The other three sides complete the cabinet structure.

A shallow lid covers the phonograph equip- ment when not in use.

A NOVEL RADIO -PHONOGRAPH THE magazine L'Antenne (Paris) recently

contained several views of the novel radio - phonograph unit shown in Fig. G. The cabinet is cylindrical in shape, with the radio set at the top and the automatic record changer and record storage cabinet in the bottom. Two doors in the front provide access to the phono- graph unit. Receivers are available both in A.C. and A.C.-D.C. types.

(Unusual cabinet styles are featured much snore in Europe than in this country, as shown by this issue. and other examples in past issues of Radio- Craft.)

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489

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RADIO -CRAFT for FEBRUARY, 1936

WAR -TIME USES OF RADIO

(Continued from page 467) found itself encircled by English battleships! These stations, equipped with very selective and extremely sensitive receivers, were able to receive communications transmitted from ship to ship, while the German High Sea Fleet was still lying at anchor at its base at Wilhelms- haven.

Although the cautious Germans used tiny buzzer transmitters for these communications, super -sensitive receivers at the English "SWS" (Shore Wireless Station) posts were able to re-

ceive these important communications. (Some of the receivers employed as many as 20 tuned R.F. stages in cascade, all simultaneously oper- ated by a single control (or "joy- stick" as it was popularly termed).

LOCATING SUBMARINES AND ZEPPELINS

These SWS stations (erected and operated by the English Intelligence Service) also employed excellently- functioning direction -finding devices. German submarines which sent their reports by radio to their base and received instructions by the same means were under constant surveillance by crews at the SWS stations. Experienced observers were able to recognize a certain sub- marine or airship, even when it changed its call signal, by peculiarities in the tone of its trans- mitter or by a characteristic dash in the send- ing of its operator. An extra -long dash, or a

skipped dot accounted for the detection of many submarines. which otherwise might have gone unrecognized for a long time. The Intelligence Service would endeavor to decipher the coded messages. while the staff of the direction -finder squads plotted the exact position of the sub- marine under surveillance. This knowledge of the submarine's exact position enabled the neces- sary action to be taken, in order to destroy it, and thus avoid the threatened cutting off of England's food supply.

A particularly exciting job for the staff of the SWS stations was the detection of Zeppelins before and during a raid over England, espe- cially towards the end.

When these great airships were attacked, and in adversity, their distress signals in many in- stances were transmitted in a condition of agita- tion which left only a feeling of pity for the brave Zeppelin operators who must have known that in a few minutes their lives would be lost.

All this excellent radin work between 1914 and 1918 was accomplished in spite of limited knowl- edge concerning amplification by electron tubes. Since then, radio technique has made tremendous strides, and superb equipment is available today for signal interception and direction finding.

But since the war many fundamentals of war tactics, and also many methods of applying radio communication have been changed and improved, and even at the present time there is discussion among militarists about further improvement of war tactics. But regardless of the opinion of the different groups which favor the "dynamic tactic." (tanks, armored cars, etc.) or of the countergroup which is in favor of the "static method of fighting a war" (trenches, etc.). all of them recognize the importance of a properly functioning communication system.

(A favorite trick to confuse the adversary

Direction finding and radio outfit of the Berlin Airport. The officer on the left turns the loop antenna mounted above the roof. The officer on right tunes the aircraft receiver. The receiver shown in the center is installed in a cast -iron cab- inet and covers the wave range from 15 to 30,000

meters.

was to send out powerful. broadly -tuned signals that interfered with regular messages by pro- ducing an unintelligible "hash" at the receiver - "jamming the ether" it was called.

Present advices seem to indicate that the new Armstrong system of amplitude -modulated trans- mission will prevent such "jamming" of signals. in future.)

WAR GAMES INDICATE RADIO

LIMITATIONS To what an extent radio communication is

applied today in modern warfare is indicated by

the fact that during the great Fall maneuvers of 1935 in upper New York State, 268 short- wave transmitters were employed by the U.S.

Signal Corps to transmit and receive the com- mands directly or indirectly sent by the main station at the headquarters in Pine Camp. If we consider the small area which was selected by the General Staff for this struggle between the RED and the BLUE armies the tremendously difficult task of the radio operators of picking out the assigned wavelength from the great wave mixture is easy to understand.

Generals who have a reputation of always asking technicians for the solution of seemingly impossible problems (and -strange as it may

seem -always getting their wishes fulfilled in the course of time) had their own opinions about these maneuvers, and about the operation of a

great many radio stations in a relatively small sector.

Please Sad Thot Yon Soue It in RAI,lO -CRAFT

SAYS GENERAL FOX CONNER:

General Fox Conner (commander of the First Army) for example. at the end of these field

maneuvers, made some caustic comments about

the efficiency of radio communication for war

purposes. The General stated in part: "Per- sonally, I think we have gone perfectly wild on

the subject of radio. We are spending an awful lot of money on radio, I think it should be cut out and spent on laboratory work for develop- ment of telephony and other forms of com-

munication." These comments of General Conner, who is

known to be one of our most able army leaders

aroused a great deal of discussion among radio enthusiasts, since radio seemed to them as valu- able to a modern army as airplanes and tanks. The radio industry. however. kept absolutely quiet concerning these remarks. and it was only some sarcastically -inclined radio engineers who could not refrain from pointing out that the Army could hardly blame the airplane industry for their misfortune during the fight over air- mail contracts, merely because private organiza- tions did the job much more efficiently.

Instead, this experience with the airmail con-

tract fight has renewed the lesson of the great war -that the army is not responsible for its

misfortunes, even the best pilot cannot fight against nature. since the air weapon is very

much dependent on weather. an experience also

confirmed by the last maneuvers in England and France. But the air weapon is not alone in having limitations: the seemingly invincible tanks also are limited in their use.

A bitter lesson in this respect was recently received by the Italians who saw their "carro veloce" (a medium -heavy type of tank, equipped with especially heavy machine guns), made de-

fenseless through the use of quite simply -con- structed lion traps. We know furthermore from statistics that of 100 soldiers poisoned by gas

only 1.73 have died against 24.65 per cent of those who were wounded by other weapons. We know also that a great many soldiers killed by

gas were members of the army which applied the gas (because of change of wind, etc.). If all these modern implements of war have their limitations, then how can we expect perfection from radio?

General Fox Conner may be right in his critic- ism if he condemns the exclusive use of radio as a means of communication. It is a recognized fact that the so- called "Schrott effect" and the "thermal agitation" limit the sensitivity and

thus the efficiency of a receiver. Also, the selectivity is limited by the demand of the armies that their stations must be easy to operate and light in weight. Therefore, it is not the tech- nicians but physical phenomena such as snow, rain and thunderstorms which interject their veto against the desires of Generals. No reason- able radio technician denies the important role of the telephone in war, but still there are some new means of radio communication in develop- ment which may be very useful as substitutes for telephony by wire.

RADIO CRAFT for FEBRUARY,

DECIMETER WAVES

As reports from Europe indicate, the English, German and Italian armies are at present very busy with experiments on wavelengths below I meter. These wavelengths (often termed "decimeter waves ") are limited to a range that extends only the distance which the eye un- obstructed by earth curvature, etc., can see.

These waves have the additional advantage that a tremendous number of these ultra- ultra- short -wave transmitters can be operated very close to one another without any mutual disturb. ance. Interception or interference is possible only by cutting into the straight line between transmitter and receiver, and even if this were accomplished the interception could be detected at once due to fading caused by the "electrical shadow" of the interceptor. Even though some of the frightful stories distributed by the Italians about these decimeter waves are not true, it is nevertheless sufficiently promising for the army to pay much attention to decimeter waves.

GENERAL HARBORD ON WAR- TIME RADIO

What Generals (who are not disappointed by the results of army maneuvers) think at a time of calm about radio may be learned from part of a statement made by General Harbord, who said: "For one great problem which had before never arisen in any big war, radio supplied a solution which could not have been offered by any other means of communication now known - that was, in providing contact between aircraft in flight and the ground. The commander can send aloft observers before whom distant battle- grounds lie revealed as the smaller fields of antiquity were to the man on a high hill. But the use of the invaluable knowledge which the observer may have gained usually depends upon its instantaneous transmission to his commander.

MODERN WAR RADIO DEVICES Since mobility therefore is one of the funda-

mental demands asked of radio stations to be used by the army, the light -weight radio unit is the standard equipment of all armies. Most of these radio stations used at present are of the so- called knapsack type. One box contains the transmitter. a second one the aerial supports and the antenna wires. The current source is often a pedal generator also transportable like a knapsack. It takes only a few minutes to make such a station ready for operation. and even less time to make it again transportable. In addition to these universal stations with very large wave ranges there are also short -wave stations in use. Most of these are crystal con- trolled, with a simple switch to change wave range and crystals. A tiny antenna. often of the umbrella type, is used for reception and transmission. These stations are light enough to be carried by one man. A small box con- taining an Edison storage battery, and a high - voltage dry battery are used as current sources. The station is carried on the hack with the small battery box in one hand.

Some of the most interesting post wartime developments are the new antennas used by sub- marines for radio transmission while the boat is under the sea level. Despite the fact that this seems quite contrary to all that we know about the propagation of radio waves, according to a dispatch from London to the New York Times, the new German submarines recently put in use are equipped with such antennas.

At the second Annual Marine Exhibition in New York, November 1935. a new receiving ap- paratus for the reception of weather maps, printed matter, etc., was displayed by RCA to be used for the transmission of radio facsimile to flying airplanes or ships at sea. There also are available in Europe radio facsimile trans- mitting units of special, light- weight design for use in airplanes to instantly send to the ground maps and photos made in the airplane.

REMOTE CONTROL Remote control by radio has been demonstrated

and was even actually applied during the World War. Since it is today a general custom to send commands to tanks, airplanes, battleships, etc.. by means of radio, it does not seem fantastic that some day not only torpedoes, but also all types of mobile craft will be directed by radio, replacing the human brain with an electro- mechanical one. Many seemingly impossible devices are still in development, others of which we do not even dare think may be ready for practical application, tomorrow,

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TESTING METAL -TUBES SETS

WITH PRESENT EQUIPMENT (Con li n lord from page 4631

ADAPTING ANALYZER TO SET

Most analyzers can easily be modified to test receivers using metal tubes. This can be done by using two adapters. One fits onto the plug ordinarily inserted into the receiver socket. Figure 1B shows this adapter which is used with a 7 -prong plug and fits into the octal socket regardless of the number of base pins the tube has.

The adapter allows the ordinary 7 -prong plug to fit into the octal socket. Note that no con- nection can be made to chassis through the shield pin contact, since we do not have an 11h pin or a 9th wire in the cable. This ground connection is not essential in testing.

ADAPTING TUBES TO ANALYZER

We now have the analyzer connected to the receiver using metal tubes. Now we have to connect the metal tube to the analyzer. This can also be done with an adapter. An adapter is on the market. which will plug into a standard 7 -prong socket and an octal base tube will fit into the adapter. This adapter is shown in Fig. I.A. This adapter will take any octal -base tube regardless of the number of base pins.

This is the simplest method and merely re- quires the purchase of two adapters. A more satisfactory way will be to purchase a 9 -wire cable and adapters. Eight wires of the 9 -wire cable are connected to the corresponding former contacts of the 8-wire cable. The 9th wire should then be connected to a tip -jack. If the analyzer has a ground or a chassis connection connect this wire to this ground connection. Otherwise mount a special tip -jack at some con- venient point for this connection.

The 9 -wire cable should be connected to an octal -base plug which will fit directly into metal - tube sockets.

Adapters will then be used to connect the plug into ordinary 4 -, 6 -, 6- and 7 -prong sockets.

If your analyzer is of the type which has a

socket on its panel for plugging the analyzer cable in, instead of connecting the wires direct to the sockets, the plug and socket should be

changed to the octal -base type. An adapter will also have to be used to plug

the octal -base tube into the 7 -hole socket of the analyzer. (If room permits. an 8 -prong socket may be used to eliminate this adapter.)

Another difference in the metal tubes is in the arrangement of the base pins. The tubes have been constructed so that they will all fit in the 8 -prong socket, even though the tube has only 5 prongs. See Figs. 1C and D. Fig- ure 1B shows the base pin arrangement for the OAR; Fig. IA, the base pin arrangement for the 6C5. Both drawings are bottom views. Notice that both tubes will fit in the same socket. the 6A8 having a prong for all 8 holes. The 6C5 will fit in the same socket, but two pin holes will be empty.

This makes a universal numbering arrange- ment possible. This must be remembered when testing these circuits. Otherwise you may not connect your meter to the desired circuit. You will find the heater and cathode connec- tions for these tubes to be the same with very few exceptions. However. the plate and grid connections vary with nearly every tube. You will have to consult the tube base connections for each type tube when testing these circuits. This will, of course. require a free point -to- point analyzer.

These tubes also have a smaller control -grid connection on the top of the tube. However, clips may be secured which will fit either tube. You can also get clips for connecting the clip from the set to your analyzer plug.

These are the main differences you will notice in the physical construction of the tubes. However, the interior elements have been im. proved to some extent. Although some of the metal tubes are very similar to glass tubes which have been manufactured for some time.

These changes in tube characteristics are going to give You some changes in readings while testing these circuits.

6H6 TESTING DATA

cept that it does not have a triode or pentode section in the same envelope. Also there is a separate cathode for each diode, while previ- ously these diodes have had a common cathode; remember this, since in many circuits using This tube, the cathodes are not connected together.

One manufacturer uses this tube as a full - wave rectifier for the detector. In some models. this is used also for A.V.C. action, and in others, a second 6H6 is used for A.V.C. The latter idea is shown in Fig. lE.

Another manufacturer uses one diode for de- tector and A.V.C. and the second diode to furnish bias for the controlled tubes when tuned to a weak station or to no station. This cir- cuit is shown in Fig. 1F.

6L7 TESTING DATA

The other tube is the 6L7. It is the biggest change from the older -type tubes. It has been designed as a first -detector, using a separate oscillator. This tube has two control -grids which will affect the plate current. However, these control -grids are shielded (by an interposed grid) from each other. A typical circuit is shown in Fig. 1G.

Testing this tube as a first -detector will not vary much from your tests of a 6A7 or 6A8. However, this tube is likely to be used in many unusual circuits. Due to these two separate control -grids, this tube will have many uses. It may be used very effectively as an R.F. ampli- fier with the second grid for A.V.C. This might mislead you while testing the circuit.

This article has been prepared from data supplied by courtesy of Sprayberry's Prac- tical Mechanics of Radin Service.

2 NEW METAL TUBES (Coatis., d from poor 311.1)

6Q7 The triode -section is a high -mu tube designed

for resistance coupling. The coupling resistance may be any value up to approximately !4 -meg.

The two diode units are independent of each other and the triode unit (except for the com- mon cathode sleeve). The diode units may be used either as a half -wave or full-wave rectifier, or a half -wave rectifier with the other unit used for delayed A.V.C.

The same external plate resistance values may be used with the 6Q7 tube as with the type 75 tube. The bias should be about %-V. more with a 250 V. supply and % -V. more with a 100 V. supply than would be used with the type 75 tube (shell tied to the cathode or ground).

(Continued Irom pape 463)

OZ4 and filtering commonly used to eliminate vi- brator noise will usually be sufficient.

The OZ4 is filled with a permanent gas rather than a vapor filling. The tube characteristics are independent of the surrounding tempera- ture.

The OZ4 has the same external form and di- mensions as other tubes of the metal line. How- ever, in this tube the metal shell serves chiefly as container and electrostatic shield for the glass bulb, whic!, is required to insulate the contained pas from the grounded shell.

Leading manufacturers of vibrator -"B" units for car -radio receivers are enthusiastic about the performance of the OZ4 in service tests which have been running for several months. It is said that synchronous vibrator rectifier ef- ficiency can be had with the OZ4 and a simple non -synchronous rectifier.

The OZ4 is rugged and has no filament to break or burn out. It is expected to simplify the power supply problem for many car -radio set receiver manufacturers during the coming season. The base of this tube is a standard octal type.

Operating Conditions and Characteristics D.C. output voltage 300 max. D.C. output current, ma..... ._ 30 min.

75 max. Peak plate current, ma 200 max. Starting voltage 300 min. Voltage drop (dynamic) 24av'g.

There are two tubes, and one in particular. which are quite different from any tubes made before. The first is the duo -diode 6H6. It is

practically the same as former diode tubes, ex-

Please Sa)/ That Yore Satu It in RADIO -CRAFT

This article has been prepared from data supplied by courtesy of Raytheon Production Corp.

RADIO -CRAFT for FEBRUARY, 1936

THE RENODE A NEW GRIDLESS TUBE

(Continued from page 468)

trodes, which must again absorb a certain number of electrons varying according to the deflection. As the beam is "ordered" so that a very insignificant number of electrons are caught by the deflectors when these are at zero poten- tials, an increase of the total number of elec- trons caught by the deflectors will practically al- ways result when an R.F. current is applied.

The momentary number caught is a function of the rise and fall (fluctuation) of the R.F. voltage, and condenser C2 will be charged to a value depending on the momentary value of the controlling voltage: i.e., the voltage of condenser C2 will vary according to the modulations of the incoming R.F. voltage.

Besides the R.F. controlling voltages we thus get impressed on the deflectors a negative po- tential that numerically varies with the R.F. modulation, creating in the apace between the deflectors a negative electric field that counter. acts the positive field from the intensifier, and thus permits less electrons to get through to the plate.

OBTAINING DETECTION

The plate current therefore will vary with the R.F. modulation: i.e., an increase of the ap- plied R.F. voltage will result in a decrease of the plate current (or detection).

Since in this arrangement the R.F. voltages on the deflectors at any time will be numerically equal but of opposite polarity, it is obvious that none of the R.F. oscillations in the input cir- cuit will be carried over to the plate or in- tensifier (auxiliary plate) circuits. In plainer language: we get rid of those annoying tend - ences to instability in the following A.F. stages, so familiar with conventional grid -controlled tubes.

The Situation is different if we hook the Renode up in a circuit like that illustrated by Fig. 2B. In this case the R.F. voltages applied to the deflectors are both equal in value and polarity, which condition naturally sets up R.F. currents in the plate and intensifier circuits, varying in concert with the incoming signals.

In both diagrams the tube works as an "or- dered beam "; however, in hookup A the beam moves brush -like, alternately towards either de- flector plate, while in hookup B the beam "swells" in the middle, so to speak, and widens out toward+ the plates, as depicted in Fig. 1.

CHARACTERISTIC CURVES With a view to further elucidating the be-

behavior of the Renode a few characteristic curves drawn by the inventor on the basis of laboratory experiments are shown.

Figure 3A shows the detector characteristic of the Renode (A) as compared with an ordinary R.F. pentode (B). The grid leak in both cases was 2 mega. (The readings on the vertical axis, left, are for the Renode, those to the right for the pentode: the units are in centimeters - i.e. readings on a large scale by means of a mirror -galvanometer -and they indicate relative values of deflector -currents plotted against in- put R.F. voltages at zero per cent modulation. To convert centimeters to inches, multiply the former by 0.3937.)

Figure 31i shows the total amplification of a Renode (A) as compared with that of an R.F. pentode (BI. Input voltage (abscissa) in mil- livolts at 30 per cent modulation is plotted

Fig. 3. Comparative cha acteristics of

against output in volts. In Fig. 3C. is shown the selectivity curve for

a Renode (A) and a pentode (B) working in identical tuning circuits. For the sake of clarity both curves are reduced to a peak of 1 V., but actually the Renode curve had its peak at 4.6 V., while the pentode reached only 3.75 V. The two dotted lines denote values of voltage obtained at a band width of 10 ka. For the pentode we find a voltage of 0.77 -V. but the Renode yields 0.47 -V. or 61 per cent less than that of the pentode. This spells: better selectivity.

THE PATENT SITUATION A peculiar condition surrounds the develop-

ment of the Renode, as explained below. Initial experiments on the Renode were started

some 5 years ago by A. Schleimann Jensen, a Danish engineer and radio editor. When. after 2 years, the fruits of his efforts were brought to the attention of the Radio Board of the Danish Post Office, which controls broadcasting in Den. mark, the Radio Board secretly granted him a large sum to support further work. Some weeks ago he concluded his experiments and placed before an audience of experts (led by the chief engineer of broadcasting) -the Renode tube.

The Renode timed its appearance on the mark- et at a psychological hour when the whole Scan- dinavian (Denmark, Norway, Sweden, and even Germany) radio industry is combining in a fight against the international tube and patent trusts.

In addition to the high prices for tubes (an American 50c tube sells in Denmark as a result of trust manipulations, for about 55.00 I), of which about Ire million are imported annually, the national receiver- production in Denmark has been liable to payment of considerable royalties to holders of certain vital patents. It is utterly impossible to build a modern tube set legally. unless sanctioned by the Dansk Radio Union (comprising 38 companies manufacturing radio equipment in Denmark), which, until now has had complete control of set production. Now, however, with the advent of the Renode, four of the larger manufacturers have withdrawn from the Union. and are pinning their faith on the new tubel

The Norwegians are in much the same fix as the Danes. as far as tube prices and patent licenses are concerned. In addition, broad- casting is having a very tough time in Nor- way right now, since the mountainous country necessitates a large number of comparatively powerful broadcasting stations. But the build- ing and expansion of such a network, to serv- ice only 175,000 listeners. who pay an aggre- gate license fee of about 3% million kroner annually, is very expensive. In an effort to ac- quire more revenue an attempt was made to increase the number of listeners by designing a very inexpensive radio set -a Norwegian edi- tion of the German "Volksempfänger," or All - Peoples Receiver. However, real production has been withheld simply because the broadcasters are openly afraid that the international tube and patent firms will hamper the practical de- velopment by taking their toll on tubes and pat- ent licenses.

We find in Sweden that the association of Swedish radio manufacturers is having a terrific battle with the tube firms, which are alleged to have attempted to exercise a regular dictatorship over the industry.

So, if the international trusts do not succeed in buying the Danish Renode people out -and I,

for one, am perfectly satisfied they will not give in -it should be obvious that the Renode spells tear on all other tube firms.

Renode and Pentode as a detector.

F47 W°

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Please Say That You Saw It in RADIO-CRAFr

493

This versatile all -round hgh -fidelity combina- tion tuner -amplifier unit was designed and built by LAFAYETTE Engineers in their labora- tories exclusively for us. A single steel case contains a COMPLETE portable sound system, preamplifier, 3- channel mixer and high -fidelity radio tuner providing "studio quality" repro- duction. It has a peak output of 35 watts; maximum output into plate impedance of 25 wafts; maximum output into 500 ohm line, 20 wafts. Harmonic content at rated maxi- mum outputs is 5 %. Gain, I10db; hum level -50 db. Model I59A. Price as illus- trated but less (12) tubes

$791!!

FREE CONSULTING SERVICE Model I59A above is but one of many Lafayette amplifiers in the complete line. Lafayette en- gineers are known the world over for their accom- plishments in the public -address field. They have assisted many radio dealers and servicemen to get into this profitable yet little worked branch of radio. For you, too, the opportunities are limitless, since Lafayette engineers will welcome YOUR ques- tions and cooperate with you in solving YOUR indi- vidual sound problems. Consult with them -in per- son at any of our five salesrooms -or by writing our

f mail order center. In the meantime pet your FREE copy of our Catalog No. 59, which lists the world's largest and most modern selection of public- address equipment at LOWEST WHOLE- SALE PRICES.

WHOLESALE RADIO SERVICE CO.. INC. 100 SIXTH AVE.. DEPT. C -26. NEW YORK. N.Y.

Send as catalog No. 59. listing P.A. Equipment. I 0 I have a P.A. Problem: see letter attached.

Address..._.

Name

City State

WHOLESALE RADIO SERVICE (Oi NEW YORK. N.Y. ID0 SIXTH AVE.

CHICAGO. ILL. ATLANTA. GA. 901 W JACKSON BLVD. 430W PEACHTREE STN W

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Brush B2S Mikes are ideally suited for public ad- dress. remote pickup, sound car and dance band work. The best low price micro- phone for amateur trans- mission work. Typical Brush Sound Cell construc- tion insures long life and satisfactory performance. Not affected by wind or severe changes in at- mospheric conditions. Operates directly into high gain amplifier. No input transformer re- quired. No distortion from close speaking. Fully guaranteed. Weight 3 oss.- overall height 0,á inches. Illustrated folder free on request. Send for yours. If your dealer cannot supply you with this big new value write

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MICROPHONES MME STANDS TWEETERS HEAD PHONES IWO SPEAKERS

New und Better CARBON RESISTORS They sure look good! And they're just as

good as they look. Ideal for applications re-

quiring non -inductive resistance dissipating I waft or less. Solid molded carbon ele-

ment. Non -fluctuating. Noiseless. Accur- ate (within 10%) values stamped and R.M.

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All resistance values. And they cost no

more! Your copy 1936 condenser and resistor DATA on request. Also sample copy

of Research Worker. See your AEROVOX jobber for those better radio parts.

CORPORATION 77 Washington St. _ Brooklyn, N. Y.

RADIO -CRAFT for FEBRUARY, 1936

A $30,000 "RADIO" INSTALLATION

(Continued from page 472)

average room, this room showed up the most minute sound. Speaker fields therefore were supplied from triple -filtered rectifiers, so that even though the entire job is a super -power, wide -frequency -range outfit, passing all the fre- quencies the human ear may grasp, operation is 100 per cent silent.

Each assembly of this super -deluxe radio - phono. installation is built to the highest stand- ards. Chassis are of aluminum %a -in. thick, and all other metal work is either black lacquered or chromium plated.

The audio system has 4 stages of push -pull using the Hiler system of double -impedance coupling in all stages, providing a flat response from below 30 cycles to beyond the audio fre- quency band. The output uses two type 845

50 -W. tubes. All filaments are heated by direct current. Low -voltage filaments are supplied by copper -oxide rectifiers, and higher- voltage fila- ments are heated from electronic rectifiers.

PATENTED PUSH -PULL DETECTOR

A most interesting feature of the system is the radio detection circuit. This consists of 2 triodes so connected that the plates each draw 1 ma. and operate 180 deg. out of phase with respect to each other. (Note that 1 tube is a

"grid leak -condenser" type and the other a

"plate detection" unit. in Fig. 2.) This is a

push -pull detector circuit protected by patents. It results in exceptionally clean tone and is of course almost impossible to overload.

Old radio fans may recall the early Miler audio circuits back in 1926 and 1927 which were not push -pull and which made use of condensers to create resonance at points where the re- latively poor speakers of the day were weak in response. Improvements, however. have enhanced the efficiency. Coupling resonance has been

designed to appear below the A.F. band; and because of the push -pull circuit. motor -boating is eliminated.

CIRCUIT ANALYSIS The circuit of the amplifier, shown in Fig. 3.

can be better understood by reference to the facts outlined below:

The two coils, LL L2. each have an induct- ance of 3,000 by. at no D.C. (all D.C. in the core is balanced out).

Coil L3 has an inductance of 3,000 hy. at 20 ma. D.C. but the primary wire is heavy. to carry the plate current of the third stage.

The secondary of T1 is used as the first choke

of the amplifier and as input transformer when

the phono. pickup is in circuit. Resonance in the amplifier is about 31_

cycles; thus no peaks are within the A.F. band.

No other system gives as much tube gain per stage. and, should any tube draw grid current. this will not harm the response.

The power stage will carry twice as much voltage input as other systems, thus with a class A rating we get 4 times the total power output when needed.

Grid and plate circuits may use separate chokes (such as the secondaries of high -class transformers), in all but the third -stage plate circuit.

Experience over a period of years has proven that a separate "B" power unit should be used for the output tubes. In this amplifier, there- fore, a separate one is needed for the first 3

A.F. stages and one for the tuner. When 3

stages are used, only two plate supplies are necessary.

REMOTE- CONTROL CIRCUIT The circuit of the remote control, Fig. 4, has

the following characteristics: In this circuit all dials in the house register

at once, thus keeping a constant load on the circuit.

The output of the 874 regulator is up to 60 ma.. constant between 90 and 95 V.

The 100 -ohm resistors in the plus leads of the meters compensate for moisture. temperature. length of line and variations in all meters. In the finished job, each meter is calibrated separ- ately and therefore all dials read alike and tune exactly to the station.

Unless such an individual rectifier system is used (that is, the rectifier doing nothing but supply current to the meters), the 874 regula- tor will flicker and at times go out, thus causing voltage surges. when the circuit is called upon to supply variable voltages and currents as in radio reception.

(The author will be glad to advise further in connection with sound installations of this type.)

REPLACEMENT TRANSFORMER LIST

The United Transformer Corp. has re-

cently issued a bulletin listing over 1,500

sets made by more than 100 manufacturers. These many different sets may be serviced

with a minimum of alteration by the use

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the type using high power class B output systems are covered.

Write to Radio -Craft for your copy -ask for Bulletin No. 922.

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Please Say That You Setr, It in RADIO -CRAFT

RADIO -CRAFT for FEBRUARY

SERVICING THEATRE SOUND SYSTEMS

(Continued from page 475)

around to the back and a cancellation of sound

waves takes place, again causing decreased am- plitude at certain frequencies, thereby making peaks in the sound response curve.

After horns or baffle boards are properly placed and mounted behind the screen, hair - felt or some other soft, sound -absorbing material should be used to cover the remainder of the space from the edge of the horn or baffle to the screen frame.

The original intention of the engineers who designed sound equipment was to present "wide range" or "high fidelity" to the theatre, since they designed the optical systems to function at from 50 to 9,000 cycles. However, the re- producing equipment until just recently would not permit such response. the average being around 100 or 125 cycles to 3,500 or 4.500 cycles. The number of high -fidelity installations is in- creasing rapidly and will present a few new problems to the Service Man. The RMA re- cently offered a tentative interpretation of "High Fidelity" as a range of frequencies of at least 50 to 7,500 cycles, with variations not to exceed 10 db. ; and a total distortion factor not to exceed 6 per cent at an output of not less than 10 W. The factors controlling high fidelity are the ability of the sound head. ampli- Ser. speakers and screen to pass a range of the above qualifications.

The tweeter horn has a small neck flaring out to a bell of some 4 or 5 ins. in dia.. and re- quires no baffle. These horns are very direc- tional and should be mounted above and as

close to the large speakers as possible, with the tweeter horn projecting through the baffle board. Since these "tweeter" units are able to handle only about t!1 the power that the larger speakers will handle with safety, blasting or overloading such units ruins the diaphragms, necessitating their replacement. The filter, however. besides providing the proper cutoff, also lowers the power input to the tweeter unit. When more than one reproducer is used, the voice coils should be paralleled. It is also nec- essary to "phase" the voice coils. that is, to have them all move in at the same time and out at the same time Using a small "C" bat- tery to get a click from the cones will gicr enough movement so that they can be checked by placing the finger tips near the web of the cone. The movements in and out should be

simultaneous. Refinished screens will present serious diffi-

culty in passing the upper part of the audio band due to the decrease in the size of the per- forations. Approximately 25 per cent of the total picture area should be perforated for I

sound. The cutoff (around 6,000 cycles) will be more noticeable with high- fidelity systems than with the older equipment.

Although auditorium acoustics may be out of the range of the Service Man's work, there are a few things he might do to improve sound reproduction conditions in some houses. Pieces of house equipment that are in resonance with certain frequencies of the audio band will not improve the sound. Peaks will be produced on the curve, as well as the rattling of the res- onating object. Reflection and reverberation are the two most important items. Use of Sabine'; formula (obtained from any good buck

on physics or acoustics) will help to calculnt, the amount of padding needed. It might b,

well to mention too. that a house can be over - draped. as well as underdraped. Sound ab- sorbing constants for different types of seats. surfaces, drapes etc. usually accompany the formula. A note of 512 cycles is suggested for use with the formula in calculating the rever- beration factor of auditoriums.

Noise filters can be used across arc lamp motors. projector motors and similar equil'- ment causing interference in the sound. A

good analyzer such as used in radio service wß,.1

will take care of the general troubles, if tL technician can measure voltage, current and re-

sistance with it. However, if he wants to be

able to meet all the problems efficiently, a good

capacity and leakage tester, a good micro:un- meter, a power -level meter, and frequency film will be of material aid. But regardless of how much lest equipment lie has. in order to get the desired results. he must. above all, be able to apply good common sense. know the funda- mental and bare the ability to analyze a sii

1936 495

AR THAT OXFORD, /"

It may be a little 5" or 6" OX- FORD Speaker in a midget set or it may be a larger 8", 11" or 14" super Auditorium model. What- ever the size or type, if it's an OXFORD unit it is delighting listeners with its rich, full toned, thrilling quality.

To get out of a radio or P.A. out-

fit all that's built into it, use OXFORD SPEAKERS. They give

you TRUE reproduction. And there is an OXFORD Speaker for

every radio and sound purpose.

REPLACEMENT SPEAKERS Full line of REPLACEMENT speakers for all radio sets. Send for complete illustrated catalog No. 351 -C or see your jobber for full particulars.

OXFORD TARTAK RADIO CORP. 350W. Huron St. Chicago, Illinois

An interference suppressor that really

works. Attaches directly to interfering

device -not to radio. Simple to install.

Sizes for every type of installation.

Write for co U? plete

details

THE AUTOMATIC ELECTRICAL DEVICES CO.

334 E. Third St., Cincinnati, Ohio

FILTRAD A SIMPLE 2 -TUBE A. C.

SHORT -WAVE CONVERTER SELF POWERED

As Featured in January Radio -Craft lDrsigu,tI In R(1Rl RI (.. Ill RLOG)

!his latest creation of Thor's offers outstanding .1 flue and performance.

Coors from 19 to 54 and 65 to 200 meters. With positive onl art band selector switch.

Unwired and less na95

Complete kit, as shown tubes, cabinet 490 $V extra

Special: FItEE DIAGRAMS sent upon reque,t for any of the Tlloit Amplifier er Tuner Hit,

MAIL ORDERS PROMPTLY FILLED

CO R 157 GREENWICH ST. NEW YORK. N. Y.

P " t Thot Fout Saw It in RADIO -CRAFT

496

and Note I the lliffereiice

Countless radio sets are working far below their peak efficiency- because poor condensers won't let them do any better! When filter condensers fail to supply the proper voltage - when cheap, inferior condensers are used -nothing about a radio can be wholly right. To test this assertion we only ask that you take a "sick" radio and equip it THROUGHOUT with Spragues. You'll be amazed at the im- provement in "pep," volume and tonal quality.

Remember: You'll never go wrong with a Sprague. Every condenser is guaranteed.

Sprague Products Co., North Adams, Mass.

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G RU NOW and 46 other inf Qrs. endorse R -T -I

RADIO -CRAFT for FEBRUARY, 1936

THE LISTENING P 0 S T FOR ALL -WAVE DX -ERS

(Continued from page 473) Japanese stations throughout the central, and eastern states so that the following list com- pletely corrected up to date should be found of value. Watch these Japanese frequencies from about 4:00 am to daylight Eastern Standard time. (List, courtesy of Akifusa Saito. Japan.)

CALL KC. KW. 3ITCY 500 100 JFCK 580 1 JO:tK-2 590 10 J2JE 590 50

JODK-2 610 10 JOTK 625 t,í JOUfi 635 t/a JO1'K 615 0.3 SI/AK 650 1 ,10131 635 0.3 ,1F'.tK 670 10 31TF'Y 674 3 JOVE 6110 t/a JOLK 680 t/a JOKK 700 JO.tK 710 3 JI'111: 720 1 JOItK 720 JOSK 735 JbOK-1 750 10 JOIIK J0114 ?80 % J01K 790 10 JOCK-1 810 10 JOII: 830 10 JOFK 850 10 JO.tK-1 870 10 \IT111- 890 1 JODI4-1 900 10 JOQK 920 bí JOAO 930 iS JONK 940

0 0.3 .100K

JOXK 980 X JOF(/ 990 0.3 JADFC 1.030 0.15 JOTS} 1.050 th 3010 1.000 t/a .10RK-2 1,085 10 JOCK-2 1,175 10

LOCATION Shinkyo, Manchukuo Tairhu, Taiwan Tokyo. Japan Tokyo. Japan (Experimental

with Irregular schedule) 1:eijo, Chosen Matheur, Japan K iamahu, Japan Akita. Japan Darien. Manchukuo Asahlga, Japan Talhoku. Talpan Il arh hi . :Manchukuo Itakndatr, Japan f*ckuoka. Japan Okayama. Japan Kanazawa, Japan Taiwan. Taiwan Kochi, Japan Kokura. Japan Oska. .talon Sendai. Japan Shizuoka, Japan Kumamoto. .Japan Nagoya. Japan Sapporo. Japan II i roshima. Japan Tokyo. .Japan Holen. :Manchukuo Kello. ('hnsen Niigata. Japan Nagasaki. Japan Nagano. Japan Kyoto. Japan Marbaahl. Japan Tokushima. Japan Faukul. Japan Fuzan. Chosen Kagoshima. Japan Toyama. Japan Osaka, Japan Nagoya, Japan

THE LATEST FROM EUROPE

The new French Government station at La Brague. near Nice, is testing with 60 kw. of power on 1,249 kc., and will begin official opera- tions shortly.

Radio Marseilles, at Marseilles. France. is also testing with 120 kw. of power on a frequency of 749 kc.

The new Toulouse -Muret PTT French station broadcasting with 100 kw, on 776 kc, was offi- cially opened in October, 1935.

Radio Lyons PTT. Lyons, France, has been broadcasting with their increased power of 25 kw. on 1.393 kc. since October, 1935.

Work on the new anti -fading aerial for Leipzig. Germany, is completed and the station has been operating with its full power of 120 kw. on 785 ke. since October 3, 1935. The station's efficiency is said to be increased 70 per cent.

A new station at Reichenbach, Silesia will utilize 5 kw. on 1.231 kc. when it is completed.

Linz. Austria, is to acquire the old 17 kw. transmitter of Vienna Rosenhuegel, to replace its present 500 W. station which broadcasts on 1,285 kc.

Salzburg. Austria is to get a new 5 kw. trans- mitter, and the power of Innsbruck. Austria is to be doubled.

LAST MINUTE REPORT ON

BROADCAST BAND DX

Just before we send this copy to press conies a report on broadcast -band foreign DX -ing from Randolph Tomlinson, Port Chester, N.Y.. that should be of interest.

"DX here has been good, fair and 'rotten.' Have had some fine nights and mornings. only to have the next 'rotten' and hear nothing! Last night the band opened up on the Europeans, and I had Toulouse, Hamburg. Copenhagen. West Regional, Bari, Lille, Marseilles, Fecamp, Poste Parisien, Frankfurt, Hamburg. and others all over the dial but too weak to identify.

"The South Americans are very fine. LR5 has , equal in strength to WJZ New almost been g

York. LR3 is a nightly visitor here, as well as PRF4, on 923, L84. LR6, LRR, LS8, LS2. CX26, all logged several times. HHK tears in here on

on 921 kc. He is 1 kc. off frequency. Fridays o eq . Y WNEL. and WKAQ are excellent. CX34 was the best of the lot with only 500 W.. but the worst difficulty is trying to get a report from these South Americans.

"Trans -Pacifies have been poor, 1YA being

Please Say That You Saw It in RADIO -CRAFT

about the only good one. 3GI, on 830 ka. seems tu be on the air for good now. and should be fine in the Spring. I have never managed to snap a Jag yet, but am still hoping."

(So it would seem as we go to press that DX- ing conditions on the Broadcast Band are tak- ing a turn for the better.- Editor)

NOTES FOR OUR SHORT WAVERS

W W V, owned by the United States Bureau of Standards puts on regular frequency trans- missions as follows: Wednesday. Noon -1:00 pm, (15 mc.), 1:15 -2:15 pm (10 mc.) 2:30 -3:30 pm (5 mc.). These are extremely useful in calibrating a S.-W. receiver.

WOR. Newark, New Jersey, has again asked the F.C.C. for permission to start building the short -wave relay W2XHI, so, (despite the de- cision against building) the short -wave station may materialize after all.

W2XE, relay of the CBS at Wayne, New Jersey. is adding two new frequencies -17.76 me., and 21.52 mc., respectively.

W8XKA. is the call of the new 5 -meter sta- tion which relays WRXK's programs on an ultra -high frequency of 55.5 mc.

WIXAL, Boston, the educational broadcaster, has been granted permission to raise its power from 5 kw. to 10 kw.

Mexico is now the possessor of one of the finest short -wave stations on the North Amer- ican Continent. The new station is XBJQ, which is owned by the National Bank of Mexico, P.O, Box 2825, Mexico, D.F., and nightly relays XEW, on a frequency of exactly 11 mc. Al- though the power is only 1 kw. the signal reaches the U.S.A. with great power, and ex- cellent modulation.

Another new station in Mexico is XEFT, "La Voz de Vera Cruz," El Primer Puerto De Mexico. Av. Independencia 28. Vera Cruz. Mexico, X EFT operates on 6.12 mc. and the schedule is 11 :00 am to 4 :00 pm, and '7 :30 to midnight. On Sunday the schedule is 9 :00 pm until early Monday morning. according to a verification received by Mr. John Shanks, of Russellville. Tennessee.

Perhaps the most important short -wave news of the month is the completion of the short- wave station "EL Mundo," of Buenos Aires, Argentina. which will relay LR1 on the broad- cast band. This relay station puts on irregular tests preparatory to opening a regular service. The first was on October 13. at which time the relay operated on 9.890 kc., under the call LSN3. The second test took place on November 6th, from 5 :00 to 7 :00 pm. under the call LSL on a frequency of 10 :25 mc. It is believed that this latter frequency will be used as a permanent channel, and that regular transmissions will shortly be started. By next month we hope to have complete information on "El Mundo," of Buenos Aires.

KKH, Kahuku, Hawaii (7.52 mc.) has been sending out a typical Hawaiian program for retransmission by CBS at 11:45 pm Monday nights. Before the program. KKH tests with KEJ (9.01 mc.) and KKQ of Bolinas, California.

Changes to Winter schedules, and frequencies have been made by the Japanese short -wave stations: The regular morning relay of JOAK, Tokyo is now being radiated by JVT (6.75 mc.) and occasionally JT..G, 6.33 mc. The schedule is 4 :00-7 :40 am.

The regular Overseas Hour from 12 :00 mid- night to 1 :00 am is now being radiated by JVN, Nnzaki, on 10.66 mc. JVN is a consider- able improvement over JVH on this schedule.

An additional overseas hour has now been added for reception on the Eastern coast of North and South America. This is radiated on Monday, and Thursday from 4 :00 to 5 :00 pm over JVM, Nazaki (10.74 mc.) and JVP. Nazaki (7.51 nie.). Reports on this transmission are especially desired. and should be addressed to the Kokusai -Den va Kaisha Ltd., Osaka Bldg., Kojimachiku, Tokyo. Japan.

HJN, Bogota, Colombia is again transmitting (on 6.07 mc.) from about 6:00 to 9:30 pm

according to Mr. John Shanks, of Russellville, Tennessee.

ORK, Ruysselede. Belgium (10.33 mc.) is now broadcasting on its winter schedule of 2 :30 to 4 :00 pm. With its increased power it is being received much better in the U.S.A. at present.

On Tuesdays. and Thursdays at 10 :00-10 :30 pm PLY. Bandoeng, Java (9.415 mc.) may be heard relaying the native Javanese programs of YDE2, Solo, Java to an American audience. Occasionally PLE (18.82 mc.) or PMA, Ban - doeng (19.35 me.) also relay this program.

RADIO -CRAFT tor FEBRUARY. 1936

OSCILLOSCOPE SERVICING OF ALL -WAVE SETS

(Continued from page 474)

as to obtain a good sensitivity pattern on the oscilloscope screen, then turn the receiver off and allow it to cool.

After the set has cooled completely, turn it on again and watch the shape of the alignment curve change!

From this observation we may learn a valu- able lesson: Before attempting to align an all. wave receiver it should be allowed to heat thor- oughly.

The variations in all -wave receiver alignment sometimes caused by imperfect variable con- denser contacts and bearings are readily seen with the oscilloscope.

CHECKING FOR PERFECT CONTACT

These variations may be observed by first aligning the R.F. and oscillator stages of the receiver in the usual manner; then detune the receiver by turning the variable condenser rotor a few degrees and return it to its original set- ting. 1( the condenser contacts and bearings are not making perfect contact, the oscilloscope screen will show that the receiver is again out of alignment.

On some receivers, it will be found that no matter how much care is taken in cleaning the condenser contacta, it still will be impossible to maintain a perfect alignment curve after the condenser rotor has been turned.

These sets require a slightly different method of alignment.

The correct procedure is similar to the method usually followed except that the variable con- denser rotor is rocked slowly back and forth across the signal frequency while the trimmers are being turned (in much the same manner as in adjusting the oscillator padder on the ordinary broadcast receiver). If this procedure is carefully followed there will be little or no change in the alignment of the receiver after

the condenser rotor has been turned. This method of balancing receivers is now

being used by many of our largest set manufac- turers and is a good one for any Service Man or set builder to follow.

IMPORTANT CONSIDERATIONS

The choice of oscillator and frequency modula- tor equipment is extremely important if it is to be used for all -wave alignment purposes. The oscillator should be stable and of sturdy con- struction. If the motor -driven type of frequency modulator is chosen, the motor preferably should be of the induction type. The electrical disturb- ances sometimes caused by brush -type motors. unless elaborate filtering is employed, make them unsuitable for short -wave alignment purposes.

Those types of synchronizing voltage genera- tors which are operated by a commutator mounted on the wobbler -condenser shaft are generally to be avoided. The slight sparking which occurs as it charges and discharges its condenser can sometimes cause considerable electrical interference in the receiver under ob- servation.

If physically possible, the oscillator and fre- quency modulator should be mounted together so as to form one complete unit. with the leads from the wobbler condenser to the oscillator made as rigid as possible. A slight change in the relationship of these leads can sometimes cause an appreciable shift in oscillator fre- quency on short waves.

It should be remembered that it is no easy or simple matter to align the modern multi -tube all -wave receiver. Time and care must be taken if we are to realize the true efficiency of the receiver.

There was a time, not so very long ago, when our set manufacturers considered an allotted time of 4 or 5 minutes extremely high for align- ing a production receiver. With the advent of commercial all -wave and short -wave receivers it has become necessary to increase this allotted balancing time, in some instances, to as high as 30 minutes!

Fig. 2. A shows connection for a diode -detector output coupling fo the vertical deflector; B shows con- nections from a resistance coupled detector; and C shows connections from a transformer -coupled defector.

/ 1NF _I_i i

5+'

t VERT

VERT\ ERT 20,0Ó0

01-M5

t OSCILLOSCORE - OSCILLOSCOPE OSCILLC5C0 E . -A-

SHORT -CUTS IN RADIO

(Continued from pngr 476)

HONORABLE MENTION CLOSED- CIRCUIT TIP JACK. This handy

jack may be made from an ordinary tip - jack. All the needed instructions are given in Fig. 9. When the phone tip is inserted, the 2

lengthened prongs spread apart and open the circuit with the heavy wire that is to be added. An ideal jack for use in test sets and many other applications.

C I i ARLES HORVATH, Ja.

HONORABLE MENTION MOISTURE SEAL. In connection with some

types of antenna installation in which soldered connections are desired, such as joints to be made on the roof, it is often very difficult to use a soldering iron or blow torch. In such cases it is often the practice to merely make a twist joint and tape it for protection. This is obviously very poor practice, and the writer has found that the use of common putty will provide a weatherproof covering under all condi- tions. Tape is used over the putty for pro- tection. See Fig. 10.

Louts B. SKI.AR

HONORABLE MENTION INSTALLATION SUPPORT. A car radio is

a heavy object, and the holder shown in Fig. 11 will be found a great help when installing or removing it from the car. The drawing is self explanatory, but mention may be made of the fact that the adjustable front seats found on most cars will be of help in adjusting the set holder.

E. T. GUNDERSON, Ja.

HONORABLE MENTION VOICE COIL REPAIR. After having re-

paired the voice coil lead on a particular speaker several times in a month, a turn was taken off to make a longer lead. The lead was wound into coil form, as shown in Fig. 12, and this seems to have cured the trouble, as the speaker has given over a year's service without trouble.

RICHARD T. SCHULTZ

HONORABLE MENTION IMPROVING TONE. Many varieties of midget

sets on the market do not have the tone quality that the owners desire. The combina- tion shown in Fig. 13 has been used to advan- tage to improve the tone of several of these sets and may be of interest to readers.

F. U. DILLioN

Please Say That You Saw It in RADIO-CRAFT

497

RAYTh EON

PARADE of All -Metal Radio Tubes

RAYTHEON - 6K7 -

6A8-Oscillator-Detector

6K7- Detector Amplifier

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6J 7- Pentode Amplifier Detector

6 F 5- Triode Amplifier

6C5- Oscillator Amplifier

0Z4 -Full -Wave Gas -filled Rectifier (exclusively Raytheon)

6146- Detector (Diode)

6 F6-Power Amplifier

25A6 -Power Amplifier

2526-Rectifier 5Z4 -Full -Wove

Rectifier

6X5 -Full -Wove Rectifier (Auto Sets)

HEADQUARTERS FOR TUBE INFORMATION

Raytheon Production Corporation

30 East 42nd Street, New York, N.Y. 55 Chapel Street, Newton, Massachusetts 445 Lake Shore Drive, Chicago, Illinois 555 Howard Street, San Francisco, Calif.

498

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Write for Catalog 653 RC SEARS, ROEBUCK and CO., Chicago

FREE RADIO Inforn>tntion

(1) -Write for FREE NEW CATALOG of Condensers. Transformers. Chokes, Sockets. Coils and technical data on re- ceiving and transmitting equipment. (2)- Attach 10e for New 32 -page Manual of most popular Short -Was e )Receivers. with Illustration, diagrams and pane lists.

Address Deot. RC -2 HAMMARLUND MANUFACTURING CO..

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COLUMBIA 18 WATTS CLASS "A" HIGH FIDELITY AMPLIFIER

With two -channel mixer for Ribbon & /or Crystal Microphones, Ph on o- P i c k u p, etc., complete with 6 tubes, $40.00 Rib- bon or crystal mike, Dy- namic Speaker. (provision for additional speakers op-

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ready to operate .

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RADIO -CRAFT for FEBRUARY, 1936

MODERN STUDIO TECHNIQUE

(Continued from page 460) the children's studio!

We mentioned before that the announcer's duties have changed a lot in recent years. In the early days of broadcasting, the announcer was the king -pin of the studio broadcast. He planned the programs so that they ended some- where near the correct time for station an- nouncement; he assisted artists and sometimes acted as accompanist: he greeted guests and artists ; he filled in when programs fell short. and in other words he was as indispensable as the microphone or transmitter.

Now. however, the announcer's duties are limited to station announcing. reading advertis- ing "patter" and obtaining studio audience re- actions to fit the program (applause at the right time, etc.). The timing of the programs and the planning of continuity (or ''script ") are taken care of by a person known as the pro- duction manager. He usually sits in the con- trol room with the operator so that he has full control over the out -going program.

HAND SIGNALS Since cooperation between announcer and pro-

duction man are essential, and since verbal com- munication between them is obviously imprac- tical, a set of hand signals has been worked up to handle this communication. Some of these signals are shown in Fig. D. The detail at A is the sign for "fadeout" at the end of the broadcast; B signifies that it is time for a local announcement; C tells the announcer to move the artist closer to the microphone; D tells the operator to cut the program after the music fadeout. and permits the relaxation that always follows a program for the artists, announcer. operator and production man : E signifies that the program must be cut -in case it is running too slow ; and F tells the orchestra leader to end the musical selection, or, in the technical vernac- ular. close off.

There are other signals such as waving the hand in a circular motion to speed up the pro- gram. A finger planted firmly against the side of the nose signifies that the program is running according to schedule, etc.

Since these signals also apply directly to the artists, and are used by announcers to signal

to vocalists, musicians and speakers, as well as between the announcer and production man, some very amusing incidents have taken place from time to time. For example there was the case of the prominent man who was giving talk. He noticed the announcer place his finger on his nose several times and misunderstanding the signal finally blew his nose violently and noisily to the consternation of the entire staff and the amusem*nt of the listening public! Since artists are usually given a course in studio signals such cases are becoming rare, though.

THE STUDIO APPARATUS

The operations which the studio or control room operator handles can be understood from Fig. 2, which shows in block form the various parta of a studio amplifier. First there are the various microphones which may vary from one to a half -dozen or more for a studio broadcast. These are all fed into a mixing panel where the sound level of each can be individually con- trolled and mixed together to produce the signal sent out over the air. From this mixing panel. the signals are fed into a low -level amplifier which is also controlled from the same panel as theemix- ing potentiometers. by means of the master gain control. From this point, the signal is fed through a high -gain amplifier which feeds the signal directly to the power amplifiers in the transmitter or onto the balanced telephone lines to remote transmitters, in the case of network programs. A very small part of this output signal is tapped off and fed through an addi- tional amplifier to operate the control -room speakers for monitoring the output. In this way the operator and production man hear the program as it is actually transmitted.

The lower part of Fig. 2 shows the corres- ponding sound level in the various parts of the studio amplifier.

The relative positions of the control -room operator who "rides the gain" and the produc- tion man. as well as the control panel are shown in a striking manner in the illustration on the cover of this issue. Incidentally, this is a view of the auditorium studio on the 8th floor of the NBC studios at Radio City.

A rather interesting and unusual studio is shown in Fig. A at the head of this article. This studio. known as the Little Theatre, is designed especial y for dramatic productions and has special lighting equipment and a glass cur- tain. Two cont of rooms are provided. one for

program monitoring and the other for con- trolling lighting effects. and the glass and opaque curtains. This studio is equipped with comfortable t h e a t r e seats for the audience and additional visitors can watch the programs from a glass enclosed balcony.

From this description of the make -up and op- eration of a modern studio the complexity of modern studio tech- nique compared to the earlier varieties can be readily understood.

C e. CONTROL ROOM C a. CIlORUS ROOM s S. SPFANEIS STUDIO S.E.L SMPE ltrv LOeeY

Fig. I, above. The floor plan of the 8th floor of the Radio City Studios

of N.B.C.

Fig. 2, right. Block diagram showing The ac- tion in the various parts of the studio amplifier

equipment.

INPUT (MICROPHONES)

D D

el AMPLIFIER (LOW-LEY

625 AMPLIFIER

L) (NIGH -LEVEL) GAIN-CONTROL

62.A CONTROL AMPLIFIER

POTENTIOMETER MONITOR / PROGRAM

D 0 D MASTER

MIXING.) GAIN'CONTROL POTENTIOMETER

POTENTIOMETERS PEP I COIL

MONITOR OUTPUT ..Y

524

-ß

PROGRAM OUrPR LEVEL (0-0e)

308 LOSS (MMMI MJ

OUTPUT LEVEL OF 616 61L0: (DYNAMIC) TRANSMITTER CORRESPONDING TO SPEECH 4 AT AOISTANCE (CALCULATED) OF 21 INCHES FROM TIE

AANSMrtTER

,y 1r,

-te

MONITOR OUTPUT LEM_

a24 De

( -3SOW MEGMTEO NOISE

LEVEL (APPROX.) (-51 se) ° RELATIVE TO MDICAIO

wEIGNTED NOLSE \ SOWNotrrnn LEVEL

LEVEL RELATIVE

301I LOU TO PR OUTPUT

MONITOR 1 (MIN) AMPLIFIER GAIN SODS GAIN ADJUSTABLE TO MAX.

ApROs. OUTPUT LEVEL OP 6155 (T'NAMIC)TRA.SMITTE4 OUTING' LEVEL INDICTED

FM SPEECH AT A DISTANCE OF 3 FT ROM YRANSTROTER

Please Say That You Saw It in RADIO-CRAFT

RADIO -CRAFT for FEBRUARY, 1936

LATEST RADIO EQUIPMENT (Continued front page 478)

and a loudspeaker (on detachable cover of carry- ing case). Control panel carries volume and tone controls, switches and level indicator.

PORTABLE RADIO RECEIVER (904)

FOUR TUBES, 2 of which are the double -pur- pose type are used in this compact portable

super. Set has pilot light: and dynamic speaker. The cabinet, in suede -like finish, has a handle for carrying. Overall size, 5 trxl0t ¡x71 ins. deep. Antenna is attached; no ground is needed.

6-W. AMPLIFIER KIT (905)

A6-W. AMPLIFIER of high gain may be built fromlethis kit. The amplifier is very

flexible, since it may be used with any type of microphone or other input, and the output has taps for 500. 16, 8, or 4 ohms. Microphone cur- rent is supplied for carbon microphones, and 10 W. is available for field excitation of dynamic speakers. Power output 6 W.: maximum gain, over 106 dl.

COUNTER TUBE TESTER (906)

(Supreme Instruments Corp.) SIMPLICITI is a feature of this counter tube

tester; an inexperienced person can readily operate it. The list of readings for various tubes is fastened to a small slide which pulls out from the bottom of the case. The large meter has (besides the English -reading "tube worth" scale) a scale for adjustment of line voltage. A large - size neon lamp is used for test purposes. All types of tubes may be accommodated.

HANDY RESISTOR KIT (907)

(International Resistance Co.) THIS container with 8 drawers is furnished

free with each purchase of a kit of 56 in- sulated resistors. The drawers are arranged in compartments with a larger one at the bottom to carry wire -wound resistors or other items. The resistors included are all of the 1 W. type and were selected to meet average service needs. The container is well finished and has handy scales and charts printed on the sides.

ALL -WAVE ANTENNA KIT (908)

HIS NEW kit comes tu the user completely assembled and ready to install. All joints are

soldered. The kit features the use of parallel feeders rather than the more usual twisted pair. The antenna is designed to be used with a dou- blet transformer, and in case the set has none,

an efficient unit is available. This kit is intended for use on the short -wave bands, but will be found to give a noticeable improvement on the broadcast band as well.

PORTABLE TIME SWITCH (909)

ANY HOME -electrical device may be turned un or off at any interval up to 12 hours by

the use of this time switch. It may be used with radio sets washing machines, lamps, or any such devices. The instrument is small and portable, so that it may be carried about con- veniently to the point of use. A good seller for the Service Man to "plug."

PORTABLE UNIVERSAL AMPLIFIER (910)

HIS AMPLIFIER is truly "all- current" since it will work on 110 to 250 V. A.C., or D.C.

lines and 6 or 12 V. batteries. Net weight com- plete is 40 lbs.. and size is 11x13x17 ins. Input is arranged for carbon or crystal microphone, radio or phonograph. The equipment may be used indoors or out and has power enough to cover an audience of 2,000 people.

ALL -WAVE ANTENNA KIT (9I I)

THE BALANCED doublet system is used in this all -wave antenna kit. A highly efficient

matching transformer is employed. All com- ponents are of the highest quality. A special grade of twisted wire is used for the feeders to insure the best possible results. All required in- sulators and wire are furnished.

NOISE REDUCTION FILTERS (912)

(Continental Carbon Co., Inc.) HE FILTERS pictured here are designed for a variety of machines which produce "man-

made" static. Two are of the plug -in type which are connected between the apparatus cord and the power socket. The other two are for permanent installation on such equipment as oil burners, neon-light transformers and the like. Some of the types use a combination of induct- ance and capacity, while others contain capacity alone.

TWO NEW BOOKS (918 -919)

TWO interesting books of interest to the Serv- ice Man and technician have just been printed

by two prominent companies. The first is called Tube Talks -it presents

some very interesting facts about tubes in gen- eral and includes a section on the tube com- plements of a large number of manufactured receivers. The latter feature alone makes it well worth the price.

(Continued on page 507)

f+ s xV/ o

Antenna kif. (908)

Noise filters. (912)

Time switch. (909) All -wave antenna. (911)

A handy resistance kit for Service Man or Dealer. (907)

Portable amplifier. (910)

499

Please Say That You Saw It in RADIO -CRAFT

Mis 1300-paye Book loa

VERYTHING /; birar.l, s new N II It l; li N li t Ii 1 tl SERVICING, reviewed in this issue of RADIO -( :R. AFT, contains every particle of information you'll need for bringing your servicing methods right up to the minute. It's bused on the experience of many of the most successful servicing organiza- tions in the U. S. Here's what it contains:

TEST INSTRUMENTS Full details on all latest commercial models and construction data for homemade units -diagrams. constants, eh. . Intl tided. Comprehensive. 393 PP.

SERVICING METHODS Most up-to -date successful method fully explalned- general procedure receiver analysis. alignment I,

Cathode -Ray method. rtc .. y,., nip

REPAIR NG PARTS This section ells Brou exactly how to repair every r eelver part -when It Is advisable to do so. Practical. 101 pp.

SPECIAL PROBLEMS Auto radio 1nstallatlo and Berrie Ina: il -wave receiver problems; ma tine radio: elimination of inferrer ente and noise; high- Ddelity recels ers; etc. 296 pp.!

SELLING SERVICE Live -wire tips on selling. advertising nd merchandising. Business forms nd records. Scores of tested money - :eking Ideas. 40 pages.

FIELD DATA Separately -hound supplement. I -f' fol 3.400 superhels. 'trouble- Shadin table for 750 receivers, ignition data, including new 1036 cars, grid bias resistor chart. etc. 240 pp-I

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500

MODEL 330. A 5 -band Sianal Generator. Sao to 17900 kc.. an on

funda ment r h rper tad. direct rendns frequency and

wavelength: unih er 1 operation. odi,Ìa

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16.00 r Ìa nnin[ cafight.

.....

RADIO -CRAFT The INGALL- WAVESIGNAL GENERATOR

TDE highest renuirentents of precision and convenience for all- around work are met in the Model 339 Signal Generator. that works on cc. or d.c. of 00-1.25 volts, to measure frequencies front 54 to 17,000 kc. and line up

channels. It also serves for determining the frequency of a station that is br- ing received.

Coincidence of generated frequency and scale reading is 1 per cent. This 111óh order of accuracy obtains In no other Instrument selling at less than twice the cost of the 339.

Many. no doubt, have been somewhat confused by the numerous types of signal generators, but will note that the best of Illem cover wide ranges on fundamentals. hare an attenuator, and permit of pressure or absence of modu- lation. Also they have a vernier dial snit are direct -reading in frequencies. accurate to at least 3 per tent. The 339 has all those advantages. besides affording wavelength determinations as well. and operation on 90 -15 volts a.r. (any commercial frequency) or d.c. And the accuracy is three tines a

s great. M and :Moreover. the 339 is sv 11 built. for lifetime use. an covers all s

fundamentally. besides permitting measurements of frequencies up to 100 owe (down to 3 meters) by resort to a slight calculation n thml. applying a sim- plified harmonic system to the 5.400 to 17.000 kc. fundamental band.

The 339 has a 6De If. oscillator, a 37 rectifier tube. so that d.e. is used on the plate- while modulation is provided by a neon tube relaxation oscillator at a frequency of about 1,000 cycles.

RADIO CONSTRUCTORS LABORATORIES 336 LIBERTY STREET REET

Dope. R M 24 N.a..r RC NEW YORK, N.Y. oeN I t of Ord.r,

e .. A Short and Long Wave Lamp Socket Aerial!

Ask your serviceman for free demonstration. Send for Bulletin 103 with complete information.

IICONTINBRTAL CARBONIael Canadian Factory

a torah Ave.. Cleveland, oToronto Ontario

MAKE YOUR OWN RECORDS y From Radio or VOICE We specialize in com- plete recording de- vices for professional and amateur work. We manufacture all types of houle and professional recording apparatus and cutting devices for any me- tallic or non -metallic disc material. Write for details On your lieds.

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AMPLIFIERS AND SOUND SYSTEMS High rpower ln. et Amolin r .ndt Systems for Watt.. ating

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"`mature and modern aellian äun,1 aY a for ban.. r m thea- tre.. church.. d din" und all t of outdoor and indoor in- stallations. 1s Also, a complete line o.1 Micro- Phones. Dynamic Speakers. Portable Sound Systems. Exponential llore.. Electric Phono. Pick Up.. phono. Motor.. Ile - Cording Equipment. Tube.. e

Write for complete catalogue. INTERWORLD TRADE CORP. Fifth Fh Ave. Now York Crty

ENTERTAINMENT SYSTEM (913)

(Continued from page 479)

the line, 175 W.; frequency response, 50 to 15.. 000 cycles. with 2 db.; 13 tubes used.

The four 2A5 output tubes are connected in push -pull parallel, and are used as triodes, the screen -grids being hooked to the plate for this use. The harmonic content is less than 5 per cent at maximum volume. The operation is class A at normal levels and class A prime at maximum volume.

FARM RECEIVER (9I4)

(Continued from page 479) unit may be tilted by a pull cord when opera- tion is not desired.

As with the usual windmill, the fin blade of this charger keeps it facing into the wind.

Equipment furnished includes a 5 ft. tower of metal, ammeter, cutout, and battery clips.

The combination of the wind charger and the low -drain superhet. are said to give results equal to a fine power line set at a greatly reduced operating cost.

for FEBRUARY. 1936

o ii-,

aw I( 6w1 l " ,SrL t ®,5wA fl

sw s fov ayró - SFD)

MOOR sw1, aw2 12 ea«irl:gsl°11 tpAO

awl.sw.4,é tr5 eussaUTTOr . - awITCMEa

34 s a 6 7 1 9 t-wlacs walrweJ

(a PULER Wlaf: & The circuit of the selective analyzer and the analyzer

cable and - plug. (917)

BANDSPREAD RECEIVER KIT (9I5)

(Continued from page 479) broadcast bands or the amateur bands may be spread over 60 to 90 per cent of the bandspread scale.

Due to the use of two high -gain A.F. stages, the volume on almost any station within the range of the set may be brought up to the very highest level. The pentode output tube provides sufficient power to overload the speaker.

The panel carries controls for volume. regen- eration, R.F. stage trimmer, and power switch.

SELECTIVE ANALYZER AND TUBE TESTER (917)

(Continued from page 479) The metal case is only 7x7x3 ins. high, mak-

ing it handy for the Service Man to carry in his tool kit.

The Selective Analyzer The selective analyzer unit is a companion.

low -priced, but very efficient, instrument. Used in conjunction with a suitable meter. it enables the user to take readings from any two contacts of the socket under test. or directly to ground.

A safety button is incorporated to protect the meter while making adjustments.

Several contacts of the selector switches are unwired to provide for future tubes.

The analyzer is supplied complete with cord, plug, adapters, and instructions. but without meter. The case measures 7x4x3 ins. deep.

This circuit shows how the tubes are used in the 13 -tube high -fidelity T. R. F. set and P. A. amplifier. The tubs action can be understood from the block detail. (913)

:4ó 67 :ió\ 11 rigi, 63 al+.F. Ar3

r 53 Ola. A TWO r`SISea Les

ST Nonn us ears cata 245,

Ñò our

T r12

aw0a a.a

sr-TYPE rlwea 51(0,0«

RADIO ENGINEERING, broadcasting, aviation and police radio, servicing, ma- rine radio telegraphy and telephony, Morse telegraphy and railway amounting taught thoroughly. Engineer- ing course of nine months' duration equivalent to three Years of college radio work. All expenses low. Cata- log free. School established 1874. Dodge's Institute, Hudson St., Valparaiso, Ind.

STOP GUESSING! Radio service Is easy when you know just inhere to look for the trouble. A Cl IC('ICKER trouble - graph and repair -pricer eliminates guesswork in what is wrong and what to charge. Used br Pro- gressive servicemen everywhere. Price He post- paid. (No Stamps./

PAUL G. FREED Publishing Division R

5053 Baltimore Ave., Philadelphia, Pa.

v vos. CONTROL 01 -«F llor,

Ac e

The circuit of the low- current battery set which operates from a battery charged from a wind -driven gen erator -note the vibrator type of high- voltage supply used. (914)

=at'

EA Ì[6

70000 ow5

IFTI

IF DIODE SÌ

Dt- r 0' WW 0 1 ( 33

)16f Mod

rFl2 30

t. .. .á.Doa S

vleaaroa -8- ox r 1

05r I e -uaF °1 «F 1 J Dm«k y

ahI r ;--- tl - < arc

Le-Mpm,«aemamY. F,.56ar- `r°errr: cue.. as ,1=+`rxoP..

50.D0( ocas

a«F

Please Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT for FEBRUARY, 1936

Here are two NEW ORSMA MEMBERS' FORUM

1Oc BOOKS

Each book contains 32 pages -and is well illustrated.

T ITEI[ALLS thousands of radio fans have built the fa-

Lmous DOERLE Short Wave Radio Receivers. 8o in- sistent has been the demand for these receivers, as

well as construction details, that this hook has been spe- cially published.

HOW TO MAKE FOUR DOERLE SHORT WAVE SETS

Contains EVERYTHING that has ever been printed a these famous r . Thne are the ta,nnus.0ts that appeared in the fmlln.ins Sun j $11015T WAVE CRAFT: "A 2 -Tube Receiver that anchn the

12.300 .Mule Msrk:' by Walter C. Docile tUec.. 1931 -Jan.. 19321. ..A 3 -Tube 'Sirnal t.

rt : " by Walter C. Docile (November. 19321.

Doerie '3 -Tuber Adapted to A. C. Operation' dub. 19331. "The Donnie 3 -Tube 'n real- Grippe; Electrified. lAucu.t. 19331 and -The Merle Goes 'Bend- Spread." Flay. 1034).

HOW TO MAKE THE MOST POPULAR ALL - WAVE 1- and 2 -TUBE RECEIVERS

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(Continued from page 480) car radio sets, this seems to be generally rec. ognized as a very unreliable piece of apparatus and the trouble will generally be found to be due to poor adjustment of the contacts or a poor grade of tungsten, or both.

Having been fortunate enough to have worked in many telephone offices for several years. where harmonic ringing converters were in use, I realize that the average Service Man who has not been so fortunate is decidedly up against it. As a general rule 4 frequencies were in use in these harmonic converters, consisting of 16 cycles (1,000), 33 cycles (2,000), 50 cycles (3.000) and 66 cycles (4,000) per second and one can readily see that if these frequencies were not up to standard at all times, interfer- ence caused either by poor adjustment or pitted contacts was very likely to arise.

When trouble is experienced with vibrator units, the equipment should be dismantled -and if the contacts are simply blackened but not pitted, they should be cleaned with commercial carbon tetrachloride and burnished with a very light steel spring, such as an old clock spring. If, however, inspection reveals that the contacts are pitted they may be smoothed down with crocus cloth. NOT emery paper (which should not be used under any consideration). The contacts should then be given a final polish by rubbing down on an oilstone. Reassemble the unit and with a gauge check the air gap be- tween the blade and contacts, which will gen- erally be found to be about .008- or .004 -in. on each side. The air -gap adjustment naturally will depend upon the speed of the armature - the higher the frequency, the closer the contacts to prevent any possible chance of sparking (which accounts for more than 90 per cent of the trouble).

For very accurate adjustment. I use a 30 V. Weston 10,000 ohm meter with a 200 -ohm shunt, which permits very accurate adjustments. After starting the vibrator, the meter and bat- tery are put across the contacts, first on one pair of contacts and then on the other. Then the contacts are adjusted until a reading of 8.5 to 9.5 V. is recorded on the meter on each contact.

FRAN% H. HAYDEN, West Side Radio Service. Alpinn, Mich.

A SCHOOL -TYPE BROADCAST STUDIO

(Continued from pnitr 481)

able experience of servicing all of the equip- ment.

The main studio is of the "live end -dead end" type while the smaller studios are of con- ventional design. Rock wool. acoustic plaster. and monk's cloth are used for acoustic treat- ment. The microphones which are used are all of the condenser type: and complete sound - effects materials are included as a part of the studio equipment.

A partial view of control room F is shown in Fig. A and here will be seen students work- ing at the mixer desk and the input control panels. This control room, in addition to the mixer, contains a low -level amplifier, a high - level amplifier, distribution panel, and battery charging equipment.

The output of the low -level amplifier is to arranged that it may be connected through a

500 -ohm transmission line to the input of the A.F. amplifying equipment (which is locate() in the transmitter room on the floor above).

The transmitter includes a dual audio channel and mixer panel, a 50 -W., crystal -controlled ex- citer. feeding a modulated R.F. amplifier and 200 -W. class B linear R.F. amplifier. A modula- tion percentage indicator of the cathode -ray tube type and an audio oscillator also form a part of this equipment (which is used for testing, as well as for instructional purposes). A com- plete power installation, and stand -by motor - generator sets are also included in the trans- mitter room.

To enable unlicensed students to operate this station equipment, a dummy antenna system is used at such times when programs are not being released over the air.

This article has been prepared from data supplied by courtesy of National Schools.

501

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A BROADCAST P.A. UNIT FOR MUSICIANS (Continued from page 481)

people regarding the reproduction of music, find difficulty in getting a system to satisfy them. To meet the demand for an outfit that will fill all requirements, a sound system containing many novel features has been developed. It is simple to operate, versatile, excellent in quality, powerful enough for ordinary purposes, neat in appearance and portable. It attempts the rather difficult feat of satisfying both the lay- man unfamiliar with electricity (particularly the musician), and the sound engineer.

The heart of this sound system is the amplify- ing unit, consisting of the amplifier proper. a high- fidelity A.C. or A.C. -D.C. outfit delivering 18 W., and a powerful 10 in. speaker. Pro- vision is made for the use of additional loud- speakers. This amplifier is mounted in a hand- some black leatherette- covered case with chromium plated trimmings, and tube and speaker grilles. The case measures 15 x 15 x 8 ins. deep, and yet there is also room for a micro- phone with cable and a folding microphone stand, thus placing within one neat carrying case a sound system complete in itself, the en- tire weight being only 29 lbs.

NOVEL APPLICATION There are really four essential ways of am-

plifying the sound output of the guitar, for instance. One is the conventional fashion of placing a microphone near the guitar, which is quite unsatisfactory because it picks up other instruments to the same extent. Some guitar manufacturers replace the instrument strings by metal strings and maintain inductive pickup or pickups near the bridge. The sound thus obtained is quite artificial and differs greatly from the natural sound.

A much better method is the use of a "crystal cartridge" such as used in crystal pickups.

The best method. however, is the use of an especially designed crystal cell unit which is simply taped down onto the instrument. Not only can this unit be removed and attached in a jiffy, and at will, but it will give most amaz- ing, realistic, faithful amplification of the weak- est tones.

One more interesting way of obtaining the same results is by using a so- called "bridge." Such a bridge can be used both as a normal bridge (which is the part supporting the strings), and as a means of translating the vibrations of an instrument into electrical oscillations so that the tone of the instrument can be reproduced and amplified faithfully.

The 2- channel input mixer in the amplifier provides many useful applications of it for the musician. Two string instruments, such as a Hawaiian guitar and a Spanish guitar. 2 violins, or 2 of any kind can play duets together.

For most purposes a string instrument play- er can play together with a phonograph or radio set. These things can, of course, be done by any instrument by using ordinary micro- phones in place of the bridge pickups. With an orchestra 1 microphore can be used for a vocalist and the other for the orchestra, each independently controlled, or 2 microphones can be used to obtain better balance for an orchestra when amplifying it. Many other uses can be found for this mixer.

This article has been prepared from data supplied by courtesy of Columbia Sound Co, Inc.

The metal -tube amplifier and the case.

Please Say That You Saw It in RADIO-CRAFT

for FEBRUARY, 1936

Over 130,000 People Find Each Issue of EVERYDAY SCIENCE AND MECHANICS of Intense Interest! EVERYDAY SCIENCE AND MECHAN- ICS is the finest scientific-technical-me- chanical constructional magazine in the field. Up- to-the- minute with news flashes of scentific events. Dozens of construc- tional articles and many popular experi- ments. Ideas from which you can make things to sell.

A Host of Interesting Subjects Covered: Woodworking- Photography- Magic- Pat- ents and Inventions -Book Reviews-Metal- working -Chem ist ry- Engineering-Micro- scopy-Electrical Experiments -Household Helps- Astronomy -Prize Contests -and other subjects.

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OUTSTANDING MERITS OF METAL TUBES

(Continued from rage 470)

means something more than compactness of sets. It means also that the tubes can perform more efficiently. The short leads of an all -metal tube are shown in Fig. D. The low inductance of these short leads permits high tube sensitivity, especially at the short wavelengths. Also. the bracing effect of these stiff stubby wires helps to make the electrode assembly rigid.

Another outstanding feature of the all -metal tubes is the excellent shielding provided by the metal shell. It is not only true that the all - metal tubes are self -shielded and require no extra shielding apparatus; it is also true that the shielding provided by the metal shell is almost perfect. There are more functions performed by this shielding than are generally realized.

FUNCTIONS OF A TUBE SHIELD

Of course. most radio men know that the main function of tube shielding is to cut down feed -back from plate to grid through fields whose paths are outside the tube. Figure IA shows how well the metal shell performs this function by

completely blocking off the lines of force be-

tween the grid lead and the plate. It is not so widely realized. however, what an

effective shield the metal shell is in other re- spects. For one thing the metal shell has a

property that is absolutely essential for good

shielding; that is, it is permanently and posi- tively grounded. This completely eliminates the sort of noise that arises sometimes in a glass -

tube set when the tube shields become corroded and make poor contact between the upper and lower shield pieces. In the all -metal tube struc- ture shown in Fig. lB, the metal shell is con- nected to the grounding pin by welds that do

not corrode and do not loosen. Another shielding function performed by the

metal shell which is not generally recognized is

the elimination of any disturbing effect of stray electrons striking the walls of the tube. This function is performed in the glass tubes by such

means as the familiar strip of graphite, on the inside of the bulb of tubes like the 6C6 and 6D6. which prevents secondary emission from the glass. In the all -metal tubes no such precaution- ary measure is necessary because the metal shell is a grounded conductor and the problems of charge accumulation do not arise. Because the metal shell performs as a shield so admirably in all these respects, set designers can now build stable and quiet amplifier stages having more usable gain than was ever before possible.

One feature of the all -metal tubes which means more and more to Service Men using them is their convenient and logical basing sys-

tem. The aligning plug and key on the metal tube's base makes it ext'emely easy to insert the tube in its socket. You hold the tube over the socket so that the plug fits into the central socket hole, turn the tube until the key lines up with the slot, press, and it is done. There is

no peering at the socket to find the heater holes and there is no fussing with shields.

Another convenience is the system of pin connections shown in Fig. 1C. These connec- tions are as uniform as possible for all the types and are easy to remember.

These are only a few of the outstanding merits of the all -metal tubes.

This article has been prepared from data supplied by courtesy of RCA Manu- facturing Co., Inc. -Radiotron Division.

I 9 3 6 503

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CAPITOL RADIO ENGINEERING INSTITUTE 14th and Park Rd. Dept. RC -2 Washington, D. C.

BOOK REVIEW FUNDAMENTALS OF RADIO, (2nd edition) by R.

R. Ramsey. Published by the Ramsey Publishing Co. 1935. Size 6x9 ins., 426 pages, cloth bound. Price $3.50.

This book is not only adapted as a text -book for classroom work but it is also excellent for the man with a technical education because it is written in a style familiar to him. Professor Ramsey has brought this second edition up to the minute. Every phase of the subject is thor- oughly treated, and the author has replaced the dead -wood found in many text books. The book is complete. well illustrated and precise. It also includes 380 problems.

Contents include: Electricity, Direct Current; Batteries: Measurement of Resistance; Alter- nating Current; Introduction to Radio; Capac- ity; Inductance; Radio Waves; Radio Current: Transmission; Detectors; Vacuum Tubes; Coupled Circuits; Aerials: Radio Resistance; Radio Telephone; Audio Amplification; Loud- speakers, etc.

THE PSYCHOLOGY OF RADIO by Cantril and All - port. Published by Harper & Brothers. Size 61/2x

91 /z ins., 276 pages. Price $3.00.

This volume is intended for those who are faced with problems involving the program side of broadcasting. It tells in detail the technique which is most satisfactory in putting over dif- ferent types of programs, what programs appeal to various classes, and in general, every possible angle which involves the listener. Many of the conclusions reached are the results of actual ex- periments, and also the compilations made after study of correspondence files of the large broad- casting chains.

Those interested in the actual program ma- terial of broadcasting will find much of inter- est in this book.

(Continued on page 508)

Fig. I. Details of metal tube construction (A and B) and pin numbers (C).

SOLID METAL TO METAL

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-B- BOTTOM VIEW

OF BASE _C_

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"A STITCH IN TIME" SAMUEL C. MILBOURNE

IT APPEARS to be one of the unfortunate habits of this radio industry of ours that it blindly ventures into new developments with-

out thought of the future or how its many a time dubiously termed "improvements" reflect upon another branch of the industry.

Therefore, we wish to bring to the attention of all Service Men radio set manufacturers, and others interested in the industry, a situation which has developed recently as a result of the introduction of the new octal tubes.

It was understood by most of its that one of the original purposes of the octal tube socket was to accommodate in one single type socket. all future developed tubes, regardless of the number of elements or pins required (up to eitht). This, they told us, would automatically eliminate the necessity for a multiplicity of special types of sockets and adapters, as an octal socket in which all of the eight holes are drilled would receive any octal tube.

This purpose is now being defeated by several radio manufacturers who are equipping their ra- dio sets with octal sockets in which only those holes required for the particular tube are pierced, leaving blank the balance of the holes.

Manufacturers using the "blank out" non- standard type of socket frustrate all the laud- able attempts previously made to standardize tube sockets and throw the whole situation back once more to the use of a special adapter for each type of "blanked out" socket.

Let us see what economic waste would result from these practices. There are estimated to be about 40,000 radio set analyzers in use at the present time. Looking over the types of tubes already issued, 3 special adapters are necessary at a selling price of 75 cents each. Therefore. as a result of this departure from standard pre - cedure, the radio service industry must pay $90.000 for adapters to service a few manufac- turers' sets.

The proponents of this scheme advance as one reason that it will reduce the possibility of set owners removing a set of tubes and replacing them in the wrong sockets. We say, the set owner is not supposed to remove his tubes. A radio Service Man who is capable of correcting set troubles should be called as it is his job. and his alone.

"Let us," as a famous New Yorker says, "look at the record." All tubes will fit the 6AS and 6P7 sockets. The 6F5, 6II6. 6J7, 6K7 and 6I.7 all fit the same type socket.

The 6C5, 6D5 and 6F5 will also fit the 6E5, 6H6. 6.17. 6K7 and 6L7 sockets. besides fitting the standard socket. The 6C5, 6D5 and 6F5 will all fit the same type socket.

The 5Y3 and 5Z4 are interchangeable as to socket, and will fit the 6A6 and OPT sockets.

Therefore, all 12 types fit a standard socket used by 2 tube types : 5 types are interchange- able in. let us say. special socket No. 1, 3 more types fit, let us say. special socket No. 2 and also special socket No. 1: 2 types, let us say, fit spe- cial socket No. 3.

Remember. what is needed is not the extra contacts on the tube sockets but just the extra holes pierced. Extra contacts cost money and we can see where n material saving can be made in this direction. but, we are sure that it costs Its much to punch 6 holes in a socket as it would cost to punch 8 holes.

We are sure that no manufacturer of test in- strument wishes to make one penny through the sale of these adapters to Service Men. al- though, a present $90,000 market is not to be taken lightly.

We, the Supreme Instruments Corp.. suggest the following procedure to be followed by radio men:

(11 When servicing sets in which one or more "blanked out" sockets are used. replace these non- standard sockets by the standard 8 hole pierced octal sockets or drill out all blank spaces on the non -standard sockets.

(2) Immediately write the radio service or- ganization to which he belongs to petition the R.M.A. for a standard octal socket procedure.

C3) Write his jobber or wholesaler asking him to aid in the elimination of this situation.

(4) If he represents one or more of these manufacturers who are using blanked out sock- ets, write them requesting an immediate aban- donment of this program.

for FEBRUARY, 1936 I- THIS MAGAZINE NEEDS NO INTRODUCTION

TO SHORT -WAVE FANS

Please Say That You Saw It in RADIO -CRAFT

SHORT WAVE CRAFT This popular monthly magazine, SHORT WAVE CRAFT, contains everything you want to know about Short Waves.

The wonders of world -wide short -wave reception are clearly described and Illustrated. Latest practical Infor- mation for radio fans, experimenters and "hams" will be found. Tells you how to build short -wave receivers and transmitters: construct sets of one and two tubes or as many as seven. eight or more. Tells best foreign stations to log and hen to tune them-includes newest and best Irrui is of the time. SI1011T IVAVE CRAP!' Is edited

by lingo Genubatit. NEW FEATURE RECENTLY ADDED -Te the shat

ware tan who has logged and obtained verification of the I number of shortwave stations from all over the world during one month, will be awarded a magnificent N silver trophy.

Special This Month Only.' For the month of January only. we otter readers of this magazine the opportunity to read radio's greatest short- wave magazine at a special saving. The regular suharrip- tlon price Is f2.50 per year. You e.m III, get SIIUIaT WAVE CRAFT for the next

8 MONTHS FOR $1.00

4 -Color Cover Over 200 illustrations 9x12 inches in size

ON ALL NEWSSTANDS

Send remittam a by cheek. money order or P.S. Postage Stamps. Register letter if it contains cash or currency.

SHORT WAVE CRAFT 99R Hudson St. New York, N. Y.

ELECTRIC DRILL CAPACITY %4" DRIL,.

WEIGHT 4i,4. lbs.

PRICE

$5.97 This Utility Drill is built for inter- mittent service, al- writ ready for in atant use. and will

accommodate straight shank drills up to !

inch. Weighs only 41_ pounds. and has a convenient on- and -oft switch mounted on the motor body. The three -jaw chuck has a ca- pacity up to is Furnished complete with 10 feet of heavy duty rubber covered

cord, and plug cap. Operates on alternating current only. 110 volts, 60 tyeles.

.'IJppityl tst ì1,1t 6 pounds.

OUR OLD CUSTOMERS KNOW THAT OUR MEW. CHANDISE IS SOLD ON A STRICT MONEY.

BACK GUARANTEE.

All shipments will be forwarded by express collect if not sufficient postage included ultb your order.

WELLWORTH TRADING CO. ItC -236 506 Palmolive Bldg.. Chicago. Ill.

Enclosed rind F for wbich ship to address below

ELECTRIC DRILL

NAME ..._.._.._

ADDRESS - CITY STATE

RADIO -CRAFT for FEBRUARY, 1936

NOW READY! VOLUME 2 of the Official

REFRIGERATION SERVICE MANUAL

. ossteJa.t

5óo POSTPAID

V tirei. r t

o r t"

The Only Complete Refrigeration Service Manual Ever Published

The new volume of the OFFICIAI. ItEFRIOF:IRATION SERVICE MANl'AI. (Volume 111 contains entirely new service data no Information of value to everyone Inter- ested in refrigei at ion.

This Manual form.: a companion and supplement to the previous OFFICIAL It N F'Iti(t E It A TI t) N SERVICE MANIA!. (Volume t). since all data in the 1935 volume are entirely new.

The curve or sales of refrigerators and replacement Parts has stea.!l'y increased year by year -even during depression year -. It is the one Industry to (make this progress. Year by year sales Increases will soon place Refrigeration In rank with the automobile industry In i mportaoe.

Partial Contents in Second Volume of "Official Refrigeration Service Manual"

Theory and Fundamenhl Laws Methods of Refrigeration Refrigerants, Lubricants and Brines Handling and Storage of Refrigerants Compression System of Refrigeration Liquid Throttle Devices Refrigeration Systems Electric Control Devices Compressors. Types. Seals. Valves. Capacities Evaporators and Cooling Units Service Tools Commercial Unit Specifications Servicing Refrigeration Apparatus Servicing Low Side Float Valve Systems Servicing High Side Float Valve Systems Servicing Expansion Valve Systems Servicing Thermostatic Valve Systems Servicing Restrictor and Capillary Tube Systems Charging Systems with Refrigerant Electrical Service: Motor, Fuses, Hookups Estimating Refrigeration Loads

OVER 350 PAGES OVER 300 DIAGRAMS Flexible, Looseleaf Binder

'fils New Refrigeration Manual is printed on a special tinily stork. This stook. although unusually thin. is ex- reptionalty strong and durable. It makes handling of the lock nark easier.

GERNSBACK PUBLICATIONS, INC. 99 HUDSON milt': ri., NUM \ "11111:, N. Y.

MAIL COUPON TODAY GERNSBACK PUBLICATIONS. Inc. ltC -236 99 Hudson Street. New York, N. Y. gentlemen: Env: oued you will nod toy remittance of $5.00. for hied end me One ropy of the OFFICIAL ItEFRIOERATII 'N SERVICE MANUAL (Volume II). I u lerstend th d this book is to be shipped to me POSTAGE PREPAID.

Nanne

Address

Cite State

OVERSEAS IRE.\I/F:II .! 'This in oh can be obtained front

POWER CONTRACTS, Ltd. 138 Southwark St., London. S.E.I. England

NEW DEVELOPMENTS IN ALL - WAVE RECEIVER DESIGN

(Cordinncd front page 4691

much for radio reproduction, but it certainly is necessary for phonograph work, since here the polumc expander comes into use. The expander is simply an amplifier which is so arranged that when a loud passage of sound comes through. it is amplified more than it would be in a conven- tional audio amplifier.

This is accomplished by a relatively simple system. as shown in Fig. 2. Here, VI acts as a straight A.F. amplifier, the incoming signal being fed in through number 1 grid. At the same time, the signal is applied to the grid of V2 which also amplifies it. the amplified signal is then rectified by the diode -connected V3. The rectified voltage appears across R9 from which it is fed through suitable filters to the No. 3 grid of V1.

The whole arrangement operates so that when a loud passage enters V2 the resultant rec- tified voltage across R9 bucks the bias on grid 3 and the amplification of the tube is increased. The use of 116 allows the degree of expansion to be controlled, while Ex is the manual volume control. While in the particular set illustrated. the expander circuit is used only for the phono- graph amplifier. it has been used with consider- able success in high -fidelity radio receivers.

Thus it will be seen that the multiplicity of tubes in some of the large new sets actually serve useful purposes. While it is conceded that the set might work fairly well with fewer tubes, the result would not be what the discriminating buyer of such equipment expects, nowadays.

NEW and SIMPLIFIED

All -Wave Antenna RCA RK -40, $5.50

Here's a genuine RCA Antenna that you can install in a few minutes. Just attach the support ropes to the two insulators and it's up. Receiver coup- ling unit is then attached to the bind- ing posts of the receiver,transmission line is cut to length, and there you are. Your customer is all set to hear stations never heard before. Factory assembled, all joints soldered.

For further Information write to Dept. R. C.

RCA Mfg. Co., Inc., Camden, N.J. A subsidiary of the

RADIO CORPORATION OF AMERICA

505

tsoao..w otr.ro < . twee..

Fig. 2. The volume expander of the set.

NEW GERMAN TELEVISION RECEIVERS

(Continued from page 470)

out the future possibilities of television. Most cathode -ray television receivers of today are only bright enough to be observed in a dimly -lit room. The illumination of the screen of the new experimental set, however, is so brilliant Rs to permit the images to be viewed even in a brightly -illuminated room!

Another and important feature of this experi- mental set -up is the image definition. which may be made as high as 400 lines. (That is, image quality equivalent to that on the modern movie screen.)

This exceptional range is due to the use of a new wide -range amplifier that I have designed. It surpasses in performance the standard hereto- fore used -the direct -coupled amplifier. The new design permits response without serious fluctuation over a frequency range of 0.5- to 1.000.000 cycles. An important factor in secur- ing this wide- frequency response is the arrange. ment of the components, as shown in Fig. C.

A PROTEST The National IIndio Sort ire Assoc.. through

the medium of its official organ. the National Technician, has registered a strenuous protest to the so-called "Radio Manufacturers Service" sponsored by the Philco Radio and Television Corp. In a lengthy resolution, they point out in detail their grievances with this new policy. They believe it represents an attempt to monop- olize a large percentage of the service business of the nation and that it tends to mislead the public into believing that the service is spon- sored by radio manufacturers in general. which of course is not so.

Please Say That Voit Sew It in RADIO -CRAFT

LIBERAL ALLOWANCE

MADE

ON YOUR OBSOLETE

INSTRUMENTS Trade in your obsolete meter and

purchase the modern service- man's Universal Tester

Volts A.C. -D.C. 5.25.100. 250 -1000 1000 ohms per volt

Milliamperes D.C. I -10. 100.1000

Capacity 001 -10 Med.

Paper o electrolytic condensers.

Inductance 1. 10,000 Henrys

D.C. Resistance .5.5,000.003 ohms.

Send full description of obsolete in-

strument you wish to trade in, and 6c in stamps for Bulletin 61 1 -PC de- scribing the Shallcross Universal Tester.

Shallcross Mfg. Company, Collingdale, Pa.

506

NEW ORpfilidabli2 Test Equipment Dependable OHMMETER

Models 405 and 405A DEPENDABLE OHM- '

METER Model 405 is an accurate double range instrument read- ing from 0 -1.000 and 0- 100.000 ohms. Meas- urements of less than V. ohm can be made. The D'Arsonval mov- ing coil meter has a guaranteed accuracy of 2 %. Provisions are made for easily adding milliammeter and volt- meter ranges provided in Model 405A. DEPENDABLE OHM- METER Model 405A is identical to Model 405 but has four addi- tional voltmeter scales of 0 -2.5. 0 -25; 0 -125 and 0 -750. There are also the current ranges of 0 -2.5 and 0 -125 milliamperes. The panel, meter and case are the same for both models, the 405 and 405A. They are both furnished complete with self -contained batteries.

Size: 71" x 4" x 3 "; Weight: 1 'L lbs. Model 405 -Complete, ready to operate $8.45 NET Model 405A-Complete, e ready to operate 4' 5 NET

Dependable MULTITESTER Model 403 -A

Service men and dealers highly praised the Model 403 Multitester -and it deserved praise. But the new improved Model 403 -A "DEPENDABLE" MULTITESTER insures even greater satisfac- tion at less cost. Em- bodying every feature of the former model, No. 403 -A is more compact, having been designed as a companion instrument to the new Model 501 ANALYZER UNIT.

2,000 ohms per volt. Ac- curacy within 2 per cent in D'ARSONVAL type moving coil meter. 3- range 0- 2.000,000 ohm- meter ; 4 -range 0 -5 -60- 250 -750 voltmeter ; 0 -500 mie roam meter.

COMPLETE. READY TO OPERATE

'1JNt

IFormt 510.65

Dependable POWER LEVEL INDICATOR

Model 421

Complete: $25.85 -Kit: $21.00 Important help for P.A. men. Measures power levels from minus 12 to plus 43 thribels. highly- accurate 5" fan -type meter calibrated from down 12 to up 10 decibeix. 500 w Icroatlgt. movement. Knife -edge mint- er. Inique 10.000 Mun constant Bnpedanre L -type al- tenuatuv Also direct - reading. 9 -range A.C. voltmeter for all frequencies.

We Issue All orders re F.O.B. New York. Terms: A deposit of 20'k is required with every

No c ataire r der. Balance may be paid on delivery.

éDEDI'CT 2% IF FULL AMOUNT IS SENT.

GRENPARK COMPANY 101 Hudson St. Dept. RC New York, N. Y.

RADIO -CRAFT

AN A.C.-D.C. BEGINNER'S SUPER. "2"

(Continued from page 477)

that constitutes the front face of the loud- speaker. This construction will permit the en- tire chassis to be fitted into a midget cabinet; and the reproducer to fit tightly against the cabinet grille. (A different reproducer may necessitate a different value for C7.)

Make sure that the coil connections of LI, and L2- I.F.T. are correct as per the detail illus- tration given, and the schematic circuit. The lead marked "brown" is a tap that the experi- menter must take from the common connection between the two primaries of the composite coil. Lead "black" is a lead inside the composite unit that must be shifted: in the commercial coil this wire is grounded, and must be un- soldered from its grounding point and swung over to terminal 3. It is possible that an im- provement will result by reversing at X -X leads 5 -6 of the L1 tickler coil (which slips inside the secondary). Another reversal of connections at X -X, leads "red" and "1," may improve op- eration.

The LI tickler coil is made by winding any fine wire (about No. 30, insulated) on a fora that will just slip inside the Ll secondary; the exact number of turns, and the location of the coil are determined by experiment -in general, about 50 to 75 turns will be sufficient, with the coil so positioned inside the secondary as to se- cure regeneration with a midway to aí -on set- ting of RI, at the highest -wavelength setting of CI.

It is preferable to use a service oscillator to align the circuits. However, the manufactured, "composite" (combination) coil, L2- I.F.T., is made to such close tolerances that the correct settings for trimmers C3 and C4 may be taken as their half -way adjustment. With this as a starting point the trimmers in shunt to Cl and C2 are adjusted for maximum signal strength from a local broadcast station, with regeneration controls Rl and R2 adjusted for least regenere- t'on consistent with good reception. After this, the Cl and C2 circuits may be checked, at 200 - and 545 -meter (approx.) settings, when listen- ing to distant stations.

The experimenter who wishes to secure in- creased sensitivity may wish to use a 10,000- to 20.000 -ohm bare -wire voltage divider as R7 -R8, moving the slider along the resistor until the optimum voltage is secured for the screen -grid of tube VI. This expedient will take care of individual tube characteristics.

Note that the only way in which the external ground makes connection to the set is capacita- tively through condenser C8. This is a safety measure in D.C. power line operation; the fused line plug is an additional safeguard (that should be included in all sets designed to operate on D. C. lines). The tuning condenser unit has a in. shaft, requiring a dial or indicator -knob with this inside diameter; or, a h -in. to V -in. reducing adapter may be used.

LIST OF PARTS

One kit of 456 kc. superhet. shielded coils. LI (frith tickler). L2- I.F.T.:

One Electrad 50,000 -ohm tapered volume control, Rl. with switch Sw.1;

One Electrad 10 000 ohm tapered volume control. R2:

Two Aerovox resistors, 2 mess., 1 W., R3, 114 ;

One Aerovox resistor, 0.1 -meg., 1 W., 115: One Aerovox resistor, 1 mea., 1 W., R6; One Electrad resistor, 2,500 ohms, 2 W., R7: One Electrad resistor, 7,500 ohms, 2 W., RS: One Aerovox resistor, 1,100 ohms, 2 W.. R9: One 2 -gang 365 mmf. variable condenser, with

456 ke. tracking section, Cl, C2; One Cornell -Dubilier 0.1 -mf. paper cond., C5: One Cornell- Dubilier 100 mmf. paper cond., C6; Manufacturer's name upon request.

Coil connections for LI and Li.

Please Sag That You Sato It in RADIO -CRAFT

for FEBRUARY, 1936

TYPEWRITER BARGAIN FREE

10 -DAY FREE

TRIAL OFFER

BRAND NEW MODEL No. .5

ONLY

10t A DAY

REMINGTON PORTABLE A brand new Remington for only loc a day. An

easy, practical Hume 'I yping Course FREE. With it anyone quickly becomes expert on this machine...the most rugged, dependable portable made. Not used or rebuilt. Standard 4 -row keyboard. Standard width carriage. Margin release on keyboard. Back spacer. Automatic ribbon reverse. Every usential eature of big office typewriters. Carrying Case FREE. Try it for 10 clays without risking a cent. H you don't agree it is the finest portable at any price, return it at our spense. Don't delay. Without obliga non, write now.

Remington Rand Inc., Dept. 189 -2, 205 East 42nd Street, New York, N.Y.

CLASSIFIED ADVERTIsem*nTS Advertisem*nts In this section are inserted at the ost of twelve rents per word for each Insertion-

'a,s, initials and address each count as one word, h should accompany all classified advertise-

ments unless pieced by a recognized advertising my. Nn less than ten monk : rented.

: \dwertisln¢ fee the March. 1910, are

s issue should be r oc, ned net later than .1.mu.irp C. 1930.

A.C. AUTO GENERATORS

TWENTY PRACTICAL AND LOW -COST CHANGES contesting old generators Into new generators and motan 100 -500 watt capacity. do or a current. with a to 400 vats. for radio operation. power. light. or welding. Also instructions for rewinding armatures. 350 definitions of electrical terns. etc. All In new, revised hawk with sim- plified Instructions and Illustrations. Endorsed by thou- sands. Only 11.00 postpaiii. Autopower, 914 -C S. Moyne Ave.. Chicago.

RADIO

RADIO ENGINEERING. BROADCASTING. ATM - tion and pollee radio. centring. Marine and Aloha Teleg- raphy taught thoroughly. All expenses low. Catalog free. Paire', Institute. Pine Street. Valparaiso, Indiana.

TRADE YOUR USED TEST EQUIPMENT ON NEW latest models Supreme. Trip.ett, Weston. RCA Osellie- graph. etc. Liberal allowance, lowest prices. Lyon -Watt Radio. Wichita. Kansas.

"RADIO 111'11.Dlllt " -'_ c YEAR 36 CRYSTAL SET, Shortwave ideas; blueprint es. Sample free. Laboratories. 131 -It Liberty. Satt Fraueiscn.

._ FREE IMPORTANT IL- - LUSTRATED BUY -

OFFICIAL INS GUIDE FOR RADIO EXPERI- MENTERS. SERV- ICE M E N. AND SHORT -WAVE FANS. -32 Pages - Teao Colors -Pr"- fusely Illustrated This Book Will Save You Money! Parked between the

r s of this 32 -page

bonk is a tremendosi array of modern radio equipment and other electrical and selen- Iltie merchant l se--the very material for which you have been looking -and at price:

c nnot possibly bnái añrndl ,.e f`:

eel ,nier m,.h'L- radii r4. r oleo nuM ira .ddr, n, i,. .Ìie -ÌÁ earni,

enl.e,n, .h e etc.

the Iteim 'nd It's In the book! Tisi "foe tt,.. k tirlli ,i :.,

y h,. a

You save buy at lowest lo stoossi le micas. Why not estart ..,HeNna look

by return n.,:l It's free! to-

day! RADIO TRADING COMPANY

97 Hudson Street, New York, N. Y.

RADIO 114114MN

CATALOG 1935

iwóaBottnaús ....- ,,., s ltoal Ñ'á i ñ[ñv[RS

RADIO -CRAFT for FèBRuARY, I 9 3 6

12 BOOKS TO HELP YOU LEARN MORE

ABOUT RADIO Illustrated at the right and left are two books in the Radio./ Craft Library

Sertes.

rU FIE ltADlb- CRAFT LIBRARY SERIES -a most complete veal authentic set of volumes -t moats In-

dividually. lm port ant diviiclons Of radio. Each hook has been designed to give anu the oplart unity to learn one or more ',ranches of radio. The authors of the hooks are well -known to everyone. Each is an expert radio man; an authority on the subject- -rash is thor- oughly familiar with the field which he represents.

All Books Uniform The volumes In the RADIO -CRAFT LIBRARY SERIES are n11 uniform. 6 x 9 Inches. Each hook ontains on an average of 50 to 120 illustrations. The

hooks are primed on an excellent grade of paper which mikes t.le type easy reading.

Here Are the Series: Book No.

RADIO SET ANALYZERS And How to Use Them By L. VAN DER MEL

Book No. 2

MODERN VACUUM TUBES And How They Work By ROBERT HERTZBERG

Book No. 4

MODERN RADIO HOOK -UPS The Best Radio Circuits By R. D. WASHBURNE

Book No. 5

HOW TO BECOME A RADIO SERVICE MAN

By LOUIS MARTIN

Book No. 6

BRINGING ELECTRIC SETS UP TO DATE

By CLIFFORD E. DENTON

Book No. 7

RADIO KINKS AND WRINKLES For Service Men and Experimenters

By C. W. PALMER

Book No. 8

RADIO QUESTIONS AND ANSWERS By R. D. WASHBURNE

Book No. 9 AUTOMOBILE RADIO AND SERVICING

By LOUIS MA_ RTIN Book No. 10

HOME RECORDING AND ALL ABOUT IT

By GEORGE J. SALIBA Book No. II

POINT -TO -POINT RESISTANCE MEASUREMENTS

By CLIFFORD E. DENTOA Book No. 12

PUBLIC ADDRESS INSTALLATION AND SERVICE

By J. T. BERNSLEV

BIG DISCOUNT OFFERED

When Five (S) Books or More Are Ordered, Deduct 20% from

Your Remittance GERNSBACK PUBLICATIONS, INC.

99 Hudson Street, New York, N. Y.

MAIL THIS COUPON TODAY!

GERNSBACK PUBLICATIONS. INC. 99 Hudson Street. New York. N. Y.

I have circled below the numbers of books to the RADIO- CRAFT I.IIIItAIRY SERIES whirh you aro to send me. and havre deducted 20% for ordering tae (5) hooks or more. I have included my remit- tance In full. at the price of 50e each, when less than live hooks are ordered.

The amount of my remittance Is (stamps, check: or money orders accepted). Circle numbers wantel:

1 2 3 4 5 6 7 8 9 10 11 12

Address

City State All books ara sent postage prpsid

Re -236

One Cornell -Dubilier .005 -mf. paper condenser. C7;

One Cornell -Dubilier 0.1 -mf. paper condenser. C8;

Two Aerovox 250 mmf. mica condensers, CO.

C10; One Cornell -Dubilier .05 -mf. paper condenser.

C11; One Cornell -Dubilier paper condenser, 0.1 -mf..

C12; One Aerovox electrolytic condenser. 35 mmf.

C13: One Solar "Little Giant" dual electrolytic con-

denser, 8 -8 mf., C14, C15; One Acratest 25 mhy. R.F. choke, RFC.; One National Union or RCA type 6F7 tube, V1; One National Union or Sylvania type 12A7 tube,

V2: Two Acratest 7 -prong sockets, for VI and V2; One Acratest 5 -in. magnetic reproducer: One Alloy Transformer midget low- resistance

A.C. -D.C. choke, 100 ohms, Ch.; One Blan power cord, with built -in 34G -ohm

resistor, R10; One Blan fuses) plug; Two titan tip -jacks (one black and one red. for

phones) ;

Hardware (wire, knob:, etc.).

LATEST RADIO EQUIPMENT (Covet in u rd from page 499)

This book is priced at 50e and can be obtained by writing to Raytheon Production Corp. in care of this magazine. Ask for No. 918.

The second book gives a full description of a

36 W. P.A. amplifier including the circuit, lay- out and a complete outline of operating it.

The amplifier is a high -fidelity unit, particu- larly adapted for permanent Y.A. installations where medium output is required. The book explains in detail the various steps in con- structing the unit as well as operating it. This includes not only the amplifier itself, but the components such as microphone, speakers, phono. equipment, etc., which is used with it.

The Service Man and P.A. man will find this little book unusually interesting.

This book can be obtained by writing to the Radolek Co. in care of this magazine. Ask for No. 919.

NEON OUTPUT INDICATOR (920)

(Globe Mfg. Co.) Service Men will be interested in this eco-

nomical output meter, which operates on the neon lamp principal. It is housed in a compact case with a panel upon which is placed the control knob and scale, and the terminals. Con- nection is made directly to the voice coil of the speaker.

PARABOLIC BAFFLE (921)

(Hope Manufacturing Co.)

This new type of baffle designed for sound work of all types utilizes the highly efficient parabolic type reflector as its basis form.

The baffle is made of aluminum and completely encloses the dynamic speaker from which the sound is projected. The use of this type of baffle provides a more efficient sound coverage in the desired direction, due to the greater effi- ciency of reflection produced by the parabolic shape of the flare. It also protects the speaker unit, since it completely surrounds it.

This new type of baffle is made to fasten to the wall or ceiling or it may be mounted on a portable stand so that it can be placed in any desired position or direction. The speaker can be tilted to any desired angle to produce the most effective sound coverage. Two sizes of baffles hold 7 or 10 in. speakers.

The aluminum baffle and Output indicator (920) speaker (921)

Please Say That You Saw It in RADIO -CRAFT

Rada Rats S

Supplying 20,000 Service-

men With Every-

thing in Radio

The New Radolek 11 in Profit Guide is NEW! BIGGER! BET- TER! The most complete Radio Parts Catalog ever pub 'shed -it's colossal -gigantic -it s the "top "! Never has there been a Radio Parts Catalog comparable to this superb book. Every page brings you ex tra profits. Completely revised - right up to the minute, bringing you everything in radio -at the right prices. Over 160 pages of valuable, money -saving "radio- buying jnformation. Over 10.000 separate Repair Parts- hundreds of new em -a complete. new selection of Radio Re. ceivers and Amplifiers. Contains the most complete, exact duplicate, replacement parts listings of volume controls, condensers, trans- formers, vibrators ever compiled. This is your book -it's FREE. Send for IT!

507

RADOLEK restricts distribution of the PROF- IT GUIDE to those actively and commercial- ly engaged in the Radio Business. Please en- close your Business Card or Letter I lead.

MAIL THIS COUPON! e> a e> I11 a 11 MMI

THE RADOLEK C0.1 1 564 West Randolph Street Chicago, III.

Big New RADOLEK I Send me FREE the I PROFIT GUIDE.

I Name

IAddress

Are you a Service Man Dealer Extant? a= mat em e> ate ar e> - e> aB

READ AND

SEND DE Learn Easily at Home This Quicker Way

No experience needed. Beginners read code quickly copy accurately. If already an op, speed up your wpm with this amazing improved Master Teleplex. Only instrument ever pro- duced which records your sending in visible dots and dashes on embossed copper tapes-then sends back your own key work. Fascinating. fool- pr/if -gets results been ose you lours by HEAR- ING as well na SEEING. Teleplex has tough the rnnle to more students in past few years than all other methods combined. We furnish complete course, lend you the New Master 'releplex. :md (arsnlml 111strnrtbnt with it III INEY- It At'K GUARANTEE. L o tv auni. easy berms. Write today for folder A -2. no ,obligation. TELEPLEX COMPANY

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SOLAR MFG. CORP. 59a6o1 Srk'th" New York City

508

MOTOR DRIVEN

Craftsman Tools COMPLETE -READY TO RUN

ELECTRIC HANDY -LATHE ' PRICE

tJ t$]57 s 1 6We üét

10 lbs.

WITH BUILT -IN MOTOR Length of Bed, 15 inches; height to spindle, 2 inches, is supplied with face plate as well as spur center for handling all types of work. This lathe is furnished with a built -in Induction Mo- tor, mounted on the head -stock. so that the drive wheel acts directly on the three -speed pulley. NO BELT REQUIRED. In shifting to the vari- ous speeds it is only necessary to lift the motor with the left hand and slide it forward or back as desired. A finger -tip switch is located con- veniently on top of the motor. Finished in gray and green enamel and comes complete with mo- tor, cord and plug cap, and special wrench. Operates on alternating current only, 110 volts, 60 cycles.

ELECTRIC GRINDER PRICE

$349 shipping weight 4 lbs.

Comes supplied with 2 genu- ine A lox ite g r i n d i n g wheels, one coarse grind- er,and one fine grinder. It is driven with a

dependable induction type high speed inner fan cooled motor with the grinding wheels mounted at opposite ends of the motor shaft. This motor does not interfere with radio reception, and has a heavy ground steel

haft and large bronze bearings, having thick felt oil- retaining wash- ers behind them, constantly lubricating the shaft and bearings and provided with oil holes for re- oiling. Complete with cord and plug cap. Operates on alternating current only, 110 volts, 60 cycles.

ELECTRIC SCROLL AND JIG SAW

PRICE

$469 Shipping Weight 10 lbs.

This is an en- tirely new type

'j of saw, pow- ered by a fan-

' ' ' cooled, induc-

geared direct- ly

_..mom fion motor ly to saw blade for max- imum power.

Blade stroke 3. ". Made of channeled steel, has 12" throat that handles work up to 24" long. 6'_" round work table, adjustable hold down shoe with guide roller to support and steady saw blade. Cord, plug and 1 blade included. Built - in motor operates on alternating current only, 110 volts, 60 cycles.

Our Old Customers Know That Our Merchandise Is Sold on a Strict Money -Back Guarantee

AU Shipments will be forwarded by Express Collect if not sufficient postage included

with your ,.rd, r.

WELLWORTH TRADING CO. 506 Palmolive Bldg., Dept. R. C. 236, Chicago. Ill.

RADIO -CRAFT for FEBRUARY, 1936

BOOK REVIEW (Co,,tiacd ¡rem pay/ 503)

MAKING A LIVING IN RADIO, by Zeh Bouck. Published by McGraw -Hill Book Co., 1935. Six* 6 z VA ins. 222 pages. Price, 52.00.

Here is a book written for the man who wants to "get into radio" but doesn't know just how to go about it. It is also directed at those who are in and want to better themselves. It is written very candidly and will serve to dispel some of the false illusions brought about by ad- vertisem*nts of the less reliable radio schools.

Both the technical and the non -technical sides of the industry are discussed, and it is certain that those interested in a radio career will find much of benefit in this new volume.

THEORY OF ALTERNATING CURRENT WAVE- FORMS by Philip Kemp. Published by Instruments Publishing Co., 1935. Size 6 x 8% ins. 218 pages.

This monograph is intended to present to the reader already familiar with alternating current theory, the facts relating to non -sinusoidal waves. The subject is treated without reference to any specific apparatus as far as possible.

The author states that while some of the ma- terial included is generally available, it is so widely scattered that the student would have great difficulty in rounding it up. He has there- fore compiled this study, and included a valuable bibliography for those who wish to pursue the subject further.

TELEVISION- THEORY AND PRACTICE, by J. H. Rayner, Published by The Sherwood Press, 1935. Size 6 x 9 ins., 196 pages.

This book treats television in its true light. that of a science which does not hesitate to face difficulties and to assess facts at their true value. As far as possible the subject has been con- sidered from the first principles and an attempt has been made to convey fundamental informa- tion which will be of real value to the student of the subject. All of the systems used in America and Europe are fully covered by text and illustrations. The book is well written by one who understands the subject, and it is pro- fusely illustrated.

Something NEW! WEATHER

FORECASTER AND

HUMIDITY TESTER

"HYGROSCOPE The Ace of Weather

Forecasters

When placed in a well -ventilated room or in the fresh air, the HYGROSCOPE foretells coming weather conditions from eight to twenty -four hours in advance. It also accurately records outdoor humidity, and when placed inside it gives the humid- ity within the house or room.

The HYGROSCOPE is automatic self- adjust- able, simple American -precision made. It can- not get out of order at any time. The dial measures 2% ", is enclosed in a 6" round hard - wood case, with either walnut or mahogany fin- ish. It is attractive for desk or living room.

OUTSIDE DIAL FORECASTS WEATHER Fair -rain -or changeable is indicated on the

outer dial when the HYGROSCOPE is placed in a well -ventilated room or out-of- doors. If indoors, place the instrument near an open w i n,!, m.

INNER DIAL SHOWS THE HUMIDITY CONTENT

The HYGROSCOPE :.ii acts as a hyg ronici Cr. Numbers on the inner dial indicate the degree of humidity present in the air and in artificially heated rooms.

SEND YOUR ORDER NOW ! Get your HY- GROSCOPE today. Your remittance in form of check or money order accepted. If you cash or unused U. S. Postage Stamps, be to register your letter. Also speci- fy $200 if you prefer the HYGRO- G SCOPE in Walnut or Mahogany. postpaid

GRENPARK COMPANY Dept. RC -236

99 Hudson St. - New York, N.Y.

Advertiser's Index

A Aerovox Corporation 494 Allied Radio Corp 501 Alloy Transformer Corp 498 Amperite Corporation 488. 502 Arrow Sales Corporation 502 The Automatic Electrical Devices Co 495

B The Brush Development Co. 494

C Capitol Radio Engineering Institute 503 Central Radio Laboratories 488 Classified Section 506 Coast -to -Coast Radio Corp 495 Columbia Sound Co.. Inc 498 Commercialite Laboratories 502 Consolidated Radio Products Co 502 Continental Carbon, Inc 500 Cornell- Dub i lier Corp 487 Coyne Electrical School 449

D Tobe Deutschmann Corporation 509 Dodge's Institute 500

E Hugh H. Eby, Inc 456 Eilen Radio Laboratories ...._...._ 509 Electrad, Inc 491 Electric Institute 452A

F Freed Radio Company 500

G General Cement Mfg. Company 504 General Electric Company Back Cover General Transformer Corp 487 GuldenGme Radio Company 496 Grenpark Company 506, 508

H Hammarlund Mfg. Company 495 Hygrade- Sylvania Corp

Inter -World Trade Corp 500

Lincoln Engineering School 498 Arthur H. Lynch, Inc 502

M Midwest Radio Corp Inside Back Cover

489

N National Radio Institute 451 National Union Radio Corp 492 New York YMCA Schools 504

O Oxford Radio Company 495

P The Plan Shop 504 Popular Book Corp 504 Precision Apparatus Corp 509

R Radio & Technical Publ. Co....._ 499 Radio & Television Institute 496 Radio Circular Company 504 Radio City Products Co 503 Radio Construction Labs 500 Radio Publications 501, 502 Radin Trading Company 504, 506 Radio Training Assoc. of America 492 Radolek Company 507 Raytheon Production Corp 497 RCA Institutes, Inc 502 RCA Mfg. Company, Inc 505 Readrite Meter Works 485 Remington Rand, Inc 506

s s. o. S. Corporation 496 Sears, Roebuck & Co 498 Servicemen's Publishing Co 502 Shallcross Mfg. Company 505 Solar Mfg. Company ._. 507 Sound Apparatus Company 600 F. L. Sprayberry School 490 Sprayberry Academy of Radio 487 Sprague Products Co 496 Standard Transformer Corp 491 Supreme Instruments Corp

Inside Front Cover T

Teleplex Company 507 Thor Radio Company 495 Triplett Electrical Instrument Co 483

W The Webster Company 486 Wellworth Trading Company 504. 508 Wholesale Radio Service Co., Inc 493 Wright- DeCoster, Inc 490

Please Say That You Saw It in RADIO -CRAFT

RADIO -CRAFT for FEBRUARY,

NEW METAL -TUBE CHASSIS SIMPLIFIES "MODERNIZ-

ING11 OLD SETS (Continued from page 474)

pert. and only a few pertinent observations need be made.

The Service Man's first step in modernization is to determine exactly the type of modernization he will employ, and, upon this, base his cost estimate. There are several possible variations:

(1) Complete modernization. using the re- placement chassis (designed by Glenn H. Brown- ing) and speaker. and scrapping the entire "works" of the old set. This is the simplest method, and. in many instances it may be the most economical.

(2) Retaining the old speaker only. (3) Retaining the entire audio system and

prover supply) (4) Retaining the power stage only, power

supply and speaker. (5) Retaining the power supply only. It is not practical to operate the old audio

system from the replacement power supply. While it is designed with a liberal factor of safety. this would be impaired with the extra load imposed by the additional tubes.

COST FACTORS

Retaining the old speaker only, may not al- ways effect an economy, for, while a $4.10 item (the speaker) is eliminated, a 70 -ma., 30 -by. choke may have to be added, plus a series resis- tor capable of carrying the same current. and of a value to bring the resistance of the corn- bination which is substituted for the speaker field, to 1,800 ohms. Also, a special impedance - matching transformer will be necessary in many instances.

Where it seems preferable to retain the power supply, speaker and power stage, the above arrangement can be used only if the power stage is a pentode. The output of the diode detector is not sufficient to swing a class A power stage -for instance, two 45s in push -pull. In the case of the class A power stage. the 2A5 or 42 should be used in the replacement chassis as a class A amplifier by connecting the screen -grid to the plate. The output impedance then approximates that of a 27. and can be coupled through any transformer having the correct impedance -approximately 7,000 ohms.

In retaining the old power supply only, the speaker field must. of course, be included in the plate current circuit, in series with or by sub- stitution for part or all of the original choke system.

General Motors model 120 Highboy. A typical example of bringing a fine old receiver up- to-date is found in the modernization of the General Motors model 120 highboy. In this set. the original reproducer was retained. The chassis and speaker are first removed, followed with the chassis shelf which is fastened with 4 wood screws to side cleats. The original panel held to the cabinet with woo dscrews, is also taken out, to be replaced with a ply or solid wood panel cut to fit. This panel is drilled to accommodate the replacement chassis and is mounted on the chassis by means of the manual - automatic volume control switch and the I V sensitivity -volume control. The main volume control and off-on switch are mounted. The escutcheon is fastened to the panel with the nuts and bolts provided for this purpose. After the bolts are tightened (and the pointer

1936 509

YOUR OBSOLETE ANALYZER MODERNIZED

INTO A TWO METER MASTER ROTARY SELECTIVE SYSTEM

WRITE FOR OUR PLAN MENTION

OF YO R OLD ANALYZER

PRECISION APPARATUS CORP. 821 EAST NEW YORK AVENUE Modernization Division -Dept. C BROOKLYN, NEW YORK

mounted). the dial card, which was previously punched (using the escutcheon as a template), is slipped over the projecting bolts and secured with the 3 extra bolts. Due to the large open- ing in the shelf, strips were built on to accom- modate the replacement chassis. No cushioning was found necessary in this installation.

The reproducer plug in the original instal- lotion fits the replacement chassis. It was only necessary to disconnect the center tap of the speaker field in the speaker cable before replac- ing the loudspeaker.

Majestic Model 91. This receiver. manufac- tured in 1928 and 1929. presents an excellent example of what can be done in the way of salvaging a considerable portion of the original installation. Both the reproducer and the power - pack were retained, with the following electrical alterations to adapt them to the replacement chassis: As the output transformer on the original receiver is integral with the tuning chassis. a new transformer was provided, hav- ing primary and secondary impedances of 8,000 and 4 ohms. respectively. The high plate voltage is fed to the replacement chassis through a 1,200 -ohm, 5 -W. resistor (from the red lead). A bleeder resistor of 7.000 ohms, 5 -W. rating. is connected between the original Majestic R.F. tube high -voltage tap (yellow), and ground. to supply field excitation for the speaker. The center -tap filament winding is not employed, and the higher current winding, with the 2 blue leads, supplies current to the heaters.

MODERNIZATION WITH METAL TUBES

Many potential customers for modernization jobs may request the use of metal tubes as a result of the publicity which has been accorded this development. The engineering that has gone into design of the replacement chassis is such as to anticipate any reasonable changes in tube structure, and such features as the metal tubes may have to offer can be taken full advan- tages of in this receiver.

The diagram of the replacement chassis with metal tubes is shown in Fig. C. Theoretically there has been no change in the circuit. It has been merely necessary to substitute 2 tubes for the 2A6 or 75, performing exactly the same functions as were effected by the dual -purpose tube.

This article has been prepared from data supplied by courtesy of Tobe Deutschmann Corp.

The circuit of the Browning 35 chassis revised for metal tubes as explained above.

PET I/OSO óke xY

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Please Say That You Sato It in RADIO -CRAFT

NEW Sets for OLD! AT 1/3 THE COST

A sensational new idea now makes it possible for you to own a crzs:nm built radio at a fraction of the cost of a fac- tory built model of equal performance! Why discard your present radio when the cabinet and much of the equipment can be utilized in an up -to- the -minute circuit which brings you superlative world -wide all -wave reception? Other features in- clude: automatic volume control. highest sensitivity and selectivity, etc. Your own radio serviceman is undoubtedly a Tobe Modernization Engineer. Tear out this ad and ask him about it. You'll be amazed when he gives you a price for modernizing your receiver. It he cannot -write for name of the nearest Tobe Modernization En- gineer.

SERVICEMEN! DEALERS! If you have not already done so. get a copy of Zeh Bouck's book on this new phase of radio Serv- icing. Nearly 1000 servicemen have already en- tered this field. Write today for Book and Free Merchandising Plan and Sales Promotion Kit.

Tobe Deutschmann Corp., Dept. C 26

Canton, Massachusetts I am a O customer O serviceman O Send me name of nearest Tobe Modernization

Engineer. I own a 10 receiver.

O I enclose 25e for Zell liouck's Book and Free Sales Promotion Kit.

Name

Address

city L

State......._.._

¿uitan*. HG -36 5 -TUBE RECEIVER

A Powerful. maroon- Moll. receiver that .ill

$5v stations under

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tube. condition.

Tn F n n grid ree n..ram.. ili amplifier.. n 'r detector

Built- r' -l"l,l 2 ulto +Irryöe r.DJ -I I,- n Kvelar type illumineta' dial. Sad o x rick gas,...,

IT ur parts. with B a ll e . . Los 10 ¡i.00.ñ

meters and

s i m p l e $14.95 Blackt.hrirrI iinish.d cabine,. 2.50 5AECIALi r thin

2.85 Complete lit. cabinet. 5 At ila for 10 -2

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I..i,,r f,,, HMI 2.00 NOTE:

wiring , .ilei mar. 1.45 NOTE: 11 nerd .8. are desired ..1.1.817 -0(13- 88ó-11l add

81.50 to

EILEN RADIO LABORATORIES High Cose Short Wave Equipment, 135 Liberty St., New Yak, N.Y.

510 -512 RADIO -CRAFT for FEBRUARY, 1936

Ni &tQpaJzQeL to 9flL alL diadio Emtvzhviszticuifi,

WITH GERNSBACK OFFICIAL RADIO SERVICE MANUALS

1935 - OFFICIAL ` y_-

RADIO ,SERVICE - MANUAL

..:...,!q -,:!t. .7;.y,.a:v ;J'C. .. ,'ri , Ji... : tV :

SERVICING Service information found in the Manuals covers all types of radio receivers. The material is extremely valuable to Dealers and Service Men. On many diagrams ap- pear voltage readings of tubes, socket con- nections, transform- er data, alignment de- tails, and other serv- ice notes.

PUBLIC ADDRESS The pages on Y.A. In- stallation will be helpful to Servi ce Men and P.A. special- ists. Such prominent features as class A and B amplifiers - single and dual chan- nel systems - attenu- ators, and mixers - superpower stages - preamplifiers and oth- er commercial devices for P.A. work are in- cluded.

ALL WAVE RECEIVERS

Information relative t.- short -wave receivers hava found their way into the Manuals. For t h e s e

standard manufactured sets, wherever possible. complete aligning details for all wave bands are included in addition t. the service material listed for other sets.

AUTO -RADIO RECEIVERS

All available service in- formation on new auto- radio sets has been in- cluded. From this data alone Service Men could derive sufficient knowl- edge to venture in specialty field -that et servicing only a u 1 -

radios.

GERNSBACK 99 Hudson Street

$7.00 List

Just as we say-"Be prepared to meet all radio servicing emergencies with the Gernsback Official Radio Service Manuals." You never know when a service jab requires that "extra' special attention. It might mean the difference between doing the job or losing it. You're safe if you have on hand the GERNSBACK MANUALS -either for regular service work or for servicing auto -radios. Get your copy today! No other radio book is comparable to the new 1935 OFFICIAL RADIO SERVICE MANUAL. In con- tents, in style of printing, in grade of paper, in illustrations, there has never been published such a comprehensive volume. This Manual contains over a thousand pages -yet it is only 114 inches thick because it is printed on a special Bible stock which is an exceptionally good stock. yet one of the thinnest and most durable papers. This 1935 Manual is the most authentic and elaborate service guide ever used in the radio industry.

('oiia«'ir /.ti of Ilse 193.7 _lliiisuul Over 1.000 pages full of disc: rIns and essential information of manufactured receivers -only data of real use in servicing is included. This new Manual is really portable since it is ex- tremely thin and light as well. Volume V continues where the preceding manual left off.

Many circuits of old sets are included. Service Men know every set has certain weak points which are really the cause of trouble. Wherever the information could be obtained, these weaknesses with their cures are printed right with the circuits. This is an entirely new and valuable addition to the Manual. All the latest receivers are included -all -wave sets, short -wave sets, auto -radio sets, midget and cigar -box sets, etc., as well as P.A. Amplifiers and equipment.

Which of These

GERNSBACK RADIO SERVICE MANUALS

Do You Need to Complete Your Files?

1934 Official Radio Service Manual Over 400 Pages. 9x12 Inches.

Over 2,000 Illustrations Flexible, Looseleaf. Leatherette Cover

List Price $3.50

1933 Official Radio Service Manual Over 70(1 Pages. 9x12 Inches.

Over 2,000 Illustrations. Flexible, Looseleaf. Leatherette Cover

List Price $5.00

1932 Official Radio Service Manual Over 1,000 Pages. 9x12 Inches.

Over 2,000 Illustrations Flexible, Looseleaf. Leatherette Cover

List Price $5.00

1931 Official Radio Service Manual 650 Pages (Including Supplements )

9x12 Inches Over 1,500 Illustrations

Vic Bible, Looseleaf. Leatherette Cover List Price $4.50

(Including Supplements)

1933 Official Auto -Radio Service Manual

(Volume 1)

Over 200 Pages. 9x12 Over 500 Illustrations.

Flexible, Looseleaf. Leatherette C.,ver List Price 52.50

PUBLICATIONS, Inc. New York, N. Y.

and mni,.rcial .

n, i,inc in,truments. The

cumulative index is even more complete than be- fore; including cross- references to sets sold under different names and type numbers. Volume V includes resistance data; socket layouts ; LF. data and voltage data. Tube data on latest tubes.

Free question and answer service -as included in our last three manuals.

OVER 1000 PAGES Ilrer :1.0011 Illualwrliunrt

Sine 9" x 12"-only I 1," thieL Flexible, /ooxe/eal I ra l Iure( t e

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-for the real auto -radio servicing "dope," you can't find a better book!

The 1935 Official Auto -Radio Service Manual

boo o, , I ,. I, . , : . ,,, or me nes.

(lt'FII'L\I1.\I Tu-ItAUlu s1ala'In'I( \IANt'.\L. It contains only auto-radio .servire "dope."

III:ItE ARE III(:IIIJI:IITS OF THE 1935 AI:TO-RADIO SERVICE MANUAL

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Th, l..htie Lg na`i n. ,. ,...i .n, ., .I "i;i n i+'i." roo -t, i°;. , . .

240 Pages Over Sau

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O 99 Hudson Street, New York, N. Y. I Enclosed you will find nay remittance ,f f.m I I which please send me promptly, POSTPAID, the OFFICIA I. I I

RADIO SERVICE MANUAL indicated.

1035 Edition t $7.00 AUTO -RADIO MANUALS 1934 Edition 4t $3.50 1935 Edition 4t $2.50 1933 Edition 4t 55.00 1933 Edition h $2.50 1932 Edition 4t SS. 00

I 1931 Edition ti) 54.50 (Including Supplements)

I Name

IAddress

I I City State

(Send remittance hyr t¢e cheek. money order. or register If it contains cash. :rd l'. S l'r . mot.' )

I I I

I I

OVERSEAS READERS' GREAT BRITAIN FRANCE Go ringe's. 9a. Green Street. Lei. Editions Radio. 42 Rue Jacob.

These books ran be obtained from the following houses: rester Square. London. England Paris

AUSTRALIA MrG ill's 183 -195. 218 Elizabeth St.. Melbourne. C. I

Please Say That You Saw It in RADIO -CRAFT

ad11LE Imo.. , t'ILINTEInr

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4äea FROM OnO EABORATOREsI/Ffl

itiebil y 7a6 )

six TUIlIflG RARGES

4%2102400 METERS

FULL SCOPE HIGH FIDELITY

PUSH BUTTOII TUIIIIIG

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amd fcoue Utitez !eativi l f r2

50 with New GIANT THEATRE- SONIC

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1 SPEAKER

TER AS LOILI as ism)

iown CE again demonstrates

its leadership by offering the world's most powerful Super De Luxe 18 -METAL Tube 6- Tuning Range radio. It is a master achievement ... today's most highly perfected, precisely built, laboratory adjusted set. It is a radio musical instrument that will thrill you with its marvelous super performance... glorious new acousti -tone... crystal -clear . "concert" realism ...and magnificent foreign reception. Before you

Send for FREE 40 -page four.cnlor catalog. It

lipictures the complete

ne of beautiful 19511 Midwest Acousti -Tone V- Spread consoles...and chassis...in actual colors.

buy any radio, write for FREE 40 -page 1936 catalog. Learn about the successful Midwest Laboratory- - To - You policy that saves you 30% to 50 %... that gives you 30 days FREE trial.

30 Days FREE Trial ! No middlemen's profits to pay. You buy at wholesale price, direct from Laboratories . . . saving 30% to 50 %. You can order your 1936 Midwest radio from the new 40 -page catalog with as much certainty of satisfaction as if you were to come yourself to our great laboratories. You save 30% to 50 %...you get 30 days free trial ... as little as $5.00 clown puts a Midwest radio in your home. You are triply protected with a One -Year Guarantee. Foreign Reception Guarantee and Money -Back Guarantee.

GUARANTEED FOREIGN RECEPTION This super radio will out- perform $200 and $300 sets on a side by side test. It is so powerful, so amazingly selective, so delicately sensitive that it brings in distant foreign stations with full loud speaker volume, on channels adjacent to powerful locals. The 18 tubes permit of advanced circuits. make it possible to use the tremendous reserve power, and to exert the sustained maximum output of the powerful new tubes.

80 SENSATIONAL ADVANCEMENTS Scores of marvelous Midwest features, many of them exclusive, explain Midwest glorious tone realism. super performance and thrilling world -wide 6 -band reception. They prove why nationally known orchestra leaders like Fred Waring, George Olsen, Jack Denny, etc., use a Midwest in Preference to more costly makes. Pages 12 to 21 in FREE catalog illustrate the new Midwest fea. tures. Study them before you make up your mind.

ACOUSTI -TONE V- SPREAD DESIGN The V -Front Dispersing Vanes established a new radio style overnight. They spread the beautiful lace -work of the "highs" throughout the room in a scientific manner... directingthe High Fidelity waves uniformly to the ear. Now, get complete range of audible frequencies from 30 to 16,000 cycles.. achieving glorious new acousti -tone ... assuring life -like crystal -clear reception ... "concert realism.

SIX TUNING RANGEtt This exclusive engineering triumph (U. S. Patent No. 96750) puts Midwest radio years ahead of ordinary sets and makes them the "World's Greatest Radio Values." Now, it is easy to make the nations of the world parade before you. You can switch instantly from American programs to Canadian, police, amateur, commercial, "secret," experimental, airplane and ship broad- casts to the finest and most fascinating programs from Europe, Asia, Australia, South America ... 12,000 miles away.

MIDWEST RADIO CORP. DEPT. 12H CINCINNATI OHIO U.S.A. Established 1920 Cable Address MIRACO All Codes

Push Button Tuning Simply pushing Silencer Button silences set between stations. Beautiful tuning lights auto- matically indicate when station is properly tuned. Release button... and station comes in perfectly. Pressing Station Finder Button (Midwest's exclusive ROBOT EAR) automatically determines proper dial position for bring - ins in extremely weak stations.

Ted Weems Enthuses Over Crystal -Clear World Reception

Dearborn, Afieb. -After com- paring many radios, I can truth- fully say my Midwest outper- forms other sets cost. ing almost twice as much. Only the new Midwest could satisfy my desire for crystal -clear, undistorted re- ception . from all over the world.

Ted N eems.

'.tee 30DAY TRIAL OFFER a. id40PAOE FOURCOLOR7eae CATALOG

MIDWEST RADIO CORPORATION Dept.12H, Cincinnati. Ohio N1;h ohhe .,o yr. my put, send me your new FREE vcatalog. complete details of your bbmal 30-day FREE treat eke., and FREE Miniature Rotating Ii-,,b, 0,1. Tin u NOT a d

User-Agents Make Easy Extra Money Check Here for details

Name....._.. ...._.._.._.._.._.._..._._.._..

Ad d r esr. r._._ .................. _. _.............. _.. _..... _.._

Town .. state __....._ "lCreck 1 II Interested In a Midwest AII.Ware Battery Radio

SHORT -WAVE RECEPTION IS POSITIVELY BETTER WITH

G -E's NEW V- DOUBLET ANTENNA

Every owner of an all -wave re- ceiver wants his set to perform at maximum efficiency. He wants uni- formly good reception - a mini- mum of noise. All this depends to a large degree on the type of an- tenna system used.

The new G -E V- Doublet All -wave Antenna System approaches the ideal more closely than any here- tofore available.

Notice the unique "V" construc- tion. The "V" provides an efficient transfer of energy from the an- tenna to the lead -in (transmission line). A special transformer, in turn, provides an efficient transfer of energy from the lead -in to the receiver and at the same time bal- ances out interference picked up by the lead -in.

Below 55 meters, the antenna oper- ates as a V- Doublet and above 55 meters, it is automatically changed to a standard antenna by the spe- cial coupling transformer. There- fore man -made interference is min- imized, giving clear short -wave reception and, without switching, excellent reception of standard broadcasts as well.

Simple to install- requires only 2 points of suspension over a 50 -foot span. Not unsightly in appearance when installed. Any length lead - in of 100 feet or over may be used. This new exclusively General Elec- tric Antenna System is exactly what every all -wave radio owner has been wanting. Mail the coupon: for complete details.

Price of antenna kit $5.95.

eral o Electric C mp , !Pk-G.7 Merchandise Department, Bridgeport, Conn, Attention: Sales Promotion Section

I am interested in the New G -E All -wave Antenna System. Without obligation on my part, I would like to have you send me details regarding it.

Nane

Street address

City State

GENERAL ELECTRIC The Original Metal -tube Radio

MERCHANDISE DEPARTMENT, GENERAL ELECTRIC COMPANY, BRIDGEPORT, CONNECTICUT

MODERN STUDIO TECHNIQUE See Page 460 · You are trained right in modern, daylight shops on Radio, Sound and Television equip- ment under the personal supervision of expert instructors - [PDF Document] (2024)

References