SO N4 Se( Page

OVER 125 ILLUSTRATIONS

I-4UGO Irt-RNSIT'AK, Editor

"COUGH BUTTON"

IN G ABC AS'T ;SO n4 Se( Page

FILM PHONOGRAPH

AIRPLANE MIKE

A LEAK DETECTOR R.F AND I.F. COILS IN F.M. RECEIVERS

F;IL SLANT ON RADIO. MINIATURE PORTABLE TRANSMITTER NEW TUBES "VIDEONEWS" THERE'S MORE DRAMA and excitement

packed into amateur reception when your communica-

tions receiver is a Hallicrafters. Back of Hallicrafters

precision engineering is long experience, and it is this

that accounts for the finer, brooder, more accurate and

dependable reception amateur owners enjoy. Lafayette

Radio offers a complete line of latest Hallicrafters

models. Time payments make owning one easy. Send

for FREE catalog today, or visit branch nearest you.

MODEL S -19R MODEL S -20R MODEL S -29

Efficient superheterodyne circuit employs 6 New improved 9 tube model. Covers the com- Precision -built communications receiver in port- tubes, of which two are double -purpose types, plete range from 545 kc. to 44 mc. in four bonds. able form. Operates on either 110 volts AC or providing 8 tube performance. Complete tun- Employs a stage of pre -selection on each band DC or from self- contained batteries. Self -con- ing range of the receiver from 545 kc. to 44 mc. for added sensitivity and selectivity. Controls: tained telescopic antenna. Receiver covers four in 4 tuning bonds. Electrical bond spread on r.f. gain, audio gain, tone control, a.v.c. switch, complete bonds: 11.26 mc. to 1490 kc. Employs eoch band. Broadcast bond coverage, beat B F O switch, bond switch, main tuning control, on r.f. stage on oll bonds, incorporates an auto- frequency oscillator, automatic volume control separate bond spread control, and "stand -by" matic noise limiter; electrical band spread. switch, built -in speaker and a separate bond switch. Built -in speaker. Circuit features elec- Built -in speaker. Controls include: main tuning spread dial. Designed for operation from any trical band spread, automatic noise limiter, r.f. -band spreod -r.f. gain -A.f. gain -band 110-120 volt 50-60 cycles o.c. line. Antenna amplifier. Designed for 110 volts 50/60 cycles switch -power switch- a.v.c. "off -on" switch connections provided for both doublet and a.c. operation, (plug and jack provided for bat- -BFO "off -on" switch -ANL "off -on" switch Marconi type antennas. Cabinet beautifully fin- teries or vibrapack operation). Steel cabinet -send-receive--standby switch. Dimensions: ished - 171/2'' x 8" s 81/2 ". $2950 measures 181/4" x 93/e" x 81/2". $4950 7" high, 81/2' wide. 13/4" deep. $5950

oston newark, n. j. bronx, n. y. jamaica, I- i.

T H E WORLD'S L A R G E S T R A D I O S U P P L Y H O U S E In Radio 1110 poât whTh1nko ¡t pli the9 lnoW..n . better.

dliiiiif"waúhtáhead `f don't new teh^;larn OU men p adló s either, w h °ready to do t to baffle rou " t Modula- al- more money? Do you want to Y Frequency Do you want fo make su eP otyons,- on your present interest in Radio, Television, on 'television, promotions,m cash in in 1 hoe Read mY job too, to win Frequency Modulation? Do you want a full -time tion, in Radio 0n01' with good pay in one of Radio's many fascinating ready more t^ branches? Or do you want to make extra money in to make below your spare time to boost your present income? If Message you want to do either of these things -you owe it to yourself to find out how I have trained hundreds of BE- J. E. SMITH, President men for jobs in Radio. MAIL THE COUPON NATIONAL RADIO INSTITUTE LOW-TODAY. Established 25 years He has directed the training of more men for Radin than anyone else -has helped men already in Radio to get ahead, and men not in Radio to get into Radio and win success. Make Me Prove I Can Train You at Home for RADIO and TELEVISION

and I u I can ! Clip the coupon mall it. train train you Radio service manager as tlia DI- norm,- at homo In your spate time to be a Radio Technician. I their four stores.'' ant to send you sample tenon free; to examine, read. Draft Registrants, Attention! See how clear and easy it is to understand. See Inns nayn Beginnen Quickly Learn to Earn SS to Sll Hundreds of on V. n, kWn,. Had.,, when they enter 1 nurse le planned to elp you get a good job in Radio. a Extra a Week in Spare Time milita n, services ice 'tare to win specialist naines young. growing field with a future. You don't have to give going The day you enroll. in addition to MY regular Course. I in the Army. Navy and Marine Corps. These names p your present job, or Spend a lot of money to become a start sending you Extra Money ,lob Sheets -start showing pay up to a times a private's or seaman's base pay. Radio Technician. I train you at hone nights In your you how spare lime. to do actual Radio repair jobs. Throughout your in addition to carrying extra rank. prestige! If Course I send plans and directions which have helped whU ARE NOT called. a are getting into Radio Many Radio Technicians Make many make $5 to $10 a week extra in spare time while en the Government is pouring millions into the learning. I send special Radio equipment: show you how Radio Industry to buy Defense equipment, on top of Sgt, $41, $51 a week to conduct experiments, build circuits. My rdi.50 training boom civilian Radio tssi'seos. whether you enlist Radio broadcasting stations employ operators, technicians. method makes learning at home Interesting, fascinating. or wait for conscription-IT'S SMART TO LEARN and pay well for trained men. Radio manufacturers pm- practical. I devote more than 10 Lesson Texts exclusively RADIO -NOW! ploy resters, Inspectors. rvicmmen in good- Poe lobe to Television, and In addition Television fundamentals with opportunities for al ancentent. Radio jobbers and arc red by cap' regular Course. dealers employ installation and servicemen. Many Radio Technicians open their stn Radio sales and repair busi- You Get This Professional Servicing Instrument Get Sample Lesson and $4 -Page Book Free nesses and make $90. $40. $50 a week. ()there hold their This Instrument makes prac- Act today. Mall coupon nec fur Sample Lesson and e4- regular jobs anal make to $10 a week fixing Radios any test be $5 tically gal will Book. They're FREE. They out Radio'. spare- in spare time. Automobile. police. aviation, commercial rolled upon to make In Radio page point Radio; loudspeaker systems, electronic devices. are service work o n both spare thine and full -time opportunities and those coming in Tele- Cewer fields offering opportunities to qualified n Sly time and full time jobs. It vision: tell about my Course in Radio and Television; ourse Includes Television and Frequency Slolulatim. can be used on the test bench. show more than 100 letters from men I trained, telling which promise to open gad jobs soon. or carried along when out on what they are doing and earning. Read my money back Charles F. Helmuth. 419 N. Mass. Ave.. Atlantic City. rills. It measures A.C. and Find out what Radio offers you. Mail the N. J.. writes: "I started Radio in the Marines. Later It.s'. voltages and currents; agreement. Cuupm In envelope or ou pennY -NOWl I took the N. R. I. Course. Now I inn my own boss, and tests resistmnrer: has a nulri- paste postcard get jobs over others who wear sure they had them. I owe band rnrlllator for aligning plenty to N. It. I. 'raining." James E. Ryan. 119 Set. old or ns w You get 1. E. SMITH, President Pebble St.. Fall River, Mass.. it -s: "I was working !hi!his inslrnnuvnt k,p as Dept. I FE. National Radio Institute in a garage when 1 enrolled with N. It. I. i am now pr+ of , '' It I t'toc Washington. D. C.

GOOD FOR BOTH SAMPLE LE SON FREE FItEEgi ON J. E. SMITH, Presiden+, Dept. I FX /. LESS '.SP. SAMPLE my National Radio Institute -, i oast!° reM' RICH REWARDS 1Tteof Washington, D. C. IN RADIO t ctical mdestand-My wssmttbles bD Dear Mr. Smith: Mail me FREE. without obligation, your les O.. Sample Lesson and 04 -Page book, "Rich Rewards in Radio." which easy tcr Itlaelvcr ver9oa to rn ,.Kadin co to A' spe;-. telle about Radio's spare -time and full -time opportunities and text, and Rein edytroubles T,R.F.. type, xplains your 50 -50 method of training men at home to be Radi" Cnaa rcceYeFa1 tand ofsec system Technicians. (No salesman will call. Write plainly.) Please Check) b o1YneA.nd cT Ti I AM doing Radio work. am NOT doing Radio work. Cte l awói.obabled y et.Y I cament. of °Ctsyou the este an section gives ,Nay to specvalkuP. esa Name Age A JasGet $etc tr tan. tel recettrelitisng ohliga Address %s^cine FREE No A thisO coupon City State 14X1

f!AC :O -CRAFT for JUNE, 1941 79 S. THE N ISSUE/ Circus i I^ t HUGO GERNSBACK, Editor-in-Chief meets ^ ReP N. H. LESSEM THOS. D. Rothe °Iy Associate Editor Art Director ¡he H °W ° :0:1119ilon R. D. WASHBURNE, Managing Editor Frpo t Icy xPer' Cost rust iO^r,lreosuré entes Vrith rotors got D ry Contents JUNE, 1941 Issue ^g A Rechorgi teries VOLUME XII .- NUMBER 12

Mailbag 707 Distinctive Calls for F.M 753 Editorial: Radio Famine Hugo Gernsback 713 Classified Radio Directory-Section III (Revised) 757 The Radio Month in Review 714 DEPARTMENTS, ETC. SERVICING Mailbag 707 New Circuits in Modern Radio Receivers-No. 45 Listing: "Treasure F. L Sprayberry 716 " -Finding and "Geo. "- Prospecting Articles in Radio -Craft 711 Operating Notes 717 The Radio Month in Review 714 An Open Letter -To the Radio Industry James H. Hardy 718 New Circuits in Modern Radio Receivers-No. 45 From the F.C.C. Mailbag 718 F. L Sprayberry 716

Selling Radio Service Willard Moody 720 Operating Notes 717 Advice to Set Owners -How NOT to Get Good Radio Service From the F.C.C. Mailbag 718 Fred Shunaman 721

RADIO SERVICE DATA SHEETS: RADIO SERVICE DATA SHEETS (See Servicing) 722, 723

No. 308-Montgomery Ward Airline Model 04BR- 1105A 722 Sound Engineering -No. 18 Conducted by A. C. Shaney 731

No. 309 -Ditto 723 Latest Radio Apparatus 754 Oriental Slant on Radio Fred Shunaman 724 Classified Radio Directory-Section III (Revised) 757 SOUND Shop Notes -Kinks-Circuits 764 New Parallel -Feed Audio Circuit Ted Powell 726 Book Reviews 763, 764

Utility Radio Receiver H Gernsback 730 F.C.C. 766

Sound Engineering -No. 18 Conducted by A. C. Shaney 731

A Radio OI' Timer Thinks Back Aways 733 Published by Radcraft Publications, Inc. Publication office: 29 Worthington Street, Springfield, Mass. Editorial and Advertising Offices: 20 Vesey Street, Latest Acoustic Speaker Housings 734 New York City. Chicago Advertising Office: RADIO -CRAFT, 520 North Michigan Avenue, Chicago, Ill. A Manufacturer Comments on "Modern Microphone Tech- RADIO -CRAFT is published monthly, on the first of the month preceding that nique" A L W. Williams 736 of date; subscription price is 52.50 per year in U. S. (In foreign countries, 75c additional per year to cover postage; Canada, 50c additional.) Entered Sound Is the Spur Leo Fenway 738 at the post office at Springfield as second -class matter under the act of March 3, 1879. TEST INSTRUMENTS Buying Test Equipment Bob Stang 740 Foreign Agents: London -Gorringe's American News Agency, 9A Green St., Leicester Square, EXPERIMENTERS w. C. 2, England. How to Build a Simple Miniature Portable Transmitter Paris- Messageries Dawson, 4 Rue Faubourg, Poissonniere, France. H. G. Cisin, M.E. 743 Melbourne -McGill's Agency, 179 Elizabeth St., Australia. Dunedin-James Johnston, Ltd., New Zealand. How fo Build and Use a Leak Detector G M. Bettis 746 * F. M. Text and illustrations of this magazine are copyright and must not be reproduced without permission of the copyright owners. Theory and Design Considerations of R.F. and 1.F. Coils in F.M. Receivers C S. Linell 750 (Including List of Articles in Past Issues of RADIO -CRAFT on Frequency Modulation) Copyright 1941 Radcraft Publications, Inc.

706 MAILBAG

AN ORIGINAL PHASE INVERTER on the grids bypasses very high frequen- New Direct- Coupled FM - AM cies, improving the signal from a crystal Dear Editor: pickup and reducing needle scratch noise. I am submitting to you a description of a WALDEMAR DE OLIVEIRA, phase inverter I developed and, surprised Civil Engineer, AMPLIFIER MANUAL with its optimum result, I would like it to Sao Paulo, Brazil. become known to other fellow amateurs By A. C. SHANEY and public address designers. Chief Engineer. Co. of America One of the most important problems CENTRAL AMERICA CALLING met by amplifier designers is certainly the Dear Editor: phase inversion for push -pull operation. We have great pleasure to inform you The phase inverter presented here is the that one of our transmitters, namely TGW, result of a careful study, conducted by logi- operating on the frequency of 1,520 kc. cal considerations and electrical calcula- p. s., will have its power increased to 10 kw. tions. in the near future, the necessary apparatus Looking for simplicity (best policy in all having been already acquired. design), the author considered the circuit The "Voice of Guatemala" will then of Fig. 1 used in D.C. direct -coupled am- operate with the following transmitters: plifiers for cardiograph purposes, employing TGW: 10 kw. on 1,520 kc.; TGWA: 10 high -amplification pentodes with low plate kw. on 15,170 (luring the day, on 9,685 dur- voltage. ing the night, with optional frequencies of 11,760 and 17,800; TGWB: 1 kw. on 6,480 kc.; and TGWC: 1 kw. on 2,320 kc. TGW, TGWB and TGWC are on the air during week -days from 7:00 to 8:00 and from 11:45 to 14:45, also from 17:15 to 23:15, C.S.T. And on Sundays from 9:30 to 16:15 and from 18:00 to 23:00. For the Layman, Serviceman TGWA is on the air during week -days Recordist and Engineer Regardless of whether you are interested In the finest from 1145 to 13:00 and from 21 to 22:45; type of phonograph reproduction. high fidelity recording. on Sundays from 11:45 to 16:15 and from sound-on-film applications. FM or AM programs, you 111 find invaluable Information in this practical handbook. 18 to 23:00. Written by the leading exponent of direct- coupled amplifiers who has spent more than 10 years improving and Having recently installed rhombic an- perfecting the famous Loftin -White circuit. tennas directed U.S.A., we towards the Explains the theory and practical application of: ' 2-MEG VOLOMe would appreciate very much if your readers Expansion CONTROL G Variable Speed Non -Overloading Push -Pull can check up our signal strength. All re- Non - Frequency Discriminating Scratch Suppression 0.5-MEG. 0.5. ports will be promptly answered, there PushPull Balanced Direct -Coupled Amplification MEG. Push -Pull High - Frequency Equalization . being no need to send stamps, coins or in- F Push-Pull Low- Frequency Equalization 2p00 ternational reply coupons. Push -Pull Volume Compression 10000 OvMS +270V Automatte Volume Limitation OMwS Thanking you in advance for the pub- Automatic Volume Control L... )1 licity you may give to this information, /5.000 Calibrated V.U. Indicator OHMS I remain Audio Spectrum Control Remote Control h Luis SCHLESINGER CARRERA, Director, Nacional de Guatemala, If you are Interested In the latest audio developments. 05- Radiodifusora you can't afford to be without this complete compilation MEG. "La Vozde Guatemala," of authentic articles on Direct - Coupled Amphffers. 32 America. Pages 81/4^ x 11 ". Over 100 diagrams and Illustrations. Guatemala, Central Priced to Cover Cost of Printing and Mailing ZOe O f- F .05-MF y Send Stamps or Coin II`=' CONCURRING IN "WHY THE AMPLIFIER CO. of AMERICA BY It is known that, if the cathode resistor SUPERHETERODYNE" 17 WEST 20TH STREET. NEW YORK. N. V R, is a few times greater than the ratio: MR. MOODY plate plus plate load resistor, to amplifica- Dear Editor: EVERYTHING tion factor, Three cheers for Mr. Moody, the man IN RADIO + R who dared defy the laboratory geniuses, Re (A) technicians and experts who foist supers. I; on an innocent public. The writer concurs completely with Mr. the signal will appear at the cathode end Moody's assertions. How often have we mi. big book serves your resistor. Connecting the entire needs. It includes sets, of the cathode heard the purchaser of one of the late and cathode of tube No. 2 to the cathode of tube models lament that, although his set is more draw, amateurppwpublicm t, test. No. 1 and grounding the grid of tube No. 2 ers, kits, (tumescent lighting. sensitive and selective and can do more than Nationally known favorites at In actual lowest possible phase inversion is accomplished. his old set, including receiving overseas puces Write Re is made today for your copy of practice the cathode resistor broadcasts on one of the shortwave bands, 10 value given BIG FREE 3 to times greater than the it is sadly lacking in a very important re- by the second member of formula (A). CATALOG / quirement -tone quality? When asked what This circuit, simplicity itself, is unfor- the "old set" was, the inevitable reply was: tunately impracticable for triodes with low "Philco (Majestic, Atwater Kent, Crosley, BURSTEIN -APPLEBEE COMPANY mu on account of the high bias developed Brunswick, etc.), model such and such," 1012 -14 McGEE STREET, KANSAS CITY. MISSOURI across R,,. To enjoy triode quality using which all persons, who have made radio a the above principle a solution was logically hobby or means of livelihood for the past imposed: reduce bias to rated value. A tap decade or two know, were T.R.F: s. RADIO TECHNOLOGY on R, at the proper bias voltage, and a Even though these "old sets" were in- RCA Institute m: r ,.. h:g. cathode signal standard embracing all phases of Radio and filter circuit preventing the ferior when we consider the detector, audio Television. Practical training with modern from reaching the grids, is the originality equipment at New York and Chicago school,, section and speaker, the tone more nearly Also specialized courses In Aviation lommwd- developed by the author. approached realism cations. Radio Servicing and Commercial Oper- than present -day mod- ating. For Free Catalog write Dept. 13C -4t. This circuit is shown in Fig. 2 where els, even expensive ones. With present -day values given from RCA INSTITUTES, Inc. are the experimental audio development such as inverse feedback, A Radio Corporation of America Service model using a double -triode 6C8 -G with plate beam power tubes and high- quality audio 75 Varick St.. New York. 1154 Merchandise Mart. Chimp load of 100,000 ohms and 250 volts plate transformers and loudspeakers, a well - Ganesriof supply. Other types of triodes and pentodes designed T.R.F. tuner is capable of repro- Pr ^Sri =1 selloscillator wnred New S19nc will work equally well, values of parts being duction with breath -taking realism. - All alignment Il. k Trouble hooting easily calculated considering load and plate The average listener is strictly a layman FF PA systems Checking resistances, amplification factor, rated bias so far as the intricacies of radio are con- i sensitivity AVC Antenas 10 second locating of auto set ignition pickup voltage and plate or plate- and screen -grid cerned, and cares not what is on the label Host of other tests. Utterly simpler. faster. more currents. Equality of plate potential makes of his radio set or what kind of circuit it accurate. Used by U.S. Army Signal Corp.. hundreds this phase inverter surprisingly suited to employs, just so it sounds good. The word of servicemen and organizations. Write now for leaflet. direct -coupled amplifiers. The filter network "superheterodyne" is pretty high- sounding GENERAL TEST EQUIPMENT CO 213 S. CROSBY AVE., KENMORE, N Y

RADIO -CRAFT for JUNE, I 9 4 1 707 MAILBAG

and, like 2 or 3 shortwave bands, is used trically complicated about the work above How to Get the advantageously by salespeople when pro- outlined, and it is really worthwhile. Later, moting sales. after having acquired some skill, the repair- BETTER Job in Radio! After all is said and done, the average man may try his hand at repairing the listener -who might be a housewife listen- more complicated clocks, the alarms and Technical Training Backed by ing to her favorite morning program while the chimes. Your Own Radio Experience busying with her chores, or a tired business- If it is considered that the clock repair Should Prepare You for a man, settled comfortably in his easy chair business does not pay, or is below the dig- BETTER Job in Radio! relaxing to the strains of some pretty nity of the highly trained service specialist, Did you t o how much money the melody -does not care a hoot for shortwave just remember that it is a good policy to lack of modern advanced training is costing you? It's worth taking time right now to programs, nor does he strain his receiver get people into the habit of coming into find out how CREI offers you a planned on domestic DX reception. He is content your shop. That point is very important and program for advancing yourself in radio. with receiving stations within his "easy - the key to wider business and increased CREI courses in Practical Radio and Tele- vision Engineering equip you with the abil- to -get" range; a job that can be done with prestige. More likely than not, the patrons ity to go after and get the better engineer- a T.R.F. -with superior tonal results. of your establishment may come to look ing jobs. The writer is aware that supers. are very upon you, a Serviceman, as a mechanical or THINK THIS OVER: important in filling a need for the amateur, electrical genius. And that kind of attitude Actual Records Shoso- as communications receivers, etc. But what on the part of your customers will not CREI graduates, s o groupp are among the highest paid in radio! CRE! rsi in could be more flagrantly misused than a hurt business, you can be very certain. more than 350 broadcasting stations! More than 5,000 radiomen have taken this course multi -tube super. with a stage of R.F., 2 WILLARD MOODY, of training! Employers are increasing!? stages of I.F. and very good sensitivity and New York, N. Y. calling upon CREI for personnel replacements and additions. selectivity, used entirely for reception of strong locals whose signal strength is so WRITE TODAY! If you are strong that the diode detector develops a RADIO -CRAFT BOOSTER a professional radioman and want to make more money. high A.V.C. voltage which practically over - Dear Editor: send for free booklet and far biases the R.F. and I.F. tubes resulting in tual Information. To help us I am a steady reader and booster of intelligently answer your in- distortion at the output? Don't say it isn't Radio -Craft. quiry please state briefly done look around for yourself. your education,- radio experi- -just Have read Willard Moody's letter as ence and present position. EMILE J. ROME, published in the February, 1941, issue of New Orleans, La. "R.-C." As for Willard Moody, I have read many of his letters published in "R.-C." and CAPITOL RADIO have found them very interesting, and would ELECTRIC CLOCK REPAIRS AS A like him to continue writing for "R. -C. ", but ENGINEERING INSTITUTE SERVICE SIDELINE FOR I sharply disagree with him on his views Dept. RC -6 3224 16th St., N. W. Wash.. D. C. THE RADIO MAN regarding Hugo Gernsback. I have followed Hugo Gernsback's editori- Dear Edit., : In New York City, at least, the majority als since the days when he wrote for Science & Invention (a ELEMENTARY of the electric clocks sold to the public good many years back). are either Telechron or General Electric, Just because Hugo Gernsback can see and, in one case I know of, G.E. uses a further than his nose doesn't mean he MATHEMATICS Telechron Timer in a special set designed should be condemned. His editorials are to switch the radio receiver on and of at farsighted and constructive. I sincerely hope you continue his writing editorials for EASY SIMPLIFIED PRACTICAL a predetermined time setting. - - It would be worthwhile for the Service- If you drop "Shop Notes, Hints and HERE Is book for the business man, the tech- man to investigate the advantages of the nician and craftsman explaining and answering electric clock repair business, since for the Kinks" from your magazine you would be every operation and meaning with interpreting omitting a department which I believe is Illustrations and examples. investment required and the return on that It Is the key to simple understanding of many is a more favor- referred -to by every reader of this maga- perplexing problems In daily life. investment, there decidedly zine. In clear, positive and definite language, the author able ratio than in the case of radio servic- popularises and clarifies every subject and helps the I will close with three cheers for reader to overcome any apparent difficulty In the study ing itself. In addition, the profit is not only of mathematics. easy to obtain, but it is there practically Radio Craft. A real home study- course In mathematics for the I. L. FRIEDMAN, student or the man who wants to achieve proficiency for the asking. In outlying districts, the or desires to brush -up on his knowledge. Brooklyn, N. Y. New ID Entire Chapter on Special Math. suburbs of metropolitan York and Jer- Mr- ematica for the Radio chnician are many people who would T sey, there Thank you, Sir, thank you! CONTENTS OF BOOK rather bring their clock to a repair man I . Arithmetio-Additfon _aubtnction- YUHtpa in their neighborhood than to cart the thing -Division. CHAPTnonER II. Factoring and Cancellation-- Fnetlone-Dsel all the way to the big city. If, then, you go mala-Percentage-Ratio-and Proportion. RADIO-CRAFT EASES SORE EYES CH AAAAA 1ÌV. after the business, you will have a profit- Howe tao tMesuureSurfaces and Capacity Dear Editor: Crometr yI. able sideline, something that will help to CHAPTER V. Povera and Involution-Roots and 6rolu- non. pay the minor expenses of your organi- What a sight for sore eyes! Was looking CHAnia VI. Mathematic. Por the Man- i d T h ' I C m Th zation. over the magazines at a stand for some- mometer conversions- Graphs Curve -VU of ONLY Further, in servicing sets using the clock thing interesting to read and like money lide Rulé -Logarithm. CHAPTER VII. Special Mathematics for type of timer, it would be valuable experi- from home, I saw the words HUGO the Radio Technician. VIII. Commercial Caleulatlem- Oc ence to have had the opportunity of work- GERNSBACK, Editor. You should have Interests -Discounts- Short Cut POSTPAID Arithmetic. ing on cheap, relatively simple clocks before used larger type for those words I've looked CHAPTER IX. Weights and Meaeu no- I tackling the complicated mechanism of such for but missed for years. I used to read alnn.nlary Matemnlirs" can la aarr(sd readdv .a your posies system. Radio News when you were Money a radio switching editor, then Send Stamps, Cash or Order. The parts are obtainable from the Elec- when some other bohunk became editor, I EC II WA tric Time Co., 915 Broadway, or from G.E. lost interest. My work (and of course \ 11 York 1017 S. Statei St. RC-641 Chicago, Supply, 585 Hudson St., both in New study) took me away from radio, but all City. the while I've been wondering just what The G.E. people, although the motors used you were doing. I've never missed anything RADIO COURSES in their clocks are the same, identical, so much as your magazine. The editorials, Start Stye, ream r is RADIO OPERATING -BROADCASTING charge more than Teleehron. This because articles, and the mental prods are just the RADIO SERVICING -a practical course Telechron owns the patent rights and kind of meat I like. Can't say how thank- RADIO AMATEUR CODE TELEVISION clocks sell for ful I am find a ELECTRONICS -1 yr. day course 2 yrs. ere. l licenses G.E. Most kitchen to magazine -HUGO Day and Evening Classes. Booklet Upon Request around $9. The motors required for servic- GERNSBACK, Editor. Just a stroke of luck New York Y.M.C.A. Schools ing cost the repairman 80e if he buys from that I needed some dope on an amplifier W. 64th Street New York City Telechron and returns the old motor; G.E. I'm making as a hearing -aid for a person sells the same thing for $1.50. that is durn near deaf. If the Serviceman charges, for a simple And listen Bud, DON'T stop those editori- RAD10TELEY151011 kitchen clock repair involving but 10 min- als. Just the thing a fellow needs to wake utes' time and the replacement of this mo- up all of us. We really are too lazy to think. Oldest. largest Radio -Television school in West trains you god pay job. Complete instruction including Radio tor, bought at 80c, he can collect $1.50 Also I'd like to see a Serviceman who is Construction and service. Broadcast Operating, Sound, intelligent to read the articles you se- Talking Pi , Television, Public Address, etc. Flexible for the work, a good profit. Given enough too be. to met specific needs of those with or wi 1 to benefit from the TLanransportation allowed to L.A. Earn room and board while of such repairs, over a period of a week, lect or too "intelligent" learning. Request Free Catalog. he will be able to expand his allowance for "Hints and Kinks." Anyone so intelligent as Dept. 6 -RC test equipment. the fellow who uses a whole column of a NATIONAL SCHOOLS Los Angeles There is nothing mechanically or elec- department he wants discontinued, as in 708 RADIO -CRAFT for JUNE, 1941 MAILBAG

Feb. Radio -Craft, should find out how much other rig, or must we get an 0 -100 as the he doesn't know. But I do agree with him article calls for before it would work satis- to continue the experimental (articles - factorily? No doubt our 0 -200 would not be Ed.). I don't know if there is much profit in as sensitive as the 0 -100, but we just won- a magazine for the experimenter, but you dered if it would not do? have done a lot more to make this a better And if there are any other changes that world to live in, than any 10 of us realize. should be made from the line -up as given Ours is the sin for not following your sug- in the Radio -Craft article would you please gestions; yours is the glory of pointing the tell us! We certainly would appreciate it. way. And we thank you very much indeed! The letter of on - Earl Russel hearing B. B. BARTHOLOMEW, á-ia- aids took my eye. Three months ago I un- Puyallup, Wash. Learn How with this! dertook to make a hearing -aid, for a per- Here's the world's most highly who praised course in practical radio son hasn't been able to find a satis- Mr. Bettis replied as follows: sen' 11 you in this factory 'aid in the 30 money no one hdahandsome 1300 -VgR4 home. last years- Dear Sir: sects hook. First. a 4f sage I used to be a sectione tg explains all ttypes pee serv- object. radio Serviceman in Your letter just reached me this morning icing test instruments-howw days of 3- element how to use them-also. the battery tubes, but from Radio -Craft and hope that I may be to build your own. Then, I stteepp-b -stpages give you a ou since then have forsaken radio for elec- of help. y -step course in tricity in the power field. It's a bigger job mad rer testing,tesakes tligadio There is an error, in the article in the repairing of than I bargained for but thanks to 3 years Seta l ra electaronic December issue, in that the depth of by latest scientific "factory meth- of laboratory work I don't mind the slow the ods." Learn radio servicing 'At -in. water line should be 1 ft. instead of this omical progress. I don't know much about "1941" Ì.e arn WHAT to t' do and 21 ft. The dual condenser unit in NOW to do it. Send for your copy wi* amplifiers but the last 'aid I've made works. trans- today. Use the coupon below mitter Fig. 12 is condenser 5 as in 3300 pp.. 708 illus., 720 review quest. The person it was intended for can use a the List of Parts. In the receiver, the dual condenser telephone and talk with anyone in the same is 4A as in the List of Mr. This Parts. Figure 15 has RADIO 740; 4Skvati, HANDBOOK room. (Without mirrors, Russel.) a slight error, and a correction in spite of the fact the person cannot hear is here Save supplied. Otherwise everything is Time with this! J TO from correct. Here's real p for servicemen you shout if your lips are an inch her 1X big manu. l -Al zo pages of valuable. time -saving. fa voueherked SPEED ear. Mr. Russel is a bit wrong about crystal rvlcing data right at your finger I his tips to help you do every semi,. UP mikes and phones. But believe prayer log Job quickly and accurately. Its The circuit shown at left is in 53 e10 SECTIONS contain for a battery -operated 'aid is a bit hope- large 275 correction of a pave of time -saving "Case portion of the Histories on Ove 3.300 receiv. less. diagram shown on pg. 365 of Alignment data for over the December '40 issue of uperhets . . Servicing I've a few experiments to complete before installation data for all Auto I finished, but after that "R. -C." ( "Building a Modern Raanddios ... Truble- ShootingCharts can call this 'aid Miniature -Tube Metal- Treasure une. REVesistor and Condenser Charts EVERYTHING! Sneed I feel I'll have exhausted the possibilities Locator "). up your service work ith ll$ola the vital servicing data NOVa of present-day equipment and parts. I'm o big hook. thankful for my laboratory training, as I in thispo.. í34 illus., 84tí11 site. don't believe the work would have been The 500 mmf. unit in the transmitting CLIP OUT! MAIL NOW! me successful without it. As it is I almost can loop is correctly rated as capacity. .. Pubi. Co., to 45 Dept RC41 L Chem I on - Astor Pl.. New York for FREE. I consider myself an authority hearing The Meissner interstage I.F. transformer Enclosed find payment for: D MODERN circulan. 5 aids. I've made them from "1- tubers" to was used but the No. 16 -5728 will probably El RADIO TROU- O BOTH books at SERVICING Money I "10 watters," and have the good fortune be OK but may take a different setting of Fit S SHARD. Saving Com. I with vari- GOOK binatlon Price to have a wide variety of people the gain control to prevent oscillation. NAME I to work with. I believe ous hearing troubles The 0 -200 microA. meter you have will ADDRESS I in -aid CITY the cause of confusion the hearing probably STATE I can hear well be satisfactory and will be just as ..MONEY -BACK IF NOT SATISFI field is that certain people sensitive if you can obtain full -scale reading with certain 'aids but it takes an unusual on the meter. use. could be made, but 'aid for anyone to It The aluminum foil should way each person re- extend to within in one or another, 2 ins. of the inside edge of custom -built job. Do not attempt the receiver case quires a and only on the front panel of the receiver. to make one for Mr. A that is just like the FREE! one Mr. B likes so well. Extension hand grips are very necessary for HERBERT SASS, sensitive operation. Mine are fastened HAMMARLUND Port Clinton, Ohio to handles, 27 ins. from each end, with small ^° bolts; and are made of stiff wire with a NEW "41" wooden spool for the hand grip similar to RADIO CATALOG THE BETTIS METAL LOCATOR the handle of a heavy 5- gallon oil bucket. The latest Hammarlund catalog with Dear Air. Bettis: It will be noted that this locator is not complete data, illustrations, draw- We built one of the Metal Locators which very sensitive to metal above ground but ings and curves on the entire Ham - in the September, really goes to town on buried lines or metal marlund line. Address Department was described, or outlined, HC -6 -1 for your free copy. 1939, issue. But it was not any too satis- that has been in the ground some time. factory. We did some changing, but still I hope this will help, and would appreciate HAMMARLUND MFG. CO., INC. we realized there was plenty of room for hearing how you come out and just what 424 -438 West 33rd Street, New York City further improvements. This you outline in luck you have. the December, 1940, issue, and as it seems G. M. BETTIS to be a great improvement, we are planning to build it! But we thought it best to write you directly, first, to be sure that the de- SAYVILLE AGAIN NRADIO SERVICE EXPERT tails as to the circuit outline might not (A Letter to Hugo Gernsback) a LEARN AT HOME IN WARE TIME be a little off from those which you sub- WITH regard to the correspondence you The demand for radio expert: grows mitted to the publishers. ever' day. Learn this paying prufessinn quote on page 687 of your May, 1941, under personal guidance of qualified en- One thing in particular we had in ques- issue of Radio-Craft, gineer and educator. Clear, fascinating in- the following may be struction and experimental kits make learning easy. tion, was whether the value of 500 mmf. of interest to your readers, and you may Leaders in the radio industry endorse R.T.A. methods. Spare time for the condenser which appears in the therefore want to quote me in this connec- profits soon pay for training. transmitting loop, is correct? tion. You certainly have my permission to NOW IS A FINE TIME TO START New National defense program requires radio trained Another question: Is the item calling for do so, as a matter of general information. factories every Service. Opportunities ancement st limitless. a "Meissner I.F. interstate transformer," Early in the days of World War I, while FREE bbo`oktc ingfWIISLRT ,A°vainingcandotryou. instead of an input type, No. 16 -5728? I was editor of Modern Electrics, I received Is there too much gain in the input, a 'phone RADIO TRAINING ASS'N. OF AMERICA call from Richard Pfund, who had IMPS Devon Ave. Dept. RC -al Chleege, III. or is this a mistake in the printing of the only recently divorced himself from the article? There being a gain of 80 in the Telefunken Wireless Telegraph Company of input and only 19 in the interstage. If America. This company, although carrying .SC4 11E there is no mistake in the printing of the :1)-C!pgPS the German name, was jointly owned by Smaller Diameter Dry Elctrolvties article of course it is correct, but we were some American gentlemen and by the Ger- just not sure ourselves, and as we want man parent organization. However, it was this one correct, the only way was to write SPE very much in the hands of Dr. Albert, who you. in turn headed the activities of the Atlan- Too: Wouldn't a Simpson 0 -200 micro- tic Communication Company. Because of vor,,, re, cow, ampere, which we already have, work in the the German intrigue and definitely un -neu- SOLAR MFG. CORP. Bayonne. New Jersey

RADIO -CRAFT for 1 JUNE, 941 739 MAILBAG

tral activities in this country, Mr. Pfund the Sayville station, as my story proves. LEARN decided to resign from the company, and Please note that my story preceded your set himself up in his own radio business in editorial, having taken place in the early the Trinity Building on lower Broadway, days of the War, in August 1914. New York City. I had worked for him sev- Perhaps this episode may be of interest RADIO eral years before, when he was still with to your readers, particularly at this time, the Telefunken Wireless Telegraph Com- once SERVICING COURSE -8 WEEKS when again we have to watch for this pany of America. very same sort of trickery. I have no doubt OPERATING COURSE-5MONTHS He 'phoned me the first week of August that we shall have secret transmitters or 1914. me known transmitters operating with all sorts 41 C fiwt. He told to come right down to see him, regardless of what I might be doing. of trickery, whereby much un- neutral in- I'LL FINANCE YOUR TRAINING formation Mad coupon today for free hook I did so. Arriving at his office, I found him and even information definitely showing how you can learn Radio in a great of excitement. He showed undermining our national defense, may be Operating, Servicing. Sound and state Television in a few short weeks in me half a dozen messages which he told me transmitted to the Axis powers. I think Coyne Shops and also bow you can radio amateurs should be on guard every pay tuition in easy monthly were from the Sayville wireless station, in- payments after graduation. tended for some German ships out in the moment, first to detect and report any sus- LEARN BY DOING Atlantic. I recall that one of them was the picious transmissions, and secondly, to be On real Radio receiving and sure that they do not fall into any sort of transmitting equipment at German commerce raider Dresden, which Coyne. Simple, easy method of was somewhere off our territorial waters. trap, whereby they might be used as tools, practical shop training. You dont unknowingly, for such activities. need previous experience. Prepare These messages told the German ships the for Radio Operators' Government news concerning the British cruiser AUSTIN C. LESCARBOURA license Exam. and for good jobs in latest Broadcast, Police Radio. Aircraft Birmingham and the French cruiser Des- Radio, Ships. Commercial Radio stations, or in service shops and cartes, as gathered from our own American radio factories. "Learn by knowledge of their whereabouts. Also, these Editor's Note-Austin C. Lescarboura is doing". the quick, modern way, messages told of the clearings of Allied ship- a radio old -timer who, as an editor and at Coyne Shops in Chicago. has au- EARN WHILE LEARNING ping from such ports as Boston, New York, as a free -lance technical writer, Job Help After Graduation Philadelphia, Baltimore and others along thored many interesting articles. More late- We assist you in getting part-time work to help pay ly Publicity Director for a number of radio living expenses and give you real employment service the Atlantic seaboard. Naturally, such mes- alter you graduate. sages were un- neutral, and were infringing companies, he is perhaps best known as the tI C. LEWIS Pros.. COYNE RADIO SCHOOL, guiding genius of "The Word Shop," his SOO So. Paulin. St., Dept.Ai -811, Chicago. M. upon our American hospitality to German your free book and details of may Par -Attar. offices at Croton -on- Hudson. e interests. GraduationPl senPlan. Mr. Lescarboura holds memberships in Mr. Pfund explained to me that he had NAME number where a of organizations including The picked up these messages at his home, Institute of Radio Engineers and the Radio ADDRESS. he an amateur receiving He had had station. Club of America (Fellow). He was decorated decoded messages, abso- CITY STATE- the thanks to the an Officier d'Académie by the French Gov- lute stupidity of the German authorities. ernment in 1919 for World War I services. INVALUABLE! It seems that the Telefunken Company used Many Radio -Craft readers will recall his BRAND the German Imperial Navy code for its se- book, "Radio for Everybody." ONLY cret messages, and when Pfund left the NEW! company, he had a copy of that particular were being code, espy code. The messages sent'in MEASURING RESISTANCE BY 25¢ . but Pfund had the code book, whereby he was able to decipher the messages. THE SUBSTITUTION METHOD He urged me to go to the French Consul Dear Editor: The most General in New York City, which I did. I Enclosed is a brief description of a test 'actforrrlulá hook print. contains brought the messages along with me. Need- box by which resistances may be measured aactually 3000 trade recipese less state, I had quite a difficult time get- by the substitution method. Icoetts ar to factory and wor ting by the clerks who were busy handling In looking back shun through my files of radio of RICHES INRRECIPES Céorkfull hundreds of French reservists who were magazines I do not find any description of n ^making ideas. anxious to return to their fatherland for this simple and rapid method. SIMPLIFIED sand tested formulas 1 PRECIICKL for making Glues. military service. I finally made myself noisy There are of shops Cements 1 Ad. hundreds and "shacks" FORM= cleaning enough to get attention, speaking French as where the meters are not calibrated for re- foi on Cmpoundso Pigments; well as English, and was introduced to the Wood Stela s; sistance reading. LFKC10R1 r Consul's right -hand man. I showed him the sown nd1Deod This method has the added advantage that tinta; Fire Proofing messages, explained the circumstances, and Extinguishers: higher voltages may be applied where need- GandI as w o r k Ina: gave him my name and address. Inks: Insecticides: ed, thus obtaining higher readings than on yPro- I in newspaper cesses: Metal Two clays later, read the a standard calibrated meter, resulting in r; Etching French Ambassador Jusserand and Fluids; Solders: that better accuracy on high values of resistors. Paper Making: Photographic Processes: Preserving British Ambassador Cecil Spring -Rice had Essences; Extracts and Flavors: Plastics; Plating Solu- By using low voltage it is possible to tions: Polishes; Preservatives; Fireworks: SeePS: called on Secretary Bryan, then Secretary Dyes: Toilet Preparations. Dentifrices and measure low resistances also with good ac- ('osmetica; Hair Preparations: Manicure Preparations: of State, and had registered a joint protest Sun Hum Creams and Lotions; Waterproofing: Waxes curacy. and countless others. regarding the un- neutral activities of the Wonder look of Useful Knowledge! Worth Its Sayville wireless station. As a result, a Those who have built test boxes such as KAyo methods-latest des. Remember-dí00Newest ey ic bd PLIFIED Navy guard was sent to Sayville, for the here described tell me they "wouldn't know formulas, and recipes-MANY NEVER BE. FORE pDaI¢SeCLOSED. purpose of checking the communication ac- how to get along without it." pp Send for. yournspynTOD Y. Remember, great for- tivities of the station. Don't you think your readers would be thtunes de fro formulas. a copy, sent postpaid anywhere Despite the Navy personnel guarding the interested? Send money order. cheek. unused U.S. stamps or coin. Sayville station, four months later a radio C. S. CARNEY, NATIONAL PLANS INSTITUTE amateur by the name of Apgar, living in Evanston, Ill. 248 -R Fifth A New York, N. Y. Jersey, I believe, succeeded in detecting of the Germans operating (Editor-We'll put it up to the readers further duplicity directly by printing it below.) the Sayville station. He took the high - pitched continuous notes being transmitted Measuring Resistance by the by the Sayville station, on a dictating phon- Substitution Method ograph record. By playing the record slow- dots and dashes 'which at There are several advantages in the sub- ly, he deciphered method of measuring resistances. the normal speed of operation were run in stitution together as a continuous note. He exposed Any meter may be used without special the situation to the Government, where- calibration. upon the Sayville station was taken over No calculations are required. definitely by Navy operators, and the No special battery is needed. fully enforcing our Ameri- trickery stopped, It permits more accurate readings by can neutrality. using the high end of the meter scale. Years later the French Government re- warded me for my efforts, with a decora- The test set is simple to build from parts tion, in 1919. found in almost any "junk box." I mention these facts to show that you Best of all it is rapid and accurate. The were quite right in your attitude regarding wiring diagram is shown on page 711.

710 RADIO -CRAFT for JUNE, 1941 MAILBAG

sary to know the exact voltage applied. Any convenient source of "B" power may be used. Resistors may be measured without removing them from the radio set, merely RADIO TRAINING by disconnecting the "B" power leads and transferring them to the test box (or an outside source of power may be used). Operating Notes. -Start with A on 1 and B on 6. Warning! If B is not on 6 at the start the meter may be damaged. Adjust G until the maximum possible How it works.- Switch A alternately is obtained. DORT ARTHUR COLLEGE-not privately owned. not operated for a college shorts out of the circuit the unknown re- Now throw A to 2 and gradually short -out profit, sistor R or a selected built and endowed by the late capitalist - portion of the re- part of the resistance in the circuit until philanthropist, John W. Gates -offers the sistance in the test box. the meter reading is the same as on Al. most thorough practical Radio training in This latter resistance is adjusted until Swing A back and forth several times to America. P. A. C. owns Radio Station the meter readings are equal. Then the se- check this setting. Then read the calibrated KPAC. which is equipped with the very lected resistance is equal to the unknown scales of the remaining resistance. This is latest type 1000 -Watt high fidelity RCA resistance, and is read on the test box scales. equal to the unknown resistance ". transmitter, operating on 1220 kc. with di- "R system. The college is The voltage is adjusted by resistor G to Construction rectional antenna Notes. -Any convenient val- authorized to teach RCA texts. give approximately full -scale readings on ues of rheostats may be used. the meter. Switch A is an S.P.D.T. knife or rotary. The Radio training covers thoroughly Air- Since the two readings are equal, the Switch B may be a rotary selector type ways. Press, Announcing. Teletype, Type- meter need not be calibrated, nor is it neces- or 4 S.P.S.T. knife switches. writing, Laboratory and practical experience at KPAC transmitter, control room and studios. Announcing is an optional part of REAL "TREASU RE" FINDING! this training: nevertheless a number of stu- Dear Editor: any articles appearing in other magazines dents annually make successful announcers. on Port Arthur College pioneered the teaching Having been a subscriber to your maga- this subject which might be of help to of radio with its first classes in 1909, and zine, Radio -Craft, for a number of years me? for thirty -one years has maintained an at- while in the radio business, I thought that Any information you can give me will be five Employment Bureau that is successful some articles on "treasure hunting" and greatly appreciated. in placing graduates in airways, broadcast radio balances night have appeared in your W. HALL WAGENER, and marine radio industries. magazine recently. I have since St. Louis, 1!o. not read it If interested in details about the Radio March, 1938. A number of articles on metal locators Course, write for Bulletin R -41 ¶n the latter part of 1937 I built a unit (so- called "treasure" finders) have appeared based on the Chilson circuit and other cir- in past issues of Radio -Craft. Unfortunately, cuits given in Radio -Craft prior to that we have no index to most articles in this PORT ARTHUR COLLEGE time. With this unit I was able to locate magazine; however, the record of pre- some buried placer gold in western Arizona. viously- published articles on this subject is PORT ARTHUR ( World -Known Port) As a result of the findings of the radio an exception (see list below). These copies TEXAS balance, I was able to mine successfully are available at 25c for current issues; 50c according to its indications and I was able for issues a year old; and $1.00 for copies to recover a total of about $2,000 in gold older than that. at a depth of 20 to 30 feet. Radio -Craft will be glad to consider for I would like to know if any articles on publication, construction articles on metal ANY RADIO "treasure hunting" units have appeared in FIX locators of the so- called "treasure " -finding New Invention Radio -Craft since January, 1938, and if so, type, particularly if these articles include mazin have you the buck numbers? I wish to re- information and illustrations concerning the Repair radl',s l'i design this equipment in order to make uf hours. Rev.olt. Complete it use of the completed equipment in actually umna,y cliff errant more effective and efficient. Do you know Comparison te h of finding buried metals. nique. Perm its

imdt $1 "TREASURE " -FINDING AND "GEO. "- PROSPECTING ARTICLES IN RADIO -CRAFT Training ra Mbe rm"ade Title Author Issue l'age 'wthout test .ruipmeent. slm. Prospecting by Radio at 1.6 Meters Joseph I. Heller June 1931 728 How to Build the Radio circuit suggestionssnugR locale thec fault Clyde J. Fitch Instantly. Plan copyrighted. Covers "Treasure" Finder June 1932 716 every radio set -new nrl old. How to Build the New E. Franklin Sarver In Manual form. Pt t,r z 11 smith ass sslhlattlre 9usmers4 "Treasure" Finder July 1933 8 in.. 112 pages. Over 1.000 complete swaddled I,rar -al mice hints. IN training is yurs only An Improved "Treasure" Locator C. W. Palmer Aug. 1934 76 mats fltUhle- different 1,10e. postpaid. ta. 114 sinetlnt Lenta for itself t timUsave 1 Newest in "Treasure" Locators Gerhard R. Fisher Dec. 1936 339 usingsl ng Sc resistor. .Invent- on Ne first Job. Limited ed by M. N.Beaman. noted uantity. Money -back guar. How to Make a Modern Radio Allan Stuart Sept. 1939 146 engineer and radio teacher. SUPREME PUBLICATIONS. Room 957 "Treasure" Locator 3727 West 13th Street Chicago. nlìnoia Building a Modern Miniature -Tube G. M. Bettis Dec. 1940 364 Metal -Treasure Locator Also see "The Radio 'Treasure' Finder." Oct. 1932, pg. 229; and, "The Radio 'Treasure' Finder." qoArtiumill May 1933. pg. 677, for additional data on this instrument. Also see "The New 'Treasure' Finder (corrections)," Nov. '33, pg. 294; and, "Treasure Locator." April 1934, pg. 610, for additional information. l,BRLLA5T5 See letter from Mr. Bettis on pg. 709 (June, 1941). 4 STANDARD TYPES of Amperite Regulators replace REMINISCENCES over ZOO types of Old -Timers Tell of Broadcasting Prior to Its 20th AC-DC Ballast Tubes now in use.... Has Anniversary patented automatic starting resistor. Thinking back over the old (lays of broad- When every announcement after the List $1.00 casting, Robert A. Simon, WOR continuity first one in a program began with "You have WRITE FOR REPLACEMENT CHART "S" director who's been a radio writer for over just heard...." Amperite Co. 561 Broadway, N. Y. C. 17 years, remembers: . When engineers bounced the mike up . When announcers identified themselves and down to clear its throat before a pro- on the air with code letters instead of their gram -that was the old carbon mike. names. Tommy Cowan was WCN and Mil- When "Hank Simmon's Showboat" and AMPERITE ton J. Cross was AJN. "Main Street Sketches" were two of the When the announcer had a switch to most popular dramatic programs on the air. Correspondence Courses In click himself and his studio on and off the . When he wrote a sample hour dramatic RADIO and ELECTRICAL ENGINEERING air. Sometimes he forgot to make the program in 1929 for a prospective sponsor switchover at the proper time, and was ELECTRICAL ENGINEERING; ¡' ';;;j there who I liked the script, but said it wouldn't do f d . I'rcpare y"uraeif. nt I.ow tust. !,r s trouble. because fulnre. Modern. Im titled. you can underalanrl ulrkl listeners wouldn't accept a full hour RADIO ENGINEERING When some writers used to use the drama. l Áár. sphmn V1..T. eu' Durk. That same manufacturer in 1940 Trains you to be per - service n real vacuum tube finest bond technician. gaper. kits furnished. Diploma on completion. paper for their scripts and the sponsors a full hour network dramatic pro- Tuition. 525. either course. Deterred payment plan. crackle often drowned out the announcer. gram. Get student FREE magazines.ns complete detis .SI ENDNOW RADIO -CRAFT for LINCOLN ENGINEERING SCHOOL, Oa III -CM. LINCOLN NEON. JUNE, 1941 711 T++is tOSIITUIFDFSK ¡I EXTq{

WITH ANY REMINGTON PORTABLE TYPEWRITER The A beautiful desk in a neutral blue -green which will fit into the decorations of any home -trimmed in black and silver -and made of sturdy fibre board -is now available for only one dollar (E1.00 COMB! NATION extra) to purchasers of a Remington Noiseless Portable Type- writer. The desk is so light that it can be moved anywhere without FOR AS LITTLE AS trouble -it is so strong that it will hold six hundred (600) pounds. With this combination of desk and Noiseless Deluxe Portable 10c A DAY Typewriter, you will have a miniature office at home. Learn the How easy it is to pay for this combination of desk and complete details of this offer. Mail the coupon today. Remington Deluxe Noiseless Portable Typewriter! Just imagine, a small good will deposit with terms as low as lOc a day to get this combination at once! You will never miss lOc a day. Yet this small sum can actually make you immediately the possessor of this amazing office at home combination. You assume no obligations by sending the coulunt.

LEARN TYPING FREE To help you even further, you get free with this special offer a 32 -page booklet, prepared by experts, to teach you quickly how to typewrite by the touch method. When you buy a Noiseless you get this free Remington Rand gift that increases the pleasure of using your Remington Noiseless Deluxe Portable. Remember, the touch typing book is sent free while this offer holds. SPECIAL CARRYING CASE The Remington Deluxe Noiseless Portable is light in weight, easily carried about. With this offer Remington supplies a sturdy, beautiful carrying case which rivals in beauty and utility the most attractive luggage you can buy. SPECIFICATIONS ALL ESSENTIAL FEATURES of large standard office machines appear in the Noiseless Portable -standard 4-row keyboard; back spacer; margin stops and margin release; double shift Remington Rand Inc., Dept. 189-6 key and shift lock; two color ribbon and auto- 465 Washington St., Buffalo, N. Y. matic ribbon reverse; variable line spacer; paper Tell me, without obligation, how to get a Free Trial of a fingers; makes as many as seven carbons; takes new Remington Deluxe Noiseless Portable, including paper 9.5" wide; writes lines 8.2" wide. There Carrying Case and Free 32 -page Typing Instruction Book- are also extra features like the card writing at- let on terms as low as 10c a day. Send Catalogue. tachment, black key cards and white letters, touch regulator, rubber cushioned feet. These Name make typing on a Remington Deluxe Noiseless Portable a distinct pleasure. Thousands of fam- Address ilies now using the Remington Deluxe Noiseless Portable know from experience how wonderful City State it is!

712 RADIO -CRAFT for JUNE, 1941 "RADIO'S GREATEST MAGAZINE" . . . . Defense priorities, especially in metals, portends important radio developments RADIO FAMINE By the Editor - HUGO GERNSBACK

UP to very recently the radio industry did not fully ap- due to the greater weight; the rotor will tend to fall back preciate the tremendous Defense effort through which by its own weight, unless some friction method is used. this country is now going. The shortage of certain On the other hand if friction is used to keep the rotor from materials which has taken place recently has caused a tumbling back due to its weight, tuning becomes more diffi- near -panic in radio manufacturing circles, because it is being cult and will not compare with the smooth tuning methods realized that it will be difficult to produce as many radio to which we have been accustomed. sets in 1941 -1942 as was the case in the preceding year. Fortunately the difficulties in the variable condenser prob- The Raw Materials division in Washington which controls lem cited here, are not unsurmountable. It is certain that all priorities of materials, has set a figure of 30% of last American ingenuity will overcome the trouble and perhaps year's requirements of certain important materials that emerge with something that might even conceivably replace established manufacturers of radio sets can use. This is par- aluminum completely, even when it can be had again. Ten- ticularly true of the key metal, aluminum. Thus, if a manu- dency of invention and progress is, that often when an indus- facturer used 100,000 lbs. of aluminum in the year preceding, try is put to the task, something better is evolved which re- he would only be allowed 30,000 lbs. for the coming year. places old methods and old materials. If an illustration is A similar condition exists in the metal nickel which is almost desired, we can point to plastics, now on a tremendous up- unobtainable at the present time; that means that permanent swing. It is certain for instance that in due time wood in magnets -in which nickel is used -for loudspeaker purposes radio sets will be completely obsolete. Even today a large are at the present time hardly obtainable. It appears that proportion of radio sets already are made with plastic cases radio manufacturers will not be able to obtain high -grade and this tendency is on the increase. permanent magnets for loudspeaker purposes for a long time Of course aluminum is used elsewhere in radio sets aside to come. from variable condensers. There are quite a few other small There are two schools of manufacturers at the present parts termed "radio findings." These, however, can easily be time, one which feels that if everybody would cut down his replaced. There are also the so -called shield -cans which production to 30 %, all of the set manufacturers no doubt heretofore, on account of the desirability of achieving light would be able to make money because they would have to weight, were made of aluminum. These will now be made of get more money for their product and due to the fact that copper or brass and there is no difficulty about this. less sets will be sold during the coming year, all manufac- There remains the electrolytic condenser used in many turers would have to charge more for their sets. That would sets. Here the substitution problem is far more difficult for mean more profit for the manufacturers. The public would the reason that in an electrolytic condenser, aluminum is get better sets for the money ar.d everybody would be satis- practically the only metal that can be used effectively. What field-in theory. The other school, mass -production minded, the electrolytic manufacturers are going to do about this will have nothing to do with a smaller production. Their problem is not immediately apparent. If no substitution can arguments run somewhat as follows: be found then it means we will have to do with only 30% "This is America, the land that makes the impossible pos- of electrolytics for the coming years, till the aluminum short- sible, the land where Yankee ingenuity was born. We will age has passed. not allow our production to lag ust for the sake of a little As for the permanent magnets in our loudspeakers, this is aluminum or nickel. We will substitute other materials for not such a very serious thing except that we may have to go these metals and go the German Ersatz artists one better. back to the permanent -type magnets which were used before We are not going to let these two metals stop our production the nickel -iron magnets had been invented. That means one iota." larger and heavier magnets and is one thing the radio manu- It remains to be seen which class will have the better of facturers do not cherish. Yes, we can go back to the electro- the argument. There is much to be said for both sides and magnetic type of loudspeaker which makes a permanent only the future can tell exactly what will happen. magnet unnecessary, but this again means using something The " Ersatz " -substitution -craftsmen, will tell you that that was discarded years ago and incidentally such loud- variable condensers now made exclusively with aluminum speakers not only cost more, but they also have been, as a can just as well be made with steel stators and rotors. In- rule, larger in size. deed, there is nothing new about this either. One of the oldest radio parts manufacturers in the business blanked -out steel There is however, a possibility that a substitute of nickel condenser in may be found in the future. The metal tungsten has been used blades the early '20's. The trouble with steel in permanent magnets for many years but tungsten is one plates is that they are magnetic and in the course of time, it will accumulate (on account of wear and tear) small iron of the metals difficult to obtain and is also rather expensive; filings which adhere to the edges of the plates like whiskers. whereas nickel is much less expensive but right now un- These are held in place due to the magnetism of the plates obtainable on account of Defense priority. and after awhile such condensers tend to short -circuit. But From all this it will be seen that a great deal of inventive we can still use brass, copper or phosphor- bronze. Zinc is a ability will of necessity be required during the coming good material and could be used but unfortunately zinc is months to find substitutes for the present radio bottleneck. also on the priorities list and cannot be obtained. As far as Personally I have no doubt that the problems can be solved the copper materials are concerned they seem to have the and will be solved in due time, if it becomes a vital necessity best chance. to solve them. The trouble here may be expressed in one word -weight. We will probably be in for a good many radio surprises All of these materials are considerably heavier than alumi- on account of all of this and it will be interesting to watch num. For this reason new designs must be evolved because American radio receiver progress during the near future. RADIO -CRAFT for JUNE, 1941 7,3 THE RADIO MONTH IN REVIEW

Laboratory, with an initial staff of 435 persons and a floor space of 200,000 sq. ft., was The "radio news" paper for busy radio men. An created. illustrated digest of the important happenings of the month in every branch of the radio field. Did you see "The Klystron Boys- Radio's Miracle Makers," by Frank J. Taylor, in an issue of the Saturday Evening Post? Worth IIEFENSE looking up, if you didn't. HOW long does it take to train a person to handle radio Tide magazine last month, in "Latin duties in Uncle Sam's armed America -a Progress Report on U. S. In- services? Only 4 months, these days, accord- ternational Radio," analyzed the pros and ing to Assoc. Press reports last month, cons of the "beam" and "network" systems which tell how the U. S. Navy has clipped a of N.B.C. and C.B.S., respectively, which 9- months' course down to 4, and of sending are competing for the South American out of the Naval Radio School at Norton broadcast listener market. Heights, Conn., 500 youths all set to take over radio duties anywhere in the U. S. or its possessions. The Export -Market (Possneck, Germany) describes the general design and applica- According to an issue of Radio Daily, the tions of the latest -type Siemens & Halske 1st Radio Intelligence Co., U. S. A. Signal electron microscope in an article entitled Corps, at Ft. Monmouth, N. J., is "seeking "Supermicroscopy-a Source of Technical amateur radio engineers and others inter- Progress." The article is useful as showing ested in shortwave radio operation." Enlist- the potentialities of this new tool. ment period: 3 years. Opportunities for officer ratings and advancement are exceptional. F.M. REPORTED Radio Daily, station WIP (Phila., Pa.) plans IN PRINT to give 24 -hour service on its FORTUNE Frequency Modulation wavelength. It is due BOMBCASTING- THUMBS UP FOR THE BRITISH! magazine last month (Cover Feature) ran a characteristically inform- to go on the air before this issue of Radio- t Robin Duff. B.B.C. War Observer, is shown broad- ative article entitled "Radio Craf is in distribution. casting an eye -witness account of the result of a Turns South," in which author William fire "blitz" on London while fires are still burning. S. Paley (C.B.S.'s young prexy) Radio broadcasting is a valuable communications told how link between the government and the people. It he had spent 7 weeks signing -up broad- FM Broadcasters, Inc., considers it an is a powerful instrument of both propaganda and cast stations in key cities serving the "interesting sidelight on F.M. reception," counter- propaganda, and as such, plays a tre- 15,000,000 radio that many persons suffering from poor mendous role in the defense of the British Isles. listeners south of the Pan- ama Canal. The new network is designed to hearing, and therefore unable to enjoy the solve the problem of supplying good North full benefits of ordinary radio reception, American programs to South American lis- find that the wider frequency range en- teners, and vice -versa. compassed by F.M. programs affords greater listening ease and pleasure. This is particularly true where the hearing deficiency is In "RCA Laboratories-A New Center in loss of sensitivity to high frequencies. for Research," a compendium of addresses by David Sarnoff and Otto S. Schairer (company President and vice- President, respec- At the 4th Annual Broadcast Engineer- tively), the objectives and directing per- ing Conference at Ohio State U., Columbus, sonnel of this new "world's largest" labora- O., more than 250 radio engineers absorbed tory, at Princeton, N. J., are outlined. "By oodles of information on F.M. Harvey the application of electronic devices to in- Fletcher of Bell Telephone Labs. thrilled dustrial processes, the Radio Age promises far -sighted technicians with his discourse on to electronize modern industry, just as the experimental tests of both binaural and application of electrical devices to industry diotic transmissions over F.M. channels. KOVAR at Here's virgin for experimenters. Westinghouse's "tube maker," B. Condret, inspects the beginning of this century created the territory the vacuum -tight Kovar- and -glass ¡oint of a high - Electrical Age," said Mr. Sarnoff, and it is voltage vacuum tube. An alloy of nickel, iron. with the idea of fostering this development, cobalt and manganese, Kovar expands and con- Add new tracts at the same rate as glass as the temperature and of meeting the expanding demands of title: Major Armstrong, "Father changes. national defense, that this huge Radio of F.M." (according to FM Broadcasters, Inc.).

A news item of last month states that experts are of the opinion that when Nazi Panzer divisions moved into France last Summer they used F.M. as a radio link between tanks. "Later reports from Britain in- VIDEO NEWS dicate conclusively that German aircraft re- Frazier Hunt, noted ra- cently shot down near London were dio commentator and equipped with F.M. transmitters," the re- foreign correspondent, is shown telecasting a news port concluded. program over Philco station W3XE, Phila., Pa. Hunt's new technique for enlivening his news The Federal Communications Commission broadcasts consists of last month gave us a new term: STL, effective use of both - A audio and video chan- meaning "studio transmitter link." total nels, augmenting his of 23 frequencies above 330 mc. are allocat- voice with motion pic- ed for these link stations, for the use of tures, maps and charts. F.M. broadcasters, only 1 link station per single broadcaster being permitted.

How far can Frequency Modulation signals be heard? Well, "it all depends." For example, the range of the giant 50 -kw. F.M. 714 RADIO -CRAFT for JUNE, 1941 THE RADIO MONTH IN REVIEW station which is going up atop 6,600-ft.-high Clingman's be 500 Peak, No. Carolina, will FILMGRAMAPHONE miles in all directions! Yep, we 500 said This film phonograph miles. Some 4 11.3 million people will be plays 90 mina., non -stop. serviced by this ultra-H.F. station. It is one Recordings are 4 paral- of the characteristics of Frequency Modu- lel sound -tracks on a single endless film. Photo lation that the range of this 44.l -mc. -chan- legend: A -Film; B-Lo- nel station will be the same during the day cating pins; C -Light in- as at night. It wouldn't take many such tensity control; D -Track aligning screw; E. F-Au- stations to make a transcontinental F.M. tomatic track changer relay network, would it? and pushbutton control; G- Film -threading gate lever; H- Automatic track number indicator; Station W2XAH is the new station which .1-Lamp housing; K- line switch. Four barrier - the F.C.C. last month authorized Finch layer photocells are used, Telecommunications, Inc., to operate at I per track. Bendix, N. J., for transmitting facsimile programs on F.M. channels between 30 and 40 mc., with 1 kw. Finch also has an Arm- the F.C.C. last month commented that 7 strong license to manufacture F.M. equip- hours of translation ment. and transcription are required to fully process an hour of recorded material. Major Edwin H. Armstrong is rolling right along with his self -made tide. The Steel -alloy sound recording blank discs F.C.C. last month gave him the high -sign with a "super glossy finish in silver blue" to utilize his present station W2XMN at and which can be processed and pressed like Alpine, N. J., for a 35 -kw. station on 43.1 aluminum recordings, are now available, ac- mc. to serve more than 12,200,000 people cording to Record Sales Co., Los Angeles, in portions of N. J., N. Y., Conn. and Pa. Calif. (an area of about 15,000 sq. miles).

WOR- Mutual's 2 recent "Defense in Ac- Gotham's pioneer school station WNYE tion" broadcasts, dramatically portraying has been given an OK to install a 1 -kw. the construction and test of a bomber and Frequency Modul>}tion transmitter on 42.1 a tank, have been recorded for distribution mc. New York City's Board of Education among 300 -odd schools. Classed as trans- is missing no bets. criptions, the discs are being released by official sanction of the National Defense Advisory Commission and the Federal Radio "Never before in a broadcast have I been Education Committee. able to pick out each instrument individually." Dr. Serge Koussevitsky speaking, after this eminent conductor heard his own Bos- A business -getter released last month by ton Symphony Orchestra as broadcast over Presto Recording Corp. was designed to Westinghouse F.M. station W1XK, at Hull, help Servicemen cash -in on the reallocation Maas. business by leaving one of the items with each customer. It was an order card, listing prices of home -recording needles and The current issue of FM magazine con- blank discs and imprinted with the Service TELEVISION "COOLIGHT"-750 FOOT -CANDLES! an article 2 -way F.M. police - tains analyzing organization's name, address and phone G.E. engineers have announced a floodlight, which radio operation in Douglas County, Ne- number, which also could be mailed to the produces daylight- intensify illumination without ex- braska. A 25 -watt car -radio transmitter in- service company (postage prepaid). treme heat, for indoor television work. The young an 18 building lady is comparing with an "ordinary" 1,000 -W. lamp, stalled atop -story several one of the three 1,000 -watt cigarette -size mercury blocks from Headquarters served excellent- lamps which are used in a single reflector. The ly to boost the field strength of the 250 - tubes, cooled with a gal. of water a minute, develop Plans are to market 18,000 Panorams 195,000 lumens of light over approx. 100 sq. ft. watt Headquarters transmitter. This simul- (Mills Novelty Co.'s slot -machine sound mo- taneous operation perfectly solved problems tion picture apparatus for restaurants, rail- presented by several low -intensity areas. road stations, etc.) in 1941, thus giving em- Both the Headquarters transmitters and the ployment to an estimated 5,000 people. The car transmitters are "voice actuated "; that RCA Indianapolis plant is building these is, speaking into the microphone automati- 16 mm. picture - sound machines (or did you cally turns on the transmitter, in this new read "Introducing 'Soundies'," in Feb. G.E. F.M. installation! Radio -Craft ?). SOUND ENGINEERS pricked -up their ears, and so would you, if you had been there, last month, when H. T. Olson of RCA told the attendees at the 4th Annual Broadcast Engineering Conference, at Columbus, O., that 60% of the radio receivers sold in America retail for less than $20, that they are table -model sets incapable of high -fidelity reproduction, and that less than 1% of the total number of radio sets sold are high -fidelity consoles, according to Radio Daily. Judging by these figures, "the surface hasn't been scratched," so far as the sale of high -fidelity radio sets is concerned. Radio's No. 1 problem: how to make Mr. Radio Listener high -fidelity conscious? CH- CH- CH- COUGH!- PARDON ME! AIRCRAFT MICROPHONE f cough drops can't do it perhaps this "cough but - This newly -developed, press -to -talk microphone was In connection 'with its plans to operate on" will. Nimble-minded WOR technical wizards designed especially for use in private airplanes and a staff of 350 technicians, devised this microphone cut-off button to momen- on yachts. It is a Universal microphone, Model CU -I, translators, etc., arily in a 24 -hour watch on overseas cut Me announcer off the air for the duration of molded bakelite. The mike is a single -button car. broadcasts, of his cough. Saves frantic waving to control room. bon type, designed to be unaffected by motor noise.

RADIO -CRAFT for JUNE, I 9 4 1 7,5 SERVICING

6507 ZVa-LL'7ECR7R, /M a.26- fRá .004 1.STA.FQAKO M f Mfg. / 500

o OS M¿ 50000 MMF WA/.5 a/- j z MEGS. rr A/f A.VC. sama a./A45

'R P M 1415G. RR P M RR M 100 04445 MMF 20 V fYCKUPJ A/E MLLMÌEQMvtALu NEW CIRCUITS I MODERN RADIO RECEIVERS In this series, a well -known technician analyzes each new improvement in radio receiver circuits. A veritable compendium of modern radio engineering developments.

F. L. SPRAYBERRY No. 45

(FIG. I.) OSCILLATOR POWER IN- As observed in Fig. 2, arrangements are course only good to set the average signal CREASED FOR LIGHT -BEAM EXCITER made to switch the entire audio circuit for level, and together with a signal level indi- OPERATION radio reception (R) in which the micro- cator such as a meter or "eye" tube can PHILCO MODEL 41623, 41-624 AND 41.625. phone is open and the pickup is grounded; serve only as a crude reference level basis. -A power tube is used as an oscillator and for recording radio programs (RR) in In Fig. 3 a bridge network using 2 diode when phonograph operation is desired the which the pickup - cutter is switched to the elements furnishes a bias for the 12K7 -GT plate voltage of the oscillator is increased output plate signal circuit with the speaker microphone amplifier which is related to the as it is switched into the special circuit for in usual operation; for phonograph opera- output signal. Diode element Dl is a volt- supplying the exciter lamp of the light -beam tion (P) where the pickup is fed into age regulation limiter while diode D2 recti- pickup. the volume control; and, for microphone fies the output signal for bias purposes. recording (M) where the microphone is According to circuit Fig. 1 will fed An increasing signal the of it into at the output trans- be observed that as the oscillator is switched the volume control, the pickup - cutter former tap causes the plate of D2 be- is to in position 1, the plate and screen -grid volt- connected to the output as before, and come relatively negative by nearly the value ages are increased by shorting -out the the speaker voice coil circuit is open. of the signal peak at this tap coupled to 22,000 -ohm series resistor. Moreover, the An additional output winding for the cut- the cathode, while the resistance bypass net- coupling of the oscillator to the 1st detec- ter is avoided simply by using the relatively work filters and divides this voltage before tor, as for reception, is broken by the high impedance of the output transformer application to the 12K7 -GT grid -return. cathode switching circuit, and a fixed con- primary for the cutter connection. Mechani- Provisions are made for a delay bias on the denser replaces the usual tuning condenser cal facilities are of course required to guide D2 plate, for no delay, and for cut -off bias in the oscillator resonant circuit. The in- the pickup - cutter while operating as a cut- of the 12K7 -GT when not in use. The delay creased plate and screen -grid voltage inter. There is no basic difference between a permits normal volume "inflection" but the creases the power output of the oscillator pickup and a cutter. circuit establishes an upper limit of out- so that it will have no difficulty in supply- put to the cutter to prevent over- cutting ing the exciter lamp. Note that the oscil- (FIG. 3.) AUDIO GAIN CONTROL FOR and distortion. lator is a power output beam type of tube. RECORDING RCA MODEL VHR -307. - Under condi- (FIG. 4.) A.F. AMPLIFIER USES CATHODE (FIG. 2.) CRYSTAL PICKUP AND CUTTER tions of recording where the variations of LOAD COMBINED microphone input are extreme, an audio PILOT MODEL T -133.-The intermediate WILCOx -GAY MODEL A.100.-Through the gain control maintains a good average cut- A.F. amplifier between the Ist A.F. stage appropriate circuit connections a single ting signal level preventing over -cutting and the output makes use of a triode -oper- crystal unit is made to perform the func- and yet not losing any instantaneous low ated pentode with a coupling transformer tions of picking -up a signal from a record input signal. primary in its cathode circuit. or of cutting a record. Any manual volume setting means is of The circuit is illustrated in Fig. 4. The

250 MME Mf.G/- .00!-

MEG.

Sa a1- 05- OSía+A0.í050 ME MEG. z,aao A.f 0.445 m+MS

6s- -2511

RADIO -CRAFT for JUNE, 1941 SERVICING

7C7 tube provides no gain because the circuit at approximately 100,000 ohms im- the cathode circuit instead of the plate cir- cathode signal voltage cannot exceed the pedance. The power gain is therefore about cuit. The cathode -to- ground circuit is fil- grid signal voltage. The primary of the 100 times and is equivalent to a voltage gain tered only for the I.F. The A.F. signal is coupling transformer is designed so that of 10 although the actual voltage is not in- then coupled into the cathode of the 2nd its D.C. resistance provides the proper bias creased. section and the output signal voltage is for the tube when triode -operated as shown. taken from the control-grid which has a By con- Regulation is very good due to no plate (FIG. 5.) DETECTOR-LIMITER CIRCUIT 50,000 -ohm load resistor. manual of 10,000 -ohm potentiometer the load and the tube when connected with a USES CONTROL -GRID OUTPUT trol the cathode load automatically adjusts itself to D.C. cathode -grid current can be varied MODEL NC COM!NUNICA- the impedance which it feeds. Moreover NATIONAL -200 from zero to saturation value. TIONS RECEIVER. -By means of a double - there is no high D.C. voltage between wind- triode, the cathode of the 1st section is load- For the usual signal the cathode -grid cir- ings as for the usual transformer connec- section cuit acts simply as a series resistor of near- ed while the cathode of the other value signal tion. is driven with the plate grounded and the ly constant but for an excessive The tube acts as an effective impedance control grid serving as the rectifier output the grid current reaches saturation, thus transforming device without contributing element. forcing an excessive voltage drop to form any gain to the stage. Roughly the same across the cathode -grid instead of across signal voltage may be delivered between the In the circuit, Fig. 5, the 1st triode ele- the load resistor. The point of saturation 6G6G grids from the 1000 -ohm secondary ment functions as the usual power detector (limiter action) may be set for any signal impedance as that entering the 7C7 grid except that the audio signal is taken from between zero and 25 volts peak. OPERATING NOTES

mentioned are numbers 1 and 2 on the unit having an S.S. 11- shaft. This set TtostUe in . factory circuit diagram. The condenser checked OK when out on the bench but as mentioned is number 1 with the U encircled soon as it was placed in the car it acted -up .... PHILCO 71 -91 -14 on the circuit diagram. again. Replacing the original control with Oscillator failure (radio set fails to tune a new one, then tearing the old one down at either high- or low -frequency end of MAJESTIC 90B showed a burned condition probably caused dial). .... by loose when car was When set was turned on sparks shot roller contacts the have been seen before, but this this in motion. (Notes out of the type 80 tube socket. Also when is a complete summary.) the 80 tube was removed the sparks still EDWARD J. WELLS, (a) Reduce cathode resistor on the type shot out of the socket. Wells Radio Service, 36 tube to 10,000 or 8,000 ohms. Never This set has the lead from the volume Pennsgrove, N. J. use less than 8,000 ohms. control running right across the 80 tube (b) Replace mica in 3 compensating con- socket and constant rubbing of this wire .... RCA 97KG densers mounted on condenser -gang. to the tube socket connections pierces the If the set is dead, and has no A.V.C. Moisture in mica will stop oscillation. insulation and causes it to short and over- action, first check the red and white wire (c) Reduce the I.F. 10 kc. and realign. heat the transformer and eventually burn from the tubular condenser container. In some cases it has been found neces- it out. Whenever repairing this receiver You'll probably find the 10 mf. section sary to replace I.F. compensating con- always re -route this wire and save the ex- dead- shorted. If defective, cut loose and densers, but this should not be done pense of buying a power transformer in replace with a new one. If not defective unless other suggestions fail to restore the future. check the 8 mf. section for dead short. operation. HAROLD R. KUNTZ, If use of the pushbuttons results in dis- Brooklyn, N. Y. low volume, cotton -covered wire used in tortion at on this model, re- (d) Remove place the 470 mmf. mica condenser oscillator coil circuit, and replace with that goes rubber-covered only to prevent mois- .... RCA U44 to the grid of the 1st -detector. ture absorption. Under certain conditions the line voltage JAMES WILSON, JR., D. K. Chapman, Replace the type 36 tube with one of in a suburb may reach a high value, putting %. (e) Florence, Alo. known value; do not rely on tube too much voltage on the tubes of the re- tester solely. ceiver, temporarily. In the case of the RCA U44, may cause breakdown of dip in this units not (f) Remove oscillator coil. Dry out, The 0.005 -mf. by- and replace. is conservatively rated. plate paraffin, If coil dam- pass condensers in both of the 6F6 tubes aged, obtain replacement from the manufacturer; checking part number seem particularly susceptible to this sort of trouble. Replacement with 600 -volt units is Radio & Television carefully, as there are early and late recommended. models of these sets, each using a dif- MOODY, coil. WILLIARD ferent New York, N. Y. JUNE, 1941 (Note: The first 3 are suggested as routine adjustments; they work fine for us. G.È. K -I07 Facsimile Made Easy with New Dry Record- The last 3 are to be used in "stubborn" .... cases.) Complaint: intermittent. Check the ing Paper, by H. W. Secor soldered connections on the tuning meter, directly inside the case, for a corroded con- A 600 -Watt Transmitter, by Larry LeKash- STEWART- WARNER NO. 91 -711 .... with a hot iron (Chassis No. 91 -711) dition. Retouching soldering man, W210P is all that's needed for a repair job. Symptom: smoking power transformer. How to Get "Response Expansion" in Your Leads grounded to shell at point of .... RCA 4 -T Audio Amplifier, by Winton P. Walter emergence, due probably to chafing action Complaint: loss of volume after approxi- resulting from failure to allow for expan- W8KPX Modulator to Build It, by mately 5 minutes' operation. Check resistor -How sion and contraction in cutting leads. R10, the 330 -ohm 1 -watt carbon resistor Harry D. Hooton, W8KPX Removal of the shell clears the short and connecting from the 10 -mf. condenser to A Booster Amplifier for Weak "Television the transformer is still serviceable. Simply the cathode of the 6A7. Check the 470,000 - enlarge the hole in the bottom shell and re- ohm 3/4-watt resistor, RS, from the 10 -mf. Signals," by Thornton Chew insulate the chafed leads. condenser to the 1st I.F. transformer. These Ultra -Small Transmitter- Receiver, JOHN E. HUSSEY, resistors must be checked while still hot for by Robert Salem, Mass. they show no defect when cold. These re- Joseph Stahl sistors if found defective, can be replaced The "Pushbutton 5" Receiver, by L. M. ATWATER KENT 61 D.C. satisfactorily with a 500 -ohm and a 500,000 - .... W9SFW This set is D.C. operated and there are ohm unit, respectively. The circuit under Dezettel, discussion is on page 91 of Gernsback 2 line chokes in series with the incoming 59 mc. Amplifier for Amateur F.M. Trans- line. There is also a filter condenser across Manual No. 7. "" mitter, E.E. the chokes. If this condenser shorts, one by Ricardo Muniz, -M or both of the chokes may burn out if the ... RCA CAR RADIO MODEL 67 -I Radio Hook -ups Department house fuse does not burn out first. When Complaint: distortion, Replace the volume this happens the set goes dead. The chokes control with a Mallory -Yaxley No. TM -242

RADIO -CRAFT for JUNE, 1941 717 SERVICING

-An Open Atter o tAQ radio industry JAMES H. HANLY Radio Engineer

is not the intention of the writer to Now because some Servicemen have re- aerial. Right off the bat the Servicemen IT crab, but, here are a few things that fused to take an interest in the installing who installed the set gave F.M. a "black the Radio Industry should straighten out of a good aerial the manufacturers have eye." Anyone hearing it operate in the very soon. now built in loops. That is like going back condition it was would never buy an F.M. Let us first take the set manufacturer to to the "dark ages." receiver. task. Present -day production facilities have When the set is installed in the house, I hate to think what they will do to the made it possible to produce reasonably - 90% of the time, it is placed as near the television receivers when we get television priced receivers. However, the manufactur- electric outlet as is possible. What happens? out our way. ers are prone to ruin what could be a per- All that the manufacturers have taught us, Well, this has been sort of a blasting fectly good receiver. about the lead -in coupling with the light against the radio manufacturers and Serv- icemen, Take the oscillator for instance, this is wires in the wall, goes out of the window. but somehow they need it. a very important part of the set. Why The loop picks up noise and even has ac- You may notice that no reference has doesn't some one build a really shielded tual A.C. voltages induced in it to produce been made to the A.C.-D.C. receivers. It oscillator? an A.C. hum. You turn the loop to turn out would take too many pages to cover this The writer is responsible for the clearing the noise and that nearly always turns out scourge of the radio industry. of radio interference for over 53,000 cus- some popular station you might like to lis- Now the amateur comes in for his share. tomers covering an area of over 130 square ten to. It costs about $1 to make up a good key - miles. What is the matter with the manufactur- click filter, but some of the boys go merrily In riding around, all day, hundreds of ers anyway? on clicking the neighbors' receivers to radio sets can be heard that are radiating Well! Even if the manufacturer turned pieces. On the whole they will cooperate waves caused by the oscillators. In our area out the ideal receiver some Serviceman 100%. the BCL (broadcast listener -Ed.) frequen- would hook the antenna post of the set to By this time you will think that your cies are (pre-reallocation -Ed.) 630 kc., a water pipe or steam radiator and let it writer is a crab of the first water, but 780 kc., 890 kc., and 1,430 kc. Quite fre- go at that. honestly, aren't the things enumerated quently a complaint is received stating that The antenna situation is a disgrace to true? a noise is heard on one particular frequency. the radio industry. Joints are not soldered, All of the important professions have Investigation will reveal something like and no thought is put into the installation. been cleaned up, why not the Radio In- dustry, one of our most this: Mr. A likes to listen to a station on The writer has found perfectly good an- important, too? 1,230 kc. but cannot do so when Mr. B is The Federal Communications Commission tennas hung in partial dead spots when a keeps the weather listening on 780 kc. This adds up to one little effort, and a different location, would eye out for infringe- thing, 1,230 less 780 equals 450. We find ments made by the amateur and the Com- bring in excellent reception. Also there are mercial that Mr. B's receiver has 450 -kc. intermedi- hundreds of sets installed without grounds. Stations. It is about time that they ates in it. This is a deplorable or some one else reached out a little farther condition to has have exist anywhere. And there is no need It always been my belief that the and did something to control the conditions of it. antenna and ground posts on a set were put of Receivers and Servicing. Then again the manufacturer takes what there to use, not for a decoration. They are Radio Amateurs have so policed their could be a perfectly good receiver and meant to be used, they are necessary for bands that very few deliberate infringe- doesn't put in any R.F. stages ahead of the the proper operation of the set. ments are prevalent. 1st- detector. Now the set is subject to Throughout the country there are a great The commercial stations work under very images of every description. Local stations many Servicemen who really know their strict regulation but a good many of them are heard in 4 or more places on the dial, stuff and do a mighty fine job on radio in- radiate a 2nd -harmonic that can be heard or the other 2 stations can be heard in the stallations. But the whole industry gets a many miles away. One station locally puts background of the one you are listening to. black eye because of the careless ones. an R9 2nd -harmonic in the 1.75 mc. band used Radio amateurs are cussed and reported to Radio Servicemen should be licensed by by the amateurs! The amateur is severe- official Washington just because the set can- the State or Federal Government so that ly criticized and put on the carpet when he not tune them out. All it takes to clean up the industry could be cleaned up. has a 2nd -harmonic, so why should a BCL a condition of this sort is shielding, and 1 Recently a nice new F.M.-A.M. combina- station be allowed to radiate on a frequency or more stages of R.F. in the set. tion was installed in our area. Your writer not assigned to it! Mr. and Mrs. Average Radio Purchaser was called in to see why the Frequency Well, your writer's neck has been stuck are not afraid to spend an extra $5 to pro- Modulation station 20 miles away was out far enough now, however it may bring duce reception. They only buy cheap when noisy. First of all the Servicemen had out some discussions that will do the Radio it is put in front of them. thrown a piece of wire on the floor for an Industry some good.

FROM THE F.C.C. MAILBAG Individually disgruntled radio fans still A Connecticut man feels that he has been Banner" obligatory on radio programs. deluge the Federal Communications Com- personally stung by "The Green Hornet" To a Detroit man who registers complaint mission with their particular complaint series. about an express company the Commission about this or that radio program. Few well - A Pennsylvania man would like to have points out that authority is confined to com- known programs -or artists- escape men- "Confidentially Yours" publicly censured. munication by means of electrical energy, tion at one time or another in such letters. The numerous contest programs invite hence it can take no action. As constantly reiterated, the Commission numerous letters to the Commission from By the same token, it cannot help a wife has no authority to censor individual pro- listeners who think they are also entitled to get her husband reinstated as an announcer grams or performers. Some idea of the typo prizes. at a particular radio station. Or make a of squawks in which the Commission lacks A letter from California complains of radio station award a prize to a woman jurisdiction may be gleaned from recent American stations rebroadcasting Hitler's who claims to be entitled to one by reason "pan" mail: speeches; a New Yorker objects to pro - of a program offer. Or require a radio sta- Various letters object to the air utter- British utterances on American stations. tion to supply an advance copy of a sched- ances by Col. Charles A. Lindbergh, Han- A New Yorker wants the Commission to uled address to anyone who might ask for it. ford McNider, Frank Gannett, Judge John require a certain official to retract a state- Nor can the Commission adopt sugges- A. Matthews, Earl Browder, and others. ment he made on the air. This is beyond the tions that fees be collected for issuing radio A New Yorker wants the radio team of power of the Commission. licenses, or for the use of radio receivers. To Burns and Allen barred from the air be- Another New Yorker is advised that there do either would require Congressional enact- cause he doesn't find some of their jokes is no statute or regulation making the play- ment of an amendment to the present Com- funny. ing of "America" or the "Star Spangled munications Act.

718 RADIO -CRAFT for JUNE, 1941 THERE IS A DIFFERENCE z 9os* ,0)**.t..11.

Individually =PEAK PERFORMANCE Packed in AMPLIFIERS PUBLIC ADDRESS SYSTEMS Special SOUND PROJECTORS INTER- OFFICE COMMUNI- CATING SYSTEMS COIN OPERATED REPRODUCERS Containers

i ..perd every In,., l.n .A. Rd,. Jenirw Indo,ry u ou oe,uwd merit. ,rute Ot tY aduCt¿on :, place ..et epr OtJ °Jd'ry4e eLeloL e Jyt ndw\O"On `be ersua,ria /S XAV,OLYnä ta44 VyOn 5" Os mF\e e b0 ° m 1oJb CO ,ßp` ò6 V o veL Ledc^SOUN - Na\ion°ae NON -MICROPHONIC P de in \O ét hte W''h0J p * c is t JLnbec ddtese ánd \On9 üND °s ataciesitióees 1n - __ * LOW -HUM LEVEL aed SOU p°LiOLm6^ce a\ Un'ptySTPPÓn oeen pFM mance e es°ep. UNIFORM CHARAC- ppCtie\s. e\ imp ck. N°ii0n al * s Wi1\ 9 ea lotloc beq peLlosd detói\ aJCC°ppG^Le N TERISTICS - Qame te4°ueQi theyaJLSI°^d'cion hi9ha^d\in9a ioate aecY * NO MATCHING m NECESSARY d YdOy wheLebeb° e 0t8 1lpml * LONG LIFE AT FULL odriesihooîn h m n!n Jb OUTPUT sect to -J_s we 99ei m0 L ia mn noL. c\Ya¢ oO\ s apeCc \

NATIONAL UNION RA 0 57 STATE STREET, NEWARK, N. J.

RADIO -CRAFT for JUNE, 1941 719 SERVICING

SELLING RADIO SERVICE

At the suggestion of RADIO-CRAF T, author Moody has selected some of the questions most frequently asked of Servicemen by the owners of radio sets in need of repair. The experienced radio Serviceman; is not stumped by such questions, his answers frequently following somewhat the patterns of the answers presented here.

WILLARD MOODY

BECAUSE the newcomer to the radio servicing field may avoid certain pre- ventable difficulties, through advice given by some one who has been "through the mill," this article attempts to impart such information as may be deemed useful and essential. To this end, questions that are typical of those likely to be asked, and the answers to those questions are here Maybe the customer talks to you over your counter presented. The first Q. and A. follows the or maybe he questions average pattern of a telephone conversation. you face to face at home. Q. What do you charge to look at a radio? In either case, do you know the answer? Experi- A. If the set is brought to the shop, there enced radio men do. is no charge for inspection and an estimate. If we go Photo - Courtesy John J. to your home there is a charge for Harnett, Proprietor, Edison inspection, not necessarily repair of $1.00. Electric Shop, New York We would advise you, however, in order to City. save yourself the cost of an inspection, that you bring the chassis and speaker in to us, which will cost you nothing for our estimate. In addition, we can give it a better check in the shop, since we have all of the necessary test equipment here. The above answer may not agree with the policies or ideas of some Servicemen who proceed on the notion that "hooking" the customer good is a worthwhile idea. Some hard though, in many cases, to convince a Serviceman: Do you notice have that the noise fancy ideas of reaping rich rewards customer that he should not buy the na- is on one station, or is it on all of in radio the sta- by overcharging, while others, it tionally- advertised brand at a cut price. But tions? What kind of an aerial have you is equally true, do not charge enough. How- you still have a trump card, one which goes got connected to the set? Have you had ever that may be, the above method of op- over big-give a 6 months' guarantee with your tubes tested lately? has several your Does the noise eration points in its favor. brand of tube. The nationally- adver- seem worse as you turn the volume con- First, the idea of no charge for inspection tised make is only guaranteed for 90 days, trol? Is it a steady humming sound and is and or a estimate. This an inducement to bring you, therefore, are going them one bet - hiss? Do you notice it particularly at night, the set into your shop. If it once gets there, ter-so that you can either get more money, or just in the daytime? Do you live near an it is likely you will or at that get the job, if for least sell your brand. El, a trolley line or a subway? Where do no other reason than that the customer is Concerning receivers, the Serviceman or you live? (General location.) Have not small you an going to lug it around unless absolutely dealer is at a distinct disadvantage, elevator in the house, a refrigerator? Is it necessary. due to limited purchasing power and low a series of heavy clicks or thumps that Secondly, the charge of $1.00 for inspec- margin of profit. It is necessary for him to bother you when listening charge to the radio? Is tion in the home will, in most cases, at least full price, especially on table models there a doctor or a dentist in your house? cover the cost of your making the call. This under $30. Your argument there is one of What current do you have (D.C. or A.C.) ? charge is a further incentive to bringing service -give a year's guarantee, exclusive After securing a clue to the interference the set back to the shop, and the customer of parts or tubes. problem -the solution to which may consist is quite likely to want to save that hard Q. What is the matter with this set? I of re- alignment of the chassis, a noise -re- earned dollar since the dollar outside service had it repaired by you, only a short time ducing antenna installation or an installa- charge is credit on the shop bill. At any rate, ago, and now it's worse than it ever was. tion of a line filter either on the radio set if the set is not repaired, due to too high an A. I see. (Politely) Have you a receipt or the offending device, whether refrigera- estimate or other reasons, you at least have showing when the set was repaired? No? tor, motor or other interference source -a the right to collect that dollar -but be sure Well, we'll check it over and let you know definite course of action may be charted. to make a fuss over the radio receiver, while when it's ready. Typical questions which then follow: you are checking it, and repair any minor The customer leaves, and you have said Q. What will an antenna cost? defects, such as a loose plug, loose antenna that you will send him a card, letting him A. (If in your section.) A noise -reducing wire or similar receiver troubles. know when to call for the set. You look up antenna installation will cost you $6.50: an- Q. Is that my price? (Tube, or receiver your repair tag or other record and find tenna $3.50, labor $3. sale.) out what was done and what is wrong now. This figure may be varied to suit the cir- A. That is the list price, but we will give If it is a matter of a tube, or some part, cumstances and will be changed according you a discount (10%, 20% or whatever you that you did not repair previously, and the to the amount of time that it will be neces- can afford to do regarding the price). set was repaired a month or two ago, see sary to spend in getting to the customer's It is wise to give some reduction off the whether you made enough on the previous home and doing the necessary work. list, in some communities, since customers job to allow you a little leeway in the matter If a private home, where you have to may see the same tube that you are selling of satisfying the customer. If possible, re- drill through the floor of the living room for 90c being sold by a large radio outfit for pair the set no charge. You may be able to and route wires through the cellar and gen- 45e. Usually, you will be more conveniently get it back either through future sales or erally work hard, then charge $10. If in a located, and the customer will save at least future repair work and recommendation to hotel, with a drop of 15 or 20 stories, with on carfare or postage that would be re- the friends of the customer. the hazard of falling off the darn roof 200 quired to buy the tube from a more or less Q. My radio is very noisy. What would feet above the ground, a little more. When distant cut -price house. Price protection ex- you recommend? the set is more than 10 stories above ground, ists in some tube brands sold to the Service- A. What kind of a radio do you have? in a metropolitan community where signal man, and in that case, you can say your Customer: A- strength is high, usually a short wire tube is a better tube that cannot be bought Q. (By serviceman) How old is it? dropped out of the window will suffice-pro- anywhere else for less money. It is very Customer: Oh, it's about 2 years old. vided a good line noise filter is used on the 720 RADIO -CRAFT for JUNE, 1941 SERVICING radio receiver, or when the set is equipped with an electrostatically -shielded loop. The plain loops will pick up too much noise. Q. Will you guarantee to take out the noise, and will I get my money back if it is still there? A. We guarantee that the set will play better, with less noise, but we cannot refund your money. We guarantee to do a good, workmanlike job, and say that in many cases a big improvement results. Q. What do you charge for getting the noise out of my radio when the refrigerator is running? A. Is the refrigerator working satisfactorily otherwise? Customer: No, it doesn't seem to start quickly, nor work right. Serviceman: My advice to you is to have FACT I, It takes a long time to it repaired. Then you will probably have build a really GOOD test in- no radio interference. When the refrigera- strument-to get the "bugs" tor is working properly, no sparking brushes out -to prove, and improve, its on the motor, then you don't get radio interference. performance and reliability. Q. There is a funny -looking antenna on Then -when it's REALLY good -and rheÿ ÌI my roof and sometimes I get a series of -why change ?. thumping sounds in my radio, so that I be jus§- os good have to turn it off. What can that be? FACT 2. Today's SUPREME In- next A. It would seem that you have a radio struments are as modern, as ac- year as amateur in your apartment house. My sug- curate, as dependable as this! gestion is that you inquire of the superin- test equipment can be built. tendent of the building. If there is a "ham" I JOE'S operating his transmitter, and you have a RADIO modern set with adequate selectivity, yours FACT 3. That is because SUPREME SERVICE\ is a legitimate complaint. Report the inter- believes in, and practices, a ference to the amateur operator who proba- policy of continuous improvement instead of just "putting a new coat of paint bly will be glad to cooperate. If not, write on an old chassis." a letter to the F.C.C. which will take care of the matter. FACT 4. A new SUPREME model is never announced until progress in radio has Q. This set needs a new condenser. I've developed a definite need for such an instrument. checked it myself and know that is the trouble. What will you charge to fix it? I FACT Ss Therefore, SUPREME will announce NO "new" models at the June radio used to build radio sets, you know (Or, I show. Which proves that SUPREME Engineers know their business they am an electrical engineer, or mechanical -that engineer- anything but a Serviceman.) and, know, and are guided by. YOUR requirements. although I know what is the matter with FACT 5. SUPREME Test Equipment for 1942 will be as it is now, your best buy, it I am bringing it to you to fix. A. (The same as for any other customer.) and "SUPREME BY COMPARISON!" Well, we'll look it over and send you a card Write for SUPREME'S current catalog. If pictures and describes the instru- with the estimate on it, and you can let us know if it is satisfactory to proceed ments your Jobber has in stock NOW -for 1942. Due to present conditions. with the work. Or, we will call you on the prices and prompt delivery guaranteed only until June 1st. telephone. If they insist on waiting for the estimate, and it is a tough job, tell them it simply Still time to get your new SUPREME Book explaining can't be helped, but the set must be left a new servicing procedure that makes an ailing radio for a thorough check -in fairness to them talk to you like a patient talks to hie doctor. Only 35e and yourself. to cover cost of printing and mailing. The representative questions which have been enumerated may have many variations. About the only rule one needs to follow is: SUPREME Instruments Corp.. Depf.RC2, Greenwood, Miss. Be fair not only Gentlemen: I enclose 35c. Please send me your new book to the customer but to referred fo above. yourself as well. If you do that you will make out all right. NAME. ADDRESS ADVICE TO SET OWNERS CITY STATE How NOT to Get Good Radio Service 3. -If he tells you the set must be re- cheaper, and believe you me, if he does, it By Serviceman FRED SHUNAMAN paired in the shop, refuse to let it out of will be cheaper! your sight. It is easier to bring the shop to 5.-Get your radio back from the shop the 1. Never bring your set to the shop, the set than to take it to the shop! If it same day! The radioman will probably want even if it is a pee -wee midget. You will must go, make him estimate the price of the to play it for several hours after it is re- provide extra employment for the Service- job before he takes the receiver out of the paired, ostensibly to test it, but really for man by letting him run to and from your house. There may be some defective part his own amusement and to wear out your home. Besides, they might damage the radio which he hasn't found with his portable test tubes so he can sell you new ones. set if they could bring all their instruments apparatus. If he finds it with the shop in- 6. -Never pay on delivery. Tell the man to bear on it. struments after having estimated the job to cone back on Saturday, and pay in two 2. -Stand over the Serviceman while he he will probably replace it free, to save a installments if at all possible. Probably he is working and give him what advice and kick -back in case your set breaks down a overcharged you on the job anyway, and encouragement you can. You know more week after he has repaired it. this is your chance to make him earn his about the set than he does-you've had it 4.- Whatever estimate he gives you, money. longer! If in spite of your help (!) he seems squawk like Donald Duck! Don't let him And if you have faithfully followed all nervous, soothe him as much as possible. A have the job till he gives you a cut of at the above rules -and I know how many of radio receiver is a delicate piece of appar- least 25 %. Ten to one he was planning to you do!: atus and needs care, precision and concen- use unnecessarily high- priced repair parts Rule 7. -NEVER CALL THE SAME tration. See that his attention doesn't anyway -so he wouldn't be troubled by a SERVICEMAN A SECOND TIME!! He wander! kick -back on his guarantee. He can do it might take revenge for the first job!

RADIO -CRAFT for JUNE, I941 721 SERVICING

Radio Service Data Sheet 308 MONTGOMERY WARD AIRLINE MODEL 04BR -1105A 11 -Tube Superhet. A.C. Operation; 5 Bands (540 -1,600 kc., 5.9 -6.1 mc., 9.1 -10 mc., 11.4 -12.1 mc., and 14.9 -15.4 mc.); Pushbutton Tun- ing; Bass and Treble Tone Controls; Phono Jack; Automatic Volume Control; Permeability Tuning; Power Output 10 watts undistorted; Power Consumption 120 watts; Push -pull Output; Phase Inversion. (See Data Sheet 309 for additional information.)

M.1 V'cro1304-1304-Ort rr rvrtúCON/R04. . r-e- 1

%tD pit R ` T' s ' 6V6GT 7 LS LW 6507 6507 ® ® 6J SGT 1cÑ o® e 6SK7 6SA7 ` 6SK7 11 6V6GT . . z o v :-itl 5x30 6SK7 H `r* CDO C: r TOP VIEW

I;I I I

Ti2 713 zii T7 T2 13 c. s..<. qwc. osc osc. I iu r- I o-{ i 6' intgling aoyE OR

STOP li I

ALIGNING INSTRUCTIONS

IRON CORE ADJUSTMENT VIEW

6V6GT BOTTOM VIEW OF CHASSIS vos...nu )7 slr,IC, 3/3331' Tr. ..e c :ii `Oit nà U 6507 6507 Y.; --Q O w c.,..c ec . . co n, vOLTO.TC, s0 a9 r>d r0333 30.1 6 -11-4 oe W so w.n .0 e,vs (18° y 7 es 6J5GT Y 7 UO J ,ur(O1.ArACT o rw 6SA7 6SK7 Ito 300 o -Y so COCCI. 0 Pl f-] n 0 o - ,,,íu-r', 6V6GT 6SK7 o CO O iAie ,00

13.3 AC 0 ..T .0 ,.1 IC 300 .113C oafn .t.3 .f1 SPKR. 6 S K7 5Y3G : 4 REAR 0F CHASSIS

R14. 1 RESISTORS 2.000 ohms, 3-W. R28. 5 meas., 1 3-W. CONDENSERS C14. 0.02 -31.. 600 V. C27. .05 x 400 V. RI. 25.000 ohms, I /3 -W. R15. 2.000 ohms. 13 -W. R29. 0.5 mea.. 13 -W. Cl. 0.005 -mf., mica C15. 30 ml. electrolytic 128..05 x 200 V. R2, 25.000 ohms. I 3 -W. R16, I meaohm, 1 3 -W. 030. 0.5 mea.. 13- W. C2. 0.002 -mf., 600 V. C16. B.C. Ose. trimmer C79..0001 mica R3, I mea., I 3 R17. 0.5 -W. mea.. 1,3 -W. R31, 0.5 mea.. 1 3-W. C3. B.C. trimmer CI7, 30 mf. electrolytic C30. .0001 mica R4. 250 ohms. I 3-W. R18. 0.5 mea., I 3 -W. 032. 0.5 mea.. 1'3 -W. C4. 9 me. trimmer x 450 w.v. C31, .1 x 200 V. R5. 2 5.000 ohms. 13- W. RI9. 0.5 mea., watts R33, 0.5 mea.. 1 3-W. C5. 500 mmf., mica C18. .0002 silver mica C32. .006 o 600 V R6. I meg.. 1.3 -W. R20. 0.5 meg.. I 3 -W. R34, 0.5 mea., 1.3 -W. C6, 0.1 -mf., 200 V., tubular C19, .00005 mica C33. .00025 mica R7. 25.000 ohms. I 3.W. R2I, 50,000 ohms. l'3 -W. R35, 0.5 mea.. l'3 -W. C7. 10 mmf.. mica C20, 9 me trimmer C34. .1 x 400 V. R8. 6.000 ohms, 2 watts R22. 0.5 -mea., 1 3-W. R36, 75.000 ohms. 1,3 -W. C8. 9 me. R.F. trimmer C21, 10 mf. electrotype C35. .05 x 400 V. 09, 10.000 ohms, 2 watts 023. 0.5 mea. O 37. 0.5 mea., I /3 -W. C9, B.C. R.F. trimmer C22. 16 ml. x 530 w.v. C36. .008 x 600 V. RIO. 1 R24. megohm 0.5 mea.. l'3 -W. O 38, 2 meas.. 1 /3 -W. CIO, 0.1 -mf., 000 V. C23. .015 o 600 V. C37. .00005 mica 01 1, 1.100 ohms, I 3-W. R25, 50.000 ohms, 1 '3 -W. CII. 0.1 -mf., 400 V. C24, .015 x 600 V. C38. .000125 mica R12. 10.000 ohms. 13- W. R26. 5.000 ohms. 1 3-W. C12, 0.02 -mf., 600 V. C25, .I x 000 V. C39, .003 x 600 V. 013, 1.500 ohms. I /3 -W. R27, 50000 ohms, I /3 -W. C13. 500 mmL, mica C26, .1 x 200 V.

722 RADIO -CRAFT for JUNE, 1941 SERVICING

309 Radio Service Data Sheet

MONTGOMERY WARD AIRLINE MODEL 04BR -1105A

I I -Tube Superhet.; A.C. Operation; 5 Bands (540 -1,600 kc., 5.9 -6.1 mc., 9.1 -10 mc., 11.4 -12.1 mc., and 14.9 -15.4 mc.); Pushbutton Tun- ing; Bass and Treble Tone Controls; Phono Jack; Automatic Volume Control; Permeability Tuning; Power Output 10 watts undistorted; Power Consumption 120 watts; Push -pull Output; Phase Inversion. (See Data Sheet 308 for schematic diagram.) SETTING PUSHBUTTONS Make a list of your 6 favorite stations. 12 MC Isocc. ec, ILM.c. 15M.c RM.c. ewe. Push out the call letters of these sta- p5,. P.C. RiF. S.F. ANT. ANT. tions from the call letter sheets supplied. COIL\ Insert a call letter in the slot on top of T15i1a1 asT16 j1T9 j1TIO 6 each pushbutton. Í(Á11C9 Next T4 pull one of the pushbuttons all PACO nT6 OCB V°aoxc. 12MC T5 SI the way out as far as it will come (pull, Ó5C with fingers on top and bottom of but- ISKYA.F q.F ANT Os. T1A.i CIS rlTll ÿT7 I"`fiT2 T3 ton). Now tune -in the station you want L*n (ITTs with the tuning knob -tune back and 1175 forth until the station is clear and dis- e.c: osc MM.C. aC.04 -C_RF 91'+1GPS'. 6.0 ANT AN ose.. ANT. tinct. Now push the button hard all the FRONT VIEW CHASSIS way in to lock the station in place (push directly on front of button). Continue setting each pushbutton in the same TRIMMER VIEW way. Pressing the proper button will now tune the station you want. If it does not do so you did not push the button radio receiver are of the band -spread hard enough to lock in place when set - type the alignment procedure is not dif- ting-up the station. ficult. However because each shortwave To change stations simply repeat the scale covers only a small portion of the procedure above. shortwave spectrum you must do the work carefully and your oscillator must SERVICE NOTES be accurate. Voltages taken from different points Do not realign the band -spread scales of circuit to chassis are measured with unless you are positive they are out of volume control at minimum, all tubes adjustment. When adjustment is neces- in their sockets and speaker connected, sary proceed as follows. with a volt -meter having a resistance of First refer to the "Iron -Core Adjust- 1,000 ohms /volt. ment View." Now turn the tuning knob Resistances of coil windings are indi- until the drive bar comes within 1/64- to cated in ohms on the schematic circuit 1 /32 -in. from the stops. (A piece of blot- diagram. ting paper is about the right thickness To check for open bypass condensers and will serve as a gauge.) The clear- shunt each condenser with another con- ance of the bar must be the same at both denser of the same capacity and voltage stops. If far off you can raise one drive rating, which is known to be good, until screw gently and equalize them. Minor the defective unit is located. adjustments may be made with the drive Excessive hum, stuttering, low volume bar adjustments. and a reduction in all D.C. voltages is Next rotate each iron core until the usually caused by a shorted electrolytic fine score marks are even with the edge condenser; open bypass condensers fre- of the coil forms. quently cause oscillation and distorted You are now ready to continue with tone. the trimmer adjustments as shown on the alignment chart.

ALIGNING INSTRUCTIONS The following equipment is required Ward's "Airline" model 04BR -I105A 5 -band con- CAUTION: No aligning adjustments for aligning: An allwave signal genera- sole receiver. should be attempted without first thor- tor which will provide an accurately cali- oughly checking over all other possible brated signal at the test frequencies as listed. causes of trouble, such as poor installa- Output indicating meter. Non- dio chassis to ground post of signal gen- tions, open or grounded antenna sys- metallic screwdriver. Dummy antennas erator with a short, heavy lead. Connect -mf., 40 tems, low line voltage, defective tubes, -0.1 200 mmf., and ohms. dummy antenna value in series with condensers and resistors. In order to generator output lead. Connect output properly align this radio set, the chas- ALIGNMENT CONDITIONS meter across primary of output trans- sis should be removed from the cabinet. Tone control -treble. Volume control former. Allow chassis and signal genera- Although the shortwave bands on this -maximum all adjustments. Connect ra- tor to "heat up" for several minutes. SIGNAL GENERATOR BAND Frequency Dummy Connection Position of Dial Pointer Trimmers Adjusted Trimmer Setting Antenna to Radio Set Band Switch Setting in Order Shown Function Adjustment Set Dial 455 k0. 0.1-mf. Grid of 6SK7 (2nd Broadcast 2 Trimmers Output Adjust to .F.) at 1.61)0 Lee. on Top maximum output F. 455 kc. 0.1-mf. Grid of 65K7 (1st LF.) Broadcast Set Rial 3 Trimmers Intorsl age Adjust to at 1.600 ke. on Top 1.F. maximum output Set 455 kc. 0.1 -nit. Grid of 65A7 Broadcast Dial 2 Trimmers Input Adjust to at 1.600 ke. on Top I. F. maximum output 3I -METER (See Trimmer View) C20 Oec. BAND 9.6 mc. 900 ohms Antenna lead 315f. Set Dial (see Trimmer View) ('S R.F. Adjust to at 9.0 me. (See Trimmer on Top) Cl Ant. maximum output 49- M ETE R Net (See Trimmer View) T14 Ose. BAND 6.1 mc. 900 ohms Antenna lead 49M. Dial (See Trimmer View) TS lt. F. Adjust to at 6.1 me. (See Trimmer View) TI Ant. maximum output 25.M EIER (See Trimmer Viewl T15 Ose. BAND 11.9 mc. 400 ohms Antenna lead 25M. Set Dial (See Trimmer Vien) TO Adjust to at 11.8 ft.F. mc. (See Trimmer View) T5 Assi. maximum output Trimmer View) I9 -METER Set Dial (See Tt8 Ose. Adjust to BAND 15.2 mc. 400 ohms Antenna lead 195f. (See Trimmer Viewl TIO R.F. at 15.2 mc. (See Trimmer Viex) T6 Ant. maximum output 1.600 kc. 200 mm!. Antenna lead (See Trimmer Viewl (T8 Ose. Broadcast Set Dial (See Trimmer View) 11.F. Adjust to DROAD- at 1.600 kc. (a maximum output CAST (See Trimmer on Top) Cs Ant. DA ND 1,400 kc. Rotate Core Tll 200 mm!. Antenna lead Broadcast Set Dial Rotate ('ore T2 R.F. Adjust to at 1,400 Ire. (See Iron-Core Adjustment View) Ant. maximum output RADIO -CRAFT for JUNE. I941 n3 SERVICING

ORIENTAL SLANT ON RADIO

The problems of the radio Serviceman in China are perhaps best illustrated in this article which considers the problems confronting the radio man whose job it is to keep the radio receiver of the Shanghailander in good operating condition. Many of the puzzling situations stem from broadcast conditions peculiar to the Orient.

FRED SHUNAMAN Serviceman from Shanghai, China

SHANGHAI, the Baghdad on the murky Whangpoo river, is the strangest and most interesting city in the world. The strangest -if not the most interesting -things about it have to do with radio. To begin with, we have more broadcast stations in this city of less than 5 million people than do most countries. There are roughly 40 stations in Shanghai. Every This illustration shows the Shanghailander has one. Two of the best, author (left); C. C. Chay, XMHA and XMHC, head Serviceman (cen- are American -owned ter); and, benchman and -operated. XMHA has a shortwave out- David Savage. let on 25 meters. The Japanese run 2 stations and the English and Germans have 1 each, happily located at opposite ends of the dial. The French operate a powerful station, and even the local Russians and Portuguese are represented on the air. With the exception of 2 or 3 doubtful "foreign" stations which spend their time broadcasting in Eng- lish or Chinese, with a smattering of propaganda for one or the other of the European belligerents, the rest of the broadcasters are other side of town while a local newspaper's on the way to the studio. If he resists and Chinese. The broadcast band runs from 600 500 -watter is working 5 kilocycles to one remains neutral, both sides are likely to go to 1,400 kilocycles, and from 1,200 up it is an side of him. gunning after him. Some of our most promi- inextricable muddle. The Serviceman spends This confusion had its roots in the begin- nent owners and station managers have al- a large part of his time explaining to cus- ning of broadcasting here in 1930 -'31, when ready been killed. tomers why they cannot hear their favorite a few discarded stations were brought in Even the life of a foreign radio announcer Peiping dramas from a 30 -watt station the from America and put on the air. There is not too dull. The one man to whom every- was "no law for radio in Shanghai." Both one in Shanghai listens -to curse or ap- the Chinese government and the foreign plaud-is said to go about his work in a powers claimed authority over radio in the bullet -proof vest and has 5 bodyguards. He area, and no nation would curb its own na- is Carrol Alcott, the Dakota -born news- tionals for fear of giving the others an ad- caster who 3 times daily comments on the vantage. The number of stations continued political situation and the excellence of to increase, with power, calls and quality Maxwell House. His outspoken adherence to depending only on the owners' whims, means democracy in general and the Chinese cause and technical ability. The climax came when in particular has earned him the combined a popular American cabaret owner went on hatred of the Japanese, Germans, Italians the air with the call (or query) RUOK. and the Chinese "puppets." His name is on After this stroke the foreign governments Wang- Ching -Wei's "honor list" of more agreed to Chinese control of radio in the than 80 undesirables, a number of whom area. Foreigners operating stations at the have been assassinated since its publication. date of agreement were permitted to con- Carrol is bearing up well under the honor, tinue on the air. "X" calls were allotted to and gets considerable comfort out of the all stations, and "RUOK" went off the air fact that he is no longer pestered by life forever! insurance agents. The word "program" is synonymous - with The warring factions go in for malicious phonograph records here. Some of the Chi- interference, or "jamming" of displeasing nese stations use living artists (notably our programs. The Alcott broadcasts were in- "glass broadcasting station" where the per- terrupted for several weeks last spring. A formers are the chief attraction of a res- strong ICW note came on the air when he taurant seating more than a thousand peo- did and stopped when his broadcast was ple), but excepting some ballroom broad- over. About the same time a small mission- casts, practically all the foreign entertain- ary -owned station, XHMD, was jammed ment is recorded. The American and most continuously, nobody seemed to know why. of the Chinese stations depend entirely on The jamming on the Alcott news broadcast advertising for their living. Some of the has started again, and station authorities believe the comes from a Exterior view of Mr. Shunaman's radio shop located foreign stations are partly or wholly sub- interference Japa- on Bubbling Well Road in Shanghai. Divided into sidized and are able to put on better pro- nese warship in the river. Retaliation by 3 parts, Shanghai comprises (I) the French Conces- grams, i.e., buy better records! None of the jamming the 2 local Jap stations is threat- sion, under direct control of the French Consul, (2) a quiet was made the International Settlement, nominally controlled stations spend as large a percentage of ened, and statement to by a Court of the Consuls of the various nationalities their time in actual advertising as do the the effect that the local station has enough makingkig up (but usually referred to American broadcasters. power to interfere seriously with shortwave as "English its population), and (3) the "Chinese area ", in Japan itself. now largely a mass of ruins. There are subdivisions: The problem of revenue is not the only broadcasters Hongkew, nominally part of the International Set- one worrying the Chinese station owner. Probably 80 per cent of the receivers in tlement but now called "little Tokyo ", and run by Jap and Chinese forces are in a struggle for use here are American. The others are most- the Japanese army; and the famous "badlands" ly English, German and Dutch (Philips). a district formerly in dispute by the Settlement and control of all means of propaganda in this Chinese government but now "controlled" chiefly by international settlement, and he is ap- There is also a Jap regenerative -detector organized gangsters, toughs and the gendarmerie, proached by the opposing sides, asked to co- 2 -stage audio on the low -price market. This and devoted fo gambling and opium-smoking, with of old murder and other equally Innocent amusements on operate-or else! If" he falls in with one set, an A.C. version the supersqueal- the side. party, agents of the other will shoot him odyne we used in 1923, is capable of receiv- 724 RADIO -CRAFT for JUNE, 1941 SERVICING

Ing most of the Shanghai stations simultaneously, but is not now available. War conditions in Japan have apparently stopped manufacture of most radio parts, and Japa- nese stores here are forced to sell mostly Chinese and American stuff. FISHING'S GOOD AT NORTH ADAMS The ancient trade -guild methods of Euro- pean companies explain the great success of American radios. I once sent to the local branches of the leading British and Ameri- bbl ` , twiikevito can radio firms-Marconi and RCA -for information on transmitting tubes. The Amer- ican concern loaded a chit -boy with a copy ... but we're not doing of every piece of literature they had and sent him over the next afternoon. The Brit- much of it this year ish firm hasn't answered my letter -yet. Thousands of Chinese studying radio went Sure, we like to fish -but these for information where they could get it- are times when fishing must take e to the American publications and American back seat. With one big Sprague companies. They became familiar with plant working exclusively on na- American apparatus, then took positions in tional defense orders and with the firms throughout China and naturally other turning out more Sprague Condensers, Koolohm Resistors pushed the stuff they understood. The well - known electron bottle is a "tube" here, not and Test Equipment for the radio trade than ever before, we've got a valve, though the elevator is a lift and a man's size we're the streetcar a tram. job to do-and Another factor favoring American re- doing it. Meanwhile, we fake this ceivers is their somewhat greater sensitivity. means of assuring our radio friends Geographical considerations have made it that, while putting national defense necessary to build highly- sensitive short- wholeheartedly first, we are neither wave receivers for America, while the short- forgetting nor neglecting them. er distances in Europe made it possible for the manufacturer to concentrate on the audio end of his receivers, as demanded by SPRAGUE the more critical musical tastes of Euro- PRODUCTS COMPANY pean audiences. Many of the older European North Adams, Mass. sets are useless at the great distances we have to receive, though some of their latest jobs are second to none. t J P.A. is important here. Shanghai has more dance -halls and night -clubs per square foot than any other city in the world, and almost all of them have some kind of public address system. Most singers will not work without a mike. All amplifiers are construct- ATOMS K (Miniature dry EINSU D ' TC PAPER ed locally, the high exchange making it im- Nsetrolytles) O RS TUBULARS FIXED MICA CONDENSERS practical to import them ready -made. Many of the microphones are also made here. The transverse- current-a type of carbon mike SHOW TIME IS HERE AGAIN -is the most popular, but American veloci- The July 1941 issue of Radio-Cm ft will carry a complete review of the Radio Parts National ty mikes are widely used, and I have seen Trade Show which opens this year at the Stevens Hotel in Chicago on June 10th and runs for a one of 4 days. In your own interest, make sure you attend this all- important event. If you miss it. crystal at our best places. however, don't fret; just refer to July Radio -Craft. on the newsstands early June. Since the value of the Chinese dollar has Reserve your July issue of Radio -Craft now. dropped to less than 1 /16th that of the American, a number of locally -built Chi- nese sets have appeared. The circuit is in- variably that of a 5 -tube super. Made in small shops, the quality varies from excellent down to solderless jobs with the under- chassis wiring done with fuse -wire. Loudspeakers, condensers of all kinds, a mediocre volume control and other parts are being made locally, and new items are appearing daily. So far, business conditions have been remarkably good, considering that the city is now an "isolated island" cut off from that interior on which it once depended for its "Every afternoon we get very life. The influx of 2 million people (including most of China's wealthy), the Uncle Charlie's Kiddie war boom and the demand for news, which Hour from the Television Studio next door! " -Re- makes radio a necessity, has offset loss the print from The Merk of the hinterland to some extent. The situa- Report. April 1941, by tion, however, is growing more and more insecure. from outside permission of Mark (( Pressure the makes Co., Inc. life in the foreign settlements daily less worth living, and residents are leaving in a stream. But Shanghai has lived through too many "fatal" situations for us to consider the present one as more than an incident.

WHAT'S NEW IN AUTO -RADIO? R'hat are the n circuit feature, of this year's models which distinguish them from last year's? For complete circuit analyses see JULY RADIO -CRAFT RADIO -CRAFT for JUNE, 941 725 SOUND

455 ABI OP FIG .1 FIG.3 FIG.4 .v PO ros` NEW PARALLEL -FEED AUDIO CIRCUIT The following article will speak for itself and requires no continent front us. It suggests a. new idea, in audio amplifier circuits, designed to achieve increased fidelity. Readers are invited to submit to Radio-Craft the result of their analyses of this "C.-T.-Coupled" circuit.

TED POWELL

AVARIATION of the parallel -feed cir- only a simple variation of the standard added that the uses of the circuit would be cuit which seems to be something new parallel -feed circuit (quite true) and that limited and it would be rather impractical is presented here for whatever it may he failed to see any really practical use from a commercial standpoint because of be worth and is hereby christened the for it. He gave the following criticism of it: the cost factor (as in the case of any paral- "C.-T.-Coupled Circuit" or "C.-T. Coupling." (1) Considerable increase of costs of parts lel -feed circuit). His technicians did not run It is rather difficult to believe that some- any "lab" tests on it because the electron- thing so obvious should over ordinary circuiting. escape the notice (2) The inductance ics industries are swamped with rearma- of radio and sound men but like Orville La of the plate chokes ment would have to be too high to maintain orders and they have much more France's voltage -doubler diode, that seems pressing work to get done. to be the case. good low- frequency response. Only a listening test has The Therefore from these two experts' state- been made of it and it seems to give (3) capacity value of the C.-T. con- slightly denser would have to be prohibitively ments we can deduce the following: While better results than the standard circuit. If Mr. Shaney's criticisms are sound of course, any of high to obtain adequate low- frequency Radio -Craft's readers happen to pos- response. they hold good for any parallel -feed circuit sess cathode -ray and sine -wave audio os- and to some extent to all impedance and cillator (4) Chokes and transformers will pick up equipment perhaps they might hum. transformer circuits. Perhaps the writer's make comparison tests of it and send in original letter was not very clear, but the their findings. (5) Uncontrollable resonance effects might become evident in a circuit involving point in question is not the merits of this series arranged condensers and induc- circuit vs. direct coupling (Loftin- White), CENTER -TAPPED COUPLING tances. but rather the merits of this circuit vs. the While transformer coupling is more or (6) Any form of direct -coupling between standard parallel -feed circuit. less passe today, it still has its uses (single - drivers and power tubes would produce There are times when transformer cou- side to push -pull coupling, modulation, driv- far less distortion. pling must be used. We most certainly would er to class AB2 or B power grid coupling, (7) For good low -frequency response ex- not direct- or even resistance -couple drivers matching such as mike to line or grid, pow- cessive costs would be involved (a gen- to class AB2 or B power grids. The relative- er tube to line or speaker, various other eralization of 1, 2, and 3). ly high grid currents flowing in these grid matching duties, isolation of circuits, etc.). circuits would cause excessive voltage drops The center -tapped or "C.-T." circuit In a telephone conversation with one of in the loading resistors and cause poor grid shown here in various forms may be useful the Kenyon Transformer Co. engineers circuit "regulation" and consequent high in AB2 or B power circuits, some sort of (after a letter was sent to them), the writer distortion. Therefore, we can safely say modulation circuits or any situation where was assured that the general assumptions that while this circuit may be commercially a parallel -feed circuit has its advantages. made by the writer (which follow later) impractical, more or less, it is slightly su- This circuit was sent in to Mr. Shaney were correct and that in the engineer's perior to the standard parallel -feed circuit for comment. He stated that though it was opinion the circuit would perform some- and will have its uses in P.A. work, custom - something new technically speaking, it was what better than the standard circuit. He built amplifiers, experimental work, modula-

DRIVERS C

SMALL BEAM POWER CLASS ABE OR B ROWER TUBES CLASS ABE AMPL /F /ERS FIG 6 726 RADIO -CRAFT for JUNE. 1941 yahleAl Zepoihoffri BOOK YOU THE RADIO your buying ! money-you'll oued uying HERE'SHERE for iv,ur only full-sized to cover- ou want more Catalog -the from cover Y rate led -Page values we when ALLvED S comp with smashing below. If for Iss erofrthe hatcribed for t ALLIEDu"Buys'wdetsmart to send in big values-on Eof the typicalicall Catalog-it's any check some ALLIED you need you this t_re i every time and easier! haven't got need quicker can you what Yyou n you 1 you've vet et Specials now. If dü money-get for the ALLIED quick servian -it will save Y yourour order couponcoup for radio ed in Use the right in the listing use, featured

ONLY ONLY WIRE SPECIAL $196 $595 NO. 14 RUBBER. COVERED STRANDED LEAD -IN POCKETRACER liere's a big value in finest - SIGNAL quallty general -purpose lead - KIT in wire. Vonsists of No. 14 VOLUME CONTROL stranded conductor. GENERATOR gauge 7- These colt sin STATION LOCATOR in - covered with lire rubber brand new. standard type RIM -DRIVE PHONO MOTOR sulatian that strips easily. volume controls in t5anpact instrument For Servicemen. Just in time for Two leads can be twisted to- popular resistances. Set era I types designed for Quick resetting radio set pushbuttons. A A bargain in a -starting phono- -ether for doublet antenna. analysis of el self wire with switrhe are Included. reuit high stability battery-operated graph motor. Fr l et ion rim -iris,' 'l'Iis same quality is sold Ideal for serf Iceman and ex- d out tea. docks on signal generator covering the through idler gives, steady 78 RPM eI sewhere at sub,tantlatq' All assortments mill Genet prin- nigher An outstanding perimenter. standard Broadcast band. Self - Absence of gears provides quirt prices. cardon but popular riple. Generates highly ilirec- bus." 8h08. Ws.: 100 feet, contain contained In 3 x 4 a 5' metal pooh- running operation. Motor salues. INot available In Iioal_Is Ile' and AF signals. lbs.: 250 feet. 6 lbs. llcrm tries what case. 3 %" 0 -100' dial with extra shock- moulted; forced ventilation selected values./ l'ay's for stage of a sures cool operation. 8" felt- ar, N 1099. 100 ft. Call itself at first rob. selve-r is defective. }'scellent large knob. Produces either strong, fns aligning steady turntable. Ideal for building pou Controls Ill" and Ie' lentele' modulated or straight CW SPECIAL AT 24J'-L Assortment of 5 rt Its. llulckb' binds o n phono unit. replacement tff o' tbs.) p signal. No external antenna or di- motors. portable record player. where ignition notre entera rect connection 85917. PER KIT... 89c to set required. Stu: 3' long. 3 %" wide: depth below NI099A. uto sel. R'itlt st-If -contained Complete with tubs, batteries, and Assortment of 10 Controls battery. Size. mounting plate, 3 ". For 110 lts. 60 250 ft. Coil. NET ... 55c .' 316a. $5.95 cycles AC. at 15 watts intent. q;1 16 Ils $1.69 Ib. B10060!uNETit.. Wt., 6 lbs. BI0095. NET T .79 85918. PER KIT B9099.erNET' 1 $1.96

ADJUSTABLE ANGLE COWL AERIAL

A s mJvitill "'my-" un, very latest and finest lope of auto aerial/ New' universal 3- section swing -angle auto antenna Is designed to SPECIAL VALUE Et any car contour. Stainless steel barrel locks to postila r by VIBRATOR BARGAINS 6 TUBE 2BAND KIT FLUORESCENT ADAPTER slight atuustment of one - Piece ye -bolt. Rust -proof Tube , ent Exceptional values in exact duplicate vibra- Kit Value! 6 Now-m, aerial is ttti bug and col- i : tloK tors. Highest quality. Wt., 2 lbs. each. t. ill built-in loop. Push- lighting .'. lapses to 29 ". Single -insu- FOR MOTOROLA SETS illtmn tuning. 2-Band Range! lias requireieu;n .41 111.1. -o oily I d' 'ntis lator fixture screws mount. Shock -proof B4711. 6 -Volt. 4- Prong. Size: 344' a 1t6'. AVC. Tone Control. Slide -Iule Dial. anuraing new liftoresteut lamp bakel ire insulator has ar. 69 cycle At' socket. mold- Ile-places Mallory 001 M. 902 51; Recited 2% Watts output. phono connect into any 105.125 volt. ed rubber gasket and a bulb. You will 5340 M. 5341: Motorola 48A333. 48A333311. etc. Torrs 535-1720 KC; 5.65 -18.3 As easy to install as light shielded lead -in cup. With 2101. MC. Kit is ready for easy assembly. want one for every alight sakcl its your waterptosf 48' law -loss loan Chassis is punched and drilled -all shop. garage. tte. Inside of reflector fin- cable. Slipped complete FOR DELCO SETS ished in white enamel. outside In durable 84e95. 6 -Volt. 4- Prong. Size: 3lí.' a 100. with adapters for 5lotocola a al Phlloo z d scwdrvertobild 6%PMPl brown wrinkle. lias patented s tie! fea- Replaces Mallory 294; 50 -40000; Chos - reiolru.r sets. One of the best auto aerial value Delo, Speaker. For 110 colts. AC -DC. ture. Ideal for service shops. work benches. we've e - r been rolet 1212966. lines. etc. Uses one able to offer! Shag. 'Vt.. 10 lbs. hones. offices. assembly wt.. 2 lbs. FOR PHILCO SETS $5.5 standard IS. 13 -welt fluorescent lamp 1147 13. 6 -V., 4- Prong. Size: 3 %' x 2'. 09820. Complete. less tubes bulb. Less lamp. Sling, t., 4 lbs. and cabinet. NET BI6119. EACH, S1,39 Replaces Mallory 5051'; l'ldlco 41 /fi /fa s 1315012. EACH. ... $2.56 9Z87 3r0. ate, 92rí B9822. Tube Kit. NET 92.30 NET EACH LOTS OF 3. EACH 125 815261. 15 'alt lamp Lots of 6. EACH 90c 89821. Walnut Cabinet NET $2.25 72c LOTS OF 6, EACH r -- MEW -ALLIED -- RADIO CORPORATION. Dept. 2 -F -1 833 W. JACKSON BLVD., CHICAGO, ILL. _ Soul me your FREE 180 -Page 1941 Catalog. Enclosed you will End E , covering my order for the Special Values checked below. Postage is enclosed. Ship C.O.D. for pu.!n, charges. ghee/ Stock No. Description luan tit. 1310060. Station Locator A I 1410095. ALLIED'S 180 PAGE Phono Motor N1099. Lead -in Wire q 135917. Volume Control Kit RADIO CATALOG /AI4( I B9899. Pocketracer f ADI 0 B4711. Motorola Vibrator B Delco Vibrator THE ONLY c I 84713. Philco Vibrator COMPLETE BOOK _s1 ID 89820. 6 Tube Kit 4a' 815012. Fluorescent Adapter FOR 1941 1115261. i6 W. Fluorescent Lamp 1316119. Auto Aerial I Name ALLIED RADI 0 CORP. 833 W. JACKSON BLVD. CHICAGO, ILL. IAddress - - - =MI ------J RADIO -CRAFT for JUNE, 1941 727 SOUND

tion circuits, as a basis for other "trick" field-storage action typical of any condenser p.-p. circuits, and so on. in any other A.C. circuit. In laboratory- and broadcast -type ampli- This explanation is not technically cor- fiers, parallel -feed is sometimes used in a rect or "rigid" as a mathematician would p.-p. transformer -coupled circuit to improve say, but it should give a rough idea of this frequency response. Of course, where p.-p. circuit's behavior. Ordinarily, even relative- circuiting is involved, the adverse core -sat- ly simple A.C. circuits cannot be fully ex- uration effects of the D.C. (direct current) plained away with word pictures and vector components of the driver plates do not analyses, and mathematics must be resort- exist to anywhere near the extent that they ed to, especially where electronic circuits do in a single -sided circuit because of the are involved. When more complicated cir- self- neutralizing action of the oppositely - cuits are involved, even vectors are Made - flowing D.C. components. However, the fre- quate and several types of higher math quency response is improved slightly for using various approximation methods (set- several minor reasons-exact balance be- ting up "equivalent" circuits) are necessary. tween the p.-p. driver plates does not usually exist at all times and some core satura- CIRCUITS tion effects with their adverse effect Oil- pilled upon In diagrams 1 to 6 we have 6 out of 8 low- frequency response (mostly 3rd -har- possible combinations of this c.-t. circuit as monic distortion) are present; leakage re- applied to both plate and grid sides of a MIDGETS .. . actance effects between transformer wind- transformer. ings are decreased with decreased currents Figa. 1, 2. Originally made special to meet the rigid -In diagrams 1 and 2 are specs. In the windings, with consequent improve- shown the simple improvements over the of Government and commercial- communication ment in high- frequency response; etc. buyers, this midget oil- filled condenser now standard parallel -feed networks as applied be- Where transformer coupling is necessary to the plates comes a standard item at a mighty low price. of drivers or plate -to -line and parallel -feed circuiting is used to im- coupling circuits. Ideal for vibrator applications, coupling, low- prove response slightly in a p.-p. transform- power transmitters and transceivers, highpower Impedance loading will result in a better er- coupled circuit, this C.-T.-Coupled Cir- bass, more gain and greater driving power. amplifiers, and for severe- service test equipment. cuit will eliminate one condenser, save chas- Hermetically sealed against moisture and oil leak- The greater the impedance of the chokes, sis space, lower circuit costs, lower intra- the better the low- frequency response, but age. Cadmium -plated brass can. Varnished -paper circuit coupling, will jacket. Center mounting eliminate any slight the higher frequencies will begin to suffer strap for added connec- unbalance effects due to inequality of con- tion. .006 400 because of the greater shunting (distribut- -.5 mfd., and 600 v. D.C.W. .006 -.I denser reactances and leakage conductances, mid. 1000; .25 in v. ed) capacity effects of the more cumbersome to 2000 D.C.W. Ask jobber and finally, will theoretically halve the for them. Ask for latest catalog -or write direct. windings. Therefore a compromise value slight distortion effects introduced by cou- must be arrived at to obtain the best over- pling condensers due to slight inductive all frequency response over the whole audio reactance effects at the highest frequencies, spectrum for any given audio amplifier sys- capacitative reactance at the lowest fre- tem and its local acoustic conditions. quencies and adverse leakage conductance effects. Roughly speaking, at the lower frequencies, if the impedance load drops to with- CORPORATION THEORY in 3 times the plate impedance of the driver, the frequency response will fall off about 1 NEW BEDFORD, MASS. To accurately explain the action of this db., and if it drops to about 3 times the IN CANADA: AEROVOX CANADA Limited Hamilton. Ow. circuit either mathematically or physically plate impedance, the response will fall off is admittedly a bit beyond the writer. How- only % -db. Thus it becomes pretty obvious SENSATIONAL ever, we can reason this way. The power that the higher the plate -load impedance SOUND OFFER factor of a transformer runs at about .7 or the flatter and more extended will be the To acquaint Sound Men Everywhere with .8 lagging. That is, the cosine of the time low- frequency response. However, increas- the unbeatable qualities of LIFETIME angle lag (cosine theta) between the cur- ing capacity effects in larger chokes (and PM. Speaker Units and Trumpets we make rent and voltage waves is .7 to .8 or so. leakage reactance, mutual capacity and in- this STARTLING OFFER - One 4' Trumpet- This makes the time angle lag somewhere List $ 4000 ductance vs. capacity resonance effects in One No.40 PM. Unit List $40.00 about 90 deg. In the case of a 1,000 -cycle One Trumpet Mounting List $1500 -A total the case of transformers in addition to these List of $ 95.00 - the complete Unit for only note, this would amount to a lag of about factors) begin to have noticeable effects $30.00 0.005 -sec. upon the higher frequencies. Generalizing CASH WITH Thus, at the transformer center -tap briefly, the higher the mu (and the plate re- ORDER ("c.-t.") which we vaguely call the "zero sistance or impedance) of an amplifier tube, Send for this point" of the E.M.F., we actually have a the higher must be the compromise value of IMMEDIATELY and get information "mid- point" E.M.F. spot which puts out load impedance to get satisfactory low -fre- on our complete line of Trumpets, Baffles, half Speakers and Microphones -at the total E.M.F. to either side of the quency response. whole is AMERICAS LOWEST PRICES! winding and at any instant just Resistance coupling will result in superior as positive with respect to one side as it is all -round frequency response, especially at THE LIFETIME CORPORATION negative to the other. 'Est ADAMS ST., TOLEDO, OHIO the higher frequencies since a far more Therefore, we have a zero point of polari- "linear" load is placed upon the driver ty, not voltage, since potentials exist be- plates. There are no capacity effects (wind- MAKE BIG MONEYat HOME! tween points and not at any single point. ings distributed capacities, winding to core NEW INVENTION Then if we have unity power factor (as in capacities and also mutual capacities be- the case of resistance networks or tuned tween windings in the case of transformers), opeatee by /blush circuits), we would also have a coincident no capacity vs. inductance resonance effects, teed zero of New. patented invention make. possible point current polarity (and not no non -linear constants such as the non- big earnings AT HOME. Replete auto- amperes). Quite obviously, if current is linear permeability vs. induction character- parts-worn articles in homes, "ores, hotels, mtaamnts.etc.,with durable sparkling w flowing in a circuit, we would not have a istics of core alloys, etc., to worry about. coat of metal -with stroke of brush. Easy.a` quick. Genuine Gold. Silver. Nickel, zero point of current amperes, strictly ium.etc. Everything furnished. Outfit The higher the values of the plate load Cadmle,complete, ready for use. shop speaking, but of current polarity at a c.-t., required. resistors, the further will the low- frequency frton. 1 hour in and this investment starts you in business. current "mid- point" would coin- response be extended, but the "tinnier" Steady repeat. Machine can pay for itself in cide with the E.M.F. mid Send TODAY for FREE SAMPLE -point since the the tone quality will become because of the FREE anweek.d illustrated BOOKLET how you can have voltage and current waves are in -phase in income from a business of YOUR OWN decreasing plate currents, and if the values SAMPLE and uiltblife upon satisfied customer. Act at once! a unity power factor circuit. of the plate resistors BOOKLET WARNER ELECTRIC COMPANY are made excessively 225 N. Wahash Aye.. Chicano. ill. ,Dnt.. 6 -A In the case of the c.-t. coupling circuit in- high, a high- frequency cut -off effect will be- volving chokes and transformers, we would come evident. Again, as in the case of im- FREE! RADOLEK'S also have the two zero polarity points at the pedance loading, the higher the plate re- 1941 RADIO PROFIT GUIDE c.-t., but now they would not be coincident sistance (and the mu) of the drivers, the Everything New In Radio at Bar - because of the 90° lag of the wave. raln Priers! Radio parts-Sets- current higher must be the compromise value of the Accessories-Ham gear - Electric Therefore, the c.-t. condenser, while block- plate loading resistors to get satisfactory appliances and supplies -Public ing off the D.C. components from low- frequency good Address Systems. Iront Walt- the trans- response with over -all Send for the Rig FREE Redolek former primary, "carries over" the plate - response. Profit Guide Now! Save Money at RamL k. current- modulating A.C. signal currents It might be added here that the higher (which RADOLEK CO., Dept. C -55 lag their driving signal modulating the values of either plate loading chokes 601 W. Randolph St.. Chicago. III. E.M.F.s by about 40 °) by the electrostatic- or resistors, the less harmful might be 728 RADIO -CRAFT for JUNE, 1941 SOUND their shunting effects upon the transformer primary as far as the low frequencies are concerned. Fig. 3. -In diagram 3 we have what is probably a circuit of theoretical interest only. Since the principal reason for parallel - feeding at the grid side of the transformer would be the elimination of grid currents from the transformer secondary to reduce leakage reactance effects, we would only be jumping from the frying pan into the fire in the case of class AB2 or B circuits. The relatively high grid currents that flow in these circuits would cause excessively high variable drops in the grid resistors with resulting poor grid circuit "regulation" and consequent high distortion. In the case of class A or AB1 circuits there are no "grid currents" (actually there are minute grid currents of several micro- amperes) and this particular circuit could be used under such conditions. However, the elimination of such minute currents from the transformer secondary should cause no *if 111111M111r, noticeably beneficial results; and the presence of the series condenser across the c.-t. with its slight reactance and leakage-con- Got to be Right to be -',";f1,1:;71 ductance effects should result in slightly in- It's ferior results as compared to the standard Nobody "bosses" Cliff Elliott, chief of the direct coupling to the secondary. Triplett inspection line. Production is up- Fig. 4. -In diagram 4 we have what may 'way up, but nobody puts the heat on "Inspection" for the slightest be a potentially useful commercial applica- variation from the most hardboiled inspection scrutiny in the Industry. tion of the c.-t. coupled circuit. As in the For it is an axiom in the whole Triplett plant -regardless of position case of 3, class A or AB1 application would be to be Triplett." probably be futile. It is AB2 or B work or the pressure of orders -"It's got to right where it may have possibilities. In these Under expanded Industrial demand there continues to be no com- efficient power circuits we have a distortion promise in those rigid Triplett standards which have become the Inter- problem arising from the fact that grid cur- of Precision and Quality. For more information rent flows. national Hallmark One of the principal sources of distortion write Section 166, Harmon Avenue. in a transformer is the leakage reactance between the sets of windings (primary, secondary, tertiary, etc.) which behaves as THE TRIPLETT ELECTRICAL INSTRUMENT COMPANY series inductances and causes mostly ampli- Bluffton, Ohio tude distortion in the form of a high -frequency "cut -off." This adverse effect is greatly increased when grid currents flow All this helps to reduce all 3 types of in the secondary windings. audio distortion at the higher frequencies. In practice, this problem in AB2 and B namely, waveform (harmonic), phase -dis- work is met by the use of suitable step - placement (phase -shift) and mostly amplitude (non -linear amplification) distortion. down transformers with low- impedance sec- A HOTEL ondaries, and consequently lower leakage Here we have another possible solution to new reactance effects, with the primaries and the problem. lower shunt capacities in the secondaries. In By using a parallel -feed circuit such as AWAITS YOU the case of high -class units, balanced, inter- this, we eliminate the grid currents from leaved, sectional windings are used which the secondary windings without sacrificing further reduce the leakage and to some transformer gain or low- frequency response tat', inNewYork extent the capacity effects. by eliminating the need for a low- impedance secondary that would otherwise be neces- This world famous establish- sary. In the case of the grid chokes, there ment, formerly the American is no leakage reactance problem involved since there is only one winding on the Woman's Club, is now one of core. Since grid currents are relatively New York's newest and finest small, the core is comparatively light and hotels. Its unique facilities in- the choke winding can be of high induc- clude six lounges, five sun -decks, tance without having too cumbersome a winding, and too -high shunt capacity effects, music studios, library, art gal- especially if the core is made of' one of the lery and three popular priced super -permeability alloys such as special restaurants. Many floors are treated mu -metal or one of the permalloys reserved exclusively for women. prepared from chemically pure "hydro- genized" iron. 1200 Rooms with Bath This means that at a good compromise value of grid impedance we can have both DAILY- Single, from $2.50; good low- and high- frequency response with Double, from $4 no sacrifice in gain; and generally superior WEEKLY- Single, from $12; results to those obtained from the step - Double, from $16 down input transformer commonly used Special Floors and Rates for Students here. However, the writer is no sound en- John Paul Stack gineer and his assumptions may be incor- General Manager rect. Perhaps some of our technician -readers can enlighten us on these points. Fig. 5. -In diagram 5 we have what would be more of a theoretical circuit than any practical set -up because of the excessive costs involved -unless, of course, the cir- -C -T COUAC /NG'R5 RRAL/EO TO RS//vGLE- cuit constructor has a plentiful supply of 5/0EO LJR/VER /N .4 chokes on hand. HOTEL ORRRLLEL-FEEO C/RCV/T 353 WEST 67tL STREET* NEW YORK Fig. 8. -In the circuit in diagram 6 we

RADIO -CRAFT for JUNE, 1941 729 SOUND

have a limited use in the case of small class would have no place to go. There is no D.C. AB2 beam -power tubes where not much potential gradient across the primary or SERVICE ENGINEERS driving power would be required. In such a any part of it, and it exists only between Here's the meter case, better fidelity would be obtained than it and the "ground" or the chassis. Since that possible with plate chokes. there is no circuit between these points, no you've been waiting for! We still have the possibility of resistor- D.C. can flow in the primary. The A.C. sig- resistor, and choke -resistor combinations. nal modulation components of the tubes' These would probably be impractical for outputs will flow back and forth through reasons explained for circuit 3. the primary since it is shunted across the In all of these circuits, a value of 0.5 -mf. tube plates. Thus we eliminate the 3 detri- is shown as the recommended capacity value mental effects of the condenser. However, for the c.-t. coupler. This is a compromise we have leakage, dielectric stress and APPLIANCE value and it can vary over a fairly wide the presence of relatively high D.C. poten- range without greatly affecting frequency tials in the transformer windings to con- TESTER response. If we use too -low a value, the sider now. Though only minor factors, we increased capacitative reactance of the might conclude that the c.-t. condenser rep- Model 417 smaller condenser will cause a slight bass resents the lesser set of evils. This d.s.f. for cut -off. If Nye use -too large a value, the circuit can be used by Servicemen in the increased value of the slight inductive re- makeshift, temporary or emergency repair AC and DC actance of the cumbersome condenser will of class AB2 or B driver circuits. Measures Volts- Amperes-Watts cause a slight amount of distortion and cut- Fig. 8. -In Fig. 8 we see the C.-T.- quickly and accurately off effects at the highest audio frequencies, Coupled Circuit as applied to a single -sided Nose you can test every household electrical appliance. and harmful leakage conductance effects driver. Thus we now have 3 possible loca- electie signs, and Industrial equipment up to 6000 nail.. will be present, although the low- frequency tions for the blocking condenser as well as LOOK AT THESE USEFUL RANGES! range will be extended slightly. Some ca- for the primary "return" lead. In the case .\II Inca :ill rmefls of At and DC oli I rashly read scales pacity from 0.1- to 1.0 -mf. should be chosen, of the condenser -at the P side of the pri- VOLTS-0 250 preferably near to 0.25 -mf., depending to mary, at the "B +" side or across the c.-t.; amPERE5-0 1 5 25 WATTS-0 30 120 600 3000. at 120 V some extent upon the impedances and fre- anti, in the case of the primary return lead O 60 200 13006000. at 240V quency characteristics of the circuits being -to ground, direct to the cathode or to the MODEL 417 NET $10.75 coupled. Whatever value is finally chosen same "B +" spot as the plate load resistor In portable. hinged rover carrying ease .. .. 511.95 Iuriuslied with la,nerfaclor classification chart and after careful tests, a high- voltage "non - or choke. .,onction curves for power- factor and line voltage. inductive" tubular condenser is recommend- Generally speaking, the preferable circuit ed in order to keep harmful leakage and is the one where the blocking condenser is Order from your distributor high- frequency inductive effects clown to a on the "B +" side of the primary and the TODAY OepenÓable 'V . .'4 minimum. return lead is run direct to the cathode. In instruments A factor entering into consideration here the case of the c.-t. circuit, the return lead is the mild series -resonance effects occur- is run to the same spot as the plate load in ring between the c.-t. condenser and the order to improve circuit balance. If the re- transformer primary halves. This resonance turn is run to ground or the cathode, only effect is not very serious since the relatively one -half of the primary will carry a D.C. RADIO CITY high ohmic resistance of the primary damp- potential and we will have some electro- PRODUCTS CO., INC. ens -out circuit resonance to such an extent static and leakage unbalancing effects. As that only slight signal E.M.F. rises occur the circuit stands, there is still a D.C. poten- N.Y. 88 PARK PLACE NEW YORK, about the resonant frequency at the lower tial difference between the 2 primary halves end of the audio spectrum. The choice of equal to the plate load drop, but now both LEOTONE an optimum value of capacity, usually about halves carry D.C. potential. No special The House of a Million Parts and million baroain 0.5 -mf., will tend to flatten -out and extend advantages are claimed for this circuit and s Floors and Warehouse of Hrd- To-Oat Parts. We invite inquiries: send an details, or samples. Also the low- frequency end of the circuit's fre- it is presented here as a thought provoker. write for better prices quantities. A FEW OUTSTANDING BUYS quency response curve. These circuits may be rather impractical -De Jur 7 7, we have a further Molded Bake - Fig. -In diagram from a commercial standpoint and perhaps Ilte Winos; extension of the c.-t. idea; it is a theoreti- may not even be anything new. However, in luding' ' 0i which might be called a direct - here in the hope resistors, 3 cal circuit they are presented that 4 -prong - k- shunt -feed or a "d.s.f." circuit. they may find some application in special 8 bd.in ing posts: circuits or serve as the bases for other wired for re- While a D.C. potential will exist in the no flow in it -incc it circuits. n.led amplitters; can be used for 3 -tuba Shortwave primary, D.C. can -ets or ...... 35c ea. _a and 0 Prong Auto condition: used Arch` Lafayette,L'Ihralnr :Zperfectl e. v ,late DMa 7' x 3' x pk': for ...M- ing keys. Bugs, Sounders, etc...... 9e ea. r 2, a.r,'. Filament Transformers; al's' x 2a.a. x 31 1' ...... 39e ea. -RCA Shielded Double -Trim 175 KC. I.F coils; UTILITY RADIO RECEIVER 1st or 2nd 19e ea. -w.E. 2000 Ohm Earphones; Incl. headband and In my Editorial for March, entitled, nor ...... $2.49úñ. sensltivo Galena Crystals; mounted I listed a number of ideas -caper ore s "Utility Radios," E- .-phone Cords; tip -up. or um-lug 19c ca. by which radio sets can be made more use- -Fixed Crystal Detectors, mntd. in attr.,ctiVO Bakelite cases: die. 1pí,' 35e ea. ful than they are today. I also mentioned Power RPM with been -Light for RPM; includes the fact that while there had many ii,, bracket; Ideal for winding or - radio combinations, we had not come polishing rig -up. display stands. lamp 59c ea. across any midget lamp - radio utility re- minimum order 51.00. 20% so far. deposit reo a i red ceivers Just to show that it can be done, I took LEOTONE RADIO CO, a Detrota midget set and combined it with a low- priced lamp, as shown in the illustra- 63 Dey St.. Dept. RC -I. New York. N.Y. Gis tion. This particular lamp, which in quantity costs less than 50e apiece, was chosen, first because of its small size, and second, be- AUDIOGRAPH cause it has a swivel arrangement whereby NE Sound Catalog the lamp can be moved forward and back- the wherever wanted. AUDIOG "APH Sound Systems repre- ward to throw light As the illustration shows, the combination sent the latest in Sound Engineering makes a rather pleasing design, and it and Desig -a complete line plus pre- looks much better in reality than the photo- tested accesso graph would lead you to believe. The lamp, of course, works independently of the radio NEW LOWER ° RICES set and you need not turn on the radio set Outstanding quality and erform- for the lamp, or vice -versa. once at prices that help you \eet any I am convinced that there is an excellent competition. market for sets of this type and if some enterprising manufacturer will get behind WRITE FOR FREE .OPT it, I am sure thousands of them can be sold. JOHN MECK INDU RIES H. GERNSBACK 1313 W. Randolph St., Chicago, Ill.

730 RADIO -CRAFT for JUNE, 1941 SOUND SOUND ENGINEERING Ttaa Poly,: and i Ìdvisoty S'atvice TotRadio-nap Sá6 .ictitats

Conducted by A. C. SHANEY

This department is being conducted for the benefit of RADIO -CRAFT subscribers. AU design, engineering, or theoretical questions relative to P.A. installations, sound equipment, audio amplifier design, etc., will be answered in this section. (Note: when questions refer to circuit diagrams published in past issues of technical literature, the original, -Bias or a copy of the circuit should be supplied in order to facilitate reply.) Fixed Plate V. 360 360 Screen -grid V. 225 270 No. 18 Control -Grid -18 -22.5 Peak A.F. grid -to -grid V. 52 72 .0/MF Zero -sig. plate ma. 78 88 O.I. 57 2`A5 SPNq MEG 57 Max.-sig. plate ma. 142 205 MS I Zero -sig. screen -grid ma. 3.5 5 Max.-sig. screen -grid ma. 11 16 MEG /N Effective load resistance, cur ., plate to plate, ohms 6,000 3,800 Ourpur Peak grid -input power, .006- TRANS milliw. 140 270 MF. Total harmonic distortion, 2 2 .25 % /000 MF 0.5- Max. -sig. power output, watts 31 47 ONMS MEG Inserting bias resistors in the cathodes of the 6SJ7s will not increase 25 the gain of the 50.000 V input stages. In fact, it will probably reduce ONMS MEG. 500 the gain between 1 db. and 3 db., depending oNMs upon the cathode resistor used. If bias for the input stages is desired (and it may be C/RCU/r 00E5 MOT BMP 1 //5V necessary if the input signal voltage is WORK PROPERLY. áq high), use a 3,000 -ohm in SEE reir FORREPSONS Ñ¿ resistor each / cathode circuit, bypassed with a 10 -mf. or CA, 20 -mf. condenser. FIG z You may replace the lower 6SC7 tube with a single 6SF5. The common 2,000 -ohm FIXED -BIAS 6L6 AMPLIFIER bias ? What screen -grid voltage and current cathode resistor should be increased in value would have to be applied? to 2,700 ohms, and the common 6SC7 10,000 - The Question .. , Can a 500 -ohm line be of any length? ohm plate -load resistor should be increased to 15,000 ohms. In regard to the amplifier shown as Fig. 1 Is the kind of wire important? in Radio -Craft for March, 1940, page 531 A 500 -ohm line can be of any reasonable LEROY W. (shown below, Fig. 1- Editor), could I use JOHNE, length, provided its D.C. resistance is not the same diagram but in place of 25 -W. out- Ideal Radio Service, too high and its shunt capacity is not too put, get 34 watts by using 25 volts fixed - Sheboygan, Wis. great. bias on the 6L6s? For a complete discussion of this phase I understand that I would have to use of the subject, refer to "A.F. Amplifier appropriate transformers, etc., but would The Answer .. . Load -Matching Technique," which appeared I have to change the rest of the schematic? In order to obtain 34 watts with mini- in the March, 1940 issue of Radio-Craft (see Although no bias resistors or condensers mum distortion, the driver circuit of the page 539). are used on the input stage of the ampli- amplifier would have to be changed so that it could deliver at least 140 milliwatts of nrlver stage should be capable of supplying the grids fier, wouldn't these resistors increase the of the class AB2 stage with the speckled peak velues at gain? Please advise. What size resistors? power to the control -grids of the fixed -bias low distortion. The effective resistance. per grid circuit. push -pull output stage. of the class AIt2 stage should be kept below 500 ohms What tube can I use to replace one of the and the effective Impedance at the highest desired re- 6SC7a so that I will have only two micro- For your convenience, I am giving com- sponse frequency should not exceed 700 ohms. one phono on with zero -impedance driver and perfect regulation, phone inputs and input? What plete data the latest publbhed rating plate -circuit distortion does not exceed 2%. In practice. plate current would two 6L6s draw at the 34- for 6L6s operating in either the 31- or 47- plate -voltage regulation. screen -grid voltage regulation. and control -grid -bias regulation should be not greater watt output level with -25 V. cathode fixed- watt condition (values are for 2 tubes): than 5.0. 5% and 3%. respectively.

ro3 tre

aw. a..a x3OV.pL

i ewe esa Cat ,,:

PILOT <.1 at:Q+) ISO i

ro»aial óo+war.: I SO) hara r0 e,atr-t:cö Çú.a3 ÌOV. '-'43411 G RADIO -CRAFT for JUNE. 1941 731 Order your copy NOW-the only

P. A. HANDBOOK A Resume of the Contents of the AMPLIFIER HANDBOOK AND PUBLIC ADDRESS GUIDE FOREWORD INTRODUCTION Definitions -decibels, frequency, input, output, impedance, etc. SECTION I- SOURCE Carbon microphones (single- button and double- button) Condenser microphones Velocity (ribbon) microphones Dynamic microphones Crystal microphones (sound -cell types, crystal diaphragm types) Cardioid microphones Contact microphones Phonograph pickups (magnetic types, crystal types) SECTION II- AMPLIFIERS Voltage Amplification Design of resistance- coupled voltage amplifiers Commercial voltage amplifier The Power Stage Class A amplifiers Class AB amplifiers Class AB1 amplifiers Class AB,. amplifiers Class B amplifiers When to apply class A, AB, and B amplification Power Supplies Half -wave rectification Full -wave rectification Voltage doublers Filter Circuits Power supply regulation, etc. Practical Hints on Amplifier Con- struction ONLY Microphonism Placement of components Tone compensation Inverse feedback Remote control methods SECTION III -DISTRIBUTION The Loudspeaker Dynamic speakers Speaker performance (frequency response, efficiency) 25 High -fidelity speakers Speaker Baffles and Housings CENTS Outdoor speaker installations MOST COMPLETE Power cone speakers A COPY Radial (360° distribution) speaker AND AUTHENTIC baffles SECTION IV- COORDINATION P.A. BOOK PUBLISHED Input impedance matching no book has yet been published which covers A MATCHLESS VOLUME T AT and Matching speakers to P.A. installa- As complete as would expect to find any engineer- tems,.l in1P one authentic vlolume °la almost you man tions unbelievable. Vet. Mg hamnxnk -this is how the radio r P. A. which It Is a fart. there is no book in finds the AMPLIFIER ANDB00K AND PUELIm AD. Prtnl covers Public Address from A to Z. essential technical data compiled Phasing speakers To bridge this gap. RADIO.CRArr ill GUIDE. With publish a complete. magnificent volume Public neallly large Effect of mismatching speakers to Address such on volume vers different subjects magnitude-en complete and uthorita branch r subdivision amplifier output tive -Nat every engaged In radio n have both coordinating conceivable theoretical andd practteal knowledge of the function cf d Address.even, A typical P.A. installation (in a and sound systems. The editorial pages THE CONTENTS are so filled with °Instruction and replete with TO actually show the scope and magnitude of the skating rink) ustrations that the volume fully ADDRESS Of justifies its title AMPLIFIER HANDBOOK AND PUBLIC USEFUL PUBLIO 1940 AMPLIFIER HANDBOOK AND PUBLIC AD. 011DF an analysis of he contents Is found t the SECTION V- DRESS GUIDE. Tain gnat II \N'DItnOK on Publie Ad. right. showing the breakdown of the material featured ADDRESS DATA AND IN- dress ninad be read and - lw thorough to..5, h, ,' , f ..tettit build th .se who e. hi s:e aicular nun, .:.t I -1'fed ..as,t c ,uipment. 1 D, i1í. p s r, .A, of FORMATION Speaker matching technique RADCRAFT PUBLICATIONS 20 VESEY STREET NEW YORK, N. Y. The ABC of Db., VU, Mu, Gm and Sm W Charts and formulas useful to the r practical P.A. sound man RADCRAFT PUBLICATIONS. INC. * 20 VESEY STREET * NEW YORK. N. Y. RC -Gal index to important articles Gentlemen, Handy Enclosed find my remittance of ^ for which send me POSTPAID. one copy of Slla and sound 1940 AMPLIFIER HANDBOOK AND PUBLIC ADDRESS GUIDE. on public address

I Send me others, for friends, also POSTPAID fry lye each. I I Name kddress Order Your Copy NOW-

I T City State 1 e%2 poupon and 1 Remit by check or money miler: register letter if you send rash or unused C.S. Postage Stamps. /hail Today! L_ J 732 RADIO -CRAFT for JUNE, 1941 SOUND

MOTORBOATING CURE The Question .. . ecotone HI- FIDELITY AMPLIFIERS I recently built the 3 -stage amplifier, diagrammed on the enclosed sheet (Fig. 2) for a steel guitar with a magnetic pickup. I am having difficulty with it. When the pickup is hooked into the input terminals, all I get is motorboating while with the input lead to the 2nd tube, the tone is good and it amplifies, but does not give sufficient volume. Also, there is some hum which disappears when the finger is touched to any part of chassis or shielding. I think the trouble is feedback, but I do not know where. The physical arrangement is exactly as diagrammed; the first 57 is shielded, as are all pickup and grid leads. . Áir?3 I would greatly appreciate a solution to ..x. t:..yv.'.4-f':... this puzzler, either direct or through the "Sound Engineering" column of Radio- 6 -8 WATT BEAM POWER AMPLIFIER Oral t. (Not Illustrated) C. W. KUNKELMAN, This amplifier has been designed ; Pendleton, Oregon sillily amplifier for all lcompleteow power applications. It Is Ideal for as a high quality p11000- amplifier Specifications: 6 Watts normal. s The Answer .. . Watts peak. Mike Input ettannrh 11011 db. gain). I 'lino input chan- I don't know where you got the circuit nel 1111 ill, gain). Tubes used: 1- 6t'6CT. I -65Cí, 1- diagram from which you built your ampli- 5W ICT. fier. It is obvious that the designer was Output Impedance: Shoo ohms to speaker. loon to Moi) alun acid. primarily interested in using the smallest LESS TUBES AND COVER number of parts and at the least expense. $1.22 Kit of matched You must surely be aware of an axiom in tubes. engineering that whenever a circuit is 7.95 $ 1.50 Protective cover. co LLL ulth tubes and c 8 haws reties ,ortahls microphone and stripped to its bare essentials, some sacri- SYSTEM consisting of 0.R high fideldy ea'ker leatherette r including stand. fice in dependability, performance, or sta- Watt Amplifier complete mounted in a scientific a high quality crystal Price $25.49 bility must be made. 14 -18 WATT AMPLIFIER 25 -30 WATT AMPLIFIER In your amplifier, stability has evidently FINISHED IN ATTRACTIVE BROWN WRINKLE FINISHED IN BROWN WRINKLE WITH BRIE been completely overlooked. There are at WITH BRILLIANT CHROME TRIM. LIANT CHROME TRIM. 3 - BEAM POWER OUTPUT. INCLINED CONTROL PANEL. least possible causes for the motorboat INVERSE FEEDBACK. INVERSE FEEDBACK. ing condition that you complain of. UNIVERSAL OUTPUT. UNIVERSAL OUTPUT. DESIGNED FOR CONTINUOUS SERVICE. BALANCED PHASE INVERSION. (1) The use of a common cathode resistor DESIGNED FOR CONTINUOUS OPERATION. in a high gain 2 -stage cascaded amplifier is This amplifier will glerate as many as ten I2- This anipl itler has been designed to meet the most I'M Speakers. It i, bleat for u rage size exam log needs of the l'A Industry. It lus ample highly unsatisfactory, particularly when auditoriums. churches and theatres . a lt trill operate power to suer larger outdoor areas as well as the cathode resistor is inadequately by- Ot kit any Modern tif a impedance microphone. practically all Indoor auditoriums. This amplifier Specifications: li W: Its nomml. IN Watts peak. i: extremely flexible as It is equipped with four passed. I would suggest that a separate Mike Input chat tel 1115 db. gain). Phono input channels which are Individually controlled. input channel (7, tlb, gains. Speefications: 25 Watts normal. 30 Watts peak. cathode resistor and bypass condenser be 2 Microphone input channels 112= ilk gain1. Tubes used: I - 415C7, 1 -dFG, 22- 6VRGT, 1- employed for the second 57 tube. r%vtiIT. 2 Phan Input rhaunels INI db. gains. Tubes used: 3 -fSl5, I -GN , 2- lull), 1 -St'4G. (2) If this does not fully correct the Output Impedances: n, 4. 8, 500 ohms. Output Impedance: 2, 4. 8. 16. 500 ohms. trouble, then the condenser which bypasses COMPLETE PORTASSE SYS- COMPLETE PORTABLE M Model 2160 less TEM consisting of 14.18 Walt COMPLETE consisting f 25 -30 Watt Ampli- the isolating resistor connected to the plate tubes and cover $11.95 Amplifier complete with tulles fier complete with tubes. 2 Heavy Hevy High WITH TUBES Duty High load of the first tube should be increased PM Speakers with chrromeafriction clutch Kit of Matched feet of speaker PRICE floor- dand high grade crystal Tubes stane to at least 4 mf. 3.00 I c u eds a streamlinedk high .Iity sil mike $38.96 (3) If some trouble still persists, the 2nd - Streamlined a,.ánh arak lsons. $32.95 $67.96 stage screen -grid circuit should be altered Decorative Cover 1.50 Price so that a separate resistor and condenser network is employed to isolate it from the screen -grid of the first stage. The reason the amplifier does not give PEDE RATE sufficient volume when your pickup is con- FPURCHASER I1VCe D nected to the input of the 2nd stage, is that under this condition, you have insuf- ficient amplification to drive the output 80 PARK PLACE DEPT. R -61 NEW YORK CITY stage to full power. You will not experience this difficulty available, a 100 -ohm potentiometer should Now Ready: Sylvania's Tube Complement Book. when you utilize the gain of the 1st stage. be placed across the winding and the mov- 1941 Edition. Improved, revised, enlarged . The hum trouble can be eliminated by ing arm grounded. The arm should be ad- more valuable than ever. Has tube replacement shielding the pickup coil as much as possible justed for some optimum setting which information for 100,380 tubes or sockets and The from body First and Only Compilation of Panel Lamp Num- external effects. produces minimum hum. You might also try bers! The patented. Hold-Tite, WIRE-0 binding The 21/2 volt winding should be center - connecting the chassis of the amplifier to keeps book together, allows you to open it flat tapped and grounded. If a center -tap is not some external ground. without cracking or tearing. Send 35c to Hygrade- Sylvania Corp., Dept. ROSO. Emporium, Pa. A RADIO OL' TIMER THINKS BACK AWAYS NIGH EFFICIENCY I University Reflex J. R. Poppele, chief engineer of WOR, who , .. When Poppele borrowed some oriental Speakers will pro- tect sound clearly has been with the Newark station since it rugs from the rug department, which was for two miles with first went on the air in February, 1922, re- on the same floor as the station, and used less than 25 watts input. Write for members the early days of radio .. . this carpeting as acoustical treatment for catalogue. , When the first transmitter was a 250 - that one and only studio. UNIVERSITY watt outfit that had been used by deForest , When its first microphone was a LABORATORIES con- 1N5 C Cite. himself in some of his experiments. This verted telephone transmitter with a phono- w Yory pioneer transmitter was bought and rebuilt. graph horn at one end. ... When all of WOR was in one small, . When the news that the station had . When WOR, on October 1, 1922, broad- crowded room in the furniture and radio been heard in Staten Island, Asbury Park cast the first international program to department at the Bamberger store. The and Brooklyn was big news, and the sta- Europe. Sir Thomas Lipton delivered an im- room was not pnly the studio, it also con- tion took a newspaper advertisement to tell pressive message, the orchestra played, and tained a piano and the transmitter. the world about it. the broadcast was heard in London.

RADIO -CRAFT for JUNE, 1941 733 SOUND

LATEST ACOUSTIC SPEAKER HOUSINGS Illustrated and described are new "Triangular" and "Bass- Reflex" Loud- speaker Housings designed to afford increased fidelity of sound -response and to affect improved sound distribution.

RADIO -CRAFT is indebted to Messrs H. C. Reinhardt and H. W. Stewart for the following descriptions of, respectively, a 3- cornered loudspeaker housing, and a new design of acoustic baffle. The descriptions include useful information on the practical applications of these New, commercially-avail - housings. able loudspeaker housings. A. -The triangular PERI "Peri- Conic" speaker en- -CONIC SPEAKER ENCLOSURE closure developed by At- The triangular shape and styling of the las Sound Corporation. new "Peri- Conic" Speaker B. -the Bass -Reflex Acous- Enclosure, Fig. tic Chamber of Ray - A, offers a number of advantages over the Lab, Inc. conventional wall speaker housing or square cabinet type of enclosure. The new Atlas Sound speaker baffle, as shown in Fig. IA, has physical dimensions and construction permitting: (A) Corner speaker mounting; (B) Side -wall mounting for oblique sound projection; (C) Central cluster arrangements in The "Peri- Conic" Enclosure is designed Figure 2C describes a more difficult in- a groups of 4 for 360° coverage. for use with all 12 -in. cone speakers, usually stallation in long hall where undesirable Many other applications or methods of those that are sold for general Public Ad- conditions of reverberation are present, due mounting can be easily to dress application. The enclosure is recom- to a vaulted roof or long and hard wall re- determined suit flecting The the sound coverage requirements of the mended for all speakers which do not ex- surfaces. speaker placements particular locations. ceed 6 ins. in depth. suggested in Figs. A and B would not be No entirely suitable because necessarily The baffle design of the "Peri- Conic" is damping material or sound absorbent the such that it prevents the back pressure wave padding is used internally, although the ex- higher output level of the speakers would of the cone speaker diaphragm from perimenter may find that a particular result in reflections of sound that would strik- of ing a flat surface, as it would inside a speaker may be aided slightly if a layer impair the quality or intelligibility of the hair -felt other material is at- reproduction. square cabinet. It might be mentioned at acoustic or this point that many broadcasting and re- tached internally. If a number of lower- powered speaker cording studios are now being constructed units are used at a low level, the sound will in a shape, TYPICAL APPLICATIONS be diffused simultaneously over the whole triangular or other than a per- audience and fect square or rectangle. The internal di- Figure 2A illustrates a typical bandstand eliminate the reverberant ef- mensions of the "Peri- Conic" Enclosure are or platform installation when the micro- fect. triangular in area, thus reducing the cabi- phone is located at one end of a rectangular Cafés and places of entertainment having net resonance to a minimum. room. The "Peri- Conic" enclosures are a circular bar or stage, with the microphone The back -pressure release cut -out, direct- mounted on both side walls, some distance located in the dead- center of the room present another kind of il- ly under the cone opening, provides a re- forward from the microphone position. coverage problem lease for the back pressure normally The from lustrated in Fig. 2D. The fact that the built sound waves, originating each are pointed at micro- up inside the enclosure. This opening, speaker, a speakers directly the being cross at point somewhere ahead phone may some concern, if a on the front panel, directs the back pres- of the microphone. This speaker set -up of- cause but number of used as sure of the cone diaphragm in the same fers smooth and uniform coverage, also re- speakers are illustrated, each one a low level, sound general direction as the pressure wave gen- ducing feedback to a minimum. The small operating at the is The of erated by the front side of the cone dia- area directly in front of the platform is uniformly distributed. uniformity phragm. This factor increases covered by vo- sound distribution eliminates the "beam ef- the overall normally the orchestra or fect" wall kick efficiency to some extent, and results in an calist without necessity of am- or reflections that often the sound back extension of the frequency response. 1.0ification. into the microphone with resultant feedback or acoustic howl. The same principles used in designing an Another similar set -up is described in acoustically perfect studio can be applied Fig. 2B. In this application it will be noted to a speaker enclosure in order to lessen that the bandstand and microphone are FOR LARGEST LOCATIONS frequency discrimination due to reverbera- located at a center point along one of the Figure 2E describes an installation that tion, standing -wave cancel ation, etc. long walls of a rectangular room. may be employed in a skating rink or indoor stadium. The noise level is very high CNAMB[:N-/ and considerable sound output is necessary OAiciCE A' to overcome the normal background noises. CNAMBER-/ Four of the "Peri- Conic" triangular baffles can be easily grouped in a cluster and sus- pended in the direct center of the location. If additional sound level is required, the corners can be utilized for mounting individual speakers directing sound to the center of the room. It is often difficult to hit upon the most perfect arrangement without some preliminary teats and investigations. Don't depend on coverage formulas -the time spent in a careful survey of the acoustical conditions will always be worthwhile. The correct phasing of speakers in mul- is extremely important. EXAONENr/AL tiple installations EXPONENTYAL ae, CE 6' A/R AND Whenever 2 or more speakers are used, A/R AND ,SOUND COLLNtN they must be connected so that all cones SOL/NO COLUMN e or diaphragms move in the same direction same time. A good method to utilize Fig. I. Details of the new baffles. A.- Phantom view of the corner -of -room, triangular "Peri- Conic" loud- at the speaker. 8.-Front phantom view of Bass- Reflex Acoustic Chamber. C -Side view. to assure phasing is to mark the terminals 734 RADIO -CRAFT for JUNE, 1941 SOUND of identical speakers in an identical manner. If the speakers are connected so that all the terminals connected to one line are identical, the speakers will be in- phase. An Qtin Only in Si3¢ and /bt«¢! aural method can also be used for deter- mining phase relationship. If 2 speakers are operating, and the sound appears to be coming from 2 distinct locations or from each speaker individually, you can be reasonably assured that they are out -of- phase. Changing -over the input connections on either speaker will rectify this condition and the sound will then appear to be coming from one source. It might be well for the sound engineer to conduct a phasing experiment in order to become acquainted with the aural test described.

BASS- REFLEX ACOUSTIC CHAMBER The second design of loudspeaker housing, the Bass -Reflex Acoustic Chamber, is pictured in Fig. B; the details of its construction are shown in Figs. 1B and 1C. The No need to sacrifice dependability when theory and basic principles developed in this seeking the convenience which pocket - speaker chamber are entirely new and dif- size instruments afford. For this series ferent. This new design it is claimed, affords the following desirable results: of WESTONS ... while truly compact in (1) Bass -reflex response. size and low in initial cost... provide (2) Desired bass cut -off. the dependability and long life which (3) Resonant tuning to give hall and are typically WESTON. In addition, auditorium acoustical conditions. they are versatile instruments; Model (4) from Perfect phasing of tones, 697, for example, providing the nec- back and front of speaker, from zero to the highest audible frequency. essary voltage, current and resistance (5) Ability to obtain the maximum ranges for efficient trouble -shooting. efficiency of the speaker unit. Let us send you full particulars on (6) Elimination of distorting vibra- these convenient, low -cost instruments. tions of the speaker cone at ultra -high and -low frequencies. Write today. The first facts brought out, by an analysis designed to secure the above results, were WESTON ELECTRICAL INSTRUMENT CORPORATION that the basic formula depended upon ob- 599 FRELINGNUYSEN AVENUE, NEWARK, NEW JERSEY taining a zero medium, for maintaining the air pressure mechanically developed inside chamber 1, Fig. IB, in perfect balance with It was found by experiment that the ef- tuning of the acoustic chamber, which is the outside atmospheric pressure. ficiency of the speaker could be varied over necessary in order to maintain a 180° out - Using this as a basic medium, it was pos- a wide range by changing the size of cham- of -phase relationship between front and sible to regulate our bass -reflex response ber 1. Although it was then possible to con- back of the motor unit, was also controlled by the size of the opening in chamber 1, trol bass -reflex response, only a very limited by proper design of the air column. which acts as an air valve. range of bass cut -off could be obtained to Up to this point, experimental verification Further research disclosed the necessity meet all conditions- The basic principle of the calculated results had progressed sat- of finding the principle upon which to com- that controlled this feature of the acoustic isfactorily, but then a new problem arose. pute the proper cubic inch size of chamber 1. chamber, it was found, was the degree of Distorting vibrations developed due to the It was found that this depended on the.size taper of the exponential air column, Fig. 1C, power of the speaker being so increased of the cone, and the flux efficiency of the between orifice A and orifice B; and, the within so compact an acoustic chamber. This permanent magnet or field coll. proper sizing of orifice B, Fig. 1B. Resonant was corrected, in part, by gluing the acoustic chamber in its construction; and, by

PLATFORM AA/RE A A properly placing an acoustic material in- OR side of chamber 1. Fig. 1B. BANC MIKE n \i .l '. A I USEFULNESS Use of the above- described construction ...- // of an acoustic chamber, in combination with C a loudspeaker -unit of proper type, results .5-?' . \ , J in a loudspeaker combination capable of re- \\\ production over a frequency range of 24 to / . / 19,000 cycles, without resonance peaks. / /. \' These SOUND acoustic chambers, being very com- ' COVERAGE' . pact, can be used for portable use as well - . - O -CLRCL/LAR BAR ARRANGE- as permanent installations. Three sizes have MENT,CAFE NLGNTCLUB been perfected, namely, for 10 -in. speakers handling up to 15 -watts power; 12 -in. -THEATRE. 504,v0 O DANCE / COVERAGE ì speakers, handling up to 25 -watts power; FLOOR, ETC. -.. 'r PArrERN J and, 15- to 18 -in. speakers rated at up to . . 50 -watts power- handling capacity. These are M/KE / ..: ` all in the box type as shown. Two more types will soon be perfected, one corner / , type and one wall type. These Bass -Reflex Acoustic Chambers '% have been proven by test to be capable of OOUNL)NERAOF solving many problems in "acoustically dif- / ficult" halls, gymnasiums, and auditoriums.

Messrs. Reinhardt and Stewart are connected with. --OANCE FLOOQ' LONG HALL, n'OLLER RiNK OR respectively. Atlas Sound Corporation, and Ray-jab, Inc.. O A GYMNAS/UM,E/C.- INDOOR 5r00/OMETC- manufacturers of the new speaker housings described in the © foregoing article.

RADIO -CRAFT for JUNE, I941 735 SOUND

Man4aetuter eomment9 on "MODERN MICROPHONE TECHNIQUE"

The following letter discusses statements, concerning directional, semi- directional and non -directional sound cell and diaphragm types of crystal microphones, published in a 3-part article in Radio -Craft.

A. L. W. WILLIAMS President, The Brush Development Co.

WE have before us the article entitled Impedance. -With the exception of a few "Modern Microphone Technique" in models equipped with step -down transform- the February issue of Radio -Craft The 3 -part article "Modern Micro- ers (for use on 500 -, 200- or 50 -ohm lines), and are taking the liberty of writ- phone Technique," which appeared seri- all crystal microphones are of the "high - ing you in regard to certain statements con- ally in the February, March and April, impedance" variety and are intended to tained therein. Our company, The Brush 1941, issues of Radio -Craft, has aroused work into the grid circuits of amplifiers Development Company, is the only com- comments pro and con in many quarters. through shielded cables. The impedance is mercial source of Rochelle salt crystals in As authors L Fletcher and H. S. Manney similar to the impedance of a condenser and this country, as far as we know. In addi- pointed out, " 'Microphone Technique,' the length of cable that can be used without tion to manufacturing piezoelectric devices as such, is a big subject to cover in a sin- serious loss of output depends on the ca- ourselves, we license others to make such gle series of articles ... and this series pacity of the microphone, higher capacities devices using our crystals. We enclose (ap- . .. has been merely an attempt to sum (lower impedances) permitting longer pended.-Editor) herewith for your atten- up some of the ideas which . are in cables. The loss due to cable capacity is, in tion a list of our licensees. current belief and use today." The diffi- practically all cases, the same at all fre- We maintain an engineering laboratory culty of pr fing an article that would quencies; in other words, cable capacity which specializes in piezoelectric problems, be approved by all the opposing groups does not cause a relative loss of "highs." and in making the following comments we in the microphone field was recognized Microphones employing a plurality of paral- are relying on the experience which we during the early stages of the prepara- lel- connected diaphragm units or parallel - ourselves have gained in dealing with crys- tion of this article, and it was only by connected sound cells have much higher tal devices. We believe there are a number using the approach fo the subject em- capacity (lower impedance) and can be used of errors and omissions in the article that bodied in this series, that some measure on much longer cables than most single - are likely to give the reader a false con- of equity between these divergent views unit microphones. ception of the qualities and limitations of could be found. Output. -As a class, sound cell micro- crystal microphones. Diametrically opposed information con- phones have lower voltage output than dia- The paragraph headed "Crystal" begins cerning the use of microphones was ob- phragm microphones. by stating that "There are 2 general types tained not only from technicians -prac- Directivity. -With at least 2 exceptions of crystal microphones on the market: (1) titioners in the field -but manufacturers (Shure "Tri- Polar" and Shure "Uniplex ") the sound cell type, and (2) the dual -dia- as well. crystal microphones are pressure -operated phragm type." Crystal microphones should "Modern Microphone Technique" was and therefore non -directional or semi- direc- be divided into the sound cell type and the intended, and to this extent has served its tional. Sound cell and small -diaphragm mi- diaphragm type, the latter including both purpose, as a background against which crophones (including double- diaphragm single and dual diaphragm. The single -dia- differing opinions on the subject could be types) are small enough in relation to high - phragm type greatly outnumbers the dual - projected. frequency wavelengths so that they are sub- diaphragm and sound cell types combined. We are happy fo present the accom- stantially non -directional. The average dia- In this connection, note that all the 6 crys- panying letter which expands one class phragm microphone, however, is larger and tal microphones illustrated at the bottom of microphones in operation; if and when somewhat more directional at the higher of page 499 are of the single -diaphragm equivalent material is submitted to Radio - frequencies. In this respect it is similar to the type. Craft on allied cl , we will be glad, average dynamic microphone and in some The "Crystal" paragraph compares fre- too, to give this material display. cases this directivity is deliberately accentu- quency response, impedance, output, etc., of Sound and Radio technicians long have ated by suitable case design. On the other the sound cell and dual- diaphragm types and lacked practical, applicational informa- hand, some of the large -diaphragm micro- much of this information is incorrect, or is tion which attempted to coordinate all phones are used with their diaphragms hori- misleading in that it is applicable to partic- the differing opinions, and associated in- zontal and the cases symmetrical about a ular microphones but not to the whole class formation and characteristics data, etc., vertical axis so that they are non- direction- of microphones. Since the comparison is be- currently available. It is hoped that "Mi- al in a horizontal plane. A few crystal mi- tween the sound cell type and only one crophone Technique" has altered this sit- crophones of special design are highly di- small part of the large class of diaphragm uation and that Radio -Craft readers now rectional. They include a Cardioid type types, we shall not attempt to take up point will feel more "at home" with microphones. ( "Tri- Polar ") which is equipped with a by point the incorrect statements but rather switch to change directivity; and a single we shall present what we believe to be a unit uni- directional microphone ( "Uni- correct summary of the properties of crys- plex"). tal microphones. crystal types now available is as follows: In addition to the misleading comparison It is difficult and often misleading to com- Response.-Sound cell microphones as a of the 2 types of crystal microphones, there pare different types of microphones since class have flatter, wider response than dia- are several statements in the "crystal" microphones in the same general class may phragm crystal microphones as a class, The paragraph that require comment as they vary even more in their properties than dual- diaphragm is an outstanding example are also apt to add confusion: representative microphones in different of a high -quality diaphragm type and has "Being more efficient in the higher fre- classes. This requires that direct compari- better response than some sound cell mod- quencies, it (sound cell) tends to overload sons between individual models of different els, but is excelled by other sound cell mod- the amplifier sooner, causing feedback." classes be avoided, or be made with great els. For example, we make a Laboratory In any microphone - loudspeaker system, caution, as otherwise the comparisons may Standard sound cell microphone which has feedback is accentuated by the presence of lead to false conceptions of the classes as such flat response through the audible range more -than -average efficiency at one part of entireties. On the other hand, general com- and beyond that it is used for calibrating the frequency range. This is true regard- parisons by classes may hide outstanding other microphones, but for the ordinary less of the type of microphone, although qualities of certain specific models. Having range one can achieve flatness with high directional microphones offer an opportuni- these limitations in mind we believe that a output more cheaply by using a diaphragm ty to reduce the effect. However, amplifier correct summary of the properties of the construction. overloading seldom, if ever, is the cause of

736 RADIO -CRAFT for JUNE, 1941 SOUND

feedback as implied in the above statement but may result from feedback. The diaphragms (of dual -diaphragm units) are smaller in diameter than the SELF -BALANCING wavelength of the highest frequency waves encountered in high -fidelity appli- ¢ DRIFT -CORRECTING cation, and thus the microphone cannot be acoustically overloaded." This statement leaves the impression that DIRECT -COUPLED AMPLIFIERS large microphones may be overloaded acoustically because they are larger than a wave- FOR DISCRIMINATING MUSIC LOVERS length. Actually, size has little to do directly with acoustical overloading and to the best Designed by A. C. Shoney of our knowledge all commercially -available operate well acousti- microphones below the These cal overload point even for very loud sounds. new amplifiers bridge the gop between the lobo. rafory and the home, and make The size is important, however, in its ef- available for the first time, extraordinary equipment at less than ordinary fect on directivity, small size usually being prices. Built in a new way, without interstage coupling required for non -directional performance condensers or transformers. Although specifically d. and this is the reason for the small size of signed to meet the strictest requirements of proles dual -diaphragm and sound cell microphone sional sound engineers, these direct. coupled amplifiers units. embody all desirable features sought by the most dis- "Like the sound cell type, they (dual - criminating music lovers. Send for literature. diaphragm microphones) are also non - directional. In other words, they behave very much like the human ear, picking up sound sometimes within a radius of 17 W. 20TH STREET, NEW YORK, N. Y. 20 or 30 feet." The only practical limitation to the range of pick -up of the human ear is the weak- $7.95 midget radio set does not reproduce ness of the sound to be "picked up" and the the full audio range and has a bad peak. loudness of interfering sounds. If the sound GEOPHYSICAL is loud enough at the source, it can be Licensees of The Brush Development heard for many miles provided that local Company. PROSPECTING sounds near the listener are sufficiently weak American Microphone Co Los Angeles, PRINTS so that they do not mask the distant sounds. Calif. The same thing holds for most all practical Astatic Microphone Laboratory, Youngs- microphones with the additional important town, limitation that the noise level of the mi- Ohio 50¢CH crophone and amplifier combination masks L. D. Cahoon & Company, Limited, Toronto, weak sounds that are picked up. The refer- Canada 7 FOR ence to the 20- or 30 -foot pick -up range has, Dictograph Products Company, Inc., New in our opinion, no foundation and is most York City $3.- misleading. Thomas A. Edison, Incorporated, Orange, In other paragraphs of the article there With any one of the modern New Jersey geophysical methods de- are still more statements upon which we Fairchild Aviation Corporation, Jamaica, scribed, instruments can be wish to comment as they place crystal mi- New York constructed to locate metal crophones in a most unfavorable light which and ore veins, subterranean The Gray Manufacturing Company, water and oil deposits, buried we think is entirely unwarranted. In the Hart- pipes, tools, or other metallic paragraph headed "Velocity," we find the ford, Conn. objects sunken in water, etc. Herz-Lasker Corporation, New York City Folder contains blueprints and detailed data following: covering each instrument. "The velocity has the flattest frequency B. A. Proctor, Inc., New York City of microphone on the mar- Folder No. I. Radloflector Pilot. Construction response any RCA Manufacturing Company, Inc., Cam- and use of 2 tube transmitter and 3 tube ket, as far as the higher and middle den, New receiver. Reflected wave principle. Visual and Jersey aural signals. frequencies are concerned." Shure Brothers, Chicago, Ill. Folder No. 2. Harmonic Frequency Locator. velocity Radiates low frequency wave to receiver. Of course, high- quality micro- Sonotone Corporation, Elmsford, New York Aural signals. phones do have very flat response but there Folder No. 3. Beat 'Note indicator. 2 well- The Turner Company, Cedar Rapids, ham. Visual and aural signals. are also on the market poor -quality velocity Iowa Folder No. 4. Radio Balance Surveyor. Ba1- Webster Electric Company, ced loop principle. Modulated transmitter. microphones which certainly do not meet Racine, Wis. \ -Isual and aural signals. this specification. On the other hand, al- American Telephone and Telegraph Com- Folder No. 5. Variable Inductance Monitor. Inductance principle. Aural signals. though some sound cell microphones tend pany Folder No. 6. Hughes Inductance Balance to have a rising characteristic at the higher Explorer. Bridge principle. Aural signal, Folder Ne. 7. Radiodyne Prospector. Balanced frequencies, others are at least as flat as lu.p principle. Very large field of penetra- the best ribbon microphone. We regret that it has been found neces- tion. aural signals. Near the end of the second column on sary to hold over for July Radio- Craft, the Each ut of blueprints and instructions enclosed In page 492 is a statement which is shocking articles "Recent Radio Tubes" and "De- heavy envelope (9''a' x 12'.4'). Blueprints 22" x 34': eight-page illustrated 8'4' a Il' folder of GO`a to us as a manufacturer of crystals and velopments in Personal Portables," original- Instructions and construction data .7 therefore as one who knows the extent of ly scheduled to appear in the June issue. Add 5e for postage this application. Also, don't forget that July Radio -Craft The complete set of folders will contain Shipping weight 2 Ms. (add 25c for ship- i$3e0 "A crystal microphone with a flat fre- the "Review of the Radio Parts ping anywhere In U.S.A.) quency response, might even be used suc- National Trade Show." cessfully for music." Although the implication of this state- TEC FAX ment is modified somewhat by other state- .1. RC-641 ments in the article, taken by itself or in D. R. Freed. head 1917 S. STATE ST. CHICAGO, ILL. combination with the rest of the matter Joseph D. R. Freed, -1:1, one of the highly - under the sub -heading "Semi- Professional," regarded old- timers of radio, died recently it is, to say the least, most unfair to crystal at his home in Riverdale, New York. He will * * * * SPEAKER HIT! microphones which have been and are used be well remembered for his many contribu- NEW! where very highest tions to the radio art, notably improvements "Peri- Conic" extensively the quality designed for the U. S. Navy during World riangular Cabinet, is desired for recording and for broadcast War I. purposes. There are, of course, low- priced 101 Sound Applications He was best known for his highly- success- o Bass Reflex Design crystal microphones which are not satisfac- ful Freed -Eisemann Improves Any 12" Speaker Radio Corporation, Walnut tory for high- quality recording but they are pioneer radio set manufacturers in 1921. Distinctive Finish engineered deliberately as low -cost units. his loss is a great shock to the radio indus- ATLAS SOUND CORP. One might as well condemn all dynamic try. 1446 39th St.. Brooklyn. N. V. FREE: CATALOG F.41 TR -12 cABINET !7 gg because the speaker used in a Dealer Net a7 speakers Describes 155 Sound Products ... I RADIO -CRAFT for JUNE, 1941 737 SOUND

T The story of how two typical Radio Servicemen, discour- toaN & SERAPNINE aged and disgruntled because RADIO SERVICE of bad business conditions, & found themselves in the SOUND ENGINEERS Sound field. It might well have been your story or the story of so many hundreds of other Servicemen who complain of how bad the servicing business is.

SOUND g the SPUR LEO FENWAY

IF YOU have been one of the millions of rade exhibit. Some one, Emil thought, made going to turn our back on yesterday's meth- visitors to the New York World's Fair a nice few dollars. And those amplifiers in ods of servicing radios. We'll not use any you, of course, know the all- important the amusement area -why, the idea of a ruse of false advertising, sales talk, or part radio played in its success. Serviceman doing a real sound selling job hocus -pocus to hide from the customer what If you went there in the morning, before was so logical, so matter-of- course- he is getting for so much money." Tony the gates opened, doubtless you were greet- Then he met Tony. agreed that was swell, knowing full well ed with a sudden blast of sound as a spieler "Servicemen tackle sound ?" Tony said. that many of the fly -by -night Servicemen tested his microphone. "Why, only a month ago I rented an am- paid the full penalty for sharp dealing and "H- E -E -R -R Y- A- A -R -R, FOLKS. It's plifier for two bucks. And y'know what? buccaneering tactics. Fascinating -" And far across the field an- When I got it back the speaker was busted. After all, there is no substitute for other barker shouts, "Step Right Up. Step Yeah. I tried my luck with sound. I got two knowledge and experience. Neither can be Right Up -" or three P.A. chassis under my bench right faked. Later, if you joined the countless thou- now. All naked and rusty skeletons, gentle The partners' next move was to send a sands who stood spellbound at the spectacu- reminders of-" letter to all of their creditors, pointing out lar "Railroads on Parade" pageant, surely "All the same," Emil cut in, "if a couple their new position, and assuring them that you must have marveled at the near- perfec- of real radio guys got together, like you they were anxious to honor their obligation of the sound system. and me, we could clean -up on the East tions. They suggested that they could set The evolution of sound amplification from Side, selling sound. I'd take over the sound aside so much a month which could be divid- the single Baldwin headphone placed in a end of the business. You could handle the ed pro rata among their creditors. Their tea cup (the earliest form of loudspeaker), usual repairs. Every lodgeroom, club, res- suggestion was received with pleasure. Un- to the giant 350 -watt amplifiers used at the taurant and other joint where groups gath- known to them, their credit rating was be- Fair is a factor of overwhelming significance er would get to know me like they know ing established at the Credit Bureau. to every Serviceman with imagination and their own landlord. Believe me, pal, with the Weeks passed. Tony had to admit that for understanding. worries of repairing sets off my mind, I'd a little guy -Emil was only 4 foot 10 -with To Emil Cohen and Tony Seraphine, East give the sound business all I got -attention, a receding chin, he had a lot of moxie. Sales Side Servicemen, it was adventure walking charm, personality, imagination, stick -to- and Service were climbing. In one restau- suddenly into their lives. It was more than it- iveness -the works." rant, Emil sold a 5- position, selective inter- that. Much more. It was the beginning of "Y'mean," Tony said, "instead of being communicating system, allowing them a few an idea that two radio men, geared in dif- my competitor, you'd be my partner ?" dollars for their 8- year-old talk -phone set. ferent branches of the craft, could do busi- "Competitor hell!" Emil grunted. "You A club in Harlem, where they run nightly ness as cheaply as one, provided they put all ain't got a competitor any more than I have. Bingo parties, bought a high -quality 12- their eggs in one basket. We're only a drop in the bucket. How much watt system. Previously, this club had been Tony conducted a small radio business in stock you got on hand? Don't tell me- using a popular broadcast receiver, with a the basement of an apartment -hotel in the mine's lousy, too! How many calls you made carbon mike. Emil made it a point to hang East Seventies. Many a time Emil had this month? See what I mean ?" around the first two or three evenings in passed Tony's place and wondered how much Tony grinned. "I've been wanting a 1st - order to meet people. The second night he he owed a month for "that dump." class service bench all my life." ran face to face with a Mrs. B. He had Emil's store, located downtown on 2nd Emil laughed. "I've been wanting," he tried many times to get past the ornate Avenue, reminded Tony of a thrift shop. said, "to get away from one all mine." doorman at the Swish -Arms, where Mrs. B Even with its conspicuous "Expert Radio "Well," Tony said. "I've a little stock. lived, but had not been successful. He had Service" sign, Tony was all for calling it a And about a hundred bucks in cash. I may been tipped off. She was in the market for blind for a bookmaker. be a sucker. Especially when most Service- a phonograph with automatic record chang- As a matter of fact, both men were hon- men know less about selling sound than er. Meeting her at the club was the most est, upright citizens trying to support their almost any other branch of radio. Still, if logical thing in the world, because she, like families . . struggling against a decline you're game to try it, so am I- provided you hundreds of other women was "nuts about that neither entirely understood. Deep down, can tell me how to stall off my creditors, the good old bingo game!" each in his own way, often looked at his until we get things going." Two months went by. The partners were microscopic business, with its competitive Emil assured him that it could be done. very optimistic. The only break in their death grapple for trade, and wondered if the He had angles. friendly relationship was quickly patched radio business would ever again equal its So, with cash assets o $274.25, they got up. It came about because Tony wanted to former glory. started. Tony's store was closed, and the start building their own sound systems. And then one day both men went to the contents moved to Emil's place of business. Emil was against it from the start. "If we." World's Fair-independently. It was Emil A new sign reading, "Cohen & Seraphine- Emil said, "use standard equipment, we'll who became imbued with the come -on tech- Radio Service & Sound Engineers" was have no apologies to make. The day for nique of radio. He discovered that people proudly hung over the door. Working like apologies, if it ever existed with factory - were not only conscious of what the Fair Trojans until the wee small hours of the made units, is past. We want our work and looked like, but also what the Fair sounded morning, both men took turns with (a), a our accomplishments to be measured by the like. paint brush; (b), a hammer; (c), saw, same standards as are the best in the sound Sound! That was the thing. Take that plane, nails. They put the repair depart- business." P.A. equipment at the Railroads on Pa- ment right in the window. Emil said: "We're And Emil didn't mean any reflection upon 738 RADIO -CRAFT for JUNE, 1941 SOUND

Tony's ability. Tony was an excellent me- chanic. But the early sound shoemakers built most of their equipment, and left most SPECIALS of their work unfinished. Emil meant to on work, not so much to pre- All of the attractive Items listed here are brand new. ALL. are in PERFECT WORKING ORDER. In many carry that rases, the parts alone total more than the price we are asking. 100% satisfaction guaranteed or your money serve the heritage of radio, but because funded. ORDER FROM THIS PAGE. Use the convenient coupon below. include sufficient extra remittance for parcel there was money to be made doing so. Post charges, else order shipped express, collect. Any excess will be refunded. C.O.D. shipments require 20^/, He canvassed most out -of- -way deposit. If full remittance accompanies order, deduct 2% discount. Send money order. certified check, new U. S. the the 'tamps. No C.O.D. to foreign countries. places. That's how he happened to hear about the auction of household furniture in ORDER TODAY LIMITED QUANTITIES PROMPT SHIPMENTS ASSURED the warehouse down by the river. Most SPEED MOTOR AMAZING BLACK LIGHT!! warehouse auctions are noisy, what with VARIABLE UNIVERSAL Powerful 300 -Watt Ultra- Vlolet Bulb furniture being moved about, etc., so, why FOR 110 VOLTS. A.C. OR D.C. The best and mort prac- Made for Dictaphone machines by American Gramophone tical source of ultra -violet not help the auctioneer with sound? Co. L'se,l. hut an excellent light for general experi- rendition. Special lever con- mental and entertainment Emil approached him the day before the trol permits variable speeds up use. Makes all fluorescent sale. He was a big surly fellow with a hall extends riront" Inch substances brilliantly lumi- -Wes of motor. Measures nescent. No transformera of pugnacious jaw. overall. any kind needed. Fits any SISO. Wt. 0 t, Nothin' doin'," he said in his gruffest J standard !snip socket Slade Q' with special filter glua per voice. "I wouldn't spend a cent for-" milting o n I y ultra -violet Yourr Prce 11... $1.55 rays to come through. Brings "But you don't have to spend anything!" out beautiful opalescent hues Emil said. "I'll install the equipment. You ALL -PURPOSE INDUCTION MOTOR in various types of mate POWERFUL rials. Swell for amateur give me 1% of the total sales." IDEAL FOR EXPERIMENTERS -101 USES parties, plays, etc., to oh :dl:1 rvicl fi, 1'n iel The following day, that auctioneer sold tain unique lighting effect,. Bulb only. Sine of bulb. STE. Wt. 1 $2,791.75, in less 4 hours. It was some- than ITEM C7 $2.00 thing of an achievement, and netted the YOUR PRPRICE

. - Automatic Timing partners a nice tidy sum for the day's work. Devices. Current Interrupters, ULTRA MAGNET Moreover, the auctioneer engaged Emil's Electric Fans. Electric Chimes, Window Displays, Photocell Con- LIFTS MORE THAN 20 TIMES services for a second auction to be held in trol Devices. Electric Vibrators. ITS OWN WEIGHT Jamaica. Emil says, "After the job is re- Small Grinders. Buffers and Polishers, Miniature Pumps. LITTLE GIANT MAGNET. Lifts peated several times, it will take little sell- Mechanical Models, Sewing Ma- 5 lbs. easily. Weighs 4 oz. )lade ing to convince the auctioneer that outright chines. Phonograph Motors. Cof- of ALNICO ne high- magnetic fee Grinders. Motion Picture steel. Complete w with keeper. purchase of the P.A. equipment is' more Projectors, Motorized Valves, World's most powerful magnet ever practical repeated Sirens, and other applications. made. The experimenter and hub than rental." loons nines about 15 watts of byist will find hundreds of us- That's taking a long view of it. Still, a poser and lia. a speed tref :1.000 cellent uses for this high quality r.p.m. When geared down. this permanent magnet. Measures 13," sound amplifier is a long -time item. sturdy unit will constantly operate an I8 -inch turntable s 1%'. Shp. Wt. % Iba. loaded with 200 lbs. dead weight- THAT'S POWER! Besides, Emil and Tony take a long view The motor is of midget dimen,ious. 3 imbrs high by ITEM NO. 88 of everything these days. They've gotten 2 inches wide by 1% Indus deep: has 4 convenient YOUR PRICE $1.00 over the idea that Servicemen are by long mounting studs: shaft is 'a" long by 3/16" diameter and runs in self -aligning. oIlretaining bearings: the MOTOR -SAW odds the most ill -paid, under -nourished best materials. perfect precision assembly and rigid NEW ELECTRIC inspection certify to Ha high quality. and assure long Now you can have all the tradespeople in the country. They've forgot- life. Designed for 110 -20 volts, 50 -60 cycles, A.C. only. fun of One, fast Jigsaw work ITEM without any of Ito difficulty. ten about the radio men who live only for YOUR RICE? $1.29 Simply steer the lightning - today, cannot think of yesterday without fast blade and see it seem- BENNETT LABORATORY BALANCE ingly melt its magic may regrets, nor of tomorrow without fear. Emil through wood, plastics and Tony have feet on the ground. A compact laboratory balance made of finest quality building board. 7200 and their tested niaierial.,. Extrenie sensitivity (to 210oths gram STROKES per MINUTE! 2 They know that selling Sound is like placing or -7tbs grain). weighs to one decimal pt. further Average cutting speed 1 foot pO,NrER -. per minute through 3/4" mean ad in a paper with a large circulation. CEmtawG awn dium hard wool. Worts 3 It reaches the most people. The more people, Evert [ Csu,iNG sow times faster than any free- lta0 aeoir hand saw. Operates on 50.60 the better the prospects are for business. cycle 110 v. Alternating Emil and Tony would like to open many a . Current. Screw adjusts blade -- I Croke from !S" to 5/18'. Serviceman's brain and pour into it a mass Off-On Switch built In handle. Complete with C ft. Power no- Mate cord and 3 saw blades. of facts, rules -of- thumb, opinions and -- ITEM NO. 97 improving in YOUR PRICE $4.85 tions about business their aunNG community. And boiled down the words of NOT ELECTRIC HUMIDIFIER FOUNTAIN the success -makers are: "Sound is the elf MING MNr5 SuSPENS,ON OLE Adds healthful moisture ti Spur." the air In winter. Evap- ANDES2sU a[a [ER orates as much as pint of water in 24 hours. Fountain than usual low priced counter scale. will handle up to grams is 14" In diem. Spray, s 100 (about 4 oz.). Bakelite pan; tool steel knife streams of water 5" ahoy, MORE F.C.C. MAILBAG edge: agate bearing for long 11f, and accuracy. Ideal fountain head. Made of spun for photographic work and lab use. Handsome stream- design. aluminum. Cornea In five is line Graduated either in metric or apothecary colors: cop- All radio transmission interstate com- system. Shipping Bronze, chrome, wet. 2 lbs. red. green. No water merce, notwithstanding its scope or terri- ITEM NO. 122 per, PRICE connections required. Ju=t torial limits, the Commission reiterates to YOUR $7.20 plug into 110 volt, 60 cycle Texan. As such, it is A.C. outlet. Current consumption few cents month. an inquiring subject 100 POWER TELESCOPE LENS KIT Complete with base switch and 8 ft. power cord. Ship- to the regulatory powers of Congress or of ping wt. 9 lb,. List price $14.95. Only a limited A O Make yo supply on hand. a delegated authority. Various court deci- telescope! you cane O to closeup view of the worlds ITEM NO. 125 $4.95 sions are quoted. out in space. See the rings YOUR PRICE -e-N- around Saturn, the mountains of A New York State resident wants au- the moon! Kit contains 3" diem.. thority to record certain radio programs as 75' focal length, ground and polished objective lens and 2 they are broadcast to the public. The Com- astronomical eye piece,, magnification 50x and 100x. mission replies that this does not come with- Complete kit with full instruction,. 1941 Catalog ITEM NO. 123 in its jurisdiction, being a matter involving YOUR PRICE $1.95 the private rights of the radio station, the NEW -EXTRA LARGE LENS KIT -contains com- A POSTAL CARD BRINGS IT TO YOU artists, and the sponsor of the program. andelpolehedeoblectiveulens. three 15¡" diemeterr7e- pieces giving 88x, 133x, and 200x. an aluminised SEND FOR IT TODAY "What procedure should be followed in the diagonal for overhead viewing, and a color filter for event of the death of a station licensee ?" Insertion In any eyepiece. ITEM NO. I inquires a Chattanoogan. In such cases the YOUR PRICEL $3.95 administrator of the estate should make ap- HUDSON plication to the Commission for an assign- SPECIALTIES CO., 40 West Broadway, N.Y.C. ment of license to be exercised pending set- IT'S EASY TO ORDER --CLIP COUPON -MAIL NOW ORDER FROM THIS PAGE. tlement of the estate. When the estate is settled, the administrator should make ap- HUDSON SPECIALTIES CO., 40 West Broadway, Dept. RC -641, New York, N. Y. I have circled below the numbers of the items I'm ordering. My full remittance of 8 (include plication for assignment of license to the shipping charges) le enclosed. party who is to carry on station operation. OR my deposit of 8 is enclosed (20% required). ship order C.O.D. for balanee. No C.0.0. An Ohio letter- writer objects to certain order fer less than 12.00. (New U. S. stamps. check or money order accepted.) Circle Item No. wanted: II. 86. 87. 122, 123, 1231- 125. 147 Berlin broadcasts. The programs in ques- 97, tion are not rebroadcast, but are received Name Address from Berlin direct. The Commission does not, of course, have jurisdiction over alien City State stations. Send remittance by cheek. stamps or money order; register letter ff you send rash or tiemps.

RADIO -CRAFT for JUNE, 1 94! 739 TEST INSTRUMENTS

"Always bear in mind that your service instruments are the tools P.M" owa e with which you earn your living. a Good equipment is expensive, but it's far better to have several good, álgt,,_ basic pieces of equipment than a zOh.W laboratory full of junk," concludes -. wee r the author, after analyzing the

9. general pros and cons of fundamental test apparatus for Service- 0.10sm -P. men. Representative circuits of actual instruments are given, and w breakdown diagrams of certain circuit details are shown.

; AS.'Psz»z ; ii"..: .a . E Fig. I. -The Radio City Model 414 in. strument is a simple versatile multitester that includes capacity ranges.

BUYING TEST EQUIPMENT BOB STANG

TFIE writer feels that there has been a plugged into a line for filament voltage for ohms. Of course, such a meter will draw lack of unbiased, comparative data on the tube. virtually no current from the circuit being the various types of test equipment Naturally the sensitivity of the instru- tested, and so will not disturb the normal available to the Serviceman at the pres- ment on A.C. will be less than on D.C. A operation of the set. The best application ent time. In his position as the seller of 6,000 ohms /volt movement is usually 1,000 here is in the testing of A.V.C. voltage, test equipment to the Serviceman -consumer ohms /volt on A.C. and this must be taken although not electronically but through the in one of the largest distributors in the into consideration in choosing the move- conventional cuprous -oxide rectifier. An world, it has been his observation that the ment sensitivity. Further, the greater the electronic voltmeter, however, is definitely average purchaser either is not clear in his movement sensitivity the higher it will not a portable piece of equipment. mind about the different kinds of similar measure in resistance with the usual 4 %- equipment that will do the job for him, or volt battery used. A 1,000 ohms /volt meter FREE -POINT TESTER else has a glorified notion of what some is usually scaled to read up to %- megohm In the application of the multitester to particular gadget will accomplish. The lat- on its highest scale, whereas the 25,000 the actual fixing of radio sets, a very handy ter misconception is due largely to high - ohms /volt meter will read as high as 20 piece of equipment is the Free -Point Tester, pressure advertising. megohms. otherwise known as the "Point -to -Point An- Since it is true that one usually gets what alyzer." This convenient arrangement of one pays for (assuming a reputable brand ELECTRONIC VOLTMETER sockets and switches is frequently available is chosen), it is the writer's intention to Recently, several Electronic Voltmeters incorporated into the multitester or can be review the various types of equipment avail- have been made available to the Service- used as an auxiliary piece of equipment. able, mentioning the duplicating features man. These make themselves very valuable It permits the analysis of the trouble, or and the feasible application of each to its in that their input impedance is practically at least the measurement of voltages and proper type of job. infinite being usually as high as 15 meg- currents, while the set is playing and with-

MULTITESTER In the actual repairing of radio receivers, ,.b probably the most frequently used instru- 0000000 r A 100000001 of ment is the multitester. Fundamentally this im saawsro is a d'Arsonval meter conveniently arranged a 0000000 vw with appropriate shunts, multipliers, recti- -Q10000002 fier and battery so that it can be used for the measurement of voltage, current and ----1/4900000Q3 t 0000000 resistance in a number of ranges of each, the actual range limitation being deter- -OQÇ000O/- o 0000000 , mined by the meter movement sensitivity; .M: ao ü G.45 and the number of ranges dependent upon -s000000r a 0000000 a the particular manufacturer in mention. a It is not to attempt to apply practical OOOOQQOr F a meter of less sensitivity than 1,000 ohms - 9 per -volt to radio service. Standard sensitivi- ties now supplied are either 1,000, 5,000 or 25,000 ohms /volt. The latter although the most versatile, is not practical for in- olalelolol corporation into portable instruments as 11..-, A 6 L D f F the movement sensitivity forbids rough 0 O handling. Most multimeters measure A.C. by recti- fying it through either a cuprous -oxide or a J thermionic rectifier. The tube rectifier A. makes a better output meter, as its scale ¡c',x74 ciü M"R n,..,M,.,.. Oz[. is linear in respect to frequency change, weiftz but it is impractical in a portable instru ment as it requires the instrument to be Fig. 3. -A satisfactory, simple signal generator is the Triplett Model 1232A. 740 RADIO -CRAFT for JUNE, 19 41 TEST INSTRUMENTS

A Z 20.000 A.C. OGT5 ZERO- OHMS 6431167. TE0 ONMS ,. e 1.000 OM.4 5 1.300 6000 ONM,; ONA,CS ".60.4.6r -AC a2-MEG. y¿j0T5 /00K CANAIO d641.12A.CV0V3 At:.c 1r fÓ CH 0,, V3 30VJOV -R00 2aáao .05 avA4.s 7MEGS. 3V O0T3 DC v0,1.5 .Oi 1ME03 A/EG.9 MEG3. 30V O7-MEG. 60V 1300 0/431.5 02-MEG. OHMS 30.0V. OH MF ;000vcvr Sa 04/M3

Fig. 2.- Bridge type of electronic voltmeter as exemplified in the RCA Junior Voltohmyst. Ranges: 0/1,000 V. D.C. at high input impedance; 0/1,000 V. A.C. at 1,000 ohms/volt : 0 /1,000 mtgs. This piece of apparatus well illustrates the great advance which has been made in test equipment over this period of the last few years. out removing the set chassis from its cabi- necessary for the alignment of conventional terpreted as an approximate power factor net. In this way it is very useful in saving or Amplitude -Modulated seta, it will be indication. Some testers have a separate time for the Serviceman in giving an esti- necessary for the alignment of Frequency - control to measure power factor. Condenser mate. Modulated receivers in which ease best re- testers can be obtained incorporating a sults will be obtained when the instrument slide -back type of vacuum -tube voltmeter TUBE TESTER is used in conjunction with an Oscilloscope. and one is available that includes an oscilla- Another indispensible piece of equipment tor for alignment purposes. around the service shop is the Tube Tester. AUDIO OSCILLATOR Immediately in any discussion of tube test- For some applications, particularly in SIGNAL TRACER ers we run into the old argument of the sound work, an Audio Oscillator is a very The Signal Tracer being the newest and emission versus the dynamic tester. It is convenient piece of equipment. If one is most versatile piece of equipment yet to ap- the author's well -based opinion that either procured, its range fpr practical applica- pear on the service equipment market is of these types of tester is fully satisfactory tion should be at least from 30 to 15,000 naturally the most talked about and at the for routine tube testing. cycles. Some Signal Generators at present same time the least understood of all service It is an accepted fact that the dynamic on the market incorporate a variable -note equipment. There is nothing fundamentally tester is more accurate in its results than audio oscillator. Others have provision for new about the signal tracer. Its application the emission type, the comparative figures only a fixed 400 -cycle note-in addition to is what is different. Basically, the signal in percentage of bad tubes detected being in their normal function. tracer is a T.R.F. set, through the detector the neighborhood of 95C/r as compared to A variable audio range is convenient in stage, and with or without an audio sec- about 98C/r. In quickness of operation and that it permits the location of otherwise tion and speaker. cheapness of price the average emission hard -to -find rattles in speakers and cabinets The rectified output of the detector tester about compensates for this difference but is otherwise not essential in ordinary usually is fed into an indicating "eye" tube. in efficiency. It becomes a matter of indi- service. To a sound man it is an indispensi- This eye by its deflection will indicate the vidual taste and particular requirements. ble piece of equipment. presence and amplitude of a signal; and There are available several combination by the calibration of its resonant R.F. cir- tube and multi-testers, and even a few that OSCILLOSCOPE also include free -point testers. These are The Oscilloscope could not fairly be good, convenient instruments to take on a termed an indispensible piece of equipment. job but are usually limited in range and It will usually be found only in the posses- not over 1,000 ohms /volt in sensitivity. sion of the more advanced Serviceman. Its Where possible, it is always best to have application is that of a dynamic piece of equipment of this sort for the outside job equipment versus the static voltage and and the better, less limited equipment in the current testers that tell only the basic facts shop where it is free from damage, the best and leave the interpretation of these facts arrangement being some kind of a rack or to the Serviceman. On the 'scope one ac- panel set -up. tually sees the "picture" or image. To determine the actual flat -top band- SIGNAL GENERATOR width of an I.F. channel, or the hum level It is impossible to properly align a mod- at various points in the set, or the per- ern radio receiver without the use of a centage of modulation of a carrier; or any Signal Generator. For normal purposes this of hundreds of other facts not readily de- instrument should have a range from 100 termined with measuring equipment the kc. or so, to at least 30 mc. It should be 'scope is a great source of enlightenment mentioned that all bands should be funda- to the advanced Serviceman. It is not a mental although calibration on the dial of beginner's piece of equipment but definitely harmonics beyond 30 mc. is convenient. the sign of the well- equipped Service Tuning should be done with a vernier dial Laboratory. arrangement with a good rugged pointer that is either covered or not easily bent; CONDENSER TESTER and accuracy should be within 2'/r. Straight The Condenser Tester is a handy bit of A.C. generators are considerably better in incidental equipment. Usually a Wien frequency stability, than the A.C.-D.C. Bridge circuit, it is remarkably accurate variety. Where the generator is to be used for its small cost. Some will test a condenser largely in the field, a battery -operated without removing it from its circuit. This model is probably preferable. is an obvious convenience. All will measure It should be modulated or unmodulated, capacity, usually in ranges from about 10 at will, and should have provision for ex- mmf. to about 50 or 60 mf. ternal modulation. This will prove valuable The bridge is usually used in conjunc- later for connecting an external sweep tion with a visual indicator or "eye" tube, modulator for use in aligning F.M. re- resonance and the opening of the eye in- ceivers. Audio modulation at 400 cycles is dicating capacity, which is read directly on standard. It is convenient to have pro- a calibrated scale. One end of the scale is vision for using the audio signal alone ex- marked OPEN and the other end is marked Breakdown circuits. Fig. 4A. -Basie circuit of ami - sion -typa tube tester; Fig. 4B. -Basic conductance ternally for test purposes. SHORTED. Resonance at one of these or dynamic tuba tester showing A.C. applied o At least 2 models are at present avail- points on all scales indicates an open or grid. The elements are independently connected able that incorporate wide -band sweep shorted condenser. The amount that the eye to the voltage supply; Fig. 5: Wien Bridge circuit for checking condensers. As indicated by the dotted modulation. Although this feature is not opens, in indicating resonance, can be in- lines, phones can be substituted for the "aye" tube.

RADIO -CRAFT for JUNE, 1 9 4 I 741 TEST INSTRUMENTS*

cuit will indicate the frequency of the signal being measured. Signal tracing devices have OPPORTNNlTS/ AD-LETS either one channel as described above, Advertisements in titis section cost 15 cents or for each Insertion. Name, address and initials mu.; several channels, one for R.F., one for the be Included at the above rate. Cash Should pan, all classified advertisements unions placed by Oscillator or I.F. output of the set, a chan- an accredited advertising agency. No advertisement nel and eye for measuring audio, an elec- for lees than ten words accepted. Ten percent di.- ottnt six Issues, twenty percent for twelve INUe6 gIGBD- tronic voltmeter circuit and a channel that objectionable or misleading advertisements not ac- will measure the watts (power) consump- nlod. Advertisements for July. 1911 issue must nL u. not l.tt.r than May Slh. tion of the set. The advantage of having MODEL RailimCraft 20 Vesey New all in one is St. York. N. Y. __ _ these channels instrument pri- __ _ 860 marily in the detection of fading and intermittent trouble, the bugaboo of radio BOOKS AND MAGAZINES service. ASSURE YOURSELF OF GREATER PROFITS BY doing radio service lobs more quickly. Authentic sema The single -channel type of instrument guides show you the way to locate and correct troubles can be considered to be a "tuned electronic In any radio receiver. Gernsback Official Radio Servie. Manuels show you how to complete more repair jobs in meter." It will do anything the multi- less time -how to earn more money by lester servicing. channel job will, with the exception that it ltadcraft Publications, 20 Vesey St., New York City. cannot be hooked up to several portions WE HAVE A FEW HUNDRED RADIO ENCYCLO- of an intermittent- condition set. Where the pedias. by S. Gernsback. second edition. original!, sold at $3.98. Book has 352 pages. weight 3 lbs., size 9 z multi- channel job is used, when the set 12 inches. Red morocco-keratol flexible binding. Senti fades $2.49 in stamps. cash or money order and book alti be or cuts out, the eye associated with forwarded exprese collect. Technlfax, 1915 So. State Street. that portion of the set that is causing the Chicago. Illinois. will open, where trouble indicating the WHAT DO YOU KNOW ABOUT AMPLIFIERS AND trouble lies. Sound Syetemot The Amplifier handbook and Public Address Guide corers P.A. from A to Z. Most complet, Several signal tracers on the market have and authentic book published on the subject. Contains 80 pages of vital information on Amplifiers, P.A. Systems. meters in place of the eyes. These are Speakers. Accessories. Pickups, Microphones. etc. Printed slightly more expensive but some Service- on fine coated stock. with numerous photographic illustrations and explanatory diagrams. and only 25c. 8H men find a meter easier to read. Page 732. The signal tracing type of instrument EDUCATIONAL COURSES Performance . Eye cannot become obsolete since it measures CORRESPONDENCE COURSES AND EDUCATIONAL Appeal Value that which is the essence of radio trans- books, slightly used. Sold. Rented. Exchanged. All suh- mission itself, namely, the signal; signal lects. Satiafaction guaranteed. Cash paid for used courses. Sensationally Priced at Complete details and bargain catalog FREE. write Nelson $17.85, Dealer Net Price. tracing is a great time saver, and when Company, 500 Sherman. Dept. F -242, Chicago. you become familiar with it, really a much Hen is an AC -DC Volt -Ohm- Milliammetor with FLUORESCENT LIGHTING all the ranges you want . easily readable on easier way to fix radio receivers. These in- the large r instrument with entra -long 6" sain. struments are expensive, however, but if Zr FLUORESCENT BENCH LIGHT $1.49. LESS TUBE. in a new uptotheminute three -tone case. OC Harold Davis, Jackson. Mississippi. Volts 0- 10.50- 250 -500 -1000 at 5000 Ohms per volt your time is worth money they are a good DC; 1000 ohms per volt AC. AC Volts 0.10 -50- 250-1000 at 400 ohms per volt: DC Ma. 0.1.10.100; investment. PHOTOGRAPHY Resistance ranges; 0 -1500 Low Ohms; 0- 150.000 Stress be Ohms and 0-7.5 and 0 -15 Megohms. Maroon case should placed at this point on 1 /100.000 OF A SECOND SPEED FLASH UNIT FOR with red and silver panel, attached handle. the necessity of avoiding duplication of Stroboscopie Photograph'. $200.00. Apt. 63, 782 West Dealer Net Price, 817.85 function in the equipment purchased. For End Are.. New York City. For Catalog Write -- Section 616, College Drive example, if you already possess a good POWER PLANTS. GENERATORS. ETC. READRITE METER WORKS, Bluffton, Ohio multimeter which can be used as an output SOME BARGAINS ON USED LIGHT PLANTS. AC meter, it would be foolhardy when purchas- generators, and totnerters, 80 to 10,000 watts. write KaI ul ight, Mlaukato. 31111n. ing a signal generator, to obtain one that includes an output meter. Do not be tempted RADIO DATAPRINTS by the convenience of compactness if SACRIFICE! 12 -TUBE LINCOLN SUPER -DELUXE efficiency and versatility are sacrificed. All -Ways Receiver, complete with 12 -inch electrodynamic W TESLA -OUDIN COILS speaker and separate power pack. Cat originally 1145. Always bear in mind that your service 8911 sacrifice for $25.00. Set is 1933 model. rarely used 20e Ea. in order for 10 and In good working condition. Excellent sensitivity and instruments are the tools with which you selectivity. A resonance tuning meter. scare -band switch. 3 (Data and Drawings only.) phonograph input terminals, an ideal set for the DX 86" Sp'k Tesla -Oudin Coil 40e earn your living. Good equipment is ex- fan. Excellent tonal fidelity. All component. mounted on (1 K.W. Exc. Trf. Data Incl.) pensive, but it's far better to have several a beautiful chromium-finished chassis. Rush! First some. CII111 8" Stil( Tesla -Ondin Coil 40e good, basic pieces of equipment than a tlrat_Krvedl D. Kreissman, 1430 Ocean Ave.. Brooklyn, (1,4 K.W. Exc. Trf. Data foci.) Z =' full t r Sp'k Oudin; 110 Vt. laboratory of junk. / "Kick Coil" type 40e AT LAST! SUCCESSFUL SYSTEM RADIO TUBE RE- _ 8" Tesla Works on Ford jusenatlon. One dollar. W.Uruuecd. Vance Lind. St. _ faul. Nebr. 11 Coil 40e 1" Sp'k Vibrator Hi -Freq. Coi140c WANTED -ADAMS -MORGAN WOODEN-CASE. BRASS - NEW! 5 ft. Sp'k. Oudin Coil & Exciter variable condenser; electrolytic detector, Tuaka Data 75e plate Bunnell meters, etc. - Or wisst do you l I R. Bernarde 40 Manning Are.. No. Plainfield, N. J. Induction PIPE á ó RADIO KITS ORE LOCATOR RADIO KITS -$3.95 UP. SINGLE BAND: ALL WAVE. 40e 5-10 tubes. Fluorescent lighting. Sue 50 %. McGee Induction Type, Data Radio, l' -2055. K.C.. Mo. Radio Type 40e TECHNICAL ART SERVICE More DATAPRINTS 40c each! DRAFTING AND ART SERVICE -A COMPLETE Service for the Industriel and Commercial Marketers. 5 Meter Superhet. Electric Refrigerator If your business or plant can't afford designing or % Meter Tr. & Rec. Wheatatone Bridge drafting staff, don't let this stop you from going ahead with that new you Intend or 20 A.C. Probe. & Ans. 2 K.W. product marketing. that Weld. Transf. catalog of mechanical or electrical items which needs 20 Telephone Hook -ups Rewinding Armatures One detailed drawings and highly retouched photographs. 100 Mech. Movements Any mechanical, electrical or radio problem can be solved 20 Motor Hook-ups String Galvanometer for you by our associated staa of designen. draftsmen Television Hook -up 20 Simple Bell Circuits and artists, and technical copywriters. write for any 20 Elec. Recorder! additional information as to methods and price for this Party Tricks Steel Wire service. Ter -Art Drafting Service, 228 Charlotte Terrace. Solenoids and Magneto Water Wheels Roselle Park. N. J. -get list. Water Turbines F Fry Eggs on Ice 1 Photo Cell and Relay DRAFTING SCHEMATIC DIAGRAMS SENO US A rough sketch of Estimates by return Experimental Photo- Ring 4 belle: 2 Wires your circuit. mall. phone Our prices are moderato: our work guaranteed. No jobs Radio Control for 20 Tesla Tricks too big or small. Wm. Kadlecek. Jr.. 440 East 85th St., Models Polarized Relay New York. N. Y. Diathermy Apparatus Induction Balance Inductor Organ Electric Pipe Thawer r. PATENTS- TRADE MARKS Special Prices: 4 prints $1.00; 10 for $2.00; Qe Booklet concerning Inventions & Patenta Single, IOe each. Get New Catalog 100 A. Porm "Evidence of Conception" With u0 instruction* for tese and "Schedule of The DATAPRINT tre Government and Attorneys Fees"-Free Co. LANCASTER, ALLWINE & ROMMEL Lock Box 322D, Ramsey, N. J. Registered l'aient Attorneys. Fig. 6- lock diagram, Supremo 436 Bowen Bldg. Washington, D. C. Veedo lyzer. 742 RADIO -CRAFT for JUNE, 1941 EXPERIMENTERS

#otv to Build a $/mp/e MINIATURE PORTABLE TRANSMITTER The miniature tubes recently announced are getting into their stride. First introduced (to any considerable extent) in the now well -known "Portable" radio receiver, they are here utilized as the basic components for a "Personal" radio transmitter that has many uses. This "walk- about", veritable radio station may be used without a license only if operated for very short distances, and under certain other restrictions, as the author points out. Complete construction details are given.

H. G. CISIN, M.E.

ALTHOUGH the Miniature -tube Porta- ble Transmitter described in this article was designed especially for police and detective work it has many other practical uses. Some of these applications will be mentioned later. The instrument is a low- powered battery - operated portable instrument, extremely compact and very light. The Transmitter is mounted in a leatherette- covered wood case measuring only 5 x 3s x 13 ins, thick. It weighs approximately 10% ounces. It is powered by an Eveready 67% volt Mini -Max "B" battery weighing 12 ounces and a 1 1/3 volt radio "A" cell of about the same weight as the "B" battery. The battery dimensions are: "B" battery, 3% x 2% x 1s ins.; "A" cell, 4s x 2% x 1s ins.

CIRCUIT As the circuit diagram discloses, this device consists of 2 microphone preamplifier stages ahead of a modulated oscillator. The first preamplifier stage employs the 1T4 super -control R.F. miniature amplifier pentode tube. The 1T4 tube was chosen after experimentation with other available types and found to be most suitable. This is resistance- capacity coupled to the next preamplifier stage which employs a 1S4 power amplifier pentode. This in turn is resistance - capacity coupled into the 1R5 pentagrid converter, used in this circuit as a modulated oscillator. Resistance coupling was used in both stages chiefly because it is difficult to obtain a miniature -type transformer of Exterior, and und th interior view, of the completed Miniature Portable Transmitter. The top photograph shows a crystal -type hand microphone which the author made up simply by mounting a stand -type the proper (and light -weight and compact) crystal microphone on the end of a conveniently -available wooden handle. The transmitter may be carried type whereas resistances and condensers are in one pocket and the batteries in another. The compactness of this instrument is evident from the photo. available everywhere. The 1R5 is the only miniature tube avail- signal is impressed on control -grid Gl. This cathode and the anode in the oscillator por- able for oscillator purposes. The modulated varies the electron stream between the tion of the circuit. The oscillator circuit includes a tuned grid winding, with gridleak and grid- condenser R3, C2, R6. 04. AAAA,.,.. R9, /0,000 at-MEd. 003MF. .50.000 003MF, =.- 1 OMMS, %4.4 50MMF connected to G3. The combined grids G2, JL r4-w. \ / OMMS 55,w / 1 G4, shield G3. The internally -connected ele- R2, 1 ment G5 serves as the suppressor -grid be- 1T4 \ 154 IRS C6, la \ L L 50MnrF. cause of its internal construction of the Y4' w tube. Its purpose is as usual to prevent secondary emission from the anode. The energy from the plate circuit is fed back to the grid circuit by means of a secondary winding, rather closely coupled to the tuned grid winding. The carrier frequency or oscillation is determined by the inductance of the T grid winding and by the capacity of the trimmer condenser, C7. RB, 2.700 Using a 30 -175 mmf. trimmer with coil CWMS, Y4-w L1 (see sketch of coil) the device tunes be- 05, 05MF, ey. J3 tween 1,500 and 1,750 kilocycles. By using 200V. of OUTPUT TO a trimmer having an increased number * oPrioNAL ANT SYSTEM plates, the frequency of the oscillator may A-y /%2V 4" CELL be reduced so that it may be varied between B". 67 %2 V -B' BATTERY `J4 500 and 750 kc. or between any other desired frequencies. Complete schematic diagram of the Miniature Portable Transmitter, The values shown in This diagram While the electrical connections involved have been double- checked as being correct for use with the particular miniature tubes used by the author. in this ultra-midget transmit- In practice, slight variations from these values may be necessary, if maximum results are to be secured, constructing in order to compensate variations in individual tubes. ter are comparatively simple, the lack of RADIO -CRAFT for JUNE, 1941 743 EXPERIMENTERS

pace will undoubtedly present a real prob- ELECTRIC LANTERNS lem to those who are not accustomed to workmanship of this nature. To save space, s3.19 3,8. No. 400. Price all resistors should be of 1/2-watt rating. OrA. f-$3.19. 1500 foot Power Beam. Two re- flectors. Steel con- CONSTRUCTION struction. Finished The bakelite panel should be prepared R,o ebony baked enamel. v. first. Holes must be drilled for the 4 pin - Takes standard 6 Bat- BG -e tery. jacks, for the single -hole mounting trimmer rJRNs condenser, for the switch and for fastening the subpanel. The aluminum subpanel is E,. next prepared as per the accompanying do sketch. The compact oscillator coil may be GROUNO roRNs fastened to the back of the panel by one GR,p p _ÿ mounting of the switch screws or a separate RaNOOM-WOUNO .5 C C Ne 360.38 w,RE No. 500. Price $1.48. mounting screw may be used. After the 3 o 1000 foot Power Beam. miniature tube sockets have been mounted, 3B Size: Height 7-. Steel 11r- construction. Finished the subpanel is fastened to the bakelite baked lacquer. Takes panel by 2 small mounting screws, the standard 6 v. Railroad jacks, switch and trimmer are mounted and 747o®® type Battery. the instrument is ready for wiring. After the wiring has been completed, test -rOp v/EW- view the circuit carefully, preferably using a con- O -- ALUM/NM 5,49-R,oNEL + tinuity meter, and try to locate opens or shorts before the battery power is applied. Details in building the Miniature Portable Trans- No. 600. Price mitter. A. -Coil winding details; B.- Sketch of alu- Next, connect the batteries and test the minum subpanel. $2.69. 1500 foot tube terminals, for rated voltages, with a Power Beam. Steel voltmeter. Make certain that the filament drawn construction. which requires a person into Unbreakable plastic terminals show no more than 11/2 volts. to talk directly lens. Takes standard Finally, turn the "on -off" switch to "off" the mike.) 6 v. Battery. and insert the 3 miniature tubes. It should Using a different (less sensitive but more hardly be necessary to warn anyone that directional and rugged) type of crystal mi- Shipping any weight for these tubes must be handled with consider- crophone, the Transmitter may be used for of the above Models police work, permitting an officer to make 3 lbs. Furnished with- able care. Do not twist the tubes, but after out Batteries. the correct socket holes have been located, reports to a central point while patroling press the tubes gently but firmly into his beat, or for similar purposes. Other place. uses of this device include mind- reading Ali merchandise in original packages -never used. The Transmitter is now ready for test acts, the making of bingo and similar an- Money -back guarantee. operation. nouncements, mobile or portable announcing systems and many other applications re- AU Shipments will be forwarded by Express TEST quiring a concealed or small -space Xmitter. Collect if not sufficient postage included. Tune a nearby radio receiver to a point WELLWORTH TRADING CO. between 1,500 and 1,700 kilocycles. Connect LIST OF PARTS 1915 So. State St. Dept. RC -641 Chicago, III. a few feet of wire to output jack J4 of the CONDENSERS Transmitter. Leave the antenna connected Three Aerovox tubular paper, type 284, to the radio set, if the set employs an an- 0.05 -mf., 200 V., Cl, C3, C5; tenna. Insert a crystal microphone into Two Aerovox mica, type 1464, 0.003 -mf., C2, jacks J1 and .12. Be sure to connect the C4; ground terminal of the jack to .12 and the Two Aerovox mica, type 1469, 50 mmf., C6, control -grid terminal to Ji. Turn switch CS; Sw.1 to the "ON" position and slowly tune One Aerovox miniature electrolytic (option- trimmer C7. A whistle will be heard on the al), type PRS, 10 -mf., 75 V., C9; loudspeaker of the radio set as the trimmer One Hammarlund isolantite trimmer, type reaches the correct tuning point. When the DTS -115, 30 -175 mmf., C7. trimmer is exactly tuned, a feedback howl RESISTORS will be set up, if the microphone is too near Two I.R.C. insulated carbon, 11/2 mega., the radio receiver. The Transmitter should 1/2 W., RI, R7; then be moved away from the set until the Two I.R.C. insulated carbon, 1/2-meg., feedback howl is eliminated. The Transmit- Y W., R4, R5; ter may then be tested by talking into the One I.R.C. insulated carbon, 0.2 -meg., Y. W., microphone. To increase the range of the R2; Transmitter, lengthen the antenna wire One I.R.C. insulated carbon, 0.1 -meg., 1/2 W., connected to J4. Another way to increase R3; the range is to connect this wire to a radia- One I.R.C. insulated carbon, 50,000 ohms, tor, water pipe or other ground. In general 1,4 W., R6; it is advisable not to employ an outside an- One I.R.C. insulated carbon, 10,000 ohms, tenna, as this may increase the range to a V4 W., R9; point where there may be interference with One I.R.C. insulated carbon, 2,700 ohms, other radio sets. 1/2 W., R8. TUBES LICENSE One Hygrade Sylvania miniature, 1T4; THE PICTORIAL It is assumed that the users of this device One Hygrade Sylvania miniature, 1S4; FLYING REVIEW are familiar with F.C.C. regulations regard- One Hygrade Sylvania miniature, IRS. FLIGHT ing the operation of oscillators. Those who Misc. Brings you all the Dha.es of world aviation and not with these rules would aeronautics in n n- technical vet educational manner are acquainted One Eveready (Mini -Max) "B" battery, do well to send to Washington for a copy Youro` the funda`mentalsi , of flying c,nd Al.l, relate sub. 67162 V. (or Burgess equivalent); )ecta. before attempting to experiment with any cell, 11/2 V., FLIGHT keens you abreast of all the major develoD- One Burgess "A" type 2F (or Nents as fast as they appear anywhere. type of transmitter, even a low -powered Eveready equivalent); ow. when planes and flying a of vital Importance device such as this one. to all. you just can't do without this highly absorb. One bakelite panel, size 4% x 31/2 ins.; ing yet instructive publication. You must be it the knr Due to the fact that the Miniature Trans- One aluminum subpanel (home -made, see Partial Con of the June mitter employs 2 preamplifier stages, it is sketch); NOV?. New Dive- Bomber-The attract live C extremely sensitive to low- volume sounds, pin -jacks, J2, J3, J4; Sting in the Whitley Tail- t"..1,7.;,.rs -color e/ Four Jl, Leant Flying ln Swivel - a provided that the proper -model crystal mi- One 4- connector battery cable; Chair -Curtiss Wright 2t -B cepy Interceptor-Bomber Over Ber- Ìu, aiona. crophone is used. This feature makes the One oscillator coil (see sketch giving speci- AntI- Aircraf Guns Sena toe for Tar Sample Copy. instrument especially well adapted for de- fications), LI; Wt`iBombaUnsinn DÌ and and Cold each r Subscript ion price tective work. (The proper model mike for One leatherette- covered wood case; Turn -Hot Canada Fighter Plane. -Book Review. ands!reign i2 ß detective work is one which will pick up One crystal microphone (hand- type); FLIGHT MAGAZINE, 50.9 weep SL, New York, N.Y. sound from all directions rather than one One crystal microphone (hearing -aid type). 744 RADIO -CRAFT for JUNE. 1941 THE FINEST RADIO BOOK WE EVER OFFERED :- the 1940 -41 Radio -Television Reference Annual With $1.00 iu6scrcrtien to FREE RADIO - CRAFT

WITH our compliments, we want to send a caps of the 1940 RADIO- TELEVISION REFERENCE ANNUAL to you FREE, if you will simply take advantage of RADIO -CRAFT magazine's special Read the summary of contents subscription offer NOW. This offer Is being made fora limited time only. The 1940 RADIO -TELEVISION REFERENCE ANNUAL has 68 pages, large sire 81/2 a Ilya, with in this FREE BOOK! aver 170 Illustrations. The contents of this book has never appeared before in handy book farm. Its pages nover practically every branch of radio sound, public address. servicing, television. construction articles for advanced radio men and technicians, time and money- saving kinks, wrinkles, useful cireuit'informa- THE 1940 RADIO -TELEVISION REFERENCE lion, "ham" transmitters and receivers, and a host of other data. ANNUAL contains a collection of the best and The Annuals have always been regarded as a standard reference work for every practical branch of radio most important articles. Covering as they do operation and service. This 1940 edition ably sustains this reputation. Every radio man wants a copy nearly of radio, they form a handy el this valuable book. lust as this book will be of unquestionable value to you, so. too. will every every branch monthly issue of RADIO -CRAFT. This magarine brings you big value every month. It keeps you reference works. In addition, many time and labor- Intelligently informed about new developments in radio and television. You want the news, want it saving kinks, circuits and wrinkles, tried and tested fully but concisely. want it first -that is why you should read RADIO -CRAFT regularly. by practicing Servicemen, experimenters and radio This very special offer It made for Just one purpose -we want you as a regular subscriber. The Annual, fans have been included. This book cannot be whose contents appears at the right, Ìi not sold, but a COPY 10 FREE to you if you subscribe now. bought anywhere at any price. Yet It is yours by merely subscribing. Use the convenient coupon SAME SIZE AS below. RADIO -CRAFT BEGINNER'S SIMPLE INEXPENSIVE CONSTRUCTION ARTICLES Itegumer's Breadboard Special - a 1 -Tube High -Gain All- Wave Receiver -Wiring Pointers for Radio Beginners-A Watch Charm Sire 1 -Tube Set -Beginner's Simple Volt - Mllliammeter- )taking 1 -Tube Broadcast Loop Receiver -A.C. -D.C. Power Supply for Battery Portables -A 1 -Tube Short -Waver with Band Coll Switching. MORE ADVANCED SET CONSTRUCTION The "High -Seas 4" Broadcast Lamp Radio -How to Build a 6 -Tube 1.4 -Volt Short -Wave Superhet for the "Ham- er Short -Wave Fan -Build the "Lunch Box 5" Super Set - a Broadcast Battery Portable -How to Build a Plug - Together 8 Tube Broadcast Set -The '5.1n -4" All -Wave Radio for A.C. Operation -An Easily -Built 3-Tube Midget Broadcast Superheterodyne Receiver. THE SERVICEMEN'S SECTION Bass Tone Control-simplified Variable Selectivity-PRe- tieal Servicing Pointers- Servicing Universal A.C. -D.C. Re- relvers- Killing the "Intermittent" Bug -A Service Shop A.C. -to D.C. Power Supply -Sideline Money for Service- men-Adding A.V.C. to any Screen -Grid T.B.F. Receiver --Iron Particles In Speaker Air Gap. TEST INSTRUMENTS A Useful Neon Lamp Tester-An InezDensive Output Meter - -Making Milliammeter Multipliers -Home-Made Eminency Modulator-The Buey Servicemen's V.T. Volt -Meter. PUBLIC ADDRESS AND AMPLIFIERS Build this Combination A.C. -D.C. Radio and Intsr -tàm- municator-Speaker Placement in P.A. Work-The Design and Construction of an Inexpensive All- Push Pull 10 -Watt Amplifier- Obscure Sources of Hum in High -Gain Ampli- liere -How to Build High- Fidelity 5 -Watt Versatile :t mplifer. "HAM" SECTION Ultra -High Frequency Antennas -The Beginner's Low -Cost amitter- Modulator Meter -Phone Monitor -The Begin- ner/ "Ilatn" Receiver -2% Meter Acorn Transceiver. TELEVISION How to Build 441 Line T.A.F. Television Receiver-Use- ful Notes on Television Antennas. MISCELLANEOUS Simple Photo -Cell Relay Set Up- Making Burglar .Alarm -Bow to Build A.C. -D.C. Capacity Betsy-How to Make Modern Radio Treasure Locator. USEFUL KINKS, CIRCUITS AND WRINKLES \taking a Flexible Coupler -Two- Timing Chime-A Simple N Y Portable Aerial -An Improvised Non Slip Screw- Driver. NEW YORK, NOTE: The book contains numerous other useful Slab, III r Circuits and Wrinkles. not listed here. PUBLICATIONS RADCRAFt (approximately) 45 ARTICLES (approximately) 170 ILLUSTRATIONS THIS COUPON BRINGS YOU THE ANNUAL 68 BIG PAGES RADIO -CRAFT 20 VESEY STREET NEW YORK, N. Y.

Gentlemen: Enclosed you will find One Dollar for which enter my subscription 1 I to RADIO -CRAFT Magazine for Eight Months. Send me ABSOLUTELY FREE and POSTPAID, my copy of 1940 RADIO -TELEVISION REFERENCE ANNUAL. This is a new order Extend My Present Subscription RADIO -CRAFT NAME ADDRESS 20 VESEY STREET CITY STATE NEW YORK, N.Y. DON'T DELAY - MAIL TODAY! RC -641 RADIO -CRAFT for JUNE, 1941 745 EXPERIMENTERS

I/ow to Build and MO a LEAK DETECTOR

Details are here given for building a Leak Detector, and using it in conjunction with a Metal Locator (the latter for tracing the course of pipes), for locating leakages of water, gasoline, oil, etc.

G. M. BETTIS

production, since this factor enables the operator to make important determinations concerning the various amplified sounds.

PIPE LINE LEAK LOCATOR This high -gain miniature -tube portable amplifier has been designed with the main idea that it would be used as a Leak De- tector for locating leaks in pipe lines underground. This Leak Detector was planned as a companion machine to the Metal Lo- cator that was described in the December issue of Radio -Craft, as the Metal Locator proved to be unusually good for exact location of buried pipe lines. One of the advantages of the basic amplifier used in this Locator is that the self - contained power supply is in a completely - shielded metal cabinet. This eliminates any power -line noise and makes it practical to use the device anywhere. The excellent fidelity obtained through use of the crystal pickup, crystal headphones, and resistance -capacity coupled amplifier, is well worth while. PRACTICAL LEAK -LOCATING Job No. 1.-There was for example a known water leak, on a water line carrying 80 pounds pressure, that was showing -up in a low place on a small creek. The water was coming down alongside on The completed Leak Detector (right) is used only after the Metal Locator has traced the underground a line a hill. path of the pipe. The latter is here shown during the process of completing this important initial step. The exact course of the line was not The second and final step, next to repairing the actual leak, is to probe through the ground, until contact known as it had been laid and covered about is made with the pipe, at 50 -foot distances until the sound of the leak is heard. The vibration pickup 3 feet (crystal microphone) is on top of the probe. deep some 20 years ago. The exact location of this line was spotted by use of the Metal Locator described in the issue THE feature of this Leak Detector is pick -up ample gain to detect very weak of the Radio -Craft previously mentioned. (See use of the new Miniature tubes in sound waves or vibrations that are truly photo, upper -left.) an amplifier operating from a single reproduced in the crystal phones. The leak was spotted by using the ampli- 45 -volt "B" battery and a single 1.5 -volt Note that the writer has placed a certain "A" cell; this gives the inertia -type crystal amount of fier with the inertia -type or vibration pick- stress on the quality of the re- up attached, and listening with the headphones every few feet, with the probe of the pickup jabbed into the ground. As the leak was approached A Leak Detector, used in conjunction with a Metal Locator to plot the underground path the sound became loud- of a pipe line suspected to be leaking, may save huge sums money er; and as it was passed the sound became of by identifying and weaker. localizing the rushing sound of the leaking fluid. Leak -detecting crews On digging down, this leak was operating in one found major city estimate that water leaks cost the city about $500 per day; companies main- almost directly under the spot of loudest sound. This saved the time, taining oil and gasoline lines have equivalent leakage expenses. It is therefore bother and evident expense of that construction and use of the efficient Leak Detector here described presents money- starting from the small creek making possibilities for the radio Serviceman. and having the line uncovered for 85 feet to the spot where the line was found to be leaking.

The completed Leak Detector (above) is frequently worth more than its weight in gold. Its accessories are the vibration pickup (left) and crystal headphones (right). A rear view of the Leak Detector shows the use of the new miniature vacuum tubes. The underside view of this instrument shows how channel -aluminum both shields and divides the high -gain stages. 746 RADIO -CRAFT for JUNE, I941 EXPERIMENTERS

This leak was about s -in. in diameter and was roughly estimated to be wasting 30 gallons of water per minute which would be 1,296,000 gallons per month and if distributed through water meters at the city of $2.25 for 4,000 gallons minimum By courtesy of the Sun. rate day Call (Newark, N. J.), would supply 324 customers at the price of Radio-Craft here pre- $729. As furnished to manufacturers or sents a well -posed pho- of water the rate is about 10c tograph, taken during a large users series of tests in an ef- per thousand which would bring in the city fort to track -down some $129.60. portion of the loss in about 3,000,000 gallons The price of this one job snore than paid of water which escape for the equipment. There were many other daily in Newark's underground pipes. It Is leaks in this small city which the same in work of this nature equipment was used to detect. Servicemen will find, that No. 2. local bottling company was a Leak Detector such as Job -A here described will fre- having to pay an excessive water bill due quently pay for itself on to a leak somewhere under their concrete a single lob. Gaetano floor. Due to exceptional noise and vibration W. Sape, head of one of Newark's squads of of their equipment and machinery it was "water -leak detectives," impossible to detect this leak during work- is here shown listening ing hours. At 3 A.M. when all was quiet the for the sound of wafer leaks, 4.126 of which were Leak Detector was used to carefully ex- located in Newark dur- amine every water outlet for the loudest ing 1940. Figures in this signal of escaping water. After one was are interest-nterest- ing: a leak at 40 lbs. identified as "it," the floor was tested for pressure through a %-ln. several feet along the probable course of hole would cost a priv- the line, and about 25 feet from the water ate user (in New Jersey) outlet the spot to dig was marked. There roughly 100 per year. was a leak in a pipe thread where it had broken in connection to a "Tee" in the water line. This saved a large bill as this bottling company could only get a bid from pipe re- pairmen by the hour. How many hours? into the ground just as shown in connection showing on top of the soil. The pipe line How much concrete flooring would they have with locating the water leak. companies check the oil each hour between to destroy before finding a leak in a build- The further from the leak, the fainter pump stations and know just when a shorting 60 by 125 ft.? What would be the was the sound; and as the leak was ap- age occurs, and can start looking immediate- amount of the bill? The actual cost of fix- proached, the louder. The leak could be ly; testing with pickup and amplifier then ing this leak was $5 after it was located easily detected 100 feet away with the will enable a lot of oil to be saved by quickly with the Leak Detector. The excess on the probe pushed into the ground, and con- locating the leak. water bill alone was about $15 per month. tacting the line, which incidentally was easi- Pressures of 800 pounds are quite often Quite a lot of water and well worth saving. ly located. As the frequency of an oil leak used on oil carrier lines to move large There are many cases similar to this - is rather low, the use of the tone control quantities of oil as rapidly as possible. This not on water lines alone but on oil carrier incorporated in the instrument was of con- pressure enhances the probability of leaks; lines and other types of lines -where a considerable help. It was used to cut down the the pipe line companies recognize this proba- siderable amount of time and work can be high- frequency noises, and to the average bility. Contraction and expansion caused by saved. person the result is very much better; how- climatic temperature changes, as well as ever I could easily distinguish the leak, but erosion caused by the elements, are also con- OIL & GASOLINE LEAKS probably my ears are more accustomed to tributors to leaks as are defects in material The probe as shown in the detail draw- this and similar noises that may be ampli- and workmanship even when every precau- ing was used with a crystal -type vibration fied with so sensitive an instrument. tion known is taken to prevent leaks. pickup and amplifier in testing an oil car- This line was buried from 114 to 2 feet The usual procedure to detect a leak in rier line for leaks. There was not a leak in the ground as are most of the oil carrier a buried pipe line is to first determine the on the line but a small '4 -in. valve was and gas lines that are used in this part of exact location of the line with the Metal open slightly with a small stream of oil the country to carry the various oil products. Locator. The Leak Detector, as shown in coming from the line that carried 300 Frequently these oil lines spring leaks, the heading illustration and diagram, is pounds pressure. This was our leak to test. and if in a sandy or gravelly soil, which is then used approximately every 50 feet with The line was exactly located with the quite common, they may leak for several the probe pushed into the ground and in con- Metal Locator and the probe was pushed days before saturating the ground and tact with the line. If there is a leak in the

Ce C/O / 74 .001-MF 1 r4 /T4 .00/CB-MF 154 .05-MF ti - . R3 R3 ( R3 R4 C// I. M,EG. LMEG. 1. MEG .MEGS. .002 -MF 4 / 46 4 4 j 5 5 5

C9 C9 01-MF .0/-MF 6

7 7 C/( C//- R5 .00214F .002-MF .002-MF- /0,000 OHM` / 314E05 .0/-MF. R2 ` -R6 2.MEGS [RvSTAL 3.14E05 (EaCH) 4MF. i /. MEO. V/BRAT OH VOL. CONTROL P/C/CUP R4 R5/ R5 e..wEGS. 10.000 2.MEG5. /0000 0wM5 Rl RS c2 5./4C63. 00,000 8A4.5- OHMS D.PST. ORS.r. SW/7C14 9F2- ! .d2 -/ Y a/AS SW/76H CELLS,OR / -4//'1 . C- BATTERY R/ -r /. M4EG. 22hv.

RADIO -CRAFT for JUNE, 1941 747 EXPERIMENTERS

pipe line the sound of this leak will be re- washing machines, vacuum cleaners, air This was tested by a doctor in his office produced in the phones. conditioning units, and their component in listening to patients' breathing, bronchi- The distance between the points of test parts. al -tubes and lungs action, and other things with the probe will depend upon the size The location of the source of noise in any that are far more familiar to a doctor than of the expected leak; the smaller the leak, rotating machine, the vibration of pipe to the writer. This comparatively makeshift or the lower the line pressure, the closer lines, and many other test -applications, have arrangement proved very satisfactory. are the test points; the converse procedure not been mentioned. is followed when searching for larger leaks CONSTRUCTION on lines at greater pressure. WATCH DETECTOR The chassis was laid out and drilled as The use of this Leak Detector is practical There are other applications of this am- shown in Fig. 2. The folded -under front on lines carrying pressures of a few pounds plifier that are possible with various types edge of the chassis was straightened out to several hundred pounds as the sound of of pickups and microphones. One was the and drilled, as shown in Fig. 3, with the the leak is amplified so that it is easily de- use by a local watch repairman in listening front panel of the cabinet matching holes tected. to watches to tell what was wrong with as shown. The aluminum channels were A leak the size of a pencil lead in an oil them by the tremendous noises or vibra- placed after the holes were drilled to permit carrier line with 300 pounds pressure will tions as they sounded when amplified. He passage of wires for the connecting stages amount to about 10 barrels per hour! could spot in watches, various things need- and batteries, and for mounting the bias - Oil ing in West Texas at most of the wells is attention that radio Servicemen would cell holder. worth about $1 per barrel and as it is term equivalent to intermittents. The front panel was made secure to the carried toward the Coast, a distance of For example, the amplifier and vibration chassis by mounting the pickup connector, some 700 miles from a number of oil fields, pickup was used in the detection of noises, control 6 with attached switch 7, control it is worth quite a bit more as the price at loose jewels, bad hair -springs, and many 14 with attached switch 15, and headphone the Coast is around $2 per barrel. This other things easily recognized by the trained jacks. The dial plates were also mounted price is determined by the gravity and ear of a competent watch repairman. with the front panel controls. quality of the oil. A 10- barrel leak would One of the crystal headphones was built A common ground of a heavy piece of waste $10 worth of oil or more per hour, into a small metal box with a metal cover copper was soldered to the chassis and ex- and if this leak is not located for a day, that was lined with sponge- rubber. Room tended across all the stages. $240 worth, or in a week $1,680 worth, or was left over the headphone for the watch The tube sockets and battery connector more depending upon the distance the oil to be placed. This proved very satisfactory sockets 18 were then mounted, and the am- must travel before reaching, let us say, the and much cheaper than use of the inertia - plifier assembled and wired as Fig. 1 shows, Coast. Various -size leaks, and the time it type pickup but was not as efficient because with all grid leads shielded as well as the takes to locate them, determine the worth of pickup of other noises. component parts of each stage with the of the oil wasted. The headphone aluminum channels. It is essential to mount type of microphone or the lower part of the The price of proper equipment to trace - pickup was connected to a piece of shielded tube shielded and cut down the middle section down these leaks is very small compared microphone cable, the other end of which of the tube shield to a height of 11/4 to the price of the oil wasted. The time the had a microphone connector for attaching -ins. carrier line is out of service amounts to a to input of amplifier. After the amplifier wiring has been lot when the carrier is transferring 50,000 checked and the batteries connected, the barrels per day which many of them do. switches are turned on and each tube con- USE BY DOCTOR nection checked with a voltmeter; then the A crystal headphone was built into a OTHER APPLICATIONS tubes, headphones, and pickup are hooked small metal can, sponge- rubber lined and to the amplifier, preparatory to trying out Some of the applications of this amplifier with an electrostatic shield of copper screen the setup. with the inertia -type pickup are testing of across face of the headphone, that then Disconnect the batteries and place them all kinds of bearings (electric motor bear- was connected to the horn -shaped part of in the cabinet, with the chain of the micro- ings for example), crankshafts, gears, gen- a doctor's stethoscope (as the diagram phone making connection erators, compressors, refrigerators, under the panel fans, shows). screw. The batteries are then held in place on top of the chassis, in back of cabinet, with an aluminum strap % -in. wide (cut A NEW BOOK TO ADD TO YOUR TECHNICAL LIBRARY from panel No. 984) and clamped to the back of the cabinet with 2 small bolts and nuts. The 45 -volt battery lies horizontally and the 1.5 -volt cell stands vertically. The AUTOMOBILE RADIO- Principles & Practice brass nuts furnished with the 1.5 -volt cell were replaced with insulated ones, similar by B. Baker Bryant to those on the 45 -volt battery, to avoid ac- cidental shorts to the cabinet. The picture, Fig. B, shows how the handle was connected (or one can do this to ACOMPLETE compilation of pertinent data on suit). how to install and service the modem auto- The Leak Detector is now complete and mobile radio receiver. All of the non -essential details which have crept into the profession have ready for actual use. As we know, the been weeded out. Each topic is treated so as to ground carries contain a precise statement of the fundamental sound waves well, and with principle involved. to assure the reader's clear un- the tremendous gain, which is adjusted by derstanding of this principle, without distracting his 14 attention by the discussion of a multitude of details controls and 7, the Leak Locator can be and mathematical expressions. which are primarily set to pick up minute sounds in the ground. for the engineer. and tend to confuse rather than for clarify statement the auto - radio -technician. A meter for checking the different vibra- A practical treatise based on practical lente by practical radio people for the practical radio - tions can be made to connect to the De- tocholclan. tector externally, or it may be built into this unit according to the diagram of Fig. 4. Brief Outline of Contents- The use of this instrument as a Leak De- Introduction -The Auto -Radio Art. tector has been tested with very good re- Features of the Modern Automobile Receiver. sults but no wild claims are made. In the Installations of Automobile Radios and final analysis, device is Antenna. this essentially a The Automobile High and Low Tension high -gain vibrations amplifier. However it Electrical Systems. Automobile Electrical Disturbances. performs perfectly in the services for which Vibrator Converters and Motor Generators. it was designed. Service Hints. Classified Automobile In- stallation Notes. and Conclusion. LIST OF PARTS Send 50e check. money order. un CONDENSERS 50c used V. S. stamps. or coin for your copy of "Automobile Radio-Princi- Three P. R. Mallory TP404, 0.001 -mf., 8C; POSTPAI D ples & Practice"-it will be sent to you postpaid upon receipt of your Three P. R. Mallory TP421, 0.01 -mf. 9C; 5,2e -6 . 9 remittance. Inches One P. R. Mallory TP436, 0.05 -mf., IOC; 64 Panes Four P. R. Mallory TP405, 0.002 -mf., 11C; St!N.0 flexible RADCRAFT One P. R. Mallory BB21, 8 mf., 12C; Numerous One P. R. Mallory BB20, 4 mf., 13C. illustrations PUBLICATIONS, Inc. and diagrams 20 Vosoy Street, Now York. N.Y. RESISTORS One International Resistance BT%, 5 mega., 1R; 748 RADIO -CRAFT for JUNE, 1941 EXPERIMENTERS

T, 0-0 4- , AM rB1 - O c_ 0 2 3 9 du BIn V -T- (-FRONT /i 2 Z . ° . 7. B A I -04

I + i 1 0 /C. e 4 A. 543-0/4 CA:STON B jYg-OM. aetCW/NUM 4--- C/MAWE

~~PtT'~~

B + 3 MEG5. Fnr top nominal amount of 35c we will send you c following calves: ?00-1 i1. One duo -tone imperishably etched Brune Name -MEG. OUTPUT OHM Plate. size 3x11 /g inches with your TUBE OF AMP( /FIER POT. B++ urelnMd Security TONE 45V 2. One Genuine Leather Billfold. site emx3 Inches CONTROL F- Ff In natural brown color. with four compartments. -METER C/RCU/T FOR GIVING V/SUAL NO/CATIONS -- This Pock etbooknis ourb free present to You. Abso- lutely no strings of any kind. We make you this gift ME. because w covet you to do s a favor by showing your name AMPL /F/ER ordering one for themoseelves. That's all. Help usmand will probt yourself. V/BPNT/ON Mail and MICRORNONE AC NOW, the ecoupon below and N L5tber Billfold will 1, forwarded to you ateouce. PROSE Ir PREMIUM DISTRIBUTING SERVICE Wrigley Bldg.. Chicago. Dept. RC -6 -41 Enclosed And 35e for which mail to the address and Genuine Lyeatert Billfold without extra colt as per your offer. 1/NE ` My Social Security Number is R 171 R 3' 6 NAME _ 2 R METAL ZOCATOR PERYSENS,T/VEr ADDRESS R WNEN CROSSING LINE. MAKE R MARF WITH TOE FROM EACH CITY STATE I - ---- T WAY ACROSS /NE CENTER OF ( /NE, MADE FROM 12" CENTER i/4-S A E. OF MARKS MADE. RON OR STEEL Te.RFAOS 1iß fle4! OETA/L OF P/AE ^ ¡ Sel.iatichal ® "WALSCO UNIBELT" ` , ADJUSTABLE DIAL BELT Three International Resistance BT %, 3 Four Amphenol 78 -7P tube sockets; THE GREATEST TIME SAVER mega., 2R; One Amphenol CCC -1 cap and chain; PO! RADIO MIN IN TEARS! tots we ern..t.W Four International Resistance BTl, 3 One Amphenol MC -IF pickup connector; 1 www Thee e a` ntWed oat MM. Ow megs., 3R; One Amphenol PC -1M pickup connector; sot. af.IN d edit M1 Two International Resistance BTI/z, 2 mega., One Burgess Z3ONX 45 -V. battery; wwe.CO PNNE LT tap o sod IN repeat 4R; One Burgess No. 44 1.5 -V. cell; assest h two mow_. Nv, 10,000 Burgess No. 5360 41 V. battery; 1 r .w . Four International Resistance BTtz, One rsr Nab. fr FLEE WALSCO CATALOG N., ohms, 5R: One Bud 973 cabinet; Or 1 E WA J. SCHOTT CO.O, Flu La C111. One International Resistance 2 -meg. dual One Bud 41 chassis; iIH g1L. A1,, control, 611; One Bud 984 panel; One International Resistance No. 22, with Two Bud 261 channels; D.P.S.T. switch, 7R; Three Bud 391 shields; FACTORY-TO-YOU SAVE TUBES One (each) Bud 980, 982, 1719, 1720 dial NB Im SEW 1941 50% Three RCA type 1T4; plates; 15 TUBE One RCA type 1S4. One P. R. Mallory MR53 1 -meg. control, 14; RADIO - PHONO One P. R. Mallory M27 D.P.S.T. switch, 15; <04Po wn 0115% N CO MISCELLANEOUS TMM MSEN, UNIT RADO -NOLO One Brush model A crystal headphones, 19; One P. R. Mallory GB -14 bias -cell holder, OHMS with TRADR-BN owl SHAM One Brush No. 310 VP -5, vibration pickup, 16; rzRSÌe Nosy M.d.lsl 20; Two P. R. Mallory 1 V. bias cells; Write I,. FREE,r.MB today. NOME ROt.12-RR N1wOT .APIO COtIOtaBON. CMdraA OW REMO Five Amphenol 78 -1M % -in. sockets (Red, Two P. R. Mallory F'. V. bias cells; Black, Green, Blue, Yellow), 17; One P. R. Mallory 420 jack; Five Amphenol 71 -M % -in. sockets (Red, One P. R. Mallory 421 jack; Black, Green, Blue, Yellow), 18; Two P. R. Mallory 366R knobs. POWER AND LIGHT ONAN A.C. ELECTRIC PLANTS supply cur rent for Radir.Transmitters and Receivers. P. A. r.system.. ne Sound Tool.. Licht. AAÌIApphe sedc.SStrnd "FACSIMILE FREDDY" put on a transmitter set up for the purpose by'Equipment in Schools. Hasqule.Thatroo and Building.a "Facsimile Freddy," WOR's facsimile car- in the classroom, at the Newark, N. J., dues is Ebod.. a e APoserlLine i 1Failure Volt A.C. -It, 32 end 110 Volt D.C. -Alw OWl toon, last month went to school. The work Y.M.C.A., sent from there to WOR, and Voltre AC -DC Type.. Manual.Full- Ao,umn.irk làll- Stareins. B99.nd op. Snipped N..dyt.RUit. of students of a cartooning class, held by from there broadcast on the regular D. W. MOAN i SONS Milt Hammer who draws "Freddy," was facsimile program. 722 NtWRet Avow, Mlnn.aWM. Mina. RADIO -CRAFT for JUNE, 1941 749 F. M.

Practical coil arrangements. A -Wired and tested R.F. and oscillator tuning assembly B-F.M. discriminator transformer, with combined and mica removed "air tuning ", to show ceramic winding forms: C -F.M: I.F. transformer for 4.3 mc. (can is 21/2 ins. long). Carron coils are illustrated. 2¢OYy and 0.2.5l9n CO/191d2rat10/it9 O R.F. AND I.F. COILS IN F.M. RECEIVERS It is believed that the following article, prepared by a coil specialist and present- ing material almost entirely new, should prove of exceptional value to Radio -Craft readers. The article concerns the design and design practices in various coils used in Frequency Modulation reception, and no reference is made to the operation of an F.M. receiver other than that necessary to describe the operation of the coils. C. S. LINELL

DURING the last 12 months radio liter- which the amplifier is able to accept, and Fortunately, this curve does not have to ature has contained a number of arti- since this band -width is determined chiefly be duplicated since the action of the limiter cles dealing with the various phases by the I.F. characteristics, we shall discuss tends to remove all increments in amplitude of Frequency Modulation from re- the I.F. amplifier before turning to the beyond a certain level as determined in the ceiver design to antennas and service. (*) R.F. and Oscillator stages. design of the receiver. The dotted line rep- Today the average reader of Radio -Craft is resents a suitable level of about 4 volts at on speaking terms with F.M. even though the limiter grid. THE I.F. STAGE situated in localities not yet having the -4.3 MC. Band -pass. then, we design an am- benefits of F.M. service. The Radio Manufacturers -If Association, plifier having a curve such as b in the same It is our plan not to describe any particu- after considerable deliberation, selected a figure and depend on the limiter to operate lar F.M. receiver or the operation of the frequency of 4.3 megacycles as a recom- as before, we may retain the ability to various circuits in an F.M. receiver since mended intermediate frequency for use in align the tuned circuits with an ordinary this has been so well covered in the past. F.M. receivers since a frequency above 4 mc. unmodulated signal at 4.3 mc. and still have The art is new and rapidly progressing; the precludes the possibility of image frequency essentially the same band -width character- information which has been printed re- interference within the band of 42 -50 me. istics as the ideal band -width curve shown quires no summary and we shall therefore An I.F. of 4.3 mc. provides a guard band at a. By using a curve of this shape, maxi- devote this article to the design and theory between the amateur 3.5 -4 mc. band and the mum band -width is not obtained at full re- of the various coils and I.F. Transformers 75 kc. transmitter frequency excursion. ceiver sensitivity, but this sensitivity would used in a representative F.M. receiver. Thus the first design factor, the frequency, not be usable in any case, since the ability The ability of an F.M. receiver to receive is already established. of the limiter to remove all traces of ampli- and demodulate commercial wide -band F.M. The ideal overall response of a perfect tude modulation, static, etc., requires a sig- transmissions depends on the band -width I.F. amplifier for use with present trans- nal of about 4V. as already stated. In ad- Bee listing at end of article. mission standards is shown in Fig. 1, at a. dition, the ability of the limiter to discrimi-

~~4./ 42 4.3 4.4 4.5 4.1 4.2 4.3 4.4 45 4.1 4.2 43 4.4 4.5 FREQ. IN MEGFJCYCL ES FREQ. /N MEG.9CYCLES FREQ. /N MEG.wCYCL FIG. I ES~~

~~750 RADIO -CRAFT for JUNE, 1941 F. M.~~

6AF6G R F rUNiNG A55E*,a[ y AWE ' GRONOEO NER7ER lERO. Ail 074075 CONOENSERS R/S .0/-M4,447tE35 07,74- 0.2= 11/5E SOEC/F,EO. /};EO w. 6AC7] 0 t W I 9 M ç R22. 7229.(wEG,//3w. 0v,sr5 250,. /MEO. 1721.500000i44S w. J R9. ) g 6N6 64C7, 6AC7` 000 .w 044E4 I °iw 20O t,((II O//M5 4O, Eavlj(( /V3. .ommer 4.17,0 -5. OR/6 a ?.w CI9 4. C2 C3 C/ 0 `25 h /ctl C6/ R/9 50, 000 C7 e f V ' 5 CEACN) /000 42. / ONM5 Cd /ON*,S -000/-/6Mi .O/- 4E0 9** *"."5 (CHCN) /,000 l ER 1230 R/4, a.0500. C2S/ w+5 ErowN I /2,25, /91E0 4/2 w 002*, R/B,R/9.R20/NCtuSrvE /i9/r /00 C/ TO CAS 4./Ct05/VE Bf toff wN/rE- J %3-w. h-w .OS-*,R 400v. R.F. and I.F. ope ation of a typical F.M. receiver. Note unit -built R.F. section enclosed within dotted lines. (See NOTE at end of article.) nate against amplitude changes increases either the 1st or 3rd method is preferable, of approximately 50 mmf. This results in a in proportion to the I.F. signal available at since fine wire usually results in finer in- total shunt capacity of 65 mmf. Calculating, its grid. sulation and increased distributed capacity, we find from substitution in the formula: Band -pass characteristics such as we re- resulting in a lower L/C ratio with conse- 1 quire may be obtained by the use of tuned quent reduction of resonant impedance. The (5) f - circuits, coupled by a mutual coupling, the author prefers the 3rd method in which 2x VLC value of which determines the pass band. the coils may be designed for the most sat- 21 RH. Consulting Fig. 2 and disregarding for the isfactory winding from a mechanical stand- that the required inductance is We moment the fact that several of the curves point. This results in coils of consistent then may calculate the approximate mutual have pronounced "double humps," we see characteristics, which are symmetrically inductance between primary and secondary as already mentioned 2). A mica that 2 circuits of constant "Q" and having loaded with shunt resistors across the pri- (formula various degrees of coupling designated as mary and secondary. These resistors have trimmer mounted on a ceramic base is k, exhibit various band -widths from which the two -fold purpose of providing (a) the chosen, since no electrical improvement we may make our selection. The value of k proper Q and (b) a dissipative circuit could be obtained from the use of either may be predicted with sufficient accuracy which prevents the rapidly changing fre- permeability or air tuning in conjunction from the formula: quency from setting up transients. The lat- with the relatively low Q necessary. Their use would result in unnecessarily increased Width of Pass Band ter may be heard as a "fuzz," particularly on loud, high- frequency passages. cost. (1) - - k So far, we have discussed the I.F. Trans- Mean Intermediate Frequency L/C Ratio. -Although treated last in this formers as a group. Actually we have 3 after which the mutual inductance, M, may discussion, the L/C ratio of the tuned cir- types: (1) Input /Interstage which are be set to the proper value from: cuit inductance to its shunt capacity must identical, (2) Limiter input, and (3) Dis- (2) M = k V Ln L, be borne in mind all during the design of criminator. the I.F. transformers. To provide a reason- The Limiter transformer differs from the In practice this value is set approximately. able amount of gain at the relatively high Input and lateratage only in that no loading Final adjustment is made in the actual am- frequency of 4.3 me., we must employ as resistor is necessary for the secondary, be- plifier, since unknowns in the form of un- much inductance as possible compatible cause it is loaded to a somewhat greater predictable capacitative and inductive cou- with stability. We know that the sum of degree by the grid current drawn by the pling occur. These may increase or decrease wiring, tube input and output, and coil dis- limiter tube. It is permissible to increase the effective coupling. tributed capacity will be approximately 15 the coefficient of coupling in the limiter Although a satisfactory curve could be mmf. We have available a midget trimmer transformer to maintain the symmetry of selected from Fig. 2 curve k .035, we find having a mid range or most stable capacity response. The difference in coupling is so that is has 2 distinct peaks with an area of reduced response between them, a condi- I CRC/BRATE VOGTMETER 1 tion entirely'unsuitable for F.M. reception. Consult now, curve Q = 55 in Fig. 3 which i I RTTEN- 1_ __ represents 2 tuned circuits having a value OSULL/970R - - TOR _ i of k = .035 suitable for our purpose but having the same "double hump" response. i Q I TEST If we vary the of the coupled circuits, . 1 L-'y T' coefficient of coupling con- maintaining the i stant, we may alter the "double humped" _J response to any intermediate value. Bear- F -- L------i ing in mind the action of the limiter, and the band -width selected, we find that by employing tuned circuits having a Q of 90 A ' a satisfactory response is secured. This - T value of Q may be calculated from the t= formula: ° 1 3 2 1.4 T s===' (3) VQ,, Q, = - or Qn = Q, = 40 'l k 5 / B B 3 If we desire the curve to be essentially "Rat topped" the formula would read: = / 1.5 4Aa' 4 (4) VQ,Q.=- orQ, =Q, =42.9 FIG.5B k ` FIG.SC Fig. 5-Testing and applicafional circuits. A -Block diagrams of coil -testing setup with which final Q. -There are several methods of ob- adjustments are made. Band -width and gain -per -stage may be measured by means of the instrument taining the required value of Q. The coils represented here. B- Diagram showing the introduction of undesired inductance at (I) due to bypassing through a long lead to ground; (2) long lead to tuning condenser; (3) long lead to screen -grid, with may be wound on high -loss cores, wound regeneration introduced due to the common inductance of the ground path between the gang and with high- resistance fine wire, or shunted ground (4) and bypass ground (4a). Long lead (5) contributes inductances to the tuned circuit but turns with a value of resistance to lower Q introduces a loss of gain. C- Detail showing how overall inductance may be incr d by moving the as shown by I, or decreased, 2; or the effective tap position raised, 3, or lowered, 4 Larger changes in from a higher value. In actual practice, tap (tracking) position may be made by moving the position of the turns above and below the tap. RADIO -CRAFT for JUNE, I941 751 F.M.

small that it is not practical in production the secondary as this is provided by the extent of stating: "If it becomes necessary to maintain and is seldom taken into ac- resistance of the diodes and their associated to replace any part be sure to put the re- count. circuits. placement part in the exact position occu- Discriminator- Transformer Design.-Un- pied by the defective part and use exactly like the Limiter, the Discriminator differs R.F. AND OSCILLATOR STAGES the same lead length originally employed." considerably from the I.F.s both in me- Frequency Modulation transmissions oc- Bearing these remarks in mind we will chanical construction and in electrical char- cupy the band between 42 and 50 mega- proceed with the actual coil design. acteristics. The voltage input to the pri- cycles. Any experimenter who has built Condenser Tuning -Ratio. -As stated, we mary of the Discriminator transformer is amateur 5 -meter receivers is familiar with wish to cover a range of 42 -50 mc. If we practically constant at about 20 volts under the small size of the coils and condensers use a condenser to tune to these frequencies usual operation. The voltage delivered to necessary to tune to these frequencies. Sev- we may employ the formula for inductance, the diode rectifier is not constant, however, eral facts, however, are usually overlooked. capacity and frequency to determine the and varies with the frequency of the ap- The length of leads from the coil, size of tuning ratio of the variable condenser plied signal at any instant. The primary the variable condenser (length of electrical (ratio of total minimum capacity to maxi- and secondary windings of the discrimina- path), bypass condenser leads, etc., all con- mum capacity). To permit a slight space tor transformer are identical to those of tribute to the inductance in the circuit. For at each end of the dial we assume a range the I.F. transformers. The coupling between greater than actually required and in the the 2 coils is made by means of 2 indepen- case of F.M. our total range will be 39 -51 dent methods. The coefficient of coupling is mc. If the inductance L is held constant we selected to give a peak separation of 250 kc. will require a condenser ratio which is for reasons which will be discussed later. equal to the square of the frequency ratio. In addition, a capacity is placed between List of Articles in Past Issues of We will therefore have: the plate end of the primary and a center - (51 mc. tap on the secondary. Radio -Craft on Frequency (6) Condenser ratio = 1.71 Let us consider the relationship between Modulation 39 mc. ' the voltages in /- this transformer and their New Circuits in Modern Radio Receivers This value 1.71 is very small and is not effect on (Dept.) : the design. It is necessary for "New Circuit Using 'Electric Eye' as F.M. ordinarily obtained with any available proper discriminator operation that the Tuning Indicator" (Pilot) ; "Direct-Coupled variable condenser. There are, however, voltages developed in the 2 halves of the Limiter Tubes Used in F.M. Receiver" (Zenith), several solutions to this problem: secondary be EXACTLY equal and 180° April 1941. "Frequency Modulation Receiver (1) We may place a large shunt uses 2 Limiters in Cascade" (Scott). capacity out -of-phase with each other. This requires Dec. '40. across the coils and use a small variable an exact electrical center -tap. Even capaci- "Supplementary Shadows Indicate F.M. Reso- nance" ( Meissner), Nov. '40. "Pushbutton Am- capacity for actual tuning. This method ties to ground must be equal and a small has the disadvantage unless compensating plitude- Frequency Modulation Changeover" that the coils condenser (a few mmf.) is ( Stromberg- Carlson), Aug. '40. "Same Tuning are very small, an extremely small variable often placed externally from the unground- Indicator Used Both for Amplitude and Fre- condenser is required for tuning. If the in- ed diode to ground to compensate for the quency Modulation Receiver" (Stromberg -Carl- ductance is reduced the L/C ratio becomes smaller diode capacity of this circuit. . son). "Tuning Indicator for Frequency - unfavorable, the parallel resonant im- Modulation Receiver" ( Stromberg- Carlson), In the operation of the discriminator the March pedance is lowered and the available gain secondary is '40. tuned to exact resonance with Recent Improvements in F.M.-Receiver Design, is small. the mean I.F. Any mis- tuning of this cir- March 1941. (2) A small series condenser (semi -fixed) cuit results in phase shift and consequent A New A.F.-Drift Correcting, Signal -Balancing. may be used between the coil and the tun- non -linear operation. Therefore, best de- Direct -Coupled F.M. 24 -Watt Audio Amplifier, ing condenser. From the loss of gain stand- sign practice dictates that we employ a coil Part I, Dec. '40; Part II, Jan. '41; Part III. point this method is superior to Method 1. wound on a ceramic form and tuned by Feb. '41. It has several disadvantages such as criti- means of an air trimmer. The primary wind- Circuit Features of the Latest Ultra -H.F. "DX" cal adjustment (stray capacities), and dif- need F.M. -A.M. Receiver, Feb. '41. ing not be so exacting since phase F.M. ficulty in obtaining proper tracking be- shift occurring in Servicing Pointers, Jan. '41. this resonant circuit will The ABC of Frequency Modulation. Dec. '40. tween the oscillator and R.F. stages. not affect the operation. For this reason Station WOR Gets F.M. Voice. Dec. '40. (3) A combination of both these systems we may use the more economical mica trim- Present Status of' F.M. Broadcasting. Dec. '40. may be used which will result in retaining mer. The primary must pass the full band- F.M. Servicing Procedure, Nov. '40. the better features of both. This Servicing F.M. consists width of frequencies from 4,225 to 4,375 kc. Receivers, Oct. '40. of placing a small Servicing F.M. Receivers, Sept. '40. semi -fixed trimmer di- with but little frequency discrimination. We rectly across the coils to provide alignment will Latest 28 -Tube DeLuxe High- Fidelity F.M. and show how this is accomplished. For at the high- frequency end of the band. A proper demodulator operation A.M. Broadcast Receiver, Sept. '40. the recovered Build This Practical F.M. Adapter, Aug. '40. standard small variable tuning condenser voltage versus frequency curve should be Choosing an F.M. Antenna, July '40. may be tapped down on coils. This linear within the tap the frequency deviation en- Data Sheets (Dept.) : " Stromberg- Carlson. No. has the same effect in limiting the tuning countered. 425 Frequency Modulation Receiver and 'Con- range as the series condenser in Method 2. The response curve of the discriminator, verter'," Feb. '40. It has the additional advantage that ad- Frequency -Modulated Programs on Your Present is a combination of the voltages developed justment of the inductance abdve and below across Receiver 1 -with This Easily -Built F.M.-A.M. the secondary due to the inductive Ultra- Shortwave Adapter, Part I, Dec. '30; the tap allows us to vary the tuning ratio coupling with the primary, and the primary Part II, Jan. '40. and accomplish tracking over the narrow voltage introduced into the center -tap. In band required. form, it resembles a "double hump" I.F. re- Its disadvantages lie in a somewhat high- sponse curve with one hump reversed to er distributed capacity and a tendency to complement the other. This resembles a let- resonate at 2 distinct frequencies. This latter "S" laid on its side. Our object is to this reason trouble is usually encountered ter fault is not important in a superhetero- make the center of the curve as straight when gang condenser operation is at- dyne, since the effect is such that it is im- as possible over the range of the frequen- tempted. possible for the oscillator to beat with the included cies in the maximum deviation of Coil Design in Theory and Practice. At undesired frequency to produce the I.F. No the transmitter. these frequencies it is ABSOLUTELY IM- padding condenser is necessary with this Inspection of curve k = .058, Fig. 2 will POSSIBLE to design a set of coils on paper circuit (general high- frequency practice show that the sides of the curve between and expect them to work perfectly. The only usually eliminates the padding condenser) the mean frequency and 75 kc. are fairly method by which perfect results may be as this adjustment may be made by as sim- straight. The peak separation in this curve obtained is to follow the preliminary design ple a procedure as bending the tap lead is 250 kc. Using this as a design factor we with actual application. where it leaves the coil. By this means its may construct our discriminator transform- Here the exact circuit and proposed lay- mutual inductance may be added or sub- er. Although the sides of this curve are not out are constructed and final inductance ad- tracted from the effective inductance tuned. absolutely straight their differences are justment is made. Coils so designed will give Design Example. the sake of design such that they cancel -For each other and a the maximum performance in THIS LAY- let us use Method 3. Connect a small "high - linear response vs. frequency results. One OUT ONLY and any attempt to install lift low -capacity trimmer" across each coil, other factor, the primary response, affects them in a similar circuit with a different assuming a wiring and input capacity, plus the shape of the curve. In operation the physical arrangement will give unsatisfac- trimmer capacity, of 22 mmf. for R.F. and resistance reflected by the closely- coupled tory results. For this reason manufacturers Oscillator circuits. For the time, ignoring secondary tends to broaden the primary ac- who supply F.M. components in kit form the maximum tuning capacity, we can cal- ceptance band to the full band -width which generally furnish the complete R.F. and Os- culate the inductance necessary to resonate satisfies the condition mentioned in the be- cillator sub -assembly completely wired and at the highest frequency (51 mc). Employ- ginning of the discussion of the discrimina- tested. Commercial receiver manufacturers ing formula (5). tor. No resistance loading is necessary on are specific in their service notes to the We find the required value to be approxi- 752 RADIO -CRAFT for JUNE, 1941 F. M.

mately .44 H. This value may be obtained sign to the primary reactance. Formulas by winding 5 turns of No. 18 bare wire, have been developed for the calculation of spaced twice its diameter, on a % -in. O.D. the ideal conditions, but due to their com- bakelite tube. Using this value of inductance plexity they are seldom used and the same In a Hurry we find by again substituting in formula (5) variables as we encountered with the design that approximately 37.7 mmf. will be re- of the I.F. transformers affect the coupling quired to tune to 39 mc. Rather than use a and alter it from the calculated value. small condenser (37.7 mmf. - 22 mmf. For our purpose we may calculate the for F-M? 15.7 mmf.) as a tuning condenser we may primary impedance based on about t/z the choose a condenser several times as large desired impedance and from formula (7) and tap down on the inductance to give the and a knowledge of the effective circuit Q same result. If we select a condenser hav- determine the approximate required mutual ing a range of about 90 to 100 mmf. we may inductance. We may assume that the cou- tap down to about 1 /6th of the total in- pled reactance will approach the required ductance. This method of design neglects value and from this starting point the the minimum capacity of the tuning con- primary may be constructed. On the R.F. denser but due to the impossibility of de- coils mentioned above this results in 2 signing these coils without actual applica- turns interwound with the primary starting tion, this discrepancy may be corrected in tfi -turn outside of the end secondary turn. the final adjustment. This method permits Oscillator Coils. -The exact construction us to utilize approximately 80% of the con- of the oscillator coil will depend on the type denser rotation to cover the required band, of circuit employed. Electron -coupled oscil- resulting in an easily read dial. lators may be used with the 6SA7 or with R.F. and Antenna Primaries. -The design a separate electron -coupled oscillator. These of the R.F. and Antenna primaries also rep- circuits require a tapped coil. Use the Meissner resent a compromise, since extreme care The position of the tap should be deter- must be taken to keep the capacity between mined experimentally to give the most suit- the primary and secondary low. One of able amount of feedback. Coupling should the most satisfactory methods is to space - be close in any case (interwound if a 6A8 wind the primary between the spaced turns converter is used). The oscillator induc- F -M RECEPTOR of the secondary. Care must also be taken tance should be adjusted to a slightly lower for immediate satisfaction! to prevent the R.F. primary from resonat- value than that used in the R.F. stages ing with the tube output and wiring capaci- and a ceramic -insulated air trimmer should The Meissner F -M Receptor is a com- ty, within the band employed. Since at be employed to assure permanence of dial best, the impedance of the primary as calibration and freedom from drift. plete, self-powered, 8 -tube converter, presented to the plate of the preceding tube By this time the reader has probably designed to add F -M reception to is far too low to permit a reasonable come to the conclusion that the design of any regular receiver -feeds directly amount of gain, it is necessary to use as tuned circuits for frequencies such as em- the input of the audio system! much inductance in the primary as possible, ployed in F.M. is a rather haphazard busi- into without conflicting with the conditions men- ness. This is true to a certain extent. We With this inexpensive unit you can tioned. A ratio of 2 primary turns to 3 sec- should remember that the principles in- have all the advantages of F-M- ondary turns represents a workable value. volved, are a starting point in the design, hi- fidelity, staticless, noise -free and The antenna primary is a less critical and their use at lower frequencies may be made with greater interference -free reproduction -right matter. The impedance reflected into a accuracy. At these lower Power output transmission line from a doublet antenna frequencies stray capacity and lead lengths on your own radio set! should be approximately 70 to 100 ohms. do not represent so large a proportion of and tone quality are limited only by The impedance of the primary may be con- the total circuit constants. your present audio system. sidered as the sum of the impedances of This article has been prepared from ma- RF stage provides maximum re- the primary alone plus that coupled into it terial supplied by courtesy of Carron Manu- by the secondary. This coupled impedance facturing Company. ception range and noise rejection- is equal to: tuning indicator for accurate adjust- Note. (2 M)' -In the bank of 3 condensers which are Extremely bypasses for the input 6A7 tube, the unit which ment-only two controls. (7) bypasses the 1,000-ohm filter resistor to ground 13" wide, 7" high Z. compact -only should be instead a 0.001 -mf. mica condenser. and 63/4" deep-beautiful, hand - where M is the mutual inductance between It may be of interest to note that condenser primary and secondary and Z. is the paral- C which shunts the heaters serves only to reduce rubbed walnut cabinet. For 110 -volt lel resonant impedance of the secondary. the impedance of the heater circuit close to the AC operation only; also available The condition maximum sockets of the assembly. This is necessary be- for transfer of cause of the relatively without cabinet if desired. List price. energy is impedance long heater wires which such that the coupled have considerable inductance and which therefore ready to operate, only $39.95! is equal to the primary impedance and the may, under certain conditions, allow a certain coupled reactance is equal but apposite in amount of feedback between these tubes. See Your Jobber Today!

1941 INSTRUCTION MANUAL DISTINCTIVE CALLS FOR F.M. Now Ready! call, for Contains complete TO provide distinctive F.M. (Fre- station operates. At the end of the call sign instructions for all quency Modulation) broadcast stations, is another letter or letters which may be Meissner Kits the Federal Communications Commission either arbitrarily assigned, or indicate in has adopted a new system of call letters some abbreviated forni the city or area in Circuit Diagrams with interposed numbers for this now com- which the station is located. Parts Lists mercially recognized broadcast service. Simplifying this description somewhat Pictorial Diagrams The new call will are letters combine letters the following examples given by the F.C.C.: Charts and and figures in a system designed to show other useful data the radio listener not only whether the sta- W41B might indicate a station operating tion is East or West of the Mississippi, but on a channel of 44.1 megacycles in Boston, ONLY 50e NET! also where to look for it on the tuning dial. whereas K43SF could be another station on In accordance with the international 44.3 megacycles in San Francisco. (The pre- TODAY FOR FREE 48 -PAGE fixes of "K" and "W" assigned to U.S. sta- numerals are obtained by taking the last 2 WRITE tions (also "N" for Navy and Coast Guard), numbers of the assigned frequency. All edu- COMPLETE CATALOG the new F.M. call letters will start with "K" cational, non -commercial stations will use if West of the Mississippi, "W" if East. the letter "E" on the end.) Address Dept. C -6 This has been standard broadcast procedure The system is adapted from the method for many years. used by Chile to designate standard broad- The 2nd and 3rd characters, however, will cast transmitters, at the same time itemizing be numerals, indicating on which of the 40 vital data about the station. Calls will not channels in the F.M. broadcast band the exceed 5 characters.

~~RADIO -CRAFT for JUNE, I 9 4 I 753 LATEST RADIO APPARATUS~~

12 -WATT BOOSTER SPEAKER shrink. This new product can be supplied cable fits. The top of this unit, known as the in continuous lengths University Laboratories of any wall thickness T -22 Suppressor, is all bakelite and there- with any inside and outside diameters.- fore 195 Chrystie St.. New York, N. Y. insulated against high voltage. Another Radio-Craft feature is the 4- pronged metal spring contact which is pushed out by a rubber "slug" against the metal cylindrical wall of the 3 -WAY AVIATION PORTABLE distributor housing in order to assure rigid RCA Mfg. Corp. contact in the face of continuous vibration. Camden, N. J. -Radio -Cra f t IN addition to standard broadcast programs, this 3 -way portable, designed especially for use in private airplanes, is TRANSMITTING CONDENSERS capable of receiving such important avia- Aerovox Corporation tion information as CAA weather reports, New Bedford, Mass. radio range courses, and airport control tower signals. Operates on self- contained batteries (life, average use, about 200 hrs.) or from an A.C. /D.C. line. Known as Model AVR -102, this portable receiver incorporates a 6 -tube, 2 -band superhet. circuit which includes a stage of R.F. and has a built -in loop antenna and a P.M. dynamic speaker. Chassis is mounted to withstand vibration. Circuit incorporates "static- limiter" switch improve MODEL 1138 is an intercommunicator to signal /noise ratio. -Radio -Craft booster speaker especially designed for paging and intercommunicating use. In this COMMUNICATIONS RECEIVER connection, it is claimed due to the extremely high efficiency of this 12 -W. speaker, it Radio Mfg. Engineers, Inc. gives the effect of an added booster ampli- III Harrison St., Peoria, Ill. fier. This high efficiency, combined with the HE new RME -99 is a modern communica- uniform frequency response of the speaker, tions receiver which boasts the following enables it to cut through background noise features: 6 bands (550 to 33,000 kc.); large, and give clear speech reproduction, even in calibrated, bandspread dial; automatic volt- airplane factories. -Radio -Craft age regulation; illuminated R -DB. meter; 6- position crystal filters; relay and break -in FLOCK REPAIR KIT control; automatic noise limiter; combination antenna input. It is a well- designed, General Cement Co. custom -built instrument made primarily for 919 Taylor Ave., Rockford, Ill. reliable amateur and commercial reception. Utilizes external loudspeaker to match. Circuit employs Loktal -type tubes. The receiver is housed in a metal case, with inclined front panel, measuring 19 x 10% x 9 ins. -Radio -Craft DIRECT -READING WAVEMETER THE feature of General this new transmitting con- Radio Company denser is not the condenser itself but 30 State St., Cambridge, Mass. rather its slip- through method of mounting. ACOMPLETE kit, everything necessary Instead of cutting a hole large enough to for repairing the flock finish used on slip through the entire condenser, it is phonograph turntables, metal cabinets, test- merely necessary to drill 2 small holes large ers, tool chests, displays, etc. enough to pass its pillar terminals; 2 small- Kit consists of "Felt -Koat" flock, "Felt - er holes take the mounting bolts.- Radio- Koat" undercoat, "Felt -Koat" undercoat Craft thinner, and a specially -developed sifter -top can for sifting flock over the undercoat. Complete directions are included.-Radio- ADJUSTABLE DIAL BELTS Craft Walter L. Schott Co. Los Angeles, Calif. TRANSPARENT ACETATE TUBING Precision Paper Tube Co, 2033 Charleston St., Chicago, Ill.

TYPE 758 -A wavemeter is a convenient instrument for measuring high frequencies in the laboratory, where quite frequently ease of operation is more important than high accuracy. The direct- reading dial in a single rotation continuously tunes to frequencies from 55 to 400 megacycles. Varia- tion in inductance is automatic, by a silver spring, attached to the rotor of the variable T is claimed that this ingenious belt speeds which condenser, slides along a silver strip I up dial repairs and increases profits to connected to the stator. -Radio -Craft Servicemen by enabling an ordinary hour's job to be done in a few minutes. DISTRIBUTOR The belt is adjustable to fit any dial and NOISE- SUPPRESSOR conies in open form, which means that the ANEW self -supporting, spirally- wound, Continental Carbon, belt can be put on without taking apart the transparent acetate tubing is shown. Inc. 13900 Lorain Avenue, Cleveland, Ohio dial mechanism. A patented zipper -like fas- Due to its superior dielectric properties, this tening gives instant, lasting connection. The tubing is recommended for many high -fre- THIS new unit does away with the heavy core of the belt is made of a highly -flexible quency and electronic uses. It is pre- formed, metal cap on the usual automobile dis- steel which does not stretch with use. - and unlike extruded acetate tubes, will not tributor suppressor into which the ignition Radio -Cra f 754 RADIO -CRAFT for JUNE, 1941 LATEST RADIO APPARATUS

VARIABLE -SPEED MOTOR abrupt climatic changes. They may be fering noises. A polarization bracket holding played -back immediately, and can be proc- the dipole to the mast permits tilting the PULLEY essed and pressed just as the usual alumi- antenna at any angle from horizontal to Ideal Commutator Dresser Co. num recording blanks. The blanks are vertical, thus permitting correct polariza- Sycamore, Ill. known as "Alco Recording Discs."- Radio- tion. Radio -Craft Craft ELECTRONIC VOLT -OHM -MF. UNIVERSAL -USE DIPOLE METER ANTENNA Radio City Products Co. Technical Appliance Co. 88 Park Place, New York, N. Y. 17 E. 16th St., New York, N. Y. MODEL 661, because of its unusual fiexi- bility, will find wide and important applications in the radio, electronic and electrical service fields as well as in the laboratory. It is an electronic tube voltmeter, ohm- meter, and capacity meter. Its input resistance is 16 megohms (low) to 160 megohms. The A.C.-D.C. voltage range is from 0.1 THIS variable -speed motor pulley is de- to 6,000 volts. Its resistance range is from ' signed for light, inexpensive machines. It 0.1 -ohm to 1,000 megohms. Its capacity mounts directly on the motor shaft and range is from 50 mmf. to 600 mf. The in- requires only a standard V -belt. Speed ra- strument employs a 41 inch rectangular tios up to 2% to 1 available; speed changes meter mounted in an all -metal case with may be made while running. Sizes up to % etched front panel. All necessary accessories h.p. are supplied with it.-Radio-Craf t Complete unit includes variable pitch pulley and adjustable sliding motor base. NEW HEARING -AID -Radio -Cra f t Western Electric Company, Inc. 195 Broadway, New York, N. Y. NEW RECORDING BLANKS THROUGH the use of newly -developed THIS instrument is a tone -compensated Record Sales Company selector trans formera utilizing ultra-H.F.- vacuum -tube hearing -aid which should Los Angeles, Calif. iron cores for maximum transfer of radio prove a boon to all hard -of- hearing persons. I N view of the shortage of aluminum, these energy, this complete dipole -rod antenna Tones heard very poorly may be greatly re- I blanks are expected to be widely accepted system may be used for the reception of enforced and those heard fairly well may be wherever acetate discs have previously been F.M.-A.M. shortwave and television signals. amplified only a small amount. Thus the used. These discs are being manufactured in The transmission line may be up to and even "Ortho -tronic Audiophone" can compensate coated forms on a steel alloy base having a exceeding 100 feet long, if necessary. This for individual types of hearing deficiency. super- glossy silver-blue finish. They are makes it possible to place the dipole at an Also, at the throw of a switch, annoying said to be unbreakable and not affected by extremely high position, away from .inter- extraneous noises fade out while essential

~~MR, SERVICEMAN: Your Dollar Buys a Lot When You Use It to Join the RSA~~

It entitles you to membership in the only national benefits the RSA offers. organization of servicemen that has the sponsorship of the RMA, the NAB, the Sales Managers Clubs, It enables you to exchange ideas with thousands of and the trade journals. good servicemen who are already members of the RSA. It entitles you to receive the house organ, the RSA membership certificate, and the RSA pocket member- Protected territories will be established as rapidly as ship card. local chapters are formed. Applicants in present chapter areas will be referred to the local chapter. It gives access to the RSA Technical Helps Bureau, Fill out the coupon, attach a $1.00 bill and mail it in and enables you to participate in all functions and today. Pon 't BR the Jost Man in out ìßugh othood to gain the )2S' ? . RADIO SERVICEMEN OF AMERICA, INC. RADIO SERVICEMEN 304 S. Dearborn Street, Chicago, Illinois 1 OF AMERICA, INC. $1.00 enclosed for 1941 National Dues in RSA. 1 "Reliable Service Assured" Name I JOE MARTY, JR., EXECUTIVE SECRETARY Address I 304 S. DEARBORN ST., CHICAGO, ILLINOIS I City State Radio-Cra

~~RADIO -CRAFT for JUNE, 1941 755 LATEST RADIO APPARATUS~~

speech sounds pass unhampered. An audio vided on the azimuth scale. The entire loop REFLEX PROJECTOR A.V.C. circuit builds up weak sounds and is weatherproofed. Its neoprene insulation acts less on strong ones, thus reducing the is oil- and gasoline -proof. -Radio -Craft Atlas Sound Corporation "shock effect" of loud sounds. 1449 39th St., Brooklyn, N. Y. There are 2 outstanding circuit features; namely, the miniature pentode vacuum tube RADIAL LOUDSPEAKER and the "stabilized feedback" circuit. The University Laboratories sensitive crystal microphone is sealed in 195 Chrystie St., New York, N. Y. the amplifier case which is slightly larger than a cigarette case. The receiver is of the magnetic type and may be had in either air conduction or bone conduction models. It is easily concealed underneath wearing apparel; its batteries are contained in a separate case. Radio -Craft

3 IN 1 "PERSONAL" PORTABLE Lafayette Radio Corp. 100 Sixth Ave. New York, N. Y. MODEL DR -54 is an intermediate size (4% ft.) "Morning Glory" reflex projector with a bell opening of 25 ins. Its effective air column is 54 ins. The "dynamic THE model 2RYR is a new "bull" type ra- reflex design" reduces the overall length of dial 360° loudspeaker, having a very high the double re- entrant trumpet to 23!4 ins. power handling capacity. It is of the long This new size is excellent for general P.A. exponential reflex driver unit design for applications.-Radio-Craf t high efficiency. A multiple acoustic throat is used to adapt the high -power driver units to the LIGHTWEIGHT MOBILE horn. The driver units are housed in a AMPLIFIER weatherproof cover as illustrated. The Thordarson Electric Mfg. Co. speaker can handle 50 watts efficiently. Of 500 W. Huron St., Chicago, III. especial use for high -power chime systems, and paging and announcing systems, cir- BECAUSE this 6 -volt mobile amplifier cuses, etc. Bell diameter is 26 ins., height weighs only 20 lbs., it is conveniently 32 ins. -Radio -Craft portable and may be used for a variety of P.A. applications. It is a compact unit meas- THIS ultra -midget "personal" portable can uring only 13% x 7!4 x 7'4 irs. Some of be used with its self- contained batteries "CIN- AXIAL" DUAL SPEAKER its suggested u-es are for military drilling or on the 110 V. A.C. and /or D.C. line. SYSTEM fields, athletic fields, parade grounds and Including the rectifier tube, it employs 5 outdoor relays. It is also well suited Cinaudagraph Speaker, Inc. for use tubes and operates on the standard broad- in police cars, fire -fighting trucks, etc. The 2 Selleck St., Stamford, Conn. cast band. The set is highly attractive in its amplifier, known as Model T- 30W12, has genuine leather -covered case. Overall di- THIS system comprises a 12 -inch "woofer," several output impedances available at the mensions are 9 ins. high, 6 ins. wide and a 5 -inch "tweeter," and a complete cross- turn of a simple rotary selector switch. A 3% ins. deep. Uses 3 standard flashlight over network. It is designed for use in high - standby switch permits immediate opera- cells and one 67!4 V. "B" battery. Its weight fidelity phonograph equipment for com- tion without the necessity of waiting until is approximately 6 lbs. -Radio -Craft mercial, professional and home use as well the filaments are heated. -Radio -Craft as for F.M. receivers. Its frequency re- LOOP -ANTENNA ATTACHMENT sponse is said to be "flat" from 30 to 12,000 c.p.s. Its useful range is reported as being SIGNAL GENERATOR RCA Mfg. Company in excess of 12,000 c.p.s.- Radio -Craft Camden, N. J. Radez Corporation 1733 Milwaukee Avenue, Chicago, III. 3 -WAY PORTABLE N inexpensive Signal Generator and Allied Radio Corp. rA Station Finder, which can be con- 833 W. Jackson Blvd., Chicago, Ill. veniently used for resetting pushbuttons, is the model B2. It is a compact unit measuring 6% x 4% ins. square, and is light in weight (45/4 lbs. with self -contained battery). The instrument is designed to cover the broadcast band (500 to 1,750 kc.) and puts out either a modulated or unmodulated signal at the throw of a switch. The dial is calibrated and requires no reference A NEW loop antenna designed as an charts. The circuit of the instrument is here rA aural -null direction finding attachment shown; a grid -blocking electron- coupled for RCA models AVR -7D, -E, -F, -G, and type of oscillator circuit is employed. -H Aircraft Receivers. The loop is available Radio -Craft - in either remote or local control forms and will operate as a direction finder on the Beacon band (195-420 kc.), or on the Bea- con and Broadcast bands (195 -420, and 459- 1,400 kc.). Designed for civilian aircraft. The antenna makes possible accurate di- MODEL B17115 is a 6 -tube superhet. a- rection finding for the civilian pilot. The way portable measuring 12% x 95,1 x electrostatic shielding and balanced wind- 65/z ins. It uses the latest 1.4 volt low -drain ings of the loop materially reduce precipita- tubes which assures long life to battery option static and allow clearer reception of eration. In addition to operation on self - weak signals. contained batteries, it may be used on any Double -ended pointers are used on the in- 110 -120 V., A.C. /D.C. line. dicators. One end shows the bearing to Has built -in loop antenna, P.M. dynamic which the loop is rotated while the other in- speaker, and a stage of R.F. (for added dicates the calibration correction for the sensitivity). Tuning range: 540 to 1,650 bearing being taken. These corrections may kc. Average battery service: 200 to 250 be inscribed directly in a blank space pro- hours.-Radio-Craft 756 RADIO -CRAFT for JUNE, 1941 CLASSIFIED RADIO DIRECTORY

~~SECTION III (REVISED) Wh ate to ilay tit CLASSIFIED RADIO DIRECTORY Handy Buying Guide, by Products and Manufacturers' Names and Addresses, for the Entire Radio Industry~~

This DIRECTORY is published in sections -1 section per month. This method of publication permits the DIRECTORY to be constantly up -to -date since necessary revisions and There is no charge for regular corrections can be made monthly. All names preceded by an. asterisk (a) indicate that light -face listings In the Classi- they are trade names. fied Radio Directory.However, if If you cannot find any item or manufacturer in this section or in previously- published dominant hold -face listings are sections, just drop us a line for the information. Canadian radio manufacturers are desired, we make a charge of 82 unable to purchase any merchandise front the States, Radio -Craft is advised. Our readers, for concern names and $1 for however, may wish to make Canadian purchases, and hence, current listings are being trade names for each bold -face continued. listing. Please write to the Ad- of completely revised Second Edition of the CLASSIFIED vertising Dept., Radio-Craft. 20 Presented here is Section III the Vesey St., New York. N. Y., for RADIO DIRECTORY. details. While every precaution is taken to insure accuracy. Radio-Craft cannot guarantee against the possibility of occasional errors and omissions in the preparation of this Classified Directory. Manufacturers and readers are urged to report all errors and omissions at the earliest moment to insure corrections in the very next issue.

N. Y., "Lumarith ", "Lumarith Protectoid ", "Cel- MONTGOMERY WARD & CO., INC. 619 W. Chi- INSULATION luloid"-PI c Ave., Chicago, III., "' Airlinet'CE, R, ST, CELLULOID -Celluloid Corp. CONTINENTAL-DIAMOND FIBRE CO., Newark. NATIONAL COMPAN.Y, INC., 61 Sherman St. Del. -FB, MI, PI Malden, Mass., "National ", "AC"-CE, FB, PI, St CORNING GLASS WORKS, Corning, N. Y. -ST 'NATIONAL, National Company Inc. CORNISH WIRE CO., INC., 15 Park Row, New NATIONAL VULCANIZED FIBRE t0., P. O. Box 311, York, N. Y. -FB, FL. PA Wilmington, Del. -FB, PI HENRY L. CROWLEY & CO., INC., I Central Ave., NORTHERN ELECTRIC CO., LTD., 1261 Shearer St., N. J.-CE Montreal, Que., Canada -R, ST, T, V Ceramics CE W. Orange, CRUMPACKER DISTRIB. CORP., 1801 Fannin St., OFFENBACH ELECTRIC CO., 1452 Market St., San Fibre FB Houston, Tex. -R, T Francisco, Calif.-CE, FB, MI, PA, PI, R, ST, T, Fiber -glas FL HAROLD DAVIS, INC., 428 W. Capitol St., Jackson, TV, V T PARISIAN NOVELTY CO., 3510 S. Western Ave., Insulation cases IC Miss. -ST, DOW RADIO SUPPLY CO., 1759 E. Colorado St., Chicago, 111. -PI Mica MI Pasadena, Calif.-CE, FB, FL, MI, PA, R. ST, T, GEORGE F. PETTINOS, INC., 1206 Locust St., Mycalex MX TV, V Phila., Pa. -FB & INC., 626 POINSETTIA, INC., 97 Cedar Ave., Pitman, N. J. Paper PA E. I. DU PONT DE NEMOURS CO., Schuyler Ave., Arlington, N. J.-PI -PI Plastics PI ELECTRAMIC INSULATORS- Stupakoff Ce- PORCELAIN PRODUCTS, INC. P. O. Box 300, Polystyrene PO Findlay, Ohio, 'Alligator " -St ramic & Mfg. Co. PRODUCTS DIV., CHISHOLM -RYDER CO., (hard RU PREMAX Rubber and /or soft) EMPIRE NOTION CO., 105 E. 29th St., New York, INC., Drawer F, Bridge Sta., Niagara Falls, Rubber (liquid) RL N. Y. -T, TV, V N. Y. -ST 644 W. 12th St., Erie, Pa.- Rubber (synthetic) RS ERIE RESISTOR CORP., SERVICE CO., INC., N.W. PI RADIO ELECTRIC Sleeving (saturated) . SS FEDERAL SCREW PRODUCTS CO., 24 S. Jefferson Cor. 7th & Arch Sts., Phila., Pa.-CE, FL, Sleeving (untreated) . SU St., Chicago, III -R T, TV MI, PI, R, ST, T, V Park PI.. New insulators ST FEDERATED PURCHASER, INC., 80 RADIO EQUIPMENT CO., 326 Elm St., Buffalo, Stand -off R, ST, T. TV York, N. Y.-CE, FB, FL, MI, N. Y. -CE, FB R, ST, , TV, V Tape friction) . . . . T (cloth FISCHER DISTRIB. CORP., 222 Fulton St., New RADOLEK COMPANY, 601 W. Randolph St., Chi- Tape (rubber) . . R York, N. Y.-CE, FB, FL, MI, PA, PI, R, ST, T, cago, III. -R, ST, T, TV, V Tubing "spaghetti" (varnished) TV TV. V THE RICHARDSON CO., Melrose Park, Chicago, FLÉRON -M. M. Fleron I Son, Inc. 111.-MI, PI, RU Varnished cambric V 113 M. M. FLERON & SON, INC., N. Broad St., SAFTEST M. M. Fleron & Son, Inc. Waxes W Trenton, N. J. "Antennex' , "Fleron ", "Saftest ", MAURICE SCHWARTZ & SON, 710 Broadway, Signaler " -Sly Schenectady, N. Y.-CE, FB, FL, M1, PA, PI, R, New York, "AC- National Company, Inc. FONDA CORPORATION, 29 W. 57th St., ST T TV, V THE ACME WIRE CO., 1255 Dixwell Ave., New N. Y. -FB SEATTLE RADIO SUPPLY CO., INC., 2117 2nd Ave., Haven, Conn. -V THE FORMICA INSULATION CO., 4614 Spring Seattle, Wash. -CE, PA PI, R, ST, T, TV, V AIRLINE-Montgomery Ward & Co., Inc. Grove Ave. Cincinnati Ohio -PI SELF- VULCANIZING RUBBERFCO., INC., 605 W. 919 Taylor Ave., AKRON PORCELAIN CO., Akron, Ohio -CE. ST GENERAL CEMENT MFG. CO., Washington, Chicago, 111. -PI, RL 111. R, TV, V ALDEN PRODUCTS CO., 715 Center St., Brockton, Rockford, -FB, PI T, SHELLEY RADIO CO., 1841 S. Flower St., Los CERAMICS CO., PLANT NO. 3, Keasbey, Mass.-FB PI, ST GENERAL Angeles, Calif.-FL,alif. -FL , ST T, TV ALLIED RADIO CORP., 833 W. Jackson Blvd., Chi- N. J. CE, St "SIGNALER. M. M. f, Son, Inc. 1 Rd., cago. III., "Knight " -FL, R, ST, T GENERAL ELECTRIC CO., River Schenectady, STUPAKOFF LABORATORIES, INC., 6627 ALLIGATOR -Porcelain Products, Inc. N. Y.-CE, MY, PA, PI, TV, V Pa., ALPHA WIRE CORP., 50 Howard St., New York, B. F. GOODRICH CO., 500 S. Main St., Akron, Hamilton Ave., Pittsburgh, "Elèctramic N. Y. -TV Ohio -PI, R, RS Insulators " -CE "AISiMag"- American Lava Corp. CARL GORR PRINTING CO., 1801 W. Byron SUN RADIO CO., 212 Fulton St., New York, N. Y. AMERICAN LAVA CORP., Cherokee Blvd. & Menu - FB, FL, PA, PI, R, ST, T, TV, V St., Chicago, 111. -PA -CE, facturers Rd., Chattanooga, Tenn., "AISiMag ", TAYLOR FIBRE CO., Norristown, Pa. -FB, PI HAMMARLUND MFG. CO., INC., 424 E. 33rd St., ST 484 Broome "Lava"-CE, New York, N. Y. -ST TELERADIO ENGINEERING CORP., St., AMERICAN PHENOLIC CORP., 1250 W. Van Buren New York, N. Y.-CE, F8 MI, PI, TV HARRISON RADIO CO., 12 W. Broadway, New St., Chicago, 111.-CE, PI, PO, ST PORCELAIN WORKS, INC., York, N. Y.-CE, FL, R, ST, T, TV, V UNION ELECTRICAL AMERICAN RADIO HARDWARE CO., INC. 476 P. N. HOPE WEBBING CO., P.O. Box 1495, Providence, O. Box 762, Trenton, J.-CE Broadway, New York, N. Y.-CE, PI, RU. ST BUTTON CO., Waterbury, Conn. R. I. THE WATERBURY ANTENNEX M. Fleron & Son, Inc. -FL -M. IMPERIAL MOLDED PRODUCTS CORP., 2925 W. -PI ELEC. & MFG. CO., E. Pitts- ANCHOR WEBBING CO., P.O. Box 555, Paw- Harrison St., Chicago, III -PI WESTINGHOUSE burgh Pa. MI, PA, PI, T TV V tucket, R. I.-SS. SU, T, TV, V -FL, INSULATION MANUFACTURERS CORP., 70N-1-Ail MILLS, INC., 112 26th St., Brooklyn, N. Y. AUBURN BUTTON WORKS, INC., Auburn, N. Y.- Blvd., III. -FB, -PI, W PI 565 W. Washington Chicago, BAKELITE CORPORATION, 30 E. 42nd St., New York, FL, MI. PA, R, T, TV, V N. Y. -PI INSULATION PRODUCTS CO., 504 N. Richland St., INTERCOMMUNICATING BARKER & WILLIAMSON, Ardmore, Pa.-CE, Pl, Pittsburgh, Pa. -PI ST INSULINE CORP. OF AMERICA, 30 -30 Northern SYSTEMS BENTLEY HARRIS MFG. CO., Conshohocken, Pa., Blvd., Long Island City, N. Y. -CE, FB, PI, ST, "13.1-14-TV TV, V B- H- Bentley, Harris Mfg. Co. E. F. JOHNSON CO., Waseca. Minn.-CE, ST BIRNBACH RADIO CO., Inc., 145 Hudson St., KELLOGG SWITCHBOARD & SUPPLY CO., 6650 S. New York, N. Y. " "Birnbach "CE, FL, ST Cicero Ave. Chicago, 111.-T BIRNBACH- Birnbach Radio Co., Inc. KNIGHT, Allied Radio Corp. CARBIDE & CARBON CHEMICALS CORP., 30 E. LAFAYETTE RADIO CORP., 100 6th Ave., New York, 42nd St., New York N. Y.-P1 N. Y -CE, FB, MI, PA, PI, R, ST, T, TV, V Aircraft A BOND PRODUCTS Cò., 13139 Hamilton Ave., De- "LAVA, American Lava Corp. troit, Mich. -TV LUMARITH, Celluloid Corp. Wired BOONTON MOLDING CO., 326 Myrtle Ave., Boon- LUMARITH PROTECTOID, Celluloid Corp. Wireless IL ton, N. J. -PI MICA INSULATOR CO., 200 Varick St., New York, L. S. BRACH MFG. CORP., 55 Dickerson St., New- N. Y. -FB, FL, MI, MP PA, PI, TV, V "AIRLINE-Montgomery Ward & Co., Inc. ark, N. J. -ST JAMES MILLEN MFG. CO. INC., 150 Exchange ALLIED RADIO CORP., 833 W. Jackson Ave., Chica- BUD RADIO INC., 5205 Cedar Ave., Cleveland, St., Malden, Mass. -CE, PI ST go, III. "Knight " -1 Ohio -PI, ST MITCHELL -RAND INSULATIÓN CO., INC., 51 AMERICAN TELEVISION CORP., 130 W. 56th St., CELLULOID CORP., 180 Madison Ave., New York, Murray St., New York, N. Y.-FL, TV New York, N. Y. -I, IL Please say you saw it in the Radio -Craft "Classified Radio Directory" RADIO -CRAFT for JUNE, I94I 757 CLASSIFIED RADIO DIRECTORY

ATLAS SOUND CORP., 1451 39th St., Brooklyn, S.O.S. CINEMA SUPPLY CORP., 636 Ilth Ave., New BROWN DEVILS-Ohmite Manufacturing Co. N. Y. -1 York, N. Y. -I BUD RADIO, INC., 5205 Cedar Ave., Cleveland, AUTOCRAT RADIO CO., 3855 N. Hamilton Ave., SUN RADIO CO., 212 Fulton St., New York, N. Y. Ohio -RF Chicago, III., "'Autocrat " -I -I, IL CANADIAN MARCONI CO., 211 St. Sacrament St., "AUTOCRAT-Autocrat Radio Co. TALK.A.PHONE MFG. CO., 1219 W. Van Buren St., Montreal, Can. -PF, RF Chicago, 111. BANK'S MANUFACTURING CO., 5019 N. -1 CONSOLIDATED WIRE & ASSOCIATED CORPS., TAYLOR AIRPHONE PROD., INC., Long Beach Muni- 512 S. Peoria St., Chicago, III. -RF Winthrop Ave., Chicago, III -I, IL cipal Airport, Long Beach, Calif. -A CONTINENTAL CARBON, INC., 13900 Lorain Ave., BARKER & WILLIAMSON, Ardmore, Pa. -1, IL TELEMOTOR CORP., 260 5th.Ave., New York, N. Y. Cleveland, Ohio -PF, RF -1 CORNELL -DUBILIER ELECTRIC S. BELL SOUND SYSTEMS, INC., 1183 Essex CORP., Plainfield, Ave., TELERADIO ENG. CORP., 484 Broome Columbus, Ohio -I St., New York, N. J. -PF, RF N. Y. -IL CRUMPACKER DISTRIB. CORP., 1801 Fannin St., BIRNBACH RADIO CO., INC., 145 Hudson St., TELEX PRODUCTS CO., 1645 Hennepin Ave., Minne- Houston Tex. -PF, RF New York, N. Y. "Birnbach " -I apolis, Minn. Manufacturing BIRNBACH- Birnbach Radio Co., Inc. -I DETERMOHM-Ohmite Co. TELEFAIR TELFONE CORP., 62 Standish Ave., W. TOBE DEUTSCHMANN CO., Canton, Mass.-PF, RF DAVID BOGEN CO., 663 Broadway, New York, Orange, N. J. -I N. Y. -I, IL TRANSFORMER CORP. OF AMERICA, 69 Wooster DOW RADIO SUPPLY CO., 1759 E. Colorado St., CLARION- Transformer Corp. of America St., New York, N. Y. "Clarion " -I Pasadena, Calif. -PF, RF COMMUNICATIONS INC., 3215 Western Ave., TRANSMARINE RADIO, INC., 1184 Broadway, Hew- ELECTRO PRODUCTS LABS., 549 W. Ran- lett, L. I., N. IL Seattle, Wash., "C`ommun -O- Phone," "Incrimina- Y.-I, dolph St., Chicago, 111. -PF, RF tor," " Electro- Phone " UNITED SCIENTIFIC LAB., INC., 440 Lafayette St., FEDERATED PURCHASER, INC., 80 Park PI., New -I New COMMUN -O- PHONE -Communications, Inc. York, N. Y. -1 York, N. Y.-PF, RF VICTOR ANIMATOGRAPH CORP., Davenport, Iowa CO- RECHT- Electronic Sourd & Music Co. FERGUSON RADIO, INC., 14553 Madison Ave., - 1 Lakewood, Ohio -RF CRUMPACKER DISTRIB. CORP., 1801 Fannin St., VOYCALL -Lake Mfg. Co., Inc. FISCHER DISTRIB. CORP., 222 Fulton St., New York, Houston, Tex -I WEBSTER- CHICAGO CORP., 5622 W. Blooming- N. Y. -PF, RF HAROLD DAVIS, INC., 428 W. Capitol St., Jackson, dale Ave., Chicago, Ill. -I FLERON M. Fleron & Miss. IL -M. Son, Inc. -I, WEBSTER ELECTRIC CO., Clark & DeKanen DeVRY CORPORATION, 1111 Armitage Ave., Chica- M. M. FLERON & SON, INC., 113 N. Broad St. go, Ill. -1 Ave., Racine, Wis. -I Trenton, N. J., "Antennex," 'Fleron," "Saftest,'1 DICTAFILM -Miles Reproducer Co., Inc. WESTERN SOUND & ELECTRIC LABS. INC., 311 W. "Signaler"-RF Kilbourn Ave., Milwaukee, Wis. IL GIRARD-HOPKINS, 1000 40th Ave., Oakland, Calif. ELECTRONIC CONTROL CORP., 2667 E. Grand -I, Blvd., Detroit, Mich. -1 -RF GUIDED RADIO CORP., 118 E. 25th St., New York, ELECTRONIC SOUND & MUSIC CO., IO Stuyvesant KITS N. Y. -PF St., New York, N. Y., "Co- Recht " -I HARRISON RADIO CO., 12 W. Broadway, New ELECTRO- PHONE-Communications, Inc. York, N. Y. -PF, RF HERBERT H. HORN, 1201 S. Olive St., Los Angeles, ELKAY MFG. CORP., 200 5th Ave., New York, N. Y. Calif. -PF INSULINE CORP. OF AMERICA 30 -30 Northern EXECUTONE, INC., 415 Lexington Ave., New York, Blvd., Long Island Citi, N. Y. -'F, RF N. Y. -I KELLOGG SWITCHBOARD & SUPPLY CO., 6650 S. FEDERATED PURCHASER, INC., 80 Park PI., New Cicero Ave., Chicago, 111. -PF York, N. Y. -I, IL Amplifier A KENYON TRANSFORMER CO., INC., 840 Barry St., FILMGRAPH -Miles Reproducer Co., Inc. New Electronic EL York, N. Y. -PF FISHER RESEARCH LABORATORY, 1961 University KNIGHT- Allied Radio Corp. Ave., Palo Alto, Calif. -IL Experimental E KOOLOHMS -Sprague Products Co. HARRISON RADIO CO., 12 W. Broadway, New Facsimile F LAFAYETTE RADIO CORP., 100 6th Ave., New York, York, N. Y. -I, IL Flocking FL N. Y. -PF, RF FISCHER M & H SPORTING GOODS CO., 512 Market St., DISTRIB. CORP., 222 Fulton St., New York, Receiving R Phila., N. Y. -IL Pa. -PE, RF Sound effects S P. R. MALLORY & CO., INC., 3029 E. Washington GUIDED RADIO CORP., 118 E. 25th St., New York, St., Indianapolis, Ind. -PF, RF N. Y. -1, IL Television T MEISSNER MANUFACTURING CO., Mt. Carmel, INCRIMINATOR- Communications, Inc. Test equipment TE III.-RF INTERCALL SYSTEMS, INC., 5th & Norwood, Dayton, MILLER W. Miller Ohio-1 -J. Co. AMERICAN RADIO HARDWARE CO., INC., 476 J. W. MILLER Broadway, York, COMPANY, 5917 S. Main St. Los KELLOGG SWITCHBOARD & SUPPLY CO., 6650 S. New N. Y. -F Angeles, Calif., "Miller Quality Products," AMPLIFIER 17 l'Mil- Cicero Ave.. Chicago, III. -I CO. OF AMERICA, W. 20th St., ler' -PE. RF New York, N. Y. KNIGHT- Allied Radio Corp. -A * MILLER QUALITY PRODUCTS W. Miller Co. AUDIO DEVICES, INC., 1600 Broadway, New York, -J. LAKE MFG. CO., INC., 2323 Chestnut St., Oakland, N. Y. -S MONTGOMERY WARD & CO., INC., 619 W. Chi. Calif., "Voycall," "Lake " -I CARRON MANUFACTURING CO., 415 S. Aberdeen cago Ave., Chicago, III., "Airline " -PF, RF LAKE -Lake Mfg. Co., Inc. St., Chicago, III. -R MULTIVOLTS- Ohmite Manufacturing Co. LAFAYETTE RADIO CORP., 100 6th Ave., New York, THE CROSLEY CORPORATION, Cincinnati, Ohio - MUSIC MASTER MFG. CO., 508 S. Dearborn St., N. Y. -I F Chicago, 111. -PF, RF LEKTRA LABORATORIES, INC., 30 E. 10th St., New FLOCK PROCESS CORP., 17 W. 31st St., New York, NORTHERN ELECTRIC CO., LTD., 1261 Shearer York, N. Y. -I N. Y. -FL St., Montreal, Que., Can. -PF, RF MIDLAND RADIO & TELEVISION SCHOOLS, INC., MAJESTIC RADIO & TELEVISION CORP., 2600 W. OFFENBACH ELECTRIC CO., 1452 Market St., San Power & Light Bldg., Kansas Mo. T 50th St., Chicago, III. -I IL City, -E, Francisco, Calif. -PF, RF JOHN MECK INDUSTRIES, 1313 Randolph St., Chi - RADIO CITY PRODUCTS CO., INC., 88 Park Pl., New York, Y. OHMITE MANUFACTURING CO., 4835 W. Flournoy cago, 111. -I N. -TE "Ohmite," MILES REPRODUCER RADOLEK COMPANY, 601 W. Randolph St., Chica- St., Chicago, III "Brown Devils," CO., INC., 812 Broadway, " Multivolts,'' "Riteohm New York, N. Y. "Filmg aph," "Dictafilm " -I, IL go, III. -F "Determohm," " -PF, RF MISSION BELL RADIO MFG. CO., INC., 831 Venice RCA MANUFACTURING CO., INC., Camden, N. J. "OHMITE- Ohmite Manufacturing Co. Blvd., Los Angeles, Calif.-1 -S WILCOX PACENT ENGINEERING CORP., 79 Madison Ave., MONTGOMERY WARD & CO. INC., 619 W. Chi- ELECTRIC CO., INC., 40th & State Line, New York, N. Y.-PF, RF Kansas City, Mo -F cago Ave., Chicago Ill., "Airline" -I PHILCO RADIO & TELEVISION CORP., Tioga & "C" WORNER PRODUCTS CORP., 1019 MUSIC MASTER MFG. CO., 508 S. Dearborn St., W. Lake St., Sts., Phila., Pa. -PF, RF Chicago, 111. -EL Chicago, III. -1 PHILMORE MFG. CO., INC., 113 University PI., NORTHERN ELECTRIC CO. LTD., 1261 Shearer St., New York, N. Y. -RE Montreal, Que., Canada -1, IL OFFENBACH ELECTRIC CO., 1452 Market St., San KNOBS (see Dials & Parts) RADIO ELECTRIC SERVICE CO., INC., N.W. Francisco, Calif. -I IL Cor. 7th & Arch Sts., Phila., Pa. -PF, RF OPERADIO MFG. CO., St. Charles, 111. LINE FILTERS -I RADIO EQUIPMENT CORP., 326 Elm St., Buffalo, PACENT ENGINEERING CORP., 79 Madison Ave., (Also see Noise Elimination Equipment) N. Y. -PF, RF New York, N. Y. -I COMPANY,OMPANY, 601 W. Randolph St., Chica. PHILCO RADIO & TELEVISION CORP., Tioga & go, 111. -PF RF "C" Sts., Phila., Pa.-1 RITEOHM- Ohmite Manufacturing Co. PHONOTONE LABORATORIES, INC., S. E. 15th & 'SAFTEST -M. M. Heron & Son, Inc. State Sts., Washington, Ind -I MAURICE SCHWARTZ & SON, 710 -712 Broadway, RADIO ELECTRIC SERVICE CO., INC., N.W. Schenectady, N. Y. -PF, RF RADIO Cor. 7th & Arch Sts., Phila., Pa. IL SEATTLE SUPPLY CO., INC., 2117 2nd Ave., -1, Seattle, Wash, -PF, RF Power filters (industrial) . . PF RADIO EQUIPMENT CO., 326 Elm St., Buffalo, N. Y. SIGNALER -M. M. Heron & Son, Inc. IL Radio set (for the home) , . -I, RF 600 LINE -Sprague Products Co. RADIO RECEPTOR -, INC., 251 W. 19th St., New SOLAR MANUFACTURING CORP., York, N. Y. -I AEROVOX CORPORATION 25th St. & Ave. Ne Bedford, Mass. - "A ", Bayonne, N. J. RF RADOLEK COMPANY, 601 W. Randolph St., Chica- RF -PF, go, 111 -1 SPRAGUE PRODUCTS CO., No. Adams, Mass., "600 AIRLINE- Montgorsery Ward & Co., Inc. RAY -LAB COMPANY, Grand Central & 11th Sts., Line," "Atoms," "Koolohms," "Telohmike " -PF, ALLIED RADIO CORP., 833 W. Jackson Blvd., Chi- Elmira Hts., N. Y. RF "Ray- lab " -I cago. Ill., "Knight " -PF, RF RAY -LAB- Ray -Lat Company STROMBERG. CARLSON TELEPHONE MFG. CO., 100 AMERICAN CONDENSER CORP., 2508 S. Carlson Rd., Rochester, N. Y. -RF RCA MANUFACTURING CO., INC., Camden, N. J. Michigan, Chicago, 111. -PF, RF SUN RADIO CO., 212 Fulton St., New York, N. Y. -I I L AMERICAN COMMUNICATIONS CORP., 123 Lib- -PF, RF REGAL AMPLIFIER MFG. CORP., 14 W. 17th St., TAYLOR PRODUCTS, York, Y. IL erty St., New York, N. Y. -PF RF AIRPHONE INC., Long Beach New N. -I, Municipal Airport, Long Beach, Calif. REMLER CO., LTD., 2101 Bryant St., San Francisco, AMPLIFIER CO. OF AMERICA, 17 W. 20th St., Calif. New York, N. Y. -PF TECHNICAL APPLIANCE CORP., 17 E. 16th St., -1 New York, N. Y. MAJESTIC ANTENNEX -M. M. Fleron & Son, Inc. -RF ROGERS- CORP. LTD., 622 Fleet St., TELOHMIKE- Sprague Products Toronto, Ont., Canada -I 'ATOMS- Sprague Products Co. Co. SEATTLE RADIO SUPPLY CO., INC., 2117 2nd Ave., BARKER & WILLIAMSON, Ardmore, Pa. -PF UNITED TRANSFORMER CORP., 150 Varick St., Seattle, Wash. -I, IL New York, N. Y.-PF BELDEN MANUFACTURING 4647 SETCHELL CARLSON, INC., 2233 University Ave., CO., W. VOGUE PRODUCTS CO., 8420 S. Ashland Ave., St. Paul, Minn. -I Van Buren St., Chicago, 111.-RF Chicago, III. -RF Please Bay you saw it in the Radio -Craft "Classified Radio Directory" 758 RADIO -CRAFT for JUNE, 1941 Toe Bette S'etvidng - 7,e iligget Ptatiti - FOR A WIDER KNOWLEDGE OF TECHNICAL SUBJECTS, READ THE

BOOKS IN THE RADIO -CRAFT LIBRARY SERIES ET into the swing of reading instructive, authoritative books on technical subjects-Radio,, Air Conditioning and Refrigeration. The RADIO -CRAFT LIBRARY SERIES is the most complete set of volumes individually treating all important divi- Book No Is sions in these fields. Each book has been written for the purpose of giving you the ABC OF opportunity to specialize in one or more of the popular branches of the various Alp CONDITIONING subjects and we know of no easier, quicker or leas expensive way to improve your sImle led In accurate knowledge. The material in each book is very helpful-you'll find them valuable in review t tecnnieal i thU your work. The authors are all well known and are authorities on the subjects on lundementals al enon' which they have written. This is the first time that you are enabled to build a library latest bronels server eerin0 Includln0 -0 of technical books by such popular writers. on Oresent Ina data Psul units. BY ALL BOOKS ARE UNIFORM Harrl0an. SOC The books in the RADIO- CRAFT- LIBRARY Book No. Il SERIES are all uniform. The size is 6 z 9 W17H inches. Each volume contains 64 pages and 14 SERVICING an average of 50 to 150 photographic Book No. ERRLV2ER5 The books are POC SE7 illustrations and diagrams. Theory of book paper GUIDE of es, printed on an excellent grade RADIO H L1100m. A Study Av011catle- and have stiff flexible covers. PRICE 50c dirli DY N Book and Pro.' lief eMneee -Set seders tardy et $°dated AO' PER BOOK. All books are sent postpaid. Radle sad G. or Articles sees BY H. Cir- ,.ralY < Conctr0tti0O ler 2I Audlo Ow1ut Ra4M McEntee' Book No. cults and oate- Set INTO Farmala+ I* 3REAKING H andY ShortCuU. Book NO. -T0 I ADIO SERVICING 50C p DINT -PMI" N0OF. 15 and BoAok ISTANCE le Instructions BC Rp for Sei° Procedura Radiod' Profitable Men BY Robort l For Unite Ic InO EupuGERADyal-the ADO Elch In0 with n. 8Y re 7heoryand Test epees of ta ^c of this Id: ErydaY berg. isle by mechen- to igerotion procedur.9. Feed. /r and leading Servle0IL 50C Ical moans, anal Radle

~~RADIO -CRAFT I 9 4 I 759 CLASSIFIED RADIO DIRECTORY~~

LOUDSPEAKERS (& PARTS) GLOBE PHONE MFG. CORP., Reading, Mass -PD TREBOR RADIO CO., Pasadena, Calif. -FC GUIDED' RADIO CORP., 118 E. 25th St., New York, UNITED TELETONE CORP., 150 Varick St., New York, N. Y. -AC, BA, CO FC, H, PD N. Y.-AC, BA, CO, ES, FC, F, H, MS, PD, S HARRISON RADIO CO., 12 W. Broadway, New UNIVERSITY LABORATORIES, 195 Chrystie St., New York, N. Y. -A, AC, BA, CO, ES, FC, F, H, MS, York, N. Y. -AC, BA, ES, H, PD PD, S UTAH RADIO PRODUCTS CO., 812 Orleans St., HAWLEY PRODUCTS CO., 201 N. 1st Ave., St. Chicago, III. -AC, BA, CO ES, FC, PO Charles, 111. -BA, CO, H THE VEGA COMPANY, 155 Columbus Ave., Boston, A. G. HINTZE, 300 W. Adams St., Chicago, 111.-G Mass., '''Vega," "Vitar " -H HERBERT H. HORN 1201 S. Olive St., Los Angeles, VEGA-The Vega Company Accessories A VICTOR Calif. -CO, G, 1-1, MS, PD ANIMATOGRAPH CORP., Davenport, Iowa Acoustic chambers . . . . AC CHARLES JACK MFG. CORP., 27 E. Phila. St., -BA, PD Baffles BA York, Pa. -H VITAR -The Vega Company RADIO MFG. 6601 Cones CO JENSEN CO., S. Laramie Ave., WALSCO- Walter L. Schott Co. Chicago, 111. -A, BA, ES, H, PD, S Cone speakers CS J. F. D. MANUFACTURING CO., 4111 Ft. Hamilton WEBSTER-CHICAGO CORP., 5622 W. Bloomingdale Ave., 111. S Electrodynamic speakers . . . ES Pkwy., Brooklyn, N. Y. -FC Chicago, -BA, H, WESTERN SOUND & ELECTRIC LABS., INC., 311 N. Field coils FC KNIGHT- ALLIED RADIO CORP. Kilbourn Ave., Milwaukee, Wis. BA, G, PD, S LAFAYETTE 100 -A, Field exciters F RADIO CORP., 6th Ave., New York N. Y.-A, AC, BA CO, ES, FC F, G. H, MS, PD, Sr Grille cloths G LEOTONE RADIO CO., 63 Dey St., New York, N. Y. MACHINERY (PRODUCTION) Grilles (molded) GM -A, BA, CO, ES, FC, MS, PD THE LIFETIME CORPORATION, 1825 Adams Horns H *ti t rc Horns (weatherproof) . . . HW St., Toledo, Ohio -A, BA, H, PD, S Horn units HU THE LINCROPHONE CO., INC., 1661 Howard Ave., vl. Utica, N. Y. -BA, PD Magnetic speakers . . . MS T. R. McELROY, 100 Brookline Ave., Boston, Mass.- Metal housings M MS Permanent- magnet dynamic M & H SPORTING GOODS CO.. 512 Market St., Phila., Pa. -AC, BA, CO, ES, FC, F, G, H, MS, Braiders B speakers PD PD, S Coil winders CW Pillow speakers PS THE MAGNAVOX COMPANY, INC., 2131 Bueter Rd., Drill presses D Speaker cements SC Ft. Wayne, Ind. -ES, PD JOHN MECK INDUSTRIES, 1313 Randolph St., Chi. Flocking F Speaker shims SS cago, 111. -AC, BA, PD Lathes (& equipment) L Stands S MILES REPRODUCER CO., INC., 812 Broadway Tube -making, Radio T Volume controls VC New York, N. Y., "Filmgraph," "Dictafilm " -ES, FC, F, H, MS, PD Wire stripper WS THE ACME WIRE CO., 1255 Dixwell Ave., New MONOBAR- Tibbetts Laboratories Haven, Conn. -FC MONTGOMERY WARD & CO.. INC., 619 W. Chi. ATLAS PRESS CO., Kalamazoo, Mich. -D, L cago Ave., Chicago, Ill., EISLER ENGINEERING CO., 751 S. 13th St., Newark, ALLIED RADIO CORP., 833 W. "Airline " -BA, H, MS, Jackson Blvd., PD, S N. J. -T Chicago, Ill., "Knight" -A, BA, CO, ES, NASH RADIO PRODUCTS CO., 6267 Gravois Ave., FLOCK PROCESS CORP., 17 W. 31st St., New York, Y. FC, F, G, H, MS, PD, S St. Louis, Mo. -G N. -F JAMES WIRE & CABLE 1014 AIRLINE -Montgornery Ward & Inc. CO., Madison Ave., Co., NATIONAL UNION RADIO CORP., 57 State Toledo, Ohio ALLISON BAFFLE CO., 207 S. 86th St., Birmingham, -8 Ala. -AC, BA St., Newark, N. J. -BA ES, H, PD, S MORRIS REGISTER CO., 2925 W. Broadway, Council Bluffs, Iowa -CW AMERICAN COMMUNICATIONS CORP., 123 Lib- OFFENBACH ELECTRIC CO., 1452 Market St., San SOUTH BEND LATHE WORKS, 425 E. Madison St., erty St., New York, N. Y.-AC, BA, F Francisco, ES, F, Calif. -A, AC, BA, CO, FC, G, South Bend, Ind. AMERICAN PHENOLIC CORP., 1250 W. Van Buren H MS PD, S -L THE WIRE STRIPPER P. Bon 2421 St., Chicago, III. A. ÒLEK, 4759 CO., O. E. Cleve- -A Melrose St., Phila. Pa.-G land, Ohio -WS AMPLIFIER CO. OF AMERICA, 17 W. 20th St., OPERADIO MANUFACTURING CO., St. Charles, New York, N. Y. -BA III. -A, AC, BA, CO, ES, FC, F, H, PD ARLAVOX MANUFACTURING CO., 430 S. Green MAGNETS SOLENOIDS St., Chicago, 111. -MS OXFORD -TARTAK RADIO CORP 915 W. & ART SPECIALTY CO., I I I5 N. Franklin St., Chicago, Van Buren St., Chicago, 111. -ES. MS, PD 111. -A, BA, H, S PACENT ENGINEERING CORP., 79 Madison Ave., ATLAS SOUND CORP., 1451 39th St. Brooklyn, N. Y. New York, N. Y. -ES AC, BA, CO, CS, ES, F, H, HU, -A, G, HW, PAR -METAL PRODUCTS CORP., 32 -62 49th St., Long PD, S Island City, N. Y. -M AUDIOGRAPH SOUND SYSTEMS, 1313 Randolph W. PHILCO RADIO & TELEVISION CORP., Tioga & St., Chicago, 111. BA, PD -A, AC, "C" Sts., Phila., Pa. -A, CO, ES, FC, G, H, MS, AUTOCRAT- Autocrat Radio Co. PD Permanent magnets . . P AUTOCRAT RADIO CO., 3855 N. Hamilton Ave., QUAMNICHOLS CO., 33rd Pl. & Cottage Chicago, III., "Autocrat " Grove, Solenoids S -PD Chicago, 111. -ES, MS PD BANK'S MANUFACTURING CO., 5019 N. Winthrop RACON ELECTRIC CO, INC., 52 E. 19th St., New ARLAVOX MANUFACTURING CO., 430 S. Green Ave., Ch,caoo 111. -A, BA, ES H PD York, N. Y. -A, AC, BA, CO, ES, FC, F, H, St., Chicago, Ill. -P THE BENWOOD LINZE CO., 1838 Washington Ave., MS, PD St. Louis, Mo. -F BELDEN MANUFACTURING CO., 4647 W. DAVID BOGEN CO., 663 Broadway, New York, RADIO ELECTRIC SERVICE CO., INC., N.W. Van Buren St., Chicago, 111. -P N. Y. -A, AC, BA, ES, PD S Cor. 7th & Arch Sta.. Phi'a., Pa. -A, AC, FISCHER DISTRIB. CORP., 222 Fulton St., New York, CANADIAN MARCONI CO., 211 St. Sacrament St., N. Y. -P BA, CO, ES, FC, F, G, H, MS, PD, S Montreal, Can. -ES, MS, PD. S GENERAL ELECTRIC CO. Schenectady, N. Y. & CANADIAN RADIO CORP., LTD., 622 Fleet St. W., RADIO EQUIPMENT CORP., 326 Elm St., Buffalo, Bridgeport, Conn. -P (Alnico) Toronto, Ont., Can. -F, G N. Y.-A, AC, BA, CO, ES, FC, F, G, H, MS, EDWIN I. GUTHMAN & CO., INC., 400 5. Peoria CARRON MANUFACTURING CO., 415 S. Aberdeen PD, S St., Chicago, III. -S St., Chicago, 111. -CO, FC, G RADOLEK COMPANY, 601 W. Randolph St., Chica- KELLOGG SWITCHBOARD & SUPPLY CO., 6650 S. CASTLEWOOD MANUFACTURING CO., 12th Ave. & go, 111.-A, AC, BA, CO, ES, FC, F, G, H, MS, Cicero Ave., Chicago, III. -P Burnett Sts., Louisville, Ky. -BA PD, S RACON ELECTRIC CO., INC., 52 E. 19th St., New CINAUDAGRAPH SPEAKERS, INC., 921 W. RCA MANUFACTURING CO., INC., Camden, N. J. York, N. Y.-P -A, BA, CO, ES, FC, F, H, MS, PD Van Buren St., Chicago, 111.-CS, ES, HW, RADIO ELECTRIC SERVICE CO., INC., N.W. REGAL AMPLIFIER MFG. CORP., 14 HU, MS, PD W. 17th St., New York, N. Y. -BA, H, MS, PD, S Cor. 7th & Arch Sts., Phila., Pa. -P CLARION- Transformer Corp. of America CRESCENT TOOL & DIE CO., 4140 Belmont Ave., JOHN A. ROEBLING'S SONS CO., 640 S. Broad St., Trenton, N. J. Chicago, 111. -ES, PD -FC METAL FOR RADIO CRUMPACKER DISTRIB. CORP., 1801 Fannin St. THE ROLA COMPANY, INC., 2530 Superior Ave., Cleveland, Ohio -ES, PD Houston, Tex. -A, BA, CO, ES, FC, G, MS, PD, f DICTAFILM -Miles Reproducer Co., Inc. ROWE INDUSTRIES INC., 3120 Monroe St., Toledo, HAROLD DAVIS, INC. 428 W. Capitol St., Jackson Ohio -AC, BA, ES, F H, MS, PD, S WALTER L, SCHOTT CO., 5266 -70 W. Pico Blvd., Miss. -A, AC, BA, CO, ES, FC, F, G, H, MS, PD, Sr Los "Walsco DOW RADIO SUPPLY CO., 1759 E. Colorado St., Angeles, Calif., " -SC Pasadena, Calif. -A, BA, CO, FC, G, MS MAURICE SCHWARTZ & SON, 710.712 Broadway, HUGH H. EBY, INC., 4700 Stenton Ave., Phila., Schenectady, N. Y. -A, AC, BA, CO, ES, FC, Pa. -A F, G, H, MS, PD, S Aluminum AL SEATTLE RADIO SUPPLY CO., INC., 2117 2nd Ave., ELECTRO PRODUCTS LABS., 549 W. Ran- Brass BR Seattle, Wash. -A, AC, BA, CO, ES, FC, F, G. dolph St., Chicago, 111.-A, VC H MS, PD, S Chassis CH ERWOOD SOUND EQUIP. CO., 224 W. Huron St., SHELLEY RADIO CO., 1841 S. Flower St., Los An- Core materials CO Chicago, 111. -AC, BA, H, PD, S geles, Calif.-A, AC, CO, FC, H, PD Foils FO FEDERATED PURCHASER, INC., 80 Park Pl., New MARK SIMPSON DISTRIB. CO., INC., 16 Hudson Graphite York, N. Y. -A, AC, BA, CO, ES, FC, F, G, H, St., New York, N. Y. -BA, S G MS, PD, S SOUND APPARATUS CO., 150 W. 46th St., New Iron (and /or steel) I FILMGRAPH -Miles Reproducer Co. Inc. York, N. Y. -ES, MS, PD Laminations LA FISCHER DISTRIB. CORP., 222 Fulton St., New York, STROMBERG- CARLSON TELEPHONE MFG. CO., Molybdenum N. Y. -A, AC, BA, CO, ES, FC, F, G, H, MS, 100 Carlson Rd., Rochester, N. Y.-CO, ES, PD MO PD. S SYRACUSE ORNAMENTAL CO., Syracuse, N. Y.- Nickel NI FLOCK PROCESS CORP., 17 W. 31st St., New York, GM Panels PA N. Y. -G SUN RADIO CO., 212 Fulton St., New York, N. Y.- Permanent magnets . . . PE FONDA CORPORATION, 29 W. 57th St., New York, A, AC, BA. CO, ES, FC, F, G. H, MS, PD, S N. Y. -ES, PD TIBBETTS LABORATORIES, Camden, Maine, "Mono - Racks RA MFG. GENERAL CEMENT CO., 919 Taylor Ave., bar"-PS R.F. -iron cores RF Rockford, III. -A, G, SC, SS TRANSFORMER CORP, OF AMERICA, 69 Wooster -cans S GENERAL ELECTRIC CO., Schenectady, N. Y. & St., New York, N. Y., "Clarion" -A, BA, ES, H, Shield Bridgeport, Conn.-PD PD, S Speaker housings (cabinets) . SP !'(case say you eaw it in the Radio -Craft "Cfaseified Radio Directory" 760 RADIO -CRAFT for JUNE, 1941 CLASSIFIED RADIO DIRECTORY

CO., 1901 Clybourn Ave., CANADIAN MARCONI CO., 211 St. Sacrament St., Stampings ST SORENG -MANEGOLD Chicago, 111. -ST Montreal, Can. -A, C, CD, CN, CT, CY, D, SP, Transformer housings TR WORKS, Pressed Metal Division, ST, V STANLEY CARDAK- Electro -Voice Mfg. Co., Inc. Tube parts TP New Britain, Conn. -ST Tungsten TU CARRIER MICROPHONE CO. 439 S. La Brea Ave., STEWART STAMPING CORP., 621 E. 216th St., New Inglewood, Calif. -CD 0, V Zinc Z York, N. Y. -ST CHICAGO SOUND SYSTEMS CO., 315 E. Grand St., New N. SUN RADIO CO., 212 Fulton York, Y.- Ave., Chicago, III. -A CY D. ST AL, CH, PA, RA, SP, ST CRUMPACKER DISTRIB. CORP., 1801 Fannin St., AC- National Company, Inc. SWEDISH IRON & STEEL CORP., 17 Battery PI., Houston, Tex. -A, C, CD, CN, CT, CY, D, H, SP, ACRO TOOL & DIE WORKS, 2815 Montrose Ave., New York, N. Y. -I, TP ST. V Chicago, 111. -AL, BR, CH, LA, RA, ST THORDARSON ELECTRIC MFG. CO., 500 W. Huron HAROLD DAVIS. INC., 428 W. Capitol St., Jackson, & Co., Inc. 111. AIRLINE -Montgomery Ward St., Chicago, -TR Miss. -A, C, CN, CT, CY, D, H SP, ST, V ALLIED RADIO CORP., 833 W. Jackson Blvd., Chi - DICTAFILM -Miles Reproducer Co., Inc. cago, Ill. "Knight " -AL CH, PA, RA, SP DOOLITTLE RADIO, INC., 7421 Loomis Blvd., Chi- ALTO MANUFACTURING CO., 1647 Wolfram St., ORE, LEAK METAL, OIL & cago, 111. -C Chicago III.-SP, ST DOW RADIO SUPPLY CO., 1759 E. Colorado St., INC., 476 LOCATORS AMERICAN RADIO HARDWARE CO., Pasadena, Calif.-A, C, CD, CN, CY, D, H, Y. BR, H, LA, PA, Broadway New York, N. -AL, SP ST, V RA, ST TP EASTERN MIKE -STAND CO., 56 Christopher Ave., AMERICAN Middletown, THE ROLLING MILL CO., Brooklyn, N. Y. -A, ST Ohio -I ELECTRO- VOICE-Electro Voice Mfg. Co., Inc. ARLAVOX MANUFACTURING CO., 430 S. Green MFG. CO., INC., 1239 5. Bend St. Chicago, 111.-PA PE, SP ST ELECTRO-VOICE Voice," - BAKER & CO., INC., 113 Astor ft., Newark, N. J.- Ave., South Bend, Ind., " Electro- "Car NI dak"-A, C, CN, CT, D, SP, ST, V EPIPHONE, INC., 142 W. 14th St., New York, N. Y. BAREX -King Laboratories Inc. Geophysical prospecting instruments. THE BALTIMORE BRASS CO., 1201 Wisconsin St., -D Baltimore Md. -BR (ore and oil) G ERWOOD SOUND EQUIP. CO., 224 W. Huron St., BUD RADIO, INC., 5205 Cedar Ave., Cleveland, Leak locators L Chicago, 111.-A, CD CN, CY, D, ST Ohio CH, PA, RA, SP FEDERATED PURCHASER, INC., Place, New -AL, Metal (treasure) locators . M CINEMA ENGINEERING CO., 1508 W. Verdugo York, N. Y. -A, C, CD, CN, CT, CY, D, H, SP, Ave., Burbank, Calif -R Pipe locators P ST, V CRESCENT TOOL & DIE CO., 4140 Belmont Ave., FILMGRAPH -Miles Reproducer Co., Inc. Chicago, III. -CH, SP, ST, TR ALLIED RADIO CORP., 833 W. Jackson Blvd., Chi - FISCHER DISTRIB. CORP., 222 Fulton St. New York, Y. T, CY, D H, SPV ST, V HENRY L. CROWLEY & CO., INC., I Central Ave., cago, III., "Knight " -G, M, P N. -A, C, CD, CN, W. Orange, N. J. -RF BARKER & WILLIAMSON, Ardmore, Pa. -G GENERAL CEMENT MFG. CO., 919 Taylor Ave., CRUCIBLE STEEL CO. OF AMERICA, 405 Lexington CAMBRIDGE INSTRUMENT CO., INC., 3732 Grand Rockford, III. -C, SP Ave., New York, N. Y. -PE Central Terminal, New York, N. Y.-G GENERAL ELECTRIC CO. Schenectady, N. Y. & DOW RADIO SUPPLY CO., 1759 E. Colorado St., ENGINEERING RESEARCH CORP., 909 Gid- Bridgeport. Conn.-A, CN, ST, V GLOBE PHONE MFG. CORP., Reading, Mass. -C, Pasadena, Calif. -CH G. PE, RA, SP, TR dens -Lane Bldg., Shreveport, La. -M, P DRIVER -HARRIS COMPANY, Harrison, N. J.-N1, TP CT, CY, D, V FISHER RESEARCH LAB., 1961 University HARRISON RADIO CO., 12 W. Broadway, New DUAL REMOTE CONTROL CO. INC., 31776 W. H, Ave., Palo L, M, P N. Y. -A, C, CD, CN, CT, CY, D, SP, , Alto, Calif. Warren Ave Wayne, Mich. -St -G, York, 1031 ELECTRO PRODUCTS LABS., 549 W. Ran- THE GOLDAK COMPANY, S. Broad- HUNTER PRESSED STEEL CO., 8th St. & Maple Ave., dolph St., Chicago, III. -RF way, Los Angeles, Calif. -G, L, M, P Lansdale, Pa. -SP EMPIRE NOTION CO., 105 E. 29th St., New York, KNIGHT -Allied Radio Corp. KAAR ENGINEERING CO., 619 Emerson St., Palo N. Y. -ST LUMENITE ELECTRIC CO., 407 S. Dearborn St., Alto, Calif. -C FAIRMONT ALUMINUM CO. Fairmont, W. Va.-AL Chicago, III.-M KELLOGG SWITCHBOARD & SUPPLY CO 6650 S. GENERAL CEMENT MFG. CO., 919 Taylor Ave., RCA MANUFACTURING CO., INC., Camden. N. J. Cicero Ave., Chicago, III. -C Rockford, 111. -AL, FO, G -G "KNIGHT-Allied Radio Corp. GENERAL ELECTRIC CO., Schenectady, N. Y. & LAFAYETTE RADIO CORP., 100 6th Ave., New York, Bridgeport, Conn.-PE, TP N. Y. -A, C, Cht CT CY, D, H, SP, ST, V MICROPHONES & ACCESSORIES LEKTRA LABORATORIES, INC., 30 E. 10th St., New GENERAL EXTRUSION CORP., 181 Long York, N. Y. -D Ave., Hillside, N. J. -AL, S. Z THE LIFETIME CORPORATION, 1825 Adams GOAT RADIO TUBE PARTS, INC., 314 Dean St.. D. Brooklyn N. Y. -ST, TP St., Toledo, Ohio -A, C, CD, CN, SP, L. F. GRAMMES & SONS, INC., 361 Union St., ST, V Allentown, Pa. -PA, ST THE LINCROPHONE CO., INC., 1661 Howard Ave., HARRISON RADIO CO., 12 W. Broadway, New York, Utica. N. Y.-CY, D V N. Y.-CH, RA, SP Accessories A M & H SPORTING GOODS CO., 512 Market St., HUNTER PRESSED STEEL CO., 8th St. & Maple Ave., Phila., Pa.-A, C, CN, CT, CY , SP, ST, V Lansdale, Pa. -ST Aircraft AC MILES REPRODUCER CO., INC., 812 Broadway, INSULINE CORP. OF AMERICA, 30-30 Northern Cable (see Wire) New York, N. Y., "Filmgraph," "Dictafilm "-G, Blvd. Long Island City, N. Y. -AL, BR, CH, CO, Carbon -type C CD, H, SP, ST PA, kA, SP ST, TR Tibbetts -type CD MONOBAR- Laboratories E. F. JOHNSON COMPANY, Waseca, Minn. -AL Condenser MONTGOMERY WARD & CO., INC. 619 W. Chi - THE JOHNSTON TIN FOIL & METAL Co., 6106 S. Connectors CN cago Ave., Chicago, III., " Airliner' -A, C, CN, Broadway St. Louis, Mo. -FO Contact -type CT CT, CV, DY. ST, V KARP METAL PRODUCTS CO., 129 30th St., Brook- NATIONAL DOBRO CORP., 400 S. Peoria St, Chi- lyn N. Y.-CH PA RA SP, ST, TR Crystal -type CY cago, III. -CY, ST KING LABORATORIES 205 Oneida St., Syra- -type D INC., Dynamic NATIONAL UNION RADIO CORP., 57 State cuse, N. Y. "Barex'' -TP Home -broadcasting H KNIGHT-Allied Radio Corp. St.. Newark, N. J. -CY, D, V L LAFAYETTE RADIO CORP., 100 6th Ave., New York, Laboratory -type NORTHERN ELECTRIC CO., LTD. 1261 Shearer St., N. Y. -AL CH, PA RA, SP Springs SP Montreal Que., Can. -C, CD, CT, CY, D, ST P. R. MALLORY & CO., INC., 3029 E. Washington Stands ST OFFENBACH ELECTRIC CO., 1452 Market St. San St. Indianapolis. Ind. -MO, TU Francisco, Calif. -A, C, CD, CN, CT, CY, H, JAMES MILLEN MFG. CO., INC., 150 Exchange Velocity -type V SP, ST, V St., Malden, Mass. -ST Vibration- pickup (inertie) type VP OLSON MANUFACTURING CO., 362 Wooster Ave., MONTGOMERY WARD & CO., INC., 619 W. Chi- Akron, Ohio -C cago Ave., Chicago, III., "Airline " -PA, RA, SP 'AIRLINE-Montgomery Ward & Co., Inc PARAPHONE HEARING AID, INC., 4300 Euclid NATIONAL COMPANY, INC. 61 Sherman St., ALLIED ENGINEERING INSTITUTE, 85 Warren St., Ave., Cleveland, Ohio -C Malden, Mass., "National,'' "AC"-CH, PA, New York, N. Y. -CT, CY PHILCO RADIO & TELEVISION CORP., Tioga & RA, SP ALLIED RADIO CORP., 833 W. Jackson Blvd., "C" Sts., Phila., Pa -A, CN, DY, D, T NATIONAL- Natio-a1 Company, Inc. PHILMORE MANUFACTURING CO., INC., 113 Uni- NEW ART SPECIALTIES. INC., 816 W. Erie St., Chicago, Ill-, *"Knight"-A, C, CD, CN, versity Pl. New York, N. Y.-C D Chicago, III. -ST CT. CY, D, H, SP, ST, V RACON ELECTRIC CO., INC., 52 E. 19th St., New OFFENBACH ELECTRIC CO. 1452 Market St., San AMERICAN CONDENSER CORP., 2508 S. Michigan, York, N. Y. -D BR, H, PA. RA, SP Francisco, Calif.-AL, Chicago, 111. -CD RADIO ELECTRIC SERVICE CO., INC., N.W. INC., 1915 S. PAR -METAL PRODUCTS CORP., 32.62 49th AMERICAN MICROPHONE CO., 7th & Sts., Phila., Pa. geles, C, CN, Cor. Arch -A, C. St., Long Island City, N. Y. -PA, RA, SP Western Ave., Los A- Calif. -A, H, SP. ST CD, CN, CT, CY, D. H, SP, ST, V PAUL & BEEKMAN, Div. of PHILA. LAWN MOWER CT, CY, D, 1250 Van Buren RADIO EQUIPMENT CORP., 326 Elm St., Buffalo, & MFG. 4250 Wissahickon Ave., Phila., Pa. AMERICAN PHENOLIC CORP., W. CO., N. Y. -A, C, CN, CT, CY, D, H, SP, ST, V TR St., Chicago, Ill. -A, CN -CH. ST, HARDWARE INC., 476 RADIOTONE, INC., 7356 Melrose Ave., Hollywood, GEORGE F. PETTINOS, INC., 1206 Locust St., Phila., AMERICAN RADIO CO., Calif. -CY. D Pa.- -G Broadway, New York, N. Y. -SP 561 Broadway, New York, RADOLEK COMPANY, 601 W. Randolph St., Chi- RACON ELECTRIC CO., INC., 52 E. 19th St., New AMPERITE COMPANY, V cago. 111.-A, C, CD CN, CT, CY, D, H, SP, ST, V York, N. Y. -PE, SP N. Y. -A, CT D. ST, ART SPECIALTY CO., 1115 N. Franklin St., Chicago, RCA MANUFACTURING CO., INC., Camden, N. J. RADIO ELECTRIC SERVICE CO., INC., N.W. III. -A, ST -A, CN, CY D, H, ST, V Market REGAL AMPLIFIER MFG. CORP., 14 W. 17th St., Cor. 7th & Arch Sts., Phila., Pa. -AL, CH, ASIATIC MICROPHONE LAB., INC.. 830 St., Youngstown, Ohio CY. D, ST New York N. Y.-CY, H, ST PA, SP, -A, RA. ST ATLAS SOUND CORP., 1451 39th St., Brooklyn, ROCKET -Shure Brothers RADIO EQUIPMENT CORP., 326 Elm St., Buffalo, N. Y. -A, CN, ST ROWE INDUSTRIES, INC., 3120 Monroe St., Toledo, N. Y. -AL CH PA, RA, P AUDIOGRAPH SOUND SYSTEMS, 1313 W. Randolph Ohio -CT RADOLEK COMIIANY 601 W. Randolph St., Chi- St., Chicago, 111. -CN, CT, CV, D. ST WALTER L. SCHOTT CO., 5266 -70 W. Pico Blvd., cago, III. -AL, BR, CH, PA, RA, SP 'AUTOCRAT-Autocrat Radio Co. Los Angeles, Calif., "Walsco" -SP R -B -M MANUFACTURING CO., Div. Essex Wire AUTOCRAT RADIO CO., 3855 N. Hamilton Ave., MAURICE SCHWARTZ & SON, 710 -712 Broadway, Corp., Hanna & Chestnut St., Logansport, Ind. -ST Chicago, III., 'Autocrat " -CY, H Schenectady, N. Y. -A, C, CD, CN, CT, CY, D, H, ROGERS -MAJESTIC CORP., LTD., 622 Fleet St., THE BRUSH DEVELOPMENT CO., 3311 -3405 SP, ST, V RADIO SUPPLY CO., INC., 2117 2nd Ave., Toronto, Can. -LA ST. TR, TP CY, SEATTLE SCOVILL MANUFACTURING CO., 99 Mill St., Perkins Ave.. Cleveland, Ohio -CT, Seattle, Wash. -A, C, CD, CT, CY, 0, H, SP, Waterbury. Conn. -BR, ST ST, VP ST, V SHELLEY RADIO CO.. 1841 S. Flower St., Los An- BUD RADIO, INC., 5205 Cedar Ave., Cleveland, SELECTAR MANUFACTURING CORP., 30 W. 15th geles, Calif.-G, PA Ohio -ST St., New York, N. Y. -A, CN, H, V Please say you sain it in thr Radio -Craft "Classified Radio Directory" RADIO -CRAFT for JUNE, 1941 761 CLASSIFIED RADIO DIRECTORY

SHELLEY RADIO CO., 1841 S. Flower St., Los An- geles, Calif. Flock FL *AC- National Company, Inc. -A C, CY, D, H, ST ALDEN PRODUCTS SHURE BROTHERS, Insulating compounds . . IC CO., 715 Center St., Brockton, 225 W. Huron St., Chicago, III., Mass.-CE, LA, PA "Shure "" "Unidyne," "Uniplex " "Rocket," ' Strato- Lacquers LA ALLIED RADIO CORP., 833 liner,' "Super -Level," "Ultra Range," W. Jackson Blvd., Chi- -Wide Paint (and /or wrinkling & cago, III., "Knight' -CE VA, WA "Zephyr"-A, C, CN, CT, CY, D, H, L, SP, ST, VP AMERICAN SHORE -Shure Brothers crystallizing) PA PHENOLIC CORP., 1250 W. Van Buren MARK St., Chicago 111.-CE, IC SIMPSON DISTRIB. CO., INC., 16 Hudson BAKELITE CORPORATION, St. New York, N. Y. -ST 30 E. 42nd St., New York N. Y. -IC SOUND APPARATUS CO., 150 W. 46th St., New BUD RADIO, INC., 5205 Cedar Ave., Cleveland, York N. Y.-C, CD, CY, D Ohio STRAtOLINER -Shure Brothers -LA CINEMA ENGINEERING CO., 1508 W. Verdugo STROMBERG-CARLSON TELEPHONE MFG. CO., Ave., Burbank, Calif. -WA 100 Carlson Rd. Rochester, N. Y.-G, H CONSOLIDATED WIRE & ASSOCIATED CORP., 512 SUN RADIO CO., 212 Fulton St., New York, N. Y.- Preceding Listings in RADIO-CRAFT'S S. Peoria St., Chicago, 111.-CE, EN, IC, LA, PA, A C, CD, CN, CT, CY, D, H, SP, ST, V A "SUPER-LEVEL -Shure Brothers CRUMPACKER TAYLOR AIRPHONE CLASSIFIED RADIO DIRECTORY DISTRIB. CORP., 1801 Fannin St., PRODUCTS, INC. Long Beach Houston, Tex. LA Municipal Airport, Long CE, Beach, Calif.-AC, C HAROLD DAVIS, INC., 428 TIBBETTS LABORATORIES, Sec. I (Revised), April '41: W. Capitol St., Jackson, Camden, Maine, "Mono - Miss.-CE bar"CY Amplifiers DOW RADIO SUPPLY TRY -MO RADIO INC. CO., 1759 E. Colorado St., CO., 85 Cortlandt St., New Antennas & Accessories Pasadena, Calif.-CE, EN, LA York, N. Y.-A, C, CD, N, CT, CY, D, H, SP, Automatic Tuners & Parts FEDERATED PURCHASER, INC., 80 Park Pl., New ST, V Auto -Radio Controls York, THE TURNER N. Y.-CE, LA COMPANY, 909 17th St., Cedar Aircraft Radio (see Receiving Sets -including FISCHER DISTRIB. Rapids, Iowa, CORP., 222 Fulton St., New York, "Turner " -A, C, CD, CN, CT, CY, Adapters and Converters) N. Y. -CE, EN IC, LA, PA, VA, WA D, H ST Battery Chargers (& Parts) FLOCK PROCESS CORP., 17 W. 31st St., New York, TURNER-The Turner Company Batteries (& Cells) Dry 6 Wet (Storage) ULTRA N. Y. -FL -WIDE RANGE -Shure Brothers Books (see Service Manuals, Books & Magazines) GENERAL CEMENT MFG. UNIDYNE -Shure Brothers CO., 919 Taylor Ave., Cabinets Cases, Parts & Services Rockford, 111.-CE, EN, IC, LA; PA, VA, UNIPLEX -Shure Brothers Chemicals for Radio WA UNIVERSAL MICROPHONE HARRISON RADIO CO., 12 W. Broadway, New CO., LTD., 424 Warren Coils & Transformers (R.F & I.F.) & Accessories York, N. Y.-CE Lane Inglewood, Calif. -A, C, CN, CY, D, H, Coin Controls (see Records & Record -Playing SP, ST, V Equipment- also Receiving Sets) INSULATION MANUFACTURERS CORP., THE VEGA COMPANY, 155 Columbus Ave., Boston, Condensers, Fixed 565 W. Washington Blvd., Chicago, III. - Mess., "Vega," "Vitar "CT Condensers, Variable CE, IC, LA, VA, VEGA -The Vega WA Company Crystals (Quartz) J. F. D. MANUFACTURING VICTOR ANIMATOGRAPH CORP., Davenport, CO., 4111 Ft. Hamilton Iowa Pkwy., Brooklyn, N. Y.-CE, EN, VA, WA -D, V Sec. 11 (Revised), May '41: VITAR -The Vega Company KNIGHT- Allied Radio Corp. Crystals (for detection- receiving) & Detectors LAFAYETTE RADIO CORP., 100 6th Ave., New York, THE VOLU -TONE COMPANY, 252 S. Broadway, Los Angeles, Calif. -V Dials & Parts N. Y.-CE, EN, IC LA, PA, VA, WA Electric Fence Controllers M & H SPRTING FOODS CO., 512 Market St., WALSCO- Welter L. Schott Co. Electronic Equipment Phila., Pa.-CE WEBSTER- CHICAGO CORP., 5622 W. Bloomingdale Electronic Musical Instruments & Parts MAAS & WALDSTEIN CO., 438 Riverside Ave., Ave. Chicago, III. -AM Y D, ST, V Facsimile Newark, N. J.-CE, EN,EN LA, PA, VA WESTERN SOUND & ELECTRIC LABS., INC., 311 W. Fluorescent & Neon Lamps (& Equipment) MAGIC ART PAINT O., Hasbrouck Heights, Kilbourn Ave., Milwaukee, Wis. -A, 6N, CY, D, Frequency Modulation Equipment N. J.-SD H, SP ST, V Hardware -Connectors & Misc. Parts & Supplies MEISSNER MANUFACTURING CO., Mt. Carmel, ZEPHYR -Shure Brothers Headphones 111.-CE, LA Hearing -Aids MITCHEL-RAND INSULATION CO., INC., 51 Mur- NOISE -ELIMINATION Hearing -Aid Parts ray St., New York, N. Y. -IC WA NASH RADIO PRODUCTS CO., 6267 Gravois Ave., EQUIPMENT Sec. II, Nov. .40 (in part): St. Louis, Mo.-CE, EN, IC, LA, PA, VA, WA Insulation NATIONAL COMPANY, INC., 61 Sherman St., Mal- den, Mass., Intercommunicating Systems "National," "AC"-CE, LA Line Filters NATIONAL -National Company, Inc. OFFENBACH ELECTRIC CO., 1452 Market St., San Francisco, Calif.-CE, IC, A Sec. III, Dec. '40: GEORGE F. PETTINOS, INC., 1206 Locust St., Phila., Magnets Pa.-CE Metal & Special Fittings (for Radio) POINSETTIA, INC., 97 Cedar Ave., Pitman, N. J.- Metal, Ore & Oil Locators WA Acoustical . . . . materials AM RADIO Industrial Microphones EQUIPMENT CORP., 326 Elm St., Buffalo, noise analyzers . . IA Noise Eliminhtion Equipment N. Y.-CE EN, LA Interference analyzers . . . . Paint, Cement & Was Products RADOLEK COMPANY, 601 W. Randolph St., Chi - Plastics cago, 111.-CE, EN Interference locators . IL Plastic Molders SAUEREISEN CEMENTS CO., 2308 Main Power St., Sharps- filters (see Line Filters) Radio Logs Maps & Globes burg, Pittsburgh Pa.-CE, IC Radio -set filters (see Line Filters) Receiving Sets (including Adapters & Converters) WALTR L, SCHOTT CO. 5266 -70 W. Pico Blvd., Wave -traps Records & Record -Playing Equipment Los Angeles, Calif., "Vìalsco"CE, EN, IC, LA, W PA, VA Sec. IV, '41: MAURICE SCHWARTZ & SON, 710 -712 Broadway, ALLIED RADIO CORP., 833 W. Jackson Blvd., Chi - Jan. Schenectady cago, III., N. Y.-CE, EN, IC, LA, PA, VA, WA "Knight" -IA, I IL Recording Equipment SEATTLE RADIO SUPPLY CO., ATOMS -Sprague Products INC., 2117 2nd Ave.. Co. Resistors & Volume Controls (Attenuators & Net- Seattle, Wash.-CE, EN IC, LA BAKER & WILLIAMSON, Ardmore Pa. -IA works) CANADIAN MARCONI SELF -VULCANIZING RUBI3ER CO., INC., 605 W. CO., 211 St. Sacrament St., Schools Washington Chicago, 111.-CE IC, PA Montreal, Can. I, IL -IA Service Manuals, Books & Magazines SHELLEY RADIO 1841 THE CELOTEX CO., S. glower St., Los An- CORPORATION, 919 N. Michigan Servicing Equipment geles Calif.-CE, LA Ave., Chicago, 111. -AM Sound Systems, Amplifiers & Accessories SMOOCH -ON MAUFACTURING CO. 572 Cor - CONTINENTAL CARBON, INC., 13900 Lorain Ave., munipaw Ave., Cleveland Ohio Jersey City, N. J.-CE -I Sec. V, Feb. '41: SUN RADIO CO., 212 Fulton St., New York, N. Y.- TOBE DEU1SCHMANN CORP., Canton, Mau. -I, CE IL Speakers (& Parts) EN TALKING DEVICES CO., 4447.44 W. Irving Perk Rd., FEDERATED PURCHASER, INC., 80 Park Pl., New Switches & Relays Television Chicago, III. -WP York, N. Y. -1 IL TELERADI HARRISON RAb1O Test Equipment- Laboratory & Production ENGINEERING CORP., 484 Broome St., CO., 12 W. Broadway, New New York, N. Y.-LA, WA York, N. Y. -IA, I, IL Tools KNIGHT- Allied Radio Corp. Transformers & Chokes WALSCO- Walter L. Schott Co. KOOLOHMS- Sprague Products Co. Transmitters (& Equipment) WESTINGHOUSE ELEC. & MFG. CO., E. Pittsburgh, Pa. -EN, IC RADOLEK COMPANY, 601 W. Randolph St., Chi - cago, III.-1 Sec. VI, March '41: ZOPHAR MILLS, INC., 112 26th St., Brooklyn, N. Y. SEATTLE RADIO -CE, IC, WA SUPPLY CO., INC., 2117 2nd Ave., Tubes (& Parts) Seattle, Wash -IA, I, IL Vibrators 600 LINE-Sprague Products Co. Wire PLASTICS SPRAGUE PRODUCTS CO. N. Adams, Mau. Literature Sprague," "600 Line," "Atoms,' "Koolohms,'1 "Telohmike " -IA, I, IL SPRAGUE -Sprague Products Co. The above back -issues of Radio -Craft are avail- 'TELOHMIKE- Sprague Products Co. able at the regular price of 25c per copy. VOGUE PRODUCTS CO., 8420 S. Ashland Ave., Next month: Section IV of the Classified Radio Chicago, Directory, revised, with new classifications, and new names and addresses added: and with obsolete PAINT, listings removed. Reserve your copy, today, from Cellulose acetate CEMENT & WAX your regular newsdealer. CA PRODUCTS Lucite L Methyl- methacrylate . . . MM Phenols P Polystyrene PO Rubber R Vinyl resins Self- designing paints & enamels SD VR Varnish VA Cements CE Wax WA AC- National Company, Inc. ALDEN PRODUCTS CO., 715 Center St., Brockton, Enamels EN Wax, phonograph WP Mass. -P Please say you saw it in the Radio -Craft "Classified Radio Directory" 762 RADIO -CRAFT for JUNE, 1941 BOOK REVIEWS

ALLIED RADIO CORP., 833 W. Jackson Blvd., Chica- go. III., "Knight" -PO BOOK REVIEWS AMERICAN PHENOLIC CORP., 1250 W. Van Buren St., Chicago, III. -CA, L P, PO flllllllllau AMERICAN RADIO HARDWARE CO., INC., 476 "GO AHEAD-GARRISON ! " -A Story of News VACUUM TUBE VOLTMETERS. by John F. Broadway, New York, N. Y.-CA, L. P Broadcasting, by A. A. Schechter. Published by Rider. Published by John F. Rider. Cloth covers. BAKER & WILLIAMSON, Ardmore, Pa. -CA, L, PO Dodd, Mead & Co. Cloth covers, size 8 x 5'/u ins., size 8'/e st 51/2 ins., 169 pages. Price $1.50. BIRNBACH RADIO CO., INC., 145 Hudson St., New 237 pages, Price $2.00. book describes York, N. Y. "Birnbech " -L This the various types of CARBIDE & CARBON CHEMICALS CORP., 30 E. We start our review of this book by giving a vacuum -tube voltmeters -how they are made and 42nd St., New York, N. Y. -VR few chapter titles selected at random: IV, I'ress hew they are used. Calibration and testing are CELLULOID -Celluloid Corporation Meets Radio; V, Storm Warnings; X, Sunshine given consideration in chapters devoted to these CELLULOID CORPORATION, 180 Madison Ave., and Disaster ; XV, Radio Tour ; XVI, Ballots at topics. Has a bibliography of 145 references. New York, N. Y., "Lumarith," "Lumarith Pro - Breakfast; XIX, Radio Newsmen Abroad. The chapters which discuss vacuum -tube volt- tectoid," "Celluloid " -CA by time you have formed meter etc., are as follows: FLOCK PROCESS CORP., 17 W. 31st St., New York, Probably this the types, I, Fundamentals N. Y. -CA, L not erroneous opinion that this book is one you of voltmeters; II, Diode types; III, Triode types; GENERAL CEMENT MFG. CO., 919 Taylor Ave., might find on nearly any reading table. IV, Slide -back types; V, Rectifier -Amplifier Rockford, 111. -PO After an apprenticeship with The New York types; VI, Tuned vacuum -tube voltmeters; VII, GENERAL ELECTRIC CO., Schenectady, N. Y. & A.F. and Logarithmic types ; VIII, Vacuum -tube Bridgeport, Conn. -CA, MM, P, PO World, Associated Press, and International News Service, the N.B.C., to voltmeters for D.C. measurements; IX, Design "KNIGHT-Allied Radio Corp. author joined eventually become Director of its News and Special Events and construction of various types; X, Calibration LUMARITH- Celluloid Corporation service department. The story he tells is a first - and Testing; XI, Applications. LUMARITH PROTECTOID -Celluloid Corporation person picture of how news is garnered for the No book on the market can come anywhere JAMES MILLEN MFG. CO., INC., 150 Exchange St., air and how it is conditioned for programming. near touching "Johnny" Rider's latest contribu- Melden Mass. -PO It's an inside story, about radio news, factual, tion to "must" books for the Serviceman. In fact, ELMER E. MILLS CORP. 812 W. Van Buren St., anyone having any technical interest in radio will Chicago, III. -CA L, PO and entertaining to the Nth degree, It's a hook find book big value. apparently does not NATIONAL COMPANY, INC. 61 Sherman St., of wide general interest and of special interest this It Melden, Mass., "National," s'AC "-CA, PO to everyone in the radio field. Carrying no obvious leave unanswered many questions the technician NATIONAL -National Company, Inc. torch, it yet is sugar- coated dynamite that effec- may propound on the subject of vacuum -tube NATIONAL VULCANIZED FIBRE CO., P. O. Box tively sells the earnestness of purpose which voltmeters; and it answers far more than the 311 Wilmington, Del. -P average radio man is ever likely to ask. PARISIAN NOVELTY CO., 3510 S. Western Ave., motivates all great news staffs. Chicago, III. -CA, L P PO THE RICHARDSON COMPANY Melrose Park (Chi- A NEW SYSTEM OF DYNAMIC ANALYSIS. SIMPLIFIED RADIO SERVICING BY COM- cago), 111. -CA L, P, PO, R Published by Supreme Instruments Corp. Paper PARISON METHOD, by M. N. Reitman. Pub- SEATTLE RADIO CO., INC., 2117 2nd Ave., SUPPLY 8% 11 ins., 28 pages. lished by Publications. Paper covers, Seattle, Wash. -L PO covers, size s illustrated, Supreme SELF -VULCANIZING RUBBER CO., INC., 605 W. Price, 35c. size 81/2 z 11 ins., well illustrated (including Washington, Chicago, 111.-R This book is ingeniously described as being an numerous complete receiver diagrams), 108 Doges( VICTORY MANUFACTURING CO., INC., 1217 explanation of a new, definite and direct servic- Price, $1.00. Washington Blvd., Chicago, 111. -CA, L, P, PO ing procedure that "makes an ailing radio set Briefly, the idea is to compare the diagrams, THE WATERBURY BUTTON CO., Waterbury, Conn. talk to you just as a patient talks to his doctor." etc., in the book, with equivalent circuits, etc., -CA, L, P PO in a particularly convenient form in the receiver under test. Tables and informa- WESTINGHOUSE ELEC. & MFG. Co., E. Pittsburgh, It presents Pe. -P the application notes for the cathode -ray type tion fur test procedure are then followed until of dynamic analyzers. the fault in equipment or components has been Chapter I describes the Veedolyzer. Succeeding located and corrected. PLASTIC MOLDERS chapters develop the application of this instru- The first 38 pages discourse on radio funda- ment in signal tracing, checking intermittente, mentals designed to acquaint the reader with the etc., and fault-finding in F.M. receivers. Analyz- elements necessary for complete understanding ing receiver faults by checking circuits is also of the COMPARISON test procedure described *t it* discussed. in the remaining pages. Cabinet molders CM q t7t '/Qctt« Shavet Small parts molders . . . . SM FREE! AMERICAN PHENOLIC CORP., 1250 W. Van Buren ABSOLUTELY St., Chicago, 111. -SM AMERICAN RADIO HARDWARE CO., INC., 476 JUST THINK OF IT -you can get absolutely Broadway New York, N. Y. -SM FREE, the useful DRY ELECTRIC SHAVE AUBURN BUTTON WORKS, INC., Auburn, N. Y.- which is shown at the left. This ELECTRIC CM, SM is BOONTON MOLDING CO., 326 Myrtle Ave., Boon- DRY SHAVER sent to you by the publishers ton N. J.-CM SM with a one -year subscription to RADIO- CRAFT. CHICAGO MOLDED PRODUCTS CORP., 1020 N. Here Are the Features or The Kolmar Ave., Chicago, 111. -CM, SM HUGH H. EBY, INC., 4700 Stenton Ave., Phila., Pa. ELECTRIC DRY SHAVER -SM Constructed of metal bronze 105 E. 29th St., New York, with attractive red EMPIRE NOTION CO., finish. Scientifically constructed to give perfectly N. Y. -SM clean shave. 5.15oí rubber Insulated cord and plug. ERIE RESISTOR CORP., 644 W. 12th St., Erie, Pa.- Constructed to last for many years. SM Operates from I10.volt, 60-tyele A.C. elac- GEMLOID CORPORATION, 79.10 Albion Ave., Elm- trie line. Carries a two -year manufacturer's hurst, L. 1. -SM guarantee. A fine quality. self- sharpening B. F. GOODRICH COMPANY, 500 S. Main St., toilet necessity. Akron Ohio -SM Send your subscription to RADIO -CRAFT IMPERIAL MOLDED PRODUCTS CORP., 2925 W. for One Year (12 Issued and rewire ab- Harrison St. , Chicago 111. -SM solutely FREE one of these remarkable Electric Dry Shavers. New INSULATION PRODUCTS CO., 504 N. Richland St., eubecribers ON are accepted or you may extend your pres- Pittsburgh Pa. -SM OPERATES ent subscription another twelve months. KELLOGG SWITCHBOARD & SUPPLY CO., 6650 S. 110 -VOLT, 60 -CYCLE 51.11 your remittance of $2.00 (plus 25e Cicero Ave., Chicago 111. -CM SM A.C. LINE for chipping charges on Shaver) to the KURZ- KASCH, INC., 1421 S. Broadway, Dayton, publishers. (Canada and foreign s -.75.) You will receive your Ohio CM SM DRY ELECTRIC SHAVER im- MICAMOLD RADIO CORP., 1087 Flushing Ave., mediately by return mall. Use Brooklyn, N. Y. -SM coupon below to enter your ELMER E. MILLS CORP., 812 W. Van Buren St., subscription. Chicago, 111.-CM, SM POINSETTIA, INC., 97 Cedar Ave., Pitman, N. J.- RADIO-CRAFT SM Vesey Street, New York, N. Y. RADIO KNOB CO., 43 E. Ohio' St., Chicago, III. - 20 SM REMLER COMPANY LTD., 2101 Bryant St., San Francisco SM Calif. -CM 20 York, N. Y. THE RICHARDSON COMPANY, Melrose Perk (Chi- RADIO -CRAFT, Vesey Street, New my of 62.00 for which enter my cago), 111. -CM, SM Gentlemen: Enclosed find remittance mbecrlption to RADIO -CRAFT for one year (12 Issues). Send me SYRACUSE ORNAMENTAL CO., Syracuse, N. Y-4 immediately FREE. ELECTRIC PRY SHAVER (Canada end foreign CM 62.75). In U. S. add only 25e additional to corer shipping chergee on TELEX PRODUCTS CO., 1645 Hennepin Ave., Minne. WE SHIP ELECTRIC DRY Shaver. spolia, Minn. -SM SHAVER THE SAME DAY Now Subscriber Batend Present Subscription TILTON ELECTRIC CORP., 15 E. 26th St., New York, N. Y. -SM YOUR SUBSCRIPTION Name THE VALPEY CRYSTALS, Box 321, Holliston, Mass. ORDER IS RECEIVIiD. - Address VICTORY MANUFACTURING CO., INC., 1217 Wash- City State ington Blvd. Chicago 111. -CM, SM CLIP COUPON (Band remittance by check. money order or unused U.S. Postage Stamps THE WATERBURY BUTTON CO., Waterbury, Conn. - Register letter if you send rash nr stamps.) RC -641 CM, SM AND MAIL!

~~RADIO -CRAFT for JUNE, 1941 763 SHOP NOTES -KINKS -CIRCUITS~~

COMBINED OVER- MODULA- VOICE COIL RUBBING TION INDICATOR, MONITOR 904e.x, ,to. adcw414.4v44 CEMENT ALL CUT ALONG HERE (PHONE), AND VOLUME AROUND ALL AROUND. LIFT OUT CONE, LEVEL METER CLEAN ANO PUBLISHERS RE PLACE, MEN .01-MF, 600V. PIECE OFwiRE NEAR ANTENNA, CEMENT AND REENTER Amplifier Co. of America 707 0.5- Data f MEG. 76 Print Co 742 SO MMF. National Plans Inst 710 Radcraft Publications, Inc 782. 748, 759 Radio & Technical Pub. Co 709 RFC. Supreme Publications 711 100 2.1 MHV MMF. SPEAKER Technifax 708, 737 VOLUME T / INDICATOR RIM INPUT ' 10,000 RADIO PARTS 6.3V. OHMS PHONE^ 1/4..._ i S'11EN a speaker voice coil rubs due to Aerovox Corporation 728 foreign particles on Amperite Co. 711 the pole piece, and Hammarlund Mfg. Co 709 10.000 no replacement of cone is available (and the Solar Mfg. Corp 709 O.I. OHMS VI O.I. cone is cemented to the iron speaker), take Sprague Products Co 725 750 a sharp razor OHMS V.I. blade and cut out the whole OHMS 4 tii 4 350K, cone very close to the metal ring. Now lift Sw.. 6POLE, oc. out the cone, 3POSITION o.I. 0-1 MA., clean the voice coil and pole RADIO SETS D.C. piece, set back the cone, and re- cement with Meissner Mfg. Company 753 aeroplane glue. Midwest Radio Corp 749 REALIZING the cost of having separate F. M. VANDERGRIFT, RCA Manufacturing Co.. Inc.....Back Cover 0 -1 ma. meters for each of these instru- Trenton, N. J. ments, I designed a simple circuit (shown here) to perform both of these functions. RADIO SUPPLY HOUSES To use it as an over -modulation indicator (or throw BOOK REVIEWS Allied Radio 0.I.), the switch to the position Corp 727 11111111111UIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII Burstein -Applebee Co 707 marked O.I., and adjust to optimum reading IIIIIIIIIIIIIIIIIIIIIIIIIIIIUIII Federated Purchaser. Inc 733 with the variable condenser after attaching RADIO AMATEUR'S HANDBOOK, by A. Fred- Hudson Specialties Co 739 a piece of wire near the antenna. Any erick Collins (1940). Published by Thomas Y. Lafayette Radio Corp.....Inside Front Cover Radolek Co 728 change in meter readings indicates over - Crowell Company. Size 51/2 x 8 ins.. cloth covers, modulation. profusely illustrated, 342 pgs. Price, 32.00. As a volume indicator (or V.I.), short the The revised 8th Edition of "Radio Amateur's Handbook" will SCHOOLS input, adjust meter to zero with the potenti- be of exceptional interest to ometer, and connect circuit. the general radio experimenter and particularly to the beginner Capitol Radio Eng. Inst 708 To use as a phone monitor, insert phones in radio who wishes to have avail- Coyne Radio School 710 and proceed as for able in convenient form. or who wishes to learn. Lincoln Engineering School 711 the over -modulation in- the bases of radio in general and its component National Radio Institute 705 dicator. receiver circuits. National Schools 708 EUGENE SIMPSON, Ten New York Y.M.C.A. chapters have been revised and corrected Schools 708 and 10 entirely Port Arthur College 711 Napert-ille, Ill. new chapters have been added. Radio Training Assoc 709 This includes new material on shortwave opera- RCA Institutes 707 tion. frequency modulation. facsimile and tele- Sprayberry Academy of Radio PHONO TURNTABLE KINK vision. Inside Rack Cover This review would be incomplete without calling attention to its exceptionally large number of illustrations, ranging from the most elemen- SOUND & RECORDING EQUIPMENT tary, to pictorial and schematic diagrams of modern radio equipment. The book is fully indexed Amplifier Co. of America 737 for you. Atlas Sound Corporation -37 It also includes a glossary of technical Lifetime Corp., The ->,t terms; tables. etc. We list a few chapter head- John Meek Industries Tan ings selected at random: University Laboratories -33 Chapter 1-Fundamentals of Radio; Chapter 4- Electricity Simply Explained; Chapter 12- Assembling Your Own Radio Receivers; Chap- TEST EQUIPMENT THE rubber belt, on turntables that are ter 18 -The Photoelectric Cell and Its Uses; driven by a motor pin against a rubber Chapter 20- Frequency Modulation. General Test Equipment Co. 707 tire, sometimes wears out. You can replace Radio CIty Products Co ISO Readrite it very efficiently and rapidly by using the EDUCATION ON THE AIR, 11th Edition. Meter Works 742 Edited by Supreme Instruments Corp 721 round rubber type of vacuum cleaner belt. Josephine H. MacLatchy (1940). Published by Ohio Triplett Electrical Instrument Co 729 The cost is 10c and makes a job State University. Cloth covers, Weston Elec. Instrument Corp 735 better than size 6 x 9 ins., 368 Price the original equipment. We use this method pages. $3.00. exclusively on RCA. The Institute of Education by Radio annually publishes a résumé of the 12 -month progress in TUBES F. M. VANDERGRIFT, this Trenton, N. J. field as seen by Ohio State University. This University, which operates WOSU, one of 27 Hygrade Sylvania Corp 733 educational stations National Union Radio in the country, annually Corp 719 COLORED DIAL LAMPS holds a conference of radio engineers and makes every effort to maintain a foremost place in the COLORED field of education by radio. CELLOPHANE MISCELLANEOUS The 11th Edition of "Education by Air." contains 13 important chapters, a few Classified Section 742 of which are Flight Magazine DIAL given below. Each of the chapter subdivisions Henry Hudson Hotel 719 is written by a specialist assigned to the work Lancaster, Allwine & Rommel 74_ of compiling respective topical information. Onan, D. W., & Sons 749 Chapters: I, International Broadcasting; Premium Distributing II. Service 749 DIAL LAMP Radio and Propaganda ; IX, Radio A Schoolroom Use Servicemen of America. Inc 755 of Radio; XI. Radio Techniques; XIII, Research Remington Rand Inc. 712 in Educational Walter L. Schott Co. 749 Broadcasting. Warner Company 728 Electric EVERY now and then you have a call Wellworth Trading Co 744 THE ELECTRIC WORD - THE RISE OF Woodstock Typewriter Co 710 for a colored dial lamp; or, in repairing RADIO, by Paul Schubert. Published by The a set with a weird and wonderful collection Macmillan Company, New York. Cloth covers, of colored dial bulbs, you find one burned out %ize tl % z 51/2 ins., 311 pages. Price $2.50. and no dial- lamp'coloring on hand. This book is a readable presentation of the Simply arrange a piece of colored cello- development of radio from its infancy. The (While every precaution is taken to insure phane between the bulb and the dial. You authentic treatment of its technical content accuracy, we cannot guarantee against the can get this colored cellophane in all colors merely highlights what is, in the main, a book and it pays to save for non -technicians. Excellent reading matter for possibility of an occasional change or omis- the colored pieces high-school students who wrapped around so many want to obtain at least sion in the preparation of this index.) things you buy. a superficial knowledge of just where radio GEORGE E. MCALLAN, stands, in its development, in relation to other Fernie, B.C., Canada growing industries. 764 RADIO -CRAFT for JUNE, 1941 SERVICEMEN SAY: -`dot //lig ee Ptopti- `EoV Satin' Setviciny -USE GERNSBACK MANUALS

Since 1931 more and more Servicemen have been 7 OFFICIAL RADIO buying GERNSBACK OFFICIAL RADIO SERVICE VOLUME SERVICE MANUAL MANUALS year after year. The authentic material, - The newest and most outstanding GERNS- easily accessible diagrams and complete service data I OFFICIAL BACK Manual published since 1931. Con- L1IVICS Service- 1 RADIO tains many features never previously make them invaluable to dealers and radio MANUAL published in any service guide. OVER men. Without a Gernsback Manual with you on a 1,800 PAGES OVER 3,000 ILLUSTRA- TIONS OVER 1,600 SETS REPRE- repair job, there's time and profit lost. Your service SENTED Complete Service Data In- the GERNS- cludes 1938 Models Not Found in Other kit or laboratory is incomplete without all Manuals All New Material -No Reprint BACK OFFICIAL RADIO SERVICE MANUALS. There or Rehash Master Index of 74 Pages Includes Sets Listed in All Other Gems- are GERNSBACK MANUALS also for servicing auto- back Manuals Stiff. Leatherette Loose - equipment. leaf Covers Size 9 x 12 Inches Net radios, refrigeration and air conditioning Weight 101/2 lbs. Price S 10.00 1935 OFFICIAL AUTO -RADIO OFFICIAL SERVICE 1936 OFFICIAL RADIO AUTO -RADIO MANUAL SERVICE MANUAL ftRYÍCt MANUAL - If you are overlooking Just packed with service data of sets manufac- servicing auto radios, then tured during 1935 and 1936. Schematic diagrams you are missing a great show speaker connections, power -transformer con- deal of business. Th, nections, R.F. and I.F. coil connections, phonograph great number of car connections and other information. OVER radios in use require con - 1,200 PAGES OVER 1,500 SETS SHOWN 't: nt servicing and you OVER 2.500 ILLUSTRATIONS Index of can make it a profitable Trade Names Complete Tube Chart Stiff, sideline to your regular Leatherette, Looseleaf Covers Size 9 x 12 Inches servicing business. This Net Weight 8 lbs. complete Manual contains schematic diagrams, Price $7.00 chassis layouts, mounting instructions and trouble shooting hints. OVER 240 PAGES OVER 500 ILLUSTRATIONS Flexible, Leatherette Looseleaf Covers Size 9 x 12 Inches Net Weight 1% lbs. Price $2.50 i OFFICIAL REFRIGERATION . OFFICIAL SERVICE MANUAL 1934 OFFICIAL RADIO REFRIGERATION . Volume 2 SERVICE MANUAL SINVICI MANUAL This is the only complete refrigeration serv- Icy This manual contains values of I.F. trans- ice manual ever published. Contains detailed of theory Official formers on superheterodyne receivers, valua- VOLUMI2 information on servicing, outlines complete list of American and methods of operation, instructions for Radio Service ble tube data, the handling of refrigerants, charging sys- Manual broadcast stations, free question and answer tems, diagnosing troubles, charts. electrical and schematic dia- -ups and a wealth of other necessary C.a./eta Ihreet.v service, service material hook grams. OVER 400 PAGES OVER 2,000 data. OVER 352 PAGES OVER 300 DIAGRAMS Flexible, Leatherette. Loose- 1933 Ive Radio a.. ..:L. ._ ILLUSTRATIONS Flexible. Leatherette, leaf Covers Size 9 x 12 Inches Net ... sun Rad,. a...... cud. Looseleaf Covers Size 9 x 12 Inches Net Weight 1% lbs. Weight 214 lbs. Price $5.00 Price $3.50

OFFICIAL AIR CONDITIONING MANUAL 1932 OFFICIAL RADIO SERVICE SERVICE MANUAL This manual is edited by L. K. Wright, who is an expert and leading authority Here is the volume which shows a step -by- on air conditioning and refrigeration. step analysis of how to service any receiver. Nearly every page is illustrated, every It is covers modern installation and individual { OFFICIAL one of the early editions and diagrams fur- many which still part carefully explained, AIR old sets, thousands of are nished of all known equipment, special CONDITIONING in use throughout the country. OVER care given to the servicing and in- 1 SERVICE MANUAL 1.000 PAGES OVER 2,000 ILLUSTRA- stallation end. Necessary tools are il- TIONS Flexible, Leatherette, Looseleaf lustrated and explained. etc. OVER Covers Size 9 x 12 Inches 352 PAGES OVER 600 ILLUS- Net Weight Leatherette, 41/ lbs. TRATIONS Flexible. Looseleaf Covers Size 9 x 12 Inches Price $5.00 Net Weight 21¡ lbs. Price $5.00 rRADCRAFT PUBLICATIONS, Inc.. 20 VESEY ST., NEW YORK. N. Y71 I,: ntlemen Enclosed find my remittance of 9 for which send me. POSTPAID. the Manuals Indicated below by a crone (xi In the panel. '() Volume 7 @ 910.00 ( ) 1936 Manual ® $7.00 ( ) 1934 Manual a $3.50 ( ) 1935 Auto - Manual @ 92.50 ( ) 1932 Manual @ $5.00 ' To order these famous Manuals, see or write to ( ) Refrigeration Manual (Vol. 2) @ 65.00 ( ) Air Conditioning Manua (R $5.00 1 your jobber or favorite mail order house. If more convenient. mail coupon directly to publishers. Name Address Clly fate ¡ PUBLICATIONS, Inc. (Send remltlanee In form of Cheek or money order; register your letter RADCRAFT if you send cash or unused S. RC-641 U. Postage Stamps.) IJ 20 VESEY STREET NEW YORK, N. Y. 765 RADIO -CRAFT for JUNE. I 9 4 I F.C.C.

CABLE. -Some cable, as well as radio, F.C.C. ACHIEVEMENT DURING 1940 circuits were disrupted as a result of the war, and the Commission speeded authoriza- IN AN annual report which incorporates total of 705 standard broadcast stations tions for new or temporary replacements. important developments since the close of (including networks) reported total time the fiscal year, the Federal Communications sales approaching $130,000,000, making a ACCOUNTING.-More than 23,000 tariff Commission chronicles new milestones in net income of nearly $24,000,000. They also schedules were filed by common carriers. the advancement of broadcasting, and cites listed a payroll of nearly $52,000,000 for The Commission adopted a revised uniform augmented duties in supervising radio, tele- nearly 25,000 employees. The report of the system of accounts for telegraph and cable phone, telegraph, and cable in connection Commission's special committee on chain carriers, to become operative in 1942. The with the national defense program. broadcasting was the subject of oral argu- new system, which conforms to Govern- This streamlined report is almost half the ment in December in connection with its ment accounting principles, will supplant size of the one last year. To summarize consideration by the full Commission. Com- one in use since 1914. some of its highlights: mission inquiry revealed some 200 domestic stations broadcasting in about 80 foreign RECOMMENDATIONS TO CONGRESS. NATIONAL DEFENSE. -The Commis- languages. Commission action in 5 broad- -None, other than those contained in the sion's cast cases was upheld by the United States Great Lakes and telegraph merger reports. particular role in the preparedness Supreme program is to "police" radio communications. Court. In consequence, it has added to its monitor- BROADCAST ing and other field facilities. Also, it must (International). - Broad- keep tab on the many persons cast service to Latin America was improved who operate by reason of the Commission electrical apparatus capable of farfiung and requiring pow- Radio Frequencies and Their almost instantaneous communication. er of at least 50 kilowatts for international Allocation program service. In this country 13 inter- So the F.C.C. is requiring all radio opera- national broadcast stations were operative. THE radio spectrum, or radio waves, is tors (about 100,000 licensees -including but one portion of the total electro- commercial and amateur) to prove their TELEVISION. -Television is now making magnetic spectrum. The electromagnetic citizenship. Common carriers are compiling substantial progress with the cooperative as- spectrum covers 8 different classes of similar data with respect to employees who sistance of that industry and the Commis- radiation -(1) electric waves, (2) radio engage in international communication. The sion. More than a score of stations geo- waves, (8) infra -red, (4) visible light, (5) Commission has banned amateur communi- graphically distributed throughout the na- ultra -violet, (6) X -rays, (7) gamma rays, cation with foreign countries, and, further, tion have been licensed to experiment with and (8) secondary cosmic rays. prohibits the use of portable long -distance various types of transmission with a view The emission of this energy may be transmitters by amateurs. Such steps are to reaching early accord on uniform stand- likened to the expanding ripples of water precautionary rather than disciplinary. The ards which will enable television to move Commission suddenly disturbed by a thrown stone. How- does not want to interfere with forward on a full commercial basis. Partici- ever, electromagnetic energy travels in all radio and wire communications any more pating stations have budgeted a total of directions. than is necessary for the national protec- $8,000,000 for this practical experimental tion. Individuals and industries concerned work. Since electromagnetic radiations have a common speed (that of light), their only are collaborating in this common contribu- In conjunction with such effort, a National tion toward the national security. Television difference is in frequency and wavelength. Systems Committee, jointly spon- may be The sored by Radio "Frequency" characterized as the relationship of radio, wire, and cable the Manufacturers Associa- number of these waves per second, and facilities to the Preparedness picture is be- tion and the Commission, has made a thorough "wavelength" as the distance between suc- ing further coordinated in planning by the study of the engineering phases of cessive waves. Defense Communications Board, created by the situation which should be helpful in ar- Executive order in September. riving at a general agreement. The con- The divisions between the various classes tinued rapid evolution of television is at- of electromagnetic radiations are not def- BROADCASTING (F.M.).-Last year, tested by developments in color reproduc- inite. The lines of separation are based largely upon the effects and the particular which marked the 20th Anniversary of tion, large -screen projection, and new serv- Broadcasting, ice demonstrations. method of producing the various emissions. was notable because of Com- Under certain conditions, some of these mission recognition of a new type of public MISCELLANEOUS RADIO SERVICES. electromagnetic impulses may be seen, felt, service in frequency modulation, popularly or heard. Of the eight classes of electro- known as "F.M." The ensuing year will of- -Increased use of radio for miscellaneous services is noted. Police stations have in- magnetic radiations, that portion classed fer practical demonstration of F.M.'s as "radio waves" covers a relatively small claimed clarity and staticless qualities. Also, creased to 6,300, aviation stations to nearly 2,000 and more than 1,000 stations are em- part of the total electromagnetic spectrum. by utilizing the high frequencies, F.M. prom- Radio facilities are extremely limited. In ises to relieve the long congested standard ployed for forest conservation work. The Commission clarified its rules with order to provide the maximum possible serv- broadcast band. ice for the benefit of the public, it is neces- Business will benefit by the new equip- respect to more than 450 special emergency stations. This class sary to control and restrict the use of the ment, sete, and servicing which F.111. re- of station has demon- its ability available channels. As transmission by radio quires. And, by being generally limited to strated to establish radio com- waves munication in time of emergency. The Com- spans great distances, it has been local coverage, this new service should have found necessary to have international agree- a stimulating effect on local programming. mission completed its final report on a special study of radio requirements for ment on the proportion of available -.chan - Distinctive call letters have been assigned. safety nels to be allocated for particular services. To date the Commission has authorized purposes on the Great Lakes and Inland Wa- 25 ters, and gathered information with To prevent interference and confusion with- F.M. stations to engage in full commercial respect in our own country, it is necessary to fur- operation. to possible like need on the Mississippi River system. There are 56,300 amateur ther apportion the frequencies in the best stations in 40,000 interests of users. BROADCASTING (Standard).-This old- operation. Some commercial operator licenses were handled dur- Besides the standard broadcast channels, er type of broadcast (which uses amplitude ing the year. Inspection was made of radio our radio spectrum is shared by other pri- modulation) should experience a marked im- installation on more than 14,000 ships and mary services, such as: fixed, marine, avia- provement in service by reason of the North at some 8,600 land stations. tion, emergency, amateur, miscellaneous, American Regional Broadcasting Agreement, experimental, Government, and broadcast effective March 29th next. Mutual interfer- TELEGRAPH. -As a remedy for many services other than standard broadcast. ence problems are expected to be eliminated ills in the highly competitive telegraph in- These general service allocations cover or minimized as a result of this compact dustry, the Commission recommended various classes of station, including: relay, between Canada, Cuba, Mexico, and the merger of the domestic telegraph companies, international broadcast, high frequency United States. and, further, urged consolidation of inter- broadcast, non -commercial education, fac- To make agreement possible, the Commis. national communication carriers domiciled simile, television, point -to -point telephone sion is effecting an orderly shift of fre- in the United States in the interests of de- and telegraph, agriculture, press, coastal, quencies without disturbing the general fense and other national needs. telegraph and telephone, ship, aircraft, broadcast structure. A total of 846 standard aeronautical, blind landing systems, air- broadcast stations were operating or under TELEPHONE. - Savings to telephone port, municipal and State police, marine construction during the fiscal year. There users aggregating $10,000,000 annually are fire, forestry, geological, mobile press, mo- were 79 new aifthorizations and 10 deletions. indicated by tariff revisions filed with the tion picture, amateur phone, telegraph and Increased use of directional antennas is Commission since its previous annual re- television, as well as experimental classes necessary in coping with the interference port. New construction amounting to more of stations. problem. During the calendar year 1939 a than $9,000,000 was authorized. The present useful radio spectrum, in 766 RADIO -CRAFT for JUNE, I941 F.C.C. which channels are now allocated, ranges from 10 to 300,000 kilocycles, or in terms of wavelengths, from 30,000 meters to 1 meter. That portion below 100 kilocycles is popularly referred to as "long waves "; from lOBEBOoKs 100 kilocycles to 550 kilocycles as "medium ST 0¢ long waves "; from 550 to 1,600 kilocycles RADIO FANS EVERYWHERE-these amazed at the wealth of information as "broadcast "; 1,600 to 6,000 kilocycles as fine ten cent text books give you an contained in these handy books. Ex- "medium short wave "; 6,000 to 30,000 kilo- excellent foundation for the study of cellent for reference-ideal for every cycles as "short waves "; and above 30,000 RADIO. They are clearly written, pro- technical library. YOUR MONEY kilocycles as "very short" or "ultra -short fusely illustrated and contain over BACK if you are not satisfied. waves." 15,000 words in each book. You'll be PROMPT SHIPMENTS The band below 100 kilocycles is occu- pied by Government and commercial longwave fixed service stations. From 100 kilocycles to the beginning of No. I No. 2 the broadcast band at 550 kilocycles, we HOW TO BUILD FOUR HOW TO MAKE THE MOST DOERLE SHORT WAVE SETS POPULAR ALL -WAVE I- end have the medium longwave stations, as fol- 2 -TUBE RECEIVERS Thousands of radtn fans have lows: the DOERLE Short Wave Receiver.. So excellent the demand excellent sets. some of which 100 to 200 kilocycles- Government and ese'ar chives, as p red In Issues of fion details. that this RADIOCRAFT. hese sets have private ship, coastal, and fixed service sta- book has been specially pub- been carefully engineered. They lished. are not only tions. Contains EVERYTHING has described °in othat hook. but it contains all of the 200 to 400 kilocycles -primarily Govern- famous receiver.. t illustrations. hookups, etc. ment aids to navigation, such as radio navigation for aircraft, and radio beacon service to ships, interspersed with airport No. 3 No. 4 on 278 kilocycles, direction finding on 375 ALTERNATING CURRENT ALL ABOUT AERIALS FOR BEGINNERS This ivario the kilocycles, and miscellaneous fixed stations. typeses This book gives the beginner aerials; lit Inverted "L the 400 to 550 kilocycles- Government and foothold In electricity and Rselio. Doubletouble Double Doublet. Electric circuits are explained. etc. It explain. noise -free reca, commercial ship and coast stations in the Ohm's Law, one of the funda. . how low impedance trans. mentale tal laws of radio. Is e mission unes wok: hy trans. maritime service centered near the inter- the generation i- leadins are used. It gives sunit current: of Iposedn detail the construction f national calling and distress frequency of the mapneeres. and suitable for longwave watts are explained. Condensers. brialsroadcast ives. for hon- 500 kilocycles (600 meters). recelvere and for ll'wve tiñrtns. C. in`trument.. uave The rest of the spectrum from the end of nóä the "broadcast" band at 1,600 kilocycles, involving the so- called "medium short ",

"short", and "ultra- short" wave bands, No. 5 NO. 6 could be pictured as a many- layered sand- BEGINNERS' RADIO 1 HOW TO HAVE FUN WITH wich, with police, amateur, aviation, Gov- DICTIONARY RADIO Are you puzzled by radio I. ernment, ship, coastal, broadcast, mobile guexe? you I Jokes, ntsniand Can define écientiffics ex Brim press, special services, experimental, tele- e with `your radio set are expained vol. ode? Pole ?KocIonization? n?°Teral! e in thl fascinating vision, fixed, forestry, and all other classes Law? Harmoic? Gravity urne. It tells how to make If you cannot define newspaper produce of stations providing varying depths of common words and dozens muic fr dances-how other. romore technical, terms visiblesilent filling. used In all radio magazine, and make a radio" s`unit. instruction books, need dce you this make` toys icdadanncee to°adio Of course, this does not mean that all book in Your library. muss. etc., etc. these bands are completely filled. Radio communication is still undergoing change, and the Federal Communications Commission, in No. 7 No. S licensing individuals and firms to use the HOW TO READ RADIO RADIO FOR BEGINNERS public's radioways, is charged with prepar- DIAGRAMS Hugo Cernsbaek. the intemetim,. All of the symbols commonly ally famous dio pioneer, author ', RAD/0 fat future, as well as for the pres- used in radio dia . are pre- are editor. hose famous go- l ing for the sented In this book. together RADIO AND TELEVISION BEGINNERS ent. Hence, some channels are held open for pictures of the apparatus and sRADIO.CRAFT are read by twithhey present and lanations millions. re another triiumph future developments, while others already an easy method to men, with this new Any be This book by Robert ginner who reads will get allocated, are subject to shift with changing OEirizenxthem.chberg. the w .-known radio thorough ground workit In din writer me ber of the di- theory, clearly explainedrs in events. frial staffn of RADIO-CRAFT simple language, and through Magazine. contains the a of many illustrations. dozen picturewinng, diagrams of Analogies are used to make the radio seta that you can mysteries of radio clew. bsimpleuild.

WORD TO THE WISE . . . A No. 0 No. ID The Commission has warned radio opera- SIMPLE ELECTRICAL TELEVISION tors that transmission of superfluous com- EXPERIMENTS Every one is asking the question How ds television w This munication is not only illegal but is distinct- Over sungsdprxrMGM book explains all of the different 10Ré:eriexppeerrhñnt vstema f television from the ly frowned upon at the present time. Hence, described in lhlsbook, coveringte simplest to the most complex. every branch of electricity-from It describes in A -13.0 style Just in enforcing this law the Commission has simple experiments with Mag- the scanned. how nets IgÑereaueet: the e is picked asked a tugboat company to explain a super- leeelo tel camera and broadcast scribed can be carriedrtrimenáe- out with to your etc. fluous ether conversation concerning family which toievenionO °Vpetlare de. difficulties, and a baseball game, which was elp`ppnËefouÉp p`ttsutef t h hoi scribed. picked up by one of the Commission's moni- toring stations. Numerous persons requesting the 1300 - BOOKS ARE ALL UNIFORM page report on chain broadcasting made Every book in the OERNSBACK EDUCATIONAL LIBRARY has 32 pages -with illustrations varying from by a committee of the Commission are in- 50 to 66 in number. Each title volume contains over 15,000 words. Positively radio'. greatest book buys) If you 24 hours and money will be Instantly refunded. formed that only a limited number of copies do not think these book. worth the price asked, return them in your were mineographed, and the supply has long since been exhausted. The official record, however, is open to public inspection at the RADIO PUBLICATIONS 20 UESEY STREET NEW YORK, N. Y. Commission's Washington offices. r The Commission has sent a note of ap- RADIO PUBLICATIONS. Dept. RT -6 -41 Ohio Co. in- 20 VESEY STREET. NEW YORK. N. Y. preciation to the Powe7 for its Gentlemen: Please send Immediately. POSTPAID. (Si tool numbers circled below. 1 am naming cents terest and cooperation in eliminating inter- -each book being 10. 2 3 4 E 0 T 8 10 ference to radio reception in a community NEW NEW in that State. Bend PBEB WUag of 4$ new 10e publleatllms. A committee for the care of refugee chil- Name Addrees dren seeks Commission permission to solicit fYty State funds by radio. Such permission is not re- Remit by cheek or money order -register letter If you send ash or unlined U. B Datage Itsmo,. quired under provisions of the Communica- !. MAIL COUPON TODAYI. d RADIO -CRAFT for JUNE, 1941 767 F.C.C.

tions Act of the Commission's rules. Deci- during "continuation of the present un- in the end increases his net income and sion rests with the individual station or the settled world conditions." ends in a better living. network. A New Yorker asks the Commission to B. F. ROBINSON, It is mostly in the matter of complaints make radio stations broadcast a song he has Spokane, Wash. with reference to broadcasting that the written. Commission has to advise lack of jurisdic- A Bismarck, N. Dak., man wants the Com- STOCK PHRASE- "RADIO- tion. The following current cases are typi- mission to require a network to carry a cal: particular religious broadcast. CRAFT FOR SERVICEMEN" A Toronto, Canada, woman objects to ra- An Asheville, N. C., man would require Dear Editor: dio commentators who "spread terror by newspapers owning radio stations to pub- I have been reading your publications for innuendo." lish the programs of competing broadcast 15 years. I have all copies of Radio News A San Francisco man dislikes the "hys- stations. beginning with 1926 to 1932, and from there terical broadcasting" of war news by a A Philadelphia man thinks he is entitled on Radio -Craft, and 'Shortwave Craft. I particular commentator. to a prize from one of the radio contest bind each year into one book. A Macon, Ga., man would prohibit net- programs. I am a Serviceman and would suggest you works from carrying news reports originat- keep one paper for Servicemen and receivers, as I for one, after 15 years of ing in Germany. AGAIN- RADIO -CRAFT FOR A Philadelphia man suggests censorship servicing, am not interested in Ham gear of news and comment by radio and press SERVICEMEN and transmitters. Let's have that and all Dear Editor: shortwave in *Shortwave & Television. I In the past I have been a regular sub - like your papers better than any others and criber to Radio -Craft and received much would not want to get along without them information and help as a Serviceman. By and I feel you have given me quite an educa- all means do not change your fine new tion in Radio and long may you prosper. For Advertisers Index method of publishing Radio -Craft. On sec- Thanks- I remain your sincere reader, ond thought the Serviceman must make his A. J. Nieaua, See Page 764 living by radio service work and here is Norfolk, Nebr. where you fit in the picture by helping him speed up with more accurate work which *Now RAOto & TELEVISION magazine.

USE OF RADIO IN SPECIAL EMERGENCIES Safety of Life and Property Being Promoted that city practically uninhabitable. The net- station licenses cooperate among themselves in Extended Use of Special Emergency work of interconnecting electric power lines in the choice and use of frequencies so as Service by Public Utilities. These uses hare has greatly reduced the hazards which would to avoid duplication and interference. For been illustrated and described in past issues be created by failure of a single plant. this and other reasons it has of Radio become corn- -Craft but are again mentioned here However, constant vigilance is required to mon practice for various public utilities in in a coordinated article. maintain the transmission lines, which con- a single area to pool their needs, one utility THERE is one class of radio station stitute this network, for the most efficient requesting the license and rendering the license issued by the Federal Communi- service. As these transmission lines nor- service while the other utilities receive this cations Commission which, though little mally carry very high voltages, and since service and contribute to the cost of opera- known, is playing an increasingly impor- they cannot be disconnected for any ex- tion on a pro -rated basis. tant role in the economic life of the nation. tended period, close coordination is needed Recent Commission authorizations illus- This particular type of license covers between the working parties and the switch- trate this arrangement. Special Emergency Stations. These stations ing central at the power house. In the New York metropolitan area there have already demonstrated their value in are a number of public utilities, including time of localized stress, and now loom as a UTILITIES EXTEND RADIO USE the New York Telephone Company, which valuable adjunct to the linking of communi- Special emergency stations make this pos- are eligible for, and have need of, special cations for widespread protection of life sible. Some utility engineers say the time is emergency radio communication. In order and property. rapidly approaching when no power dis- to reduce the capital investment and to Special emergency stations have rendered tribution system or gas, oil, or water dis- receive the maximum benefits from this type valuable service in regional disasters, such tribution system operating over a large area of communication, the New York Telephone as the New England hurricane and in time will be considered fully equipped unless it Company has taken the lead and is con- of flood when the normal means of com- has a radio communication system to aug- structing a sufficient number of special munication are destroyed or are rendered ment the wire, telegraph, telephone, and emergency stations to serve all utilities in inoperative. It would be difficult to obtain carrier- current (wired -radio) communica- that metropolitan area. (Italics ours. information as to casualties and extent of tion systems. Editor) - damage, and even more difficult to restore There is a particular, day -to -day emer- This radio service will be made available communication, were it not for the tem- gency demand for radio communication, by for the handling of only such communica- porary facilities which can be rapidly estab- public utilities within the metropolitan dis- tions as meet the definition of emergency in lished to meet such emergencies. The use tricts. To illustrate: the Commission's rules and regulations. In of special emergency stations in this con- Should an automobile run into a light order that the cost of operation may be re- nection is probably the most spectacular pole and knock it down, electrical voltages covered, and to prevent this new system use to which these stations are now put. of dangerous potentials are exposed and from becoming a burden on the general tele- The Long Lines Division of the American endanger passers -by. Also, there have been phone subscriber, the telephone company is Telephone and Telegraph Company, as well occasions in which a street car has run to make charges to the various utilities con- as many local telephone companies, have over n pedestrian and in order to remove cerned, in much the same manner as to the been issued licenses for special emergency the victim it has been necessary to jack up telephone and teletype subscribers. In other stations. Special equipment has been de- the street car from the rail. Without radio words, a definite charge per call will be signed for the purpose. This equipment can communication, it is necessary for a service made and the company will be given a guar- be stored in a chest. In time of emergency, truck to be dispatched from some far.quar- antee in the form of minimum service it can be loaded in a truck, driven to the ter to the scene even though a truck with charge. scene, and quickly and easily set up for proper equipment might be working only a On January 1 of this year, 76 special operation. When so used, the design of block or two away. emergency systems involving 368 individual these stations permits either communication Other emergency services of this nature transmitters had been authorized by the between construction crews at the scene of include repairs of wires downed because of Commission. the emergency or the interconnection of sleet, and restoration of power to hospitals, The rules and regulations governing spe- regular land lines in such manner that regu- etc. To meet these situations, the Commis- cial emergency station' appear as Part 10 lar subscriber communication can be re- sion allocates appropriate frequencies and of the Rules and Regulations of the Federal established. issues authorizations to public utilities in- Communications Commission, which are Aside from service in time of disaster, terested solely in metropolitan area service. available in pamphlet its from the Super - these stations are in growing daily use by fnjendent of Documents;¿9pvernment Print- public utilities. For example: POOLED CHANNELS ink Otllcç, Washington, D. C., at a cost of The economic life of our country has be- Inasmuch as the number of frequencies be ak cosy. Information and application come so dependent upon electricity that a available for such assignment is extremely forms mdq be 'obtained either from the sudden and complete disruption of electric limited, it is required that those publie_ Washington :headgyarters' Of the Commis - service to any large metropolis would make service units eligible to receive emergency ,,sign or from any - (e field offices. 768 ranted m O.S.A. R:A kplp-CRAFT file .JUNE, 1941 TRAIN NOW FOR TECHNICAL RADIO WORK

~~I GIVE YOU FULL RADIO EQUIPMENT TO DO OVER 100 ACTUAL EXPERIMENTS~~

~~You )1 re Pre--conditioned with REPAIR EXPERIENCE In Your Own Home!~~

TRAINING PREPARES YOU FOR A BUSINESS OF YOUR OWN OR GOOD RADIO JOBS AT EXCELLENT PAY Specially designed to help you make fast progress, SPRAYBERRY Training starts right at the beginning of Radio ... unfolds each subject in a simplified, logical, understandable style. You easily learn in your spare hours ... AT HOME or AT CAMP. Course covers Television, Frequency Modulation, Signal Tracing, Mobile Radio (Auto- Tank), Aviation Radio, Electronics, Facsimile Radio, Radio Set Repair and Installation Work and other essential subjects

CASH IN ON RADIO'S RICH OPPORTUNITIES There is good money to be made. My Training will give you quick access to excellent opportunities. Sprayberry Methods are thorough and practical. Your Training will not interfere with your present work. You get PROFESSIONAL TEST EQUIPMENT plus EXPERIMENTAL OUTFITS. Includes 146 RADIO PARTS for building a complete Re- ceiver, RADIO TOOLS and a modern TESTER -ANALYZER. You also receive 8 BIG SHIP- MENTS OF RADIO EQUIPMENT. I show you how to create Radio defects ... how to correct them. ALL EQUIPMENT BECOMES YOUR PERSONAL PROPERTY!

~~LEARN MORE ABOUT SPRAYBERRY TRAINING~~

~~AND HOW EASY IT IS TO START~~

Regardless of previous education or experience. I can fit you for a good -paying Radio job. My BUSINESS BUILDERS will show you how to put your Equipment to actual use in handling money- making Radio Service Jobs shortly after you begin Training. You can EARN WHILE YOU LEARN. Get complete details AT ONCE in my new, valuable 52 -page FREE BOOK. Mail coupon below.

~~REMEMBER UNDER RMONERY- BACKUAGREEMENT~~

~~ACAUEHY OP RADIO a SPRAI'RERRti Pres. O.. RADI L. SVrwrrryplace. N. MciNF. y IN F. t¡niversitrC E 420-F HAKE D. IiIW TO ... Washington. ,.at:E .. p ...... ine Ati' .. Please vend~~

~~.. stoat' twwirsrd Address ' ur 1`n` Ma, in envelope Ct Tesr rnuM'n oft th is Boost your Summer Profits the p/0Way! -47V~~

P-5 Radiola Model portable -Way Batteries Plays on AC, DC, Tuned Loop Superhet with Antenna AVC Action Full Case Washable Durable, Speaker M. Dynamic Alnico P. THESE RADIOLA MODELS, TOO, are selling like hotcakes! Lend it and you'll sell it while their set is in your shop! SUMMER'S THE SEASON for sales by they can carry upstairs, downstairs, servicemen! For in summer, service all around the house ... and right customers want an extra radio more out the front door, when they wish! than ever- particularly if that extra Servicemen the country over are Radiola Model 515 Superb radio will play anywhere... with foreign reception in an "extra ' the boosting their incomes the RADIOLA radio! Plus a continental -style cabi- superb performance of this RADIOLA way with the only line of radio net...large. easy -reading dial...and ... RF Stage for Model P -5 stepped -up sensitivity! three -way portable. receivers specifically designed for Six RCA Preferred Type Tubes. Six Salesmanship? The salesmanship servicemea tc sell. Try it yourself. tuned circuits. Tus, built -in antennas for long and short waves. No is in the set! Just"lend" them the P -5 Sec the great new RADIOLA line at your wonder it's a super seller. while you work on their regular re- distributor's. Combine bus- ( ceiver. Let them discover the con- loess with more business: sell venience of "another" radio: a radio sets when you sell service! All RADIOLA Models Are Equipped Exclusively with RCA Preferred Type Tubes

Radiola Model 511 A RADIOLA mo i you can sell nearly everywhe -a set that's packed with valuel Beautit ul antique - C ivory plastic chit. -t. Five. RCA Pre - F7= ^rred Type T -ht : to a sensitive su- Made by RCA Manufacturing Co., Inc., Camden, N. J., U$. A. er`.eteod. .,. v,ith ful: AVC ion. 5" elect,. dynamic speaker. A Service of the Radio Corporation of America .arec, built-in sword loop antenna. In Canada, RCA Victor Company, Ltd., Montreal'