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OVER 125 ILLUSTRATIONS

011C11 G3/1@,00°ß GpWßY 'lßGJ311GJ1g` F.M. ADVANCES V.-T. OSCILLATORS FIXING FLUORESCENT LIGHTS

1841 V.--T.- VOLTMETERS NEW UTILITY TESTER HOME RECORDING HINTS SONOVOX and, so far, we've hardly even mentioned its

GREATER METER PROTECTION !

Not only is the RCA Junior Volt - Ohmyst one of the handiest, most versatile and amazingly efficient instruments OHMS ADJ. on the market today ... Not only does it pave the way for faster, more accurate resistance and both a -c and d -c voltage .otn aase Is this your Aa readings ... Equally important, special a.e:r mna Voltmeter? a:wrs.w.e,.. D -C protective features remove much of the danger of a costly meter burnout should you grab hold of ira.Ya ' more voltage than you had expected or accidentally check a "hot" resistor. Extremely rugged meter construction also guards against mechanical damage. This means that, besides giving you more for your money in the first place, this sensa- tional little instrument protects your investment. What's more, the Junior VoltOhmyst will quickly pay for itself in the time it saves on a wide variety of jobs.

A LONG -TIME INVESTMENT IN BETTER, FASTER WORK

The RCA Junior VoltOhmyst is a "junior" It has six full scale voltage ranges from 3 to 1000 volts from 0.1 to 1,000,000,000 in price alone. In actual use it is an instru- and measures resistances RCA ohms ! It eliminates time -taking shorting of leads and Junior ment that does a man's -size job plus. Costing zero resettings when changing ohmmeter scales. One only a little more than you'd pay for an widespread ohms scale assures extreme accuracy and easy readability. In brief, the RCA Junior VoltOhmyst ordinary volt -ohmmeter, it gives you Elec- provides you with a quick, accurate and easy - to . use VOLTOHMYST tronic Push -Pull operation with all the time - means of checking every conceivable A.V.C., A.F.C., and trouble- saving features of the famous FM discriminator circuit, or Oscillator Grid Voltage, with the signal present. checking bias cells or insulation Rider VoltOhmyst circuits and with the resistance, obtaining practically any needed resistance addition of an isolated A -C Rectifier -type Volt- and d -c voltage reading... as well as handling any a -c 3495 meter with 1000 ohms per volt sensitivity. voltage checking job that might pop up in your work -at an absolute minimum price. Net Price Complote. Stock Ne.165 It measures d -c voltages with constant meter impedance of 11,000,000 ohms on all ranges. This means a See it at your nearest RCA distributors -or write for sensitivity up to 3,666,666 ohms permit.' Yet it is extremely bulletin. It is an instrument that no wide -awake tech- stable ! It will not disrupt operation of sensitive circuits. nician can afford to miss ! Sooner or later,why not now?

SOMETHING TO REMEMBER WHEN YOU BUY TEST EQUIPMENT Although moderately priced, RCA Test Equipment is not D ,p built down &MIC -DÉMONSTRATOR a' "to a price." Instead, it is built up to a standard of efficiency -the highest o,0.6 in the field today. It is designed in the firm belief that the "cheapest" equipment any service technician can buy is the equipment which is quickest to pay for itself in the time it saves him, plus the extra jobs it permits him to handle. Moreover, RCA Test Equipment is built around the famous and Sea the temes pioneer Rider "Signal Tracing" system which replaces old -style, hit -or- Dynamic Dame Learn hew RC mics service methods with a quick, systematic course of procedure. "Signal Equipment solves Tracing" has proved its tremendous value, not only to leading technicians, problems tastar but to leading laboratories and manufacturing plants as well. It is your safest, surest road to faster, more accurate work with consequent greater profits -and the RCA -Rider Chanalyst, that originally made this system possible, is your "Open Sesame!" to its many benefits. Not what you pay for your Test Equipment -but what your Test Equipment pays you. That's what really counts. And RCA's policy of "Minimized Obsolescence" protects your investment!

YOUR KEY TO SYSTEMATIC

SERVICING FOR GREATER PROFITS ,

RCA MANUFACTURING7irOatoo CO., INC., CAMDEN, N. J. A Service of The Radio Corporation of America. In Canada: RCA Victor Company Limited, Montreal e a RADIO Technician

Many a week make $3O S40 $ 50

I will train you at home For many Good Spare Time and Full Time Radio Jobs

1. E. SMITH, President, National Radio Institute Radio is a young, growing field with a You Get This Professional Servicing Instrument Established 25 years future. It offers many good pay spare time This instrument makes He has directed the training of more men for the Radio and full time job opportunities. And you Industry than anyone else. practically any test don't have to give up your present job, go you will be called upon away from home, or spend a lot of money Set Servicing pays to make in Radio serv- to become a Radio Technician. I train you ice work on both spare many Radio Tech- at home nights in your spare time. time and full time nicians $30, $40, $50 jobs. It can be used a week. Others hold Jobs Like These Go to Men Who Know Radio on the test bench, or along when out their regular jobs Radio broadcasting stations employ Radio Tech- carried and on calls. It measures and make $5 to $10 nicians as operators, maintenance men voltages extra a week in spare pay well for trained men. Radio manufacturers A.C. and D.C. employ testers. inspectors, servicemen in good and currents; tests resistances; has a multi- time. pay jobs with opportunities for advancement. band oscillator for aligning any set, old or new. Radio jobbe?s and dealers employ installation You get this instrument to keep as part of your and servicemen. Many Radio Technicians open N. R. I. Course. their own Radio sales and repair businesses Broadcasting Stations em- and make $30, $40, $60 a week. Others hold ploy operators, in- their regular jobs and make $5 to $10 a week DRAFT REGISTRANTS fixing Radios in spare time. Automobile, police, If you ARE called and are then a Radio Tech- stallation, mainte- aviation, commercial Radio, loudspeaker sys- nidan. you'll be eligible for a communications for technical rating. nance men and Radio tems, electronic devices, are newer fields offer- wbr ofr the service: in line Rh extra PSY. Technicians in other ing good opportunities to qualified men. And you now have an oppor- which promises If you ARE NOT called. capacities and pay my Course includes Television, tunity to get into Radio at a time when the to open many good jobs soon. Government is pouring millions of dollars Into well. the Radio Industry to buy Defense equipment. on top of boom civilian Radio business. Why Many Radio Technicians Make Either way -it's smart to train for RADIO NOW! a Week s 31,,p, i Loudspeaker System $30, $40, $50 Find Out How N. R. I. Teaches You Radio - is one of the country's large in- Radio already building, installing, Television- Mail Coupon and operat- dustries even though it is still young and grow- and servicing ing. The arrival of Television. the use of Radio Act today. Mail coupon now for Sample Lesson ing is another grow- principles in industry, are but a few of many and 64 -page Book. They're FREE. They point ing field for well recent Radio developments. More than 28,000,- out Radio's spare time and full time opportuni- 000 homes have one or more Radios. There are coming in Television: tell about trained Radio Tech- telephones. Every year mil- ties and those more Radios than my Course in Radio and Television : show more nicians. lions of Radios go out of date and are replaced. than 100 letters from men I trained. telling 'ì Millions more need new tubes, repairs, etc. what they are doing and earning. Read my Over 6,000,000 auto Radios are in use and thou- money back agreement. Find out what Radio sands more are being sold every day. In every offers you. Mail coupon in envelope or paste on branch Radio is offering more opportunities for penny postcard -NOW. which I give you the required knowledge of $10 to $20 a Weak In Spare Time Radio at home in your spare time. Yes, the few .1. E. SMITH, President, hundred $30. $40, $60 a week jobs of 20 years Dept. 1CX, National Radio Institute I repaired some Radio sets when I was on my D. C. tenth 10e0o1. I realty don't see how you can ago have grown to thousands. Washington, give so much for each a small amount of money. 1 made $800 in a year and a half, and Many Make $5 lo $10 a Week Extra I have made an average of $10 to $220 a week -Just spare time. in Spare Time While Learning riirg .JOHN JERRY. 1529 Arapahoe St.. Denver, Colo. BOOK The day you enroll, in addition to my regular FREE Course. I start sending you Extra Money Job Makes $SO to $60 a Week Sheets -start showing you how to do actual OF "I am making between 850 and $60 a week Radio repair jobs. Throughout your Course I NAS pREDS ,- after all expenses are paid, and I am getting send plans and directions which have helped all the Radio work I can take care of, thanks time while to N. B. I." H. W. SPANGLER. 12654 S. many make $6 to $10 a week in spare NMÉN MAKE Gay St., Knoxville, Tenn. learning. I send special Radio equipment: show you how to conduct experiments, build circuits. MOREMONEY tÁICNrRE,1,yR; too. My Course includes Television, D , Operates Public Address System [ ",tIN;FiJkDáp "I have a position with the Los Angeles Civil - Service, operating the Public Address System in the City Hall Council. My salary is 5170 a month." R. H. ROOD. R. 136, City ]tall, Los Angeles. Calif.

1 J. E. SMITH, President, Dept. 1CX National Radio Institute, Washington, D. C. 1 without obligating me, mail your Sample lesson and 64 -page Book FREE. will write plainly.) J'amp& ¿won 1 I am particularly Interested in the branch of Radio checked below. (No salesman call. Q Radio Service Business of My Own Loudspeaker Systems. Installations and Service VorkSloree Auto iRnadio Installations and Service want to send a sample lesson. "Broadcast, 1 I you p Spare Time Radio Repair QQ All -Wave Television Superheterodyne Receiver Station Operator All- around Servicing Technician 1 Q Broadcasting decide.) Principles." It covers the basic interferences in (If you have not decided which branch you prefer -ma l coupon now, for information to help you euperheta and how they are rectified. It brings out 1 the importance of the preselector, mixed first- Age detector, local oscillator, intermediate frequency I Name I.F. amplifier, tracking, peak and band pass adjustments, band switching and modification for Address adapting to Television reception. All subjects covered with special emphasis on servicing. You can I City State 23FR2 get this lesson FREE. Just mail the coupon. t>!a1asssrlega RADIO -CRAFT for MARCH, 1941 513 ..gn the ISSUE! NEXT Ile Interference HUGO GERNSBACK, Editor -in -Chief Rodiorm lElectromedtcol N. H. LESSEM THOS. D. PENTZ APParotus Radio Offers Associate Editor Art Director N Y A Amer- 'Training uth R. D. WASHBURNE, Managing Editor icó s Tester Modernize YourYO Ampli Tracing Signal- .F . Contents MARCH, 1941 Issue VOLUME XII -- NUMBER 9

Mailbag 515

Editorial: Utility Radios Hugo Gernsback 519 DEPARTMENTS, ETC. The Radio Month in Review 520 Mailbag 5 5 SERVICING The Radio Month in Review 5; o New Circuits in New Circuits in Modern Radio Receivers -No. 42 Modern Radio Receivers-No. 42 F. L. Sprayberry 5 2 F. L. Sprayberry 522 Operating Notes Operating Notes 523, 525 523, 525 RADIO SERVICE DATA SHEETS: Fluorescent Lighting- Latest Sideline for Servicemen -Part II No. 302 Union Radio Interference John T. Bailey 524 -National Model W2 526 No. 303 RADIO SERVICE DATA SHEETS: -Crosley "Glamour- Tone" Model 2688 (Chassis Model 26) No. 302 -National Union Model W2 526 528 Engineering No. 303- Crosley "Glamour- Tone" Model 26BB (Chassis Sound -No. 15 Conducted by A. C. Shaney 544 Model 26) 528 Latest Radio Apparatus 563 Classified Radio Directory -Section VI (Conclusion of Ist F.M. Edition) 569

Recent Improvements in F.M. Receiver Design Shop Notes- Kinks -Circuits 575 J. A. Worcester, Jr. 530 Book Reviews 525, 576 TEST INSTRUMENTS A General Utility Tester for Servicing Electrical Appliances Published by Radcraft Publications, Inc. Publication office: 29 Worthington Street, Springfield, Mass. Editorial and Advertising Offices: 20 Vesey Street, Shepherd Litt 535 New York City. Chicago Advertising Office: RADIO -CRAFT, 520 North Vacuum -Tube Voltmeters- Theory and Practice Willard Moody 537 Michigan Avenue, Chicago, Ill. RADIO -CRAFT is published monthly, on the first of the month preceding that Build Your Own Versatile Modern Multi -Tester Milton Reiner 540 of date; subscription price is $2.50 per year in U. S. (In foreign countries. 75c additional per year to cover postage; Canada, 50c additional.) Entered at the post office at Springfield as second -class matter under the act of SOUND March 3, 1879. Sound Engineering -No. 15 Conducted by A. C. Shaney 544 * Home Recording- Theory and Practice of Sound -on -Disc Foreign Agents: I. Queen 547 London-Gorringe's American News Agency, 9A Green St., Leicester Squar e, Modern Microphone Technique -Part II, The Microphone and W. C. 2, England. Its Relation to the Amplifier H S. Manney 552 Paris- Messageries Dawson, 4 Rue Faubourg, Poissonniere, France. Melbourne -McGill's Agency, 179 Elizabeth St., Australia. Independent Power Supplies Improve Audio Output Joel Julie 555 Dunedin-James Johnston, Ltd., New Zealand. ELECTRONICS * Vacuum -Tube Oscillators and How They Work ....J. A. Dowie 557 Text and illustrations of this magazine are copyright and must not be reproduced without permission of the copyright owners. RADIO DEVELOPMENTS * The "Acceletron" Generates Energy of 2,300,000 Volts! 561

514 MAILBAG

REGARDING HEARING -AIDS Dear Editor: INFORMATION %'u.i' BEEN LOOKING FOR! I have just finished reading Earl Russell's presumptive and faintly amusing letter in the February issue of Radio -Craft. I feel that this calls for a reply, as some of your readers may take this gem of stupidity seriously. Get Started Now! As the old saying goes "Where ignorance Full or Spare Time it LEARN SERVICING is bliss, 'tis folly to be wise." However, .. without leaving home is more than folly and just plainly ridicu- with This! lous, for the ignorant to assume the cloak This inexpensive. big 1300 - These Ghirardi Page book gives you the com- of wisdom, as Mr. Russell does when he plete famous Ohlrardi training presumes to give advice to others on the Books Will course in practical radio service work. The ally book In subject of hearing -aids. A case, one might Help You the world that teaches you say, of the deaf leading the deaf (astray). everything you need to know right in your own home - Mr. Russell "advises" the near -deaf that -at unbelievably easily. and in your sparo time. the hearing -aid amplifiers described by the low cost! Theory from A to Z Test Equipment First. writer and by Mr. A. C. Shaney do not LFRED A. GHIRARDI, the author of these thorough 420 -pane -course in books, is one of the foremost writers of Test Instruments- Theory, De. have nearly enough volume to be of real 'lotions. Diagrams f all service. Although Mr. Russell has been re- practical radio texts and is an outstanding au. Commercial Instruments. How thority on radio instruction. His wide experience they Work. Construction Data, etc. pairing radio sets for 20 years, it is evi- as a radio engineer, radio instructor, radio Trouble-Shooting-Next, ali dent that he has no conception of the magazine editor and technical consultant to newest apart -cut factory meth. 1300 PAGES firms and for all! difference between power amplification and many prominent radio manufacturing Testing makes of ° radio 708 ILLUS. servicing organizations has built for him an "`sett REVIEW voltage amplification. of radio knowledge (and aiñIe t`élearly and 720 unusually wide background stteo-by -step- QUESTIONS in these three books. Every one In designing an amplifier for hearing -aid that is reflected Repairing -Then how to Align and Adjust eive of them is acclaimed as being outstandingly how to Repair r Replace faulty part.. Advanced work, the object to be attained is voltage superior to anything in its field. They have "Factory" methods explained fully. earned for themselves an enviable reputation for Promotion -How to Manage. Promote and amplification. The minute voltages generated dvertiseABusiness a radio service shop for greatest profits. thoroughness, and the ability to make every by the crystal must be amplified enormously brings an illus- phase of the subject clear and easy to learn for MODERN RADIO SERVICING you high will be trated gold mine of servicing knowledge -all based on so that sensitivity obtained. even the merest beginner. That is why they are practical servicing experience! 720 Self- FoiaminaUon Such a device is then suitable for the use the favorites of radio beginners, servicemen and Review Questions check even' step of your stud, experts alike, and are used as the main texts in progress. Order yours now -costs you only $4 to learn of a hard -of- hearing person. the basic radio theory and servicing courses radio Berries tvork this EASY way! Money bask If Of course, there are some people who of leading radio schools in every English- speak- not satisfied after 5 -Day Trial. are practically stone -deaf. Many of these ing country in the world. They have had to be "tops" to earn such honors! RADIO HANDBOOK people like to refer to themselves as "near - r4;s6 5lor deaf." Presumably, Mr. Russell falls into SAVE SERVICING this category. Such people have no use what- TIME wityyh This! soever for a sensitive hearing -aid. They turn Time la LEARN FUNDAMENTALS of 'what ° radio on a 10 -watt amplifier full blast, put their setapt you called upon to ear against the loudspeaker and complain with This! Ode new Acre one inexpensive gu. nteed to in e you Time. Chock full that the outfit does not have nearly enough volume le a complete Radio of factory-checked "bench volume to be of any real service to them. Education for you-all tho that will Basic Fundamentals clearly every Job you do Money for Such people need great power amplifica- explained and Illustrated That mean More right from elementary you! tion. They require an amplifier capable of Electricity and Sound up 518 BIG B'//x11 PAGES- delivering large amounts of power to the through the entire field of 134 ILLUS.. DRAWINGS. Radio and Television - the CHARTS. TABLES - Give translating device. In such amplifiers, the equivalent of a N -Rook Vital Information on: A.C. plate of the last tube must Radio Course all condensed Time -Saving Trouble Case current Into 1 big volume. Histories for 3,313 receivers be large so sufficient power is deliv- compiled from actual se that YOU LEARN AT HOME! ice records-1 -F Peaks for 15.000 Superhets- Trouble- ered to actuate the speaker or earphone Ohlrardl will train you with plenty of volume. quickly -right in your own Geavt1Ratios -AutA RadiRadio . Cann chair at home. Hie ex- Lallation. Servicing. Inter- ference Of course most nearly stone -deaf people planations are crystal- clear, Servicing and OnReecorder Interesting. easy to under- 518 PAGES (near -deaf) know very well that a power stand. And because ft's so 972 PAGES Condenser 6, Resister tCharta 134 ILLUS. amplifier must be large. That's why Mr. easy to learn Radio from it. 508 ILLUS. -Grid Bias Resistors-Color S. and Navy codes-Wire Coils- MANUAL SIZE the U. Army REVIEW Transformerss ,Tables m Russell says "Hearing is the objective, not and radio school. everywhere 856 size. Tooamuch emphasis has been put on use this very same book in Q UESTIONS tChaiail Lamps- Ballast Resistors -Filters. their radio training course. No math -no previous train- Used by thousands of service shops. Order yours now. size. Why ?" ing is necessary. Here's a 850.00 course that you get Money back if not satisfied! complete for only $4. Orderyour copy NOW -money back He then answers his own question by if not satisfied. Books Shipped Postpaid Anywhere stating that the customer wants an ' -aid THEM DAYS ENIMMYa that can be concealed. In the case of the USE 5 IRADIO 6 TECHNICAL PURL CO Send for any or all or 45 Astor PI., New York.Dept.RC31 nearly stone -deaf person, the hearing -aid these books today. Keep of Enclosed find payment for, and the r 5 days In look over OUR rush to me postpaid with your cannot be concealed, but in the case of the at your leisure. Then f 5.Day Money -Back Guarantor; t fully tisfied return RISK! CI No. I-MODERN RADIO SERVICING average hard -of- hearing person, the hearing - them in good condition 54. (54.50 foreign.) aid can be a o will refund your o No. 2 - RADIO TROUBLE -SHOOTER'S concealed to great extent and tiandll hase price imme- HANDBOOK t 53. 153.50 foreign., it should be, especially as most diately. can't lose. o BOTH SERVICING BOOKS at 50.50 Special therefore Money-Saving Combination Price 157 foreign), persons so afflicted are extremely FREE CIRCULARS o No. 3 - RADIO PHYSICS COURSE at $4. sensitive 50 foreign) . Send for FREE, descriptive. illustrated 254. regarding their infirmity. circulars'. NAM'. SPECIAL FOR BOTH SERVIC ADDRESS MONEY- SAVING en -. cm STATE .. Mr. Russell's unwarranted attack upon . BOOKS IF m FREE. Illustrated literature scribing - Please d PURCHASED TO- . COMBINATION nooks r1 No. Ì n No. 2 n No. 3. the medical profession furnishes further OFFER GETHER II evidence of his lack of knowledge. In his MMMMIMsMMalMaMlaliMIMIMMI opinion, a man who has spent 20 years Correspondence Courses In fixing radio sets is far better qualified as a RADIOanedsan TRICAI £NGIN££RING OPERATORS hearing -aid specialist, than a man who RADIO studied 6 years at a university, specializing ELECTRICAL ENGINEERINGo;t g? trical fi Id. Prepare yourself. at low Cost. for' secure on the structure and troubles of the human RADILadern. ira lified, you ca understand quickly. = WANTED Exvn r°d'o O ENGINEERING f'"° e Tho Defense Program is creating -in. ear and who spent years after graduation n ddrcea. Aneto ecuu National Trains y super-service nel vacui fiore numerable openings for Commercial Radio Oper- serving his fellow men e. kits furnished. iploma on completion. is the time to capitalise on your radio to bring them better Tuition.TaILIOn. 52 . cimar course. ator,-Now Deferred Vnygret plan. training and experience by obtaining a Commercial hearing. FREEGet c Dices of enool calo( WOW! mogez Ines, eomDlltO Oefalls. SÉNÁ NDW! Radio Operator's License and taking advantage of Mr. Russell considers the many opportunities presented. My recent pub- the carbon micro- LINCOLN ENOINEERINO SCHOOL, Got 931 -C27. (11100tH NEBR. lication "RADIO OPERATORS' LICENSE GUIDE" phone far superior to the crystal mike. Of has been especially prepared as a Guide for those course, that is his privilege. He also thinks radio men having the necessary training and ex- It's Your Job perience but who are unaware of the exact require- that the magnetic earphone is much better Today ments for a Commercial Radio Operator's License- to for Containing over 1.250 questions and answers to the than the crystal earphone. As he so quaintly prepare a better radio new type examinations, it will enable you to suc- phrases it, "the crystal hasn't got it." I do job tomorrow! cessfully pass the examinations. Today's opportunities with Ro to radiomen TECHNICAL Postpaid cheek Money Order. not know exactly what he means by "it," but TRAINING. CREI advanced technical training has been Only 83.00 -Send or if he means that the crystal lacks sensitivity tried and approved by more than 5000 radiomen. CREI will equip you with tho ability to go after -and get a WAYNE MILLER in comparison with the carbon mike or better radio job. Free book gives details. Write today. the 205 West Wacker Drive CAPITOL RADIO ENGINEERING INSTITUTE Chicago. Illinois Dept. RC-3 3224- 16th St., N.W. Washington. D. C. RADIO -CRAFT for MARCH, 1941 515 MAILBAG

magnetic earphone, I leave it to your read- swer. It has been found that a technical ers to judge as to the extent of his technical magazine or one that is often referred -to knowledge. opens better with the present binding be- With further reference to the sensitivity cause it lies flat. Most of the radio maga- of the "Miniature Tube Audits Amplifier" zines are now bound in this fashion. which I described in the October, 1940, issue, Incidentally, we would like to point out to I might remind you that I demonstrated Sr. Madridano that not only 5c magazines SERVICING COURSE -8 WEEKS this amplifier to the editors of Radio -Craft use this type of binding. There is for in- and showed them that it was possible to hear stance, Life, .a 10e magazine, and more im- T7,tèa OPERATING Ìl`MatteK 5MONTNS the ticking of a high -grade watch more than portant than this -The Reader's Digest, a . (.. e.. S4gni a foot away from the microphone. In fact, 25c magazine, with the identical binding, I'LL FINANCE YOUR TRAINING everyone who listened to the performance and with the largest circulation in the Mail coupon today for free book showing how you can learn Radio of this amplifier was amazed at its extremely world! Operating, Servicing. high sensitivity. on i few short weeks in James Allen's kink "Locating Breaks Coyne Shops and also how you can Incidentally, practically all the well - in Leads" appeared in the Oct. 1940 issue pay tuition In easy monthly known of high - payments after graduation. manufacturers -quality deaf with the wrong illustration. The illustration aide are now turning out compact hearing - LEARN BY DOING shown there was for an "Improvised Beat - On real Radio receiving and aids using-guess what- miniature tubes Frequency Oscillator" published in the No- transmitting equipment at and crystal mikes. It certainly looks as Coyne. Simple, easy method of vember issue. practical shop training. You don't though all the world is out of step but Earl. The illustration for James Allen's kink need previous experience. Prepare H. G. CISIN, for Radio Operators' Government is so simple that we did not think it neces- license Exam. and for good jobs in New York, N. Y. Broadcast. Police Radio, Aircraft sary to run it as a correction. It merely Radio. Ships. Commerce' Radio stations or in service shops and consists of a 1,500 V. transformer, the pri- radio factories. "Learn by RE: "BURGLAR ALARM" mary of which is connected to the 110V. doing ", the quick, modern way. at Coyne Shops in Chicago. Dear Editor: A.C. line and the high -voltage secondary EARN WHILE LEARNING I'm just a beginner in this popular busi- terminating in well- insulated test leads.- Job Help Attar Graduation ness of radio and maybe I'm all wrong. In Editor We assist you in getting part -time work to help Day living expenses and give you real employment service your January issue of Radio -Craft in the alter you graduate. "Shop Notes -Kinks -Circuits" section there H. C. LEWIS Pres., COYNE RADIO SCHOOL. is a diagram for a very good burglar alarm. THE VERSATILE AMPLIFIER SOO So. Paulina St., Dept 31.BH, Chicago. III. In its present wiring form, wouldn't the free book and details of easy Pay-After-Pay- After- Dear Editor: Graduation d1'n. roar Why transformer always be using current? I am attempting to build the "Versatile NAME not in connect the "tripping" device, the Amplifier," in 1940 issue Then described the Oct. ADDRESS primary of the transformer? there of Radio- Craft, as a hearing -aid for a friend would be current being used while the alarm CI7'Y STATE J of mine. He now has one of the old type was disturbed. a mike bone He Am I would using carbon and conductor. wrong? If so I appreciate said the bone conductor gave him better a'zRADIO SERVICE EXPERT the help of all who can show me why I'm results with that type, but far from satis- ,10, IN SPARE TIME wrong. (No pun intended, Mr. Kuntz.) Y LEARN AT HOME factory. What I want to know is what would .-.1 demand for radio experts grows JOSEPH C. SEVER, every in o° be the best way to couple the output to a under personal guidance of qualifiedaled Forest City, Pa. engineer and m bone conductor if the Xtal Phones prove n entakts learning easy. Leadersiron in the radio industry endorseske R.T.A. unsatisfactory. methods. Spore time DroSte soon pay for training. You are not entirely wrong. The method J. W. BAKE, NOW IS A FINE TIME TO START you suggest will work, but generally is not Kansas City, Mo. New radio preferred. The reason is that your method In radio Ifarieseanprogrami ry branchrafe f ds Service... Opportunities for advancement almost limitless. requires high voltage (110V.) being car- This letter was sent to the author whose FREEWrite today for and radio ried through long leads from the trans- R.T.A. training can do y reply follows. former to the metal gate. This in itself is a In order to couple the bone conductor to RADIO TRAINING ASSN. OF AMERICA disadvantage and probably against the of amplifier in place of the 1559 D Ave. Dept. RC -a1 Chlesgo, 111- the output the safety code of many localities. Then, too, crystal phones it will be necessary for you a high voltage would have to be broken at to obtain a coupling transformer having a R111010TELEVI51011 the gate contacts, resulting in excessive primary impedance of 8,000 ohms and a sparking. Finally, there would always be the secondary impedance which will match that Oldest, largest RadioTetevieien hoot In West train. you possibility of live voltage on the metal gate of your bone conductor. Naturally, the pri- for good pay fob. Complete instruction including Radio which would to any Construction and Service. Broadcast Operating. Sound. prove dangerous per- mary of the output transformer will be in Taming pictures, Television, Publie Address, etc. Flexible son touching it. Mr. Kuntz's method is plan to meet specific needs of those with or without ¡ohs. the plate circuit of the 1S4 tube: Transportation allowed to L.A. Earn mom and board while safe all- around and the generally accepted learning. Request Free Catalog. H. G. CISIN, one. -Editor New York, N. Y. NATIONAL SCHOOLS, LoesÁ tits LIKES "RADIO -CRAFT" . . ALMOST VERY MUCH RADIO COURSES Dear Editor: LIKES OUR SIGNAL CHASER Mid -Term Classes Now Starting Speaking lightly about the Radio -Craft Dear Editor: RADIO OPERATING-BROADCASTING magazine as a whole, I find it always in- We built the signal chaser shown in the RADIO SERVICING -a practical course RADIO AMATEUR CODE TELEVISION teresting and worth more than its price. Sept. issue of "R.-C." It performed better ELECTRONICS-1 )T. day course 2 yrs. e I like very much each and every article pub- than our expectations of it were. It was Day and Evening Classes. Booklet Upon Request. Messrs. New York Y.M.C.A. Schools lished in the magazine, especially of built into a case which measured 101/2 ins. 4 W. 64th Street New York City A. C. Shaney's, Sprayberry's, etc. I like also high, 9 ins. wide, and 4 ins. deep. The only the way you "streamline" it. changes were in using a 5Z4 and a 1,700 - Your present way of binding is a very ohm speaker field. cheap one good only for 5 -cent magazines. The eye to close first. PATENTS- TRADE MARKS would tuning failed at I am hoping that someday you give we the "B-! -" lead from Booklet concerning Inventions & Patenta former way of After changed back the magazine its plate to the tuning eye operated OK Form "Evidence of Conception" with binding. target instructions for use and "Schedule of from then on. So we came to the absolute Government and Attorneys Fees"-Free By the way, I wish to know if the kink conviction that the "B-} -" lead was shown LANCASTER, ALLWINE & ROMMEL of Mr. James Allen, appearing in the Radio - connected to the wrong terminal on the Registered Patent Attorneys. issue, 255, is Craft for this month's page 6E5. Bowen Bldg. Washington, D. C. 436 appropriately illustrated. This is our first trip into the Mailbag. I am a subscriber to Radio -Craft for If you have any all -wave signal genera- about 3 years now. I am determined to stick tor circuits that are as good as that of the RADIO TECHNOLOGY always to Radio -Craft. My only regret is Signal Chaser, send them along with "R -C," RCA Institutes offer an Intensive course o that I wish I had subscribed to Radio -Craft high standard embracing all phases of Radi So long, and thanks a million for the end Television. Practical training with modern much earlier. (Thank youl- Editor) equipment at New York and Chicago schools. MANUEL MADRIDANO, Signal Chaser and Radio -Craft and, we Also specialized courses in Aviation Communs hope, a signal generator. cations, Radio Servicing and Commercial Oper Sta. Cruz, Manila, Philippine Is. ating. Catalog Dept. RC-41. PAGEL BROS., RCA INSTEITUTES, Inc. The binding of Radio -Craft was changed Radio Service, A Radio Corporation of America Service reason. "Handiness" is the an- Bloomington, Ill. 75 Varlek St.. New York, 1154 Merchandise Mart, ChIMI, for a good 516 RADIO -CRAFT for 'MARCH, 1941 MAILBAG

A "P.A. BROADCAST" zine between these with stitch about '/r -inch away. Now How do you do, Gentlemen of the P.A. twist thumb and forefinger. The cover will tear away from stitch just Audience: This is Stanley Dowgiala speak- the Use Meissner ing to you over Station PAS (Public Ad- as it would if you have a few dozen maga- dress System) and bringing valuable infor- zines in a pile on a high table and they fall on mation to all you P.A. men to help you to to the floor. Magazine sliding on get better P.A. jobs. magazine with disgusting results. Now take the old binding and give it the On October 12, 1940, at 8:30 P.M., the finger test. The binding will not budge. Democratic National Committee in Jersey All of my old magazines have their covers. City rented a P.A. system from me. I in- Many of the new type do not. A big ad- stalled this on their decorated truck and vantage of the old type is that it has an their meeting began. Many speakers had index on its edge. I think it's about time spoken and it came to my attention that the to get back to the good binding. President was to speak on the air, so I notified the chairman and he announced the ANDREW M. ELLIOTT, surprise to a large audience. Ingram, Pa. In the meantime, I got a small A.C. -D.C. ()See "Cosmic Rays Shortest Wave- radio set, with a built -in antenna, and I length in the World," Radio -Craft, Sept. tuned -in the station. I waited for the Presi- 1937; more detailed information appears in dent to speak while the meeting was going the book "Earth, Radio and the Stars," by on. Then I used a special dynamic mike and Prof. Harlan True Stetson. relayed the President over the P.A. system. May we refer the matter of binding to the I merely put the mike close to the radio reply given in this issue to Senor Madridano. loudspeaker, tuned -in the radio set full - volume, and then the P.A. system at 9 P.M. The President was heard distinctly for over FROM PORTLAND TO 3 blocks and the people were amazed at PORTLAND how it was done. It also won me a tip and Dear Editor: many favors. I made the President speak for himself at that meeting. Some of you On page 658, of the May, 1940, issue of gentlemen ought to try it sometime. Radio -Craft, is a problem (No. 159), sub- mitted by Mr. I also rent my P.A. system for bus rides Ettinger of Portland, Pa., telling about he and supply them with recording music. I the trouble was having with PRECISION - BUILT PRODUCTS also run dances sometimes code interference on the broadcast band of at a charge of a receiver. The 25c a couple and also use records. Then description of the type of FOR PERFECT interference as given by him, PERFORMANCE again, I am called out to weddings to play brings to mind a quite similar happening that I ex- record music. I buy all types of nationally - perienced Progressively Engineered sold records. I cover a while back. The answer given the political meetings by you, to his every year from October to election. Many trouble, in my estimation does not present a solution FOR THE EXPERIMENTER clubs invite me to play music for them at to his problem. My reason for contesting you is best Complete Receiver Kits their dances or other affairs. I also cover explained by the following relation of my experience "Essential"' Kits for Receivers theatres for special occasions such as an- in question: nouncements, prizes, amateur hours, etc., F -M Parts and Receivers In June 1940, while Television and I have installed many in theatres for aboard the S.S. Receiver Kits Mauna off their own use which they bought from me. Kea the Pacific Coast of Guate- All -Wave Tuning Assemblies a I even had an application from a Funeral mala, small Emerson receiver (I don't Antenna, R -F and Oscillator Coils recall the model number, Parlor to install equipment for a special but it was an Wireless Phono Oscillator Unit occasion and to play organ music for special A.C. -D.C. 5 -tube model of about 1939. It I -F Transformers of all kinds funerals when their equipment went hay- was one of those whose cabinet was mount- Tuning Condensers, Dials, Switches ed in an wire. I mix with all types of people. My extra stand to tip the whole receiver back FOR THE SERVICEMAN business name is: The Society Radio and in order to gain a better view of the dial from above) suddenly began New ANALYST P.A. Service. bringing SIGNAL CALIBRATOR Always remember this: never try to get in London, Berlin, and other 49- Wave Traps Line Filter rich fast; and, treat your customers with meter stations on the high -frequency end of Audio Filter Primary Windings the standard broadcast band, in respect. Give them what they want; always the vicinity Replacement Antenna. R -F and Oscillator Coils of 1,400 -1,500 kc. At the same time, semi - satisfy them and you will be richly reward- Replacement I -F Transformers local standard broadcast ed. Remember their recommendations get stations (among Exact Duplicate Replacement Coils them TGQ in Quezaltenango, 1 results. Be honest in your work and most of Guatemala I-F Transformer Replacement Guide all, were coming through as well, at their prop- Coil be presentable and show your person- places Repair and Rewinding Service ality and smile to people. Most of all, ad- er on the dial. vertise your business by printing your name There was no shortwave band on the re- FOR THE AMATEUR and address on your P.A. speaker cases and ceiver, merely the single -band standard broadcast. The mixing -up of 49 -meter short- SIGNAL SHIFTER SIGNAL BOOSTER carry some of your business cards with SIGNAL SPOTTER SIGNAL SPLICER you. wave signals and standard broadcasters resulted in a rather serious mess of image TRAFFIC -MASTER SIGNAL RESONATOR I hope all of this information is of value TRAFFIC SCOUT UNI- SIGNAL SELECTOR you is me. This is whistles. Images, involving the 3rd -har- to as it to Stanley monic of MC 28-56 Converter Antenna Relay Dowgiala now signing off, and wishing you the high- frequency oscillator, is what I took them be. My R -F Relays Insulators t he best to explanation of luck. was: STANLEY DOWGIALA, FOR THE SOUND ENGINEER Jersey City, N. J. Suppose the receiver used a 460 -kc: I.F., and the dial was set at 1,400 kc. Then the High -Fidelity P -A Tuner H.F. oscillator would be working at 1,860 "Utility" TRF P -A Tuner kc. The 3rd -harmonic of the H.F. oscillator Dual -Band Super P -A Tuner LIKES OUR NEW BINDING ... . at that time would be 5,580 kc. Then a signal Specially Designed Assemblies ALMOST 460 kc. higher, or 6,040 kc., would appear as Custom Engineered Equipment Dear Editor: an image on the original 1,400 kc. Portable Phono-Recorder Unit Recently I visited the Buhl Planetarium And that's just what happened. The 49- WRITE FOR FREE CATALOG NOW! in Pittsburgh. There I saw an experiment on meter stations were held long enough, and Brand new Meissner General Catalog for 1941 Cosmic Rays. I would like to know what with plenty volume, to identify them and now being mailed. A postal card will bring you- is known about these rays to date, their establish their frequency. The ship's radio this valuable guide to dependable Precision-Built effect on radio waves, and operator, when told the receiver was bring- parts and equipment. You can't afford to be with- the simplest cir- out it so your request cuit diagram of the receiver used to receive ing in London on the broadcast band mail TODAY: them.() wouldn't believe it and had to come aft Dept. C -3 May I go on to say (changing the sub- where the receiver was, and operate the con- ject) that I very much dislike the present trols himself, before he'd be convinced. He method of binding. brought in London, Berlin, and several code To better appreciate my opinion, slightly stations which he identified and knew their dampen thumb and forefinger. Place maga- (Continued on page 545)

RADIO -CRAFT for MARCH, 1941 5 17 SERVICEMEN SAY :-73t iliyyee Ptopts - 70e hattet S'et icing -USE GERNSBACK MANUALS

Since 1931 more and more Servicemen have been buying GERNSBACK OFFICIAL RADIO SERVICE VOLUME 7 OFFICIAL RADIO MANUALS year after year. The authentic material, SERVICE MANUAL The newest and most outstanding GERNS- easily accessible diagrams and complete service data BACK Manual published since 1931. Con- make them invaluable to dealers and radio Service- tains many features never previously 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- kit or laboratory is incomplete without all the GERNS- cludes 1938 Models Not Found in Other Manuals All New Material -No Reprint BACK OFFICIAL RADIO SERVICE MANUALS. There or Rehash Master. Index of 74 Pages Includes Sete Listed in All Other Gernè- are GERNSBACK MANUALS also for servicing auto- back Manuals Stiff, Leatherette Loose - refrigeration and air conditioning equipment. leaf Covers Size 9 x 12 Inches Net radios, Weight 10% lbs. Price $10.00 1935 OFFICIAL AUTO -RADIO .OFFICIAL SERVICE 1936 OFFICIAL RADIO AUTO-RADIO MANUAL SERVICE MANUAL SLRVICE MANUAL . If you are overlooking Just packed with service data of seta manufac- servicing auto radios, then tured during 1936 and 1936. Schematic diagrams you are missing a great show speaker connections, power -transformer con- deal of business. The 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 1,600 SETS SHOWN stant 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 600 ILLUSTRATIONS Flexible, Leatherette Looseleaf Covers Size 9 x 12 Inches Net Weight 1% lbs. Price $2.50 OFFICIAL REFRIGERATION i OFFICIAL SERVICE MANUAL 1934 OFFICIAL RADIO REFRIGERATION - SERVICE MANUAL Volume 2 This is the only complete refrigeration serv- 19)4 This manual contains values of I.F. trans- ice manual ever published. Contains detailed Official formers on superheterodyne receivers, valua- information on servicing, outlines of theory ble tube data, complete list of American and methods of operation. instructions for Radio Service the handling of refrigerants, charging sys- Manual broadcast stations, free question and answer tems, diagnosing troubles, charts. electrical service, service material and schematic dia- hook -ups and a wealth of other necessary ca.N.., a..9. grams. OVER 400 PAGES OVER 2,000 data. OVER 362 PAGES OVER 300 Loose - 1913. 1994 Rdia .inn... DIAGRAMS Flexible. Leatherette, ILLUSTRATIONS Flexible, Leatherette, leaf Covers Size 9 x 12 Inches Net Full Ralle Senk Guide' 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 This manual is edited by L. R. Wright, SERVICE MANUAL 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 one of the early editions and covers modern installation and individual OFFICIAL which part carefully explained. diagrams fur- many old sets, thousands of are still nished of all known equipment. special AIR CONDITIONING in use throughout the country. OVER care given to the servicing and in- I 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 Net Weight 362 PAGES OVER 600 ILLUS- 4% lbs. TRATIONS Flexible, Leatherette, Looseleaf Covers Size 9 x 12 Inches Price $5.00 Net Weight 2% lbs. Price $5.00 rRADCRAFT PUBLICATIONS. Inc., 20 VESEY ST., NEW YORK, N. Y.n t_ -J Gentlemen: l0i mied Had my remittance of $ for which send me. POSTPAID, the Manuals Indicated below by a cross (x) in the panel. () Volume 7 @ $10.00 ( ) 1936 Manual @ $7.00 ( ) 1934 Manual @ $3.50 ( ) 1935 Auto - Manual @ $2.50 ( ) 1932 Manual @ $5.00 t To order these famous Manuals, see or write to Refrigeration Manual (Vol. 2) @ ( ) Air Manual @ () 65.00 Conditioning $5.00 1 your jobber or favorite mail order house. If more convenient, mail coupon directly to publishers. Nonio , Address I City State RADCRAFT PUBLICATIONS, Inc. (Send remittance In form of cheek or mousy order; register your letter It you send cash or unused U. 8. Postage Stamps.) RC341 L------J 20 VESEY STREET NEW YORK, N. Y. 518 RADIO -CRAFT for MARCH, 1941 "RADIO'S GREATEST MAGAZINE"

. . novelty radio sets if they also have utility will UTILITY be more marketable RADIOS By the Editor - HUGO GERNSBACK

T is an established fact that among the 35 million -odd radio But the most stupid part of such devices is that clock makers receivers in use in America today there has always been an still persist in believing that the day has 12 hours instead of 24! excellent market for so- called "novelty" radio sets. For years, Rather than making 24 -hour clocks, they give us 12 -hour clocks. there have been crops of odd radios, many of which were So if we set the alarm for 7 o'clock in the morning and the radio designed primarily with the idea of novelty, and their appeal robot dutifully wakes us up, at that hour, it will just as dutifully for sales was based mainly on novelty rather than utility. go off at 7 P.M. with no further ado. That means that we have Years ago, in his magazine, SHORT -WAVE CRAFT, the writer de- to hand -set it in some way and trust to our memory that next signed what Vas then the first briefcase radio. It was described morning it will be set right or we will oversleep. A 24 -hour clock in the June, 1932, issue of that magazine. It was completely self - with half of the dial dark, and half of it in a light color, is the contained, including loudspeaker, built in an ordinary briefcase. answer to the problem. Then if a cheap clock mechanism with a Many experimenters constructed this set from the design given good timing device that can be set easily is produced, many radio at that time. It took the radio industry exactly 6 years to catch manufacturers no doubt will adopt it. up with this idea; subsequently they were manufactured in quan- Speaking of utility sets, I can think of any number of these; tities and still are. Here was a novelty set which at the same time but I will only give a few examples for which I know there will had utility. Nor was it a freak set. be a good market. There is for instance, the Ladies' Boudoir Radio, Of course, there have been many novelty sets and every month small but stylish, with modern perfume bottles at each side and brings numerous new ones. To mention only a few of them, we other attachments of use to any woman, of which there are many. have had globe sets where the radio receiver was installed inside For the he -man, I can readily imagine a Den Radio which we might a terrestrial globe. We have tamp radios where the radio set is also call Smokers' Delight Radio. Executed in the modern manner, contained in the foot of the lamp, the shade being the loudspeaker. the radio set has pipe holders on each side to hold a number of We have had book radios; and bed radios combined with lamps. pipes conveniently. There can be an electric lighter with cord We have had radio sets where the casing was made entirely of attached, tash tray, even a cigarette drawer or case can be pro- plate -glass mirror. The list is really endless. Some of these sets vided for. If styled correctly, it will sell well. have a popularity which is maintained come and go; others certain Some years ago, I designed an Executive's Desk Radio which for many years. has on top a lamp with a green shade, pen and pen holders on The writer here wishes to make the observation that construc- clips, pencils, etc. There was also a novelty each side, and front space for tors who have sudden inspirations as to either or utility clock provided on face of the radio set. It was described in Feb. without consulting a stylist. the radio sets often rush into production and March, 1937, Radio -Craft. This was a project for home con- This to the writer's mind is the most important deficiency of these struction, and for this reason, it was of course not styled properly. sets. A radio set, no matter how good, will fall by the wayside and I styled is a for it. . unless it is not only designed right still believe if right there market can never attain a real sale Most midget in use can be with an attractive is sets today provided but styled right. lamp on the top for very little additional cost. It seems rather Nevertheless, few radio constructors are stylists. They may know the midget-set manufacturers have not turned to this do not what lines, what strange that all about radio but understand pleasing Midget -Lamp Radio utility so far, but rest assured sooner or later, decorative effects or modernistic touches should be added to make product. and they will. a radio set a fast -selling It takes an artist a stylist Radio. Here we also need a clock he has knack he Then there is the Kitchen to do this and if the for this sort of thing, should as the woman of the house needs a timer which will be severely alone and allowed to do the designing. It is one arrangement left turn on either the radio set or an alarm when a given time is up thing give a homely analogy be a good manufacturer of -to -to so that the roast or the cake will not burn or get overdone. There felt but quite another to be a good fashion modiste and make a several pencil holders; also a place for a beautiful hat from a common piece of felt. could be, in addition, recipe book and one of those gadgets dear to every woman's heart There should also always be a distinction between the gadget - -a mechanical list of what to buy. Lovelty type of radio set and well- styled utility- novelty type of et; the latterlisually will former will not. And for the bedroom, we need a good Bedroom Radio done in sell well whereas the have There are any number of utility radio sets which as yet await the modern manner, which should a clock arrangement to in morning. It can be provided handsomely with big markets - believe it or not. By utility, I refer to a radio set wake you up the that not only performs as a radio set but has a separate utility a night -light on top of the radio receiver which can be used when- Many people like to sleep with a neon night - in addition. There have been, for instance, a number of clock ever wanted. small radio sets. Here we have with light and this is easily included as utility on a midget set. Then the the utility of a time -piece combined of who always of radio. The great trouble with these sets has been that the clock male member the household thinks something usually has been of inferior quality. Usually such clocks are not during the night, can easily use a memo pad which is also incor- self- starting and if the the porated into the set. This can be lifted from a small rack, molded current is turned off momentarily, which clock stops and must be hand started. The best utility idea of these into the casing and at the same time, you pull out -a pencil You memo sets is the type where the clock can be set by means of a mecha- has a tiny electric light attached at its end. write your nism, so without turning on any light in the room except for the stream that the set will be turned on or off at a pre -determined' write. time. Thus, many people dislike alarm clocks but like a clock - of light directed against the end of the pencil while you operated radio which turns on at a given time in the morning Then going to the children's room, we can have the Children's and wakes them up by pleasant music rather than by a shrill Radio set made in gay colors, as indeed they are even being made alarm. Again the manufacturers of these devices have fallen far now. BUT we provide them with the following utility: a savings short, in that with few exceptions, the time- setting device is diffi- bank can be incorporated readily into a midget receiver which cult to manage and is not reliable. We know of several of these does not operate unless you put in a nickel or a dime, when it types which we had in our own home and which tended to go off will play for a determined number of hours, say 3. This is a simple at the weirdest hours of the night, waking us up at the wrong utility, that will appeal to children and parents alike, and will time, mainly due to faulty contacting arrangements. provide another good radio seller. RADIO -CRAFT for MARCH, 1941 cíe THE RADIO MONTH IN REVIEW

The "radio news" paper for busy radio men. An of B.B.C. broadcasts show that an English nightly program to America aims to de -bunk illustrated digest of the important happenings German news broadcasts. of the month in every branch of the radio field. The proprietor of a bar in Padua was fined $25, and had to park a month in jail, for listening to a British news broadcast, A.P. reported from Rome last month.

A U.P. report from London tells of the execution last month, at Pentonville Prison, of 2 German spies caught with a portable radio transmitter said to have been intended to be used to send information to Germany. The current hit show "The Corn la Green," was broadcast to its author in Lon- don because the war prevented his seeing the show in New York, columnist Charles A. Wagner last month reported in The Mirror (New York). DEFENSE AMERICA'S defenses were strengthened last month when Major Edward ( "Amateur Hour ") Bowes passed over to the Navy full title to his 61 -ft. yacht Edmar, and 30 -ft. light- cruiser Edmar, Jr. Radio amateurs, who may have occasion to contact the War Department, now can call the Department's radio net control station WAR. Frequencies for amateur contact are: 4.025 mc., 3.5 to 4. mc., 1822 me., and 14. to 14.4 mc. Chairman Stephen Voorhees of the Ad- visory Board of Industrial Education last month urged radio manufacturers in the COLOR TELEVISION BY WIRED -RADIO Metropolitan area to aid employees to ob- Illustrated here is the new "off- side" television camera designed for use in Columbia Broadcasting System's method of Color Television. A demonstration of this direct pick -up system last month, which was attended tain the free instruction being given by by Radio -Craft, disclosed many improvements over the indirect pick -up system demonstrated a little New York vocational schools, in radio serv- over a month previously. "Cold light" illumination with fluorescent lights, for example, was a stellar icing, code, and theory. feature. Proper phasing of the 3- color, 6-sector, motor- driven color -disc in the receiver, with its companion at the transmitter (across the street), was obtained by means of a receiver pushbutton control. Last month the American Radio Relay League announced the appointment of a in the opinion of ABROAD the New York Daily News representative and 6 regional advisors to it may be the "Queen Bee flying torpedo." the Amateur Radio Committee of the De- DEATH snuffed out the lives of The only authoritative advice which Radio - fense Communications Board. Other groups 7 members of the British Craft has to report on these Queen Bees - represented on this Committee: Federal Broadcasting Co.'s staff at and this readers will recall -is the use of Communications Commission, Army, Navy, the B.B.C. Headquarters in London, last these radio -controlled airplanes as robot and the National Youth Administration. month, when a Nazi bomb traced its lethal gunnery targets. The News gives this data path into the building during a broadcast. on their type of construction: biplane, about Commercial cooperation in the Defense 18 ft. long and 20 ft. span. Program includes the following: Crosley The Associated Press reports that, according to the "Princeton (N. J.) listening cen- From China comes an A.P. report that the ter" Germany in recent months has been brdadcast of one of President Roosevelt's waging an increasingly intense propaganda fireside addresses over XMHA, American war against the U.S. via S. -W. radio. station in Shanghai, allegedly was jammed by Japanese interference. A U.P. report from Alexandria, Egypt, mentions the use of a "secret weapon" in An issue of PM newspaper, last month, an air attack against the Italian Navy; uses a column to tell how C.B.S. recordings

SONOVOX -SPEECH FOR THE DUMB! Motion picture fans and broadcast listeners, alike were amazed, when they witnessed recent talking picture and heard broadcast programs, in which a person dumb -unable to utter a word for many years -was able to make himself perfectly understood! A vibrator, somewhat like an electric shaver, when held fo his throat supplied the necessary "artificial larynx. "; REFUGEE RADIO shown here are Kay Kyser, It was indeed a "Merry Christmas" and a "Happy Jinny Sims, and (right) New Year" for little Allan Whittaker, a refugee from Gilbert Wright. war -torn Europe, here shown exchanging Season's Greetings with his "mommy" during an N.B.C. broadcast to and from Europe last month. Many "back home" thus heard the voices of their lparentsoved ones for the first time since they had been parted.

520 - RADIO -CRAFT for MARCH, 1941 .HE RADIO MONTH IN REVIEW

POLICE 2 -WAY VEST -RADIO! (Cover Feature) New York City's Police Commissioner Lewis Val- entine (left) and Mayor LaGuardia, help Patrol- man William Proctor model the 2 -way vest - radio set developed by Gerald S. Morris, Supt. of the Police Telegraph Bureau. Cost: $165; range, about 1,000 ff.; weight, about II lbs. Photo -Wide World Photos.

Radio Corp. has opened an office in Wash- "Cavalcade of America," special record- ington, D. C., to speed production by better ings of 12 outstanding historical dramas, is cooperation with Government depts. . available at nominal cost to schools front the Air Radio and Instrument Co. is conducting Association of School Filon Libraries in New special classes designed to train enrollees York City. for Defense jobs paying $125 to $200 per HEARING" RUBBER IMPURITIES The above mo. . National Union Radio Corp. has photo shows the set-up in Bell Telephone Laboratories for testing the dielectric properties agreed to give a month's salary, carry group Each jar of Dorothy Gray, Ltd., Throat of "pigmented" rubber containing not only color- insurance, and re- employ staff members, Cream now has packed with it a 2 -sided ing matter but also fillers and reinforcing agents. who join voluntarily transparent phono record. Played A capacity - inductance bridge and D.C.-resistance the Colors or by draft. -back, it galvanometer Hygrade Sylvania Corp. will carry spouts instructions. are used in taking measurements. the group insurance of its enlisted employees, will re- employ them, and in addi- old stand -by: "And what would you like Latest idea Santa to bring you for tion to giving a month's salary to 1 -year by Muzak for getting its ad- Christmas ?" enrollees, offers an additional, equivalent vertising -free music into private homes, sum to enrollees for 3 to 6 years' Service profitably (for Muzak), involves the use of Bell Telephone Laboratories last month an "injector box" which in. the Army or Navy. . . . In a full - connects to the was granted Patent No. 2,221,956, by Ar- page advertisement in newspapers, last master antenna of apartment houses. Apart- thur E. Schuh, for a "soap" that greatly re- month, American -owned and American - ment leasees merely tune to Muzak's wave- duces grain noise in sound- recording wax controlled R.C.A. called attention to the length for all -music programs; and perhaps "mothers." The usual crystallization of the manner in which its 27,000 employees are pay a slightly higher rental. recording wax is eliminated by the "soap," serving in the Defense Program. a compound of stearic acid, montan wax, F. W. Woolworth's Xmas attraction (at sodium carbonate, and basic lead carbonate, its Church and Vesey Sts. store in New the New York Times reported. SOUND York City), a Talking "Santa," deserves ONE of the newest uses of special mention. An interphone system en- The "Statewide Telephone Meeting" of Public Address systems: a abled a remote commentator to listen -in, via the New Jersey Bell System, last month, "drive -in" church, in St. a transducer (loudspeaker operable as a brought 14,000 Company employees together Petersburg, Florida, where patrons remain microphone) concealed in the body of a in one huge family to hear President Bar- in their car -seats and honk their "Amen's." 3- foot -high Santa Claus doll, to comments nard deliver a holiday message. Employee of persons who came upon the figure, un- groups in a total of 17 municipalities were expectedly, at the foot of a flight of stairs, joined by the copperwire network; terminal and to startle the natives out of their equipment included 60 loudspeakers and aplomb by a well -put quip or two; or even 90 amplifiers that enabled all to hear the to hold a conversation, from his place of State -wide roll call and ensuing program, concealment on another floor, with the all directed from the Mosque Theatre in more hardy customers who ventured to reply Newark; station WOR aired part of the to leading questions, as for example the program over the Mutual broadcast net.

BONE "HEARING" TEST An important part of the work of the New York League for the Hard -of- Hearing, Inc., is the giving of hearing tests. The "bone conduction" test NEW ELECTRON MICROSCOPE of this little, girl's hearing The new streamlined version of the RCA Electron has lust been completed Microscope, shown here, was demonstrated to the and the verdict is: OK! Institute of Radio Engineers last month. Magnify- ing up fo 100,000 times it exceeds by 20 to 50 times the magnification possible with any optical microscope; instead of glass lenses it uses lens -effects obtained electronically. The Gold Medal of the American Institute of the City of New York is scheduled to be given to Dr. Wendell M. Stanley, in February, for his work in demonstrating the properties of the 'tobacco mosaic virus," a particle seemingly neither molecule nor organism) so tiny it is Invisible except to the Electron Microscope.

RADIO -CRAFT for MARCH, I941 521 SERVICING

wrivwwO 50L6GT 10 MEG 1250-IGT MF 2 MEGS. MF L z P

MEG lw SEIM Go MMF

PU. 0.25- , .005- .m x.MS MEG. O.5\ MF OHMS .002- MEG. 140 MF OHMS. 1.000 (EACH) OHMS 15/ MF. MEGS. + + 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. 42

(FIG. I.) INDIVIDUAL DEGENERATION AP- and the radio tuner is detuned so that no the filaments easier to filter, and permits a PLIED TO PHONO PICKUP CHANNEL signals will be received. The radio volume much simpler connection for battery EMERSON MODEL ET. -A degenerative cir- control with the usual grid coupling con- operation. cuit couples the speaker voice coil to the densers then serves as a tone control and pickup so the degenerative the volume must be controlled at the pickup (crystal) that (FIG. 4.) VARIABLE TREBLE AND BASS unit. The circuit is shown in Fig. 2. Provided 1 action applies over the entire pickup chan- COMPENSATORS AS TONE CONTROLS nel without regard to any other means used that the pickup circuit makes use of a high in the A.F. amplifier alone. series resistor, the pickup need not be re- STEWART- WARNER MODELS 11-8D1 TO It is well known that every component moved from the circuit for radio reception 11.8D9 AND 11.8D1 -Z TO 1143D9- Z.-By- because the grid circuit is with the high in is capable of not shunted passing frequencies across the up- the signal circuit contribut- too low ing something to the harmonic content or an impedance for satisfactory per section of the volume control by means volume. of condenser (4) in Fig. 4 provides high - distortion of reproduction. Hence by in- frequency cluding every possible item in the electrical compensation. Varying the im- (FIG. 3.) RECTIFIER ELEMENT USED AS pedance to the top of the volume control by part of the signal circuit within the degen- means erative action it is possible to minimize the FLOATING FILAMENT STABILIZER of a potentiometer (67) permits con- distortion SILVERTONE (SEARS, ROEBUCK & CO.) tinuous control of the treble. range of to the greatest degree. The circuit response. shown in Fig. 1, as applied to the pickup has MODEL 6721 AND 6761. -One of the elements a special advantage, in that it greatly im- of the power supply rectifier (25Z6GT) is As the condenser section (53) of the bass proves the linearity or "flatness" of the placed in series with the filament system compensator is made more or less effective audio response. In this way the attenuation thus acting simply as a series resistor and by means of another potentiometer (68) the of high frequencies due to the pickup would having alight voltage regulating qualities. degree of bass compensation naturally be compensated -for to some degree. This circuit represents an improvement in changes. As the impedance across (53) re- efficiency as the 2 rectifier elements are in duces, the ratio between the high and low series thus reducing slightly the resistance frequencies becomes more nearly normal. (FIG. 2.) DIRECT " PHONO" CONNECTION required in series with the filament circuits. This same adjustment increases the im- MADE IN SMALL RECEIVER Moreover the resistance changes in the pedance from plate to ground of the 1st RCA MODEL 10X. -The phonograph jack plate circuit of the rectifier element in the A.F. amplifier and reduces the phase angle is wired permanently in the Ist audio input filament circuit as in Fig. 3, are in the same of this impedance (58 and 68) practically requiring no switching to change from radio direction as the voltage changes, that is, to zero so that there is little or no fre- to phonograph operation. they both increase and decrease at the same quency discrimination. Thus tone is con- For phonograph operation the phono ter- time. This, of course, tends to stabilize the trolled by 2 potentiometer actions acting on minals are simply plugged into the jack current in the circuit, makes the voltage at different parts of the audio spectrum.

POWER 65Q'7. IST. A.F TRANS. 25266T

LGGO 2 .004- (5B) MEGS. MP .004- OHMS MF

A. V. C. H 305GT INSGT IN5GT BO .0. IA7GT 110 MF. MMF. TO 1H56T POWER LINE (57) IO (68) 40 MEGS. - MEGS. 30 MF TREBLE (53) MEG. MG CONTROL 0h08- BASS o O CONTROL

522 RADIO -CRAFT for MARCH, 1941 SERVICING

(FIG. 5.) WAVETRAP PLACED IN R.F. transmitted at this frequency to the detec- (Continued from bottom of 2nd column) CATHODE CIRCUIT tor tube. ing, keep the chassis away from the loop This circuit shown in Fig. 5, permits full or oscillation may occur. EMERSON MODELS FA -374 AND FA -408.- effectiveness of the trap without detuning This change cannot be made on any of As a parallel resonant circuit in series with the antenna, or R.F. plate circuits, without the plastic cabinet 5R sets (5R1 and 5R3). the cathode of the R.F. tube the wavetrap making any adverse impedance changes in The plastic cabinet sets of this series will for 455 kc. (I.F.) acts as an R.F. degenera- the R.F. plate circuit, or in the antenna. exhibit circuit oscillation if they are stepped - tive circuit at 455 kc. As the cathode varia- It permits resistance coupling of the R.F. up beyond the present limit of sensitivity by tions are substantially those of the grid at and detector tubes with less than the usual this means. 455 kc. there is no essential net voltage to be danger of I.F. interference. STEWART- WARNER CORP.

.. GENERAL ELECTRIC A63 OPERATING NOTES GAB I.FT and allows water to leak in which will run /'tOIL(sI¢ in . . . into the set through the small holes in the back cover. The set and the bulkhead of the . . CROSLEY MODEL 159 -32 -VOLT car form a natural trough. The holes men- SNORTED T RECEIVER tioned are seats for grounding straps on the 6,000 OHM 05 -MR, _ 1 RESISTOR BURNED á00V. When one of these come in you can bet inside of the cover. OUT, REPLACE WITH your shirt (almost) that it will be one or The remedy I used was to remove the 10,000 OHM ,1 WATT 250V. G.E. A 63 more of the common ailments that we have set, dry it out very thoroughly, realign, and usually found. Squealing and oscillation, then before installing, scrape the paint away while tuning, is usually due to the 8 -mf., from around the holes on the back cover and Symptoms: set hums, audio section is op- 200 -V. condenser in the chassis (vibrator solder the holes shut. erative, but no stations are received. Trouble unit is separate from chassis). This is con- M. C. TURNER, very likely is a shorted condenser as shown nected from "B+" to ground. Loss of vol- Langdon, N. Dak. in the sketch. ume and tone is caused by the 6 -mf., 25 -V. condenser connected from the type 43 tube .... ATWATER KENT 55 . A.C.-D.C. SETS IN GENERAL cathode to ground. When replacing these (a) This set would work OK for hours at open condensers use of a higher volt- types a time and then suddenly burst out in a age rating. Common too is the need for set - strong 60 -cycle A.C. hum. A quick but casual ting-up the vibrator points after they have check of tubes, filter condensers, etc., showed about 3 years. The been in service for vibra- nothing wrong, but a jar test of the 43 tube tor is of the synchronous type, and usually, showed a cathode -to- heater short which was it will be found that with a little filing the intermittent. points can be adjusted again by means of (b) There is a custom, slavishly followed, the 4 adjustment nuts provided. of inserting a 0.006 -mf. condenser from plate -to- ground of the output tube. Yet I ALL 2 -VOLT SETS USING ON -OFF have found in several sets using 43 -type SWITCHES THAT GROUND THROUGH REPLACE WITH tubes that reception is cleared up, tone ren- SHAFT 1-WATT CARBON 3,000 -OHM dered more life -like and background hash RESISTOR NORMALLY GROUNDS eliminated by taking out this condenser. THROUGH SHAFT OFÇ A-NEG. (c) Many of these sets have circuits 17' rX If this set is "dead" and no click is heard which oscillate from 1,000 kc. to 1,600 kc. BATTO s- N when the 27 A.F. driver is pulled out of its because there is not enough load in the an- RETURN socket, check for an open cathode resistor tenna circuit. This condition is remedied by 1 ADO PIPIGTAIL (shown in sketch). removing (usually 0.001 -mf.) con- NEG. SWITCH GROUND the small TO BATTERY CONTACTS WILLARD MOODY, denser between antenna and primary coil New York, N. Y. and one 0.02- 0.05 -- 2 -VOLT SET WITH ON- OFFSWITCH substituting from to -mf. -1 condenser. GROUNDED THROUGH SHAFT- . MIDGETS (Using 35Z5GT Rectifier) (d) Most of these sets have a limiting When the set is inoperative and the pilot resistor of 150 to 600 ohms between the burned out, check the 35Z5GT before A common fault in these sets is intermit light cathode of the R.F. tube and the volume con- the This has a tapped tent fading, and then blaring out, at in replacing pilot. tube trol. The trouble is that sometimes these heater, which furnishes voltage for the pilot. tervals of about a minute, after the volume resistors limit too much and you cannot get One side of the heater often burns out, thus has been turned up. The shaft becomes a that last bit of "umph" when listening to a a high voltage across the pilot light, poor conductor to ground on these switches, placing weak station. The remedy is to take this and burning it out instantly. after they have been in use for a year, due resistor out and connect the volume control to oil and oxidized metal. Best repair is to THOMAS PREWITT, direct to the cathode. solder a pigtail connection from the movable Plainfield, Ind. J. C. RAVELLE, switch arm to ground directly. These Newark, N. J. switches usually ground the "A -" battery . . STEWART-WARNER (models 5R4, 5R5, lead and the "B -" return (which is through 5R6 and 5R7) .... ZENITH (Chassis 5709) a bias resistor). Increasing sensitivity of 6R chassis in I recently had this model in for service wood cabinets. In those locations where ex- with a complaint of weak and noisy recep- .... 1937 PHILCO FORD RADIOS treme sensitivity is necessary in a radio tion and the tuning eye 6T5 also did not set, the 5R wood cabinet models (5R4, 6R5, work. SHEET SOLDERED 5R6 and 5R7) can be stepped up by the in- HOLES I first checked the 6T5 socket and found VENTILATOR OVER troduction of a slight amount of regenera- the 1 meg. resistor between the plate and This change can easily be made as tion. target open. Replacing the resistor only BULKHEAD follows: caused the eye to work very weakly on a Disconnect the 0.05 -mf. condenser No. 23 strong signal. I next checked the A.V.C. re- HOLES IN from the suppressor -grid terminal of the RECEIVER REAR VIEW OF RADIO, sistors and condensers and found them OK. SNOWING BACK COVER 12SK7 socket. In the Underwriters -approved The rather unusual trouble was found in a sets (model 03 -5R, etc.) connect it instead -1937 P1-111 leaky coupling condenser that connects the C0- to the "B terminal of the volume control. -" antenna coil with the preselector coil. SETTO FORD SETS- This is the terminal nearest the 12SQ7 sock- (Please note that this is not the 1st R.F. et, and is clearly indicated in the tube socket coil.) Replacing this condenser with a A common complaint is no reception, or voltage layout of the service manual. In 0.000025 -mf. mica condenser completely possibly, reception of only 1 non -approved models (07 -6R, etc.) connect strong local cured the trouble. station. This complaint usually comes in condenser No. 23 to ground. after a heavy rain! If you remove the front After the condenser change has been The defective condenser is white and looks cover of the machine you are usually greet- made, re -align the receiver. It is especially like a resistor, and is mounted inside the ed by a shower of water. The whole trouble important to re- adjust trimmer No. 9, the preselector coil. lies in the fact that the cowl ventilator rub- broadcast oscillator padder, exactly as ex- C. R. PRESTON, ber gasket becomes "dead" on the '37 cars plained in the service manual. When align- Grafton, W. Va.

RADIO -CRAFT for MARCH. 1 941 523 SERVICING

FLUORESCENT LIGHTING Mast Sideline tot S'etvicemen This is the 2nd in a series of articles on fluorescent lighting as it applies to the radio Serviceman. Part I in the January issue deals with the theory of these lamps, their characteristics and the circuits úsed in their application. Part II, presented here, pays special attention to the interference which may be created in radio receivers by the mercury arc between the lamp electrodes; and to means of combating this interference. PART II RADIO INTERFERENCE JOHN T. BAILEY

EVERY wide -awake radio Serviceman is on the watch for new fields of service from which he can derive some extra revenue, provided that these new fields do not require him to buy new test instruments, stock special parts, interfere with his regular work schedule, require too much study in some phase of electrical work in- harmonious with his present knowledge and experience in the radio or electronic field.

BUSINESS PROSPECTS Note how placing the The suppression of radio interference is radio set a few feet more an activity distant from a noise -pro- that the Serviceman has accepted ducing fluorescent lamp as his legitimate professional responsibility, may completely eliminate and since he is well qualified by experience noise pick -up. in this field and has the necessary equipment to cope with this problem, it is natural that the advent of new electrical devices, oil burners in the past, electric razors recently and now fluorescent lamps, should mean added business for him. The public has been quick to recognize the many benefits of fluorescent lighting, the result being that new lighting installations are being installed everywhere. Inas- much as fluorescent lighting is a new and specialized method of producing illumination, the sale of fluorescent equipment may night clubs, stores, residences and similar the revenue from this work may not justify best be left to experienced representa- establishments where artificial illumination its solicitation, it will no doubt lead to tives of the lamp and fixture manufacturers and radio are desired simultaneously, of future radio repair and sales work. but after the installation is made there may radio interference complaints. This is the be a few instances, such as in restaurants, opportunity for the radio man and although MERCURY -ARC INTERFERENCE It is well known to all radio Servicemen that when a circuit is interrupted, the spark OF generated will oftentimes create a frying TYPES RADIATION sound in nearby radio receivers. A fluores- AND REMEDIES cent lamp when operated on 60 -cycle alternating current is, by the nature of its SHIELD AND GROUND operation, turned on and off 120 times per LEAD-IN second. The mercury arc established between the lamp electrodes causes sparking at the electrodes where the circuit is interrupted, thus giving rise to radio interference which may be radiated in one of 3 ways: (1) Direct radiation to antenna or lead - y. It is evident by reference in from lamp bulb. aiaaIi/oia to the animated illustration at left that un- (2) Direct radiation to antenna or lead - LAMP RADIATION avoidable radiation of in from power line supplying lamp. interference from fluorescent lamps may be great- (3) Line feedback from the lamp to radio ly mitigated if proper set by way of power line. attention is given to the location of the radio sets Oftentimes, interference may be traced FILTER AT RADIO lead -in with respect fo not to only one of the above -mentioned the offending lamp; and forms of radiation but may be found to come proper placement of a line noise filter. from a combination of any or all of them. l/%Z///l//// While the fluorescent lamp can justly be LINE FEED -BACK praised for the efficient way in which it 0 transfers ultra -violet energy into visible radiation for the use of the human race, it m should be reprimanded for shifting a small amount of energy into that part of FILTER AT LAMP the spectrum which we would like to have free for radio reception. A graph plotted 01:1 ® ., with relative interference against frequency _E r i-fsatiilall= would reveal that the broadcast frequencies LINE RADIATION from 550 to 1,600 kilocycles are most affected. For higher frequencies, the noise is not 524 RADIO -CRAFT for MARCH, 1941 SERVICING usually objectionable because of the low the line thus acquiring a ground potential. field strength and because the energy is (3) Surround the lamp with a grounded confined to narrow bands. wire -mesh screen. This, of course, can be done In addition to the radiation set up by the only in certain instances where the appear- arc stream, during the starting period, ance of a screen would not be objectionable. the starter device may give rise to some The mesh should be large enough so as not electrical noise. The condenser included in to reduce the transmission of light materi- the starter (dubbed a "jitterbug" by the ally. In some fixtures where the lamps are trade because of its lively efforts to estab- enclosed by glassware or plastic it is possi- lish the arc ih the lamp) to minimize noise ble to install a screen cylinder between the originating at this point is quite effective glass and lamp. If this is done, provisions and unless the condenser is defective no must be made for relamping. trouble should be expected from the starter. (4) For radio receivers with built -in di- To check this condenser, remove the start- rectional antenna systems, adjust the posi- er from its socket after the lamp has tion of the radio set to pick up a minimum started. If the noise increases, then the con- of noise. back to the radio set through its power is When is A portable, battery -type radio set is supply circuit. This energy may never reach denser not defective. the starter the radio located under one end of the lamp it may handy for bulb radiation sleuthing since the set if the length of the line is large because of impedance, be impossible to remove the starter without line feedback factor is eliminated by this the line there- removing lamp. In these cases, remove method of probing for noise. fore when the line is short the possibility the of feedback is lamp and starter, replace the lamp and with greater. Line feedback can be by a short, insulated wire stripped about '/4- LINE RADIATION eliminated the use of filters either at the lamp or at the inch on each end short the 2 terminals in The power lines feeding the lamps may socket for several seconds. Then radio set. The method of filtering at the the starter serve as a source of radiation to the radio lamp may require many filters if many remove the wire and the lamp will start. If set or to the antenna system unless the level remains the same it may or lamps are contributing to the general noise the noise separation is about 10 feet as explained level. However, if individual filters are ap- may not be defective and a new starter under the discussion of bulb radiation.', The should be tried. A shorted condenser will plied to the nearest lamps, noise trouble same general precautions apply about shield- should abate. Applying a filter at the radio cause the lamp electrodes to glow without ing the lead -in but, in addition, noise re- arc to strike. receiver is positive in protection against allowing the duction can be obtained by applying a feedback but requires greater high -fre- grounded shield to that part of the power quency attenuation and probably will re- BULB RADIATION line near the radio set. In many instances quire greater current-carrying capacity Direct radiation from the lamp bulb is this is not possible because the wires are than individual filters at the lamps. As in of a low order of strength and falls off inaccessible within the walls or ceiling but any power line noise reduction work, in- rapidly as the distance between the lamp for extension cords in residences this rem- ductive - capacitative filters are more effec- and radio is increased. Although the magni- edy could be easily applied. If the power tive than merely capacitative reactances, but tude of this bulb radiation varies with the lines are run in metal conduit or are of the cost is greater. watts consumption of the lamp, bulb radia- the BX type make sure that good high - The generation of noise radiation by tion or radiation emanating from the supply frequency bonding is in effect at all junc- fluorescent lampe is inherent in the opera- lines feeding the lamp can be avoided by tion boxes. tion of all discharge -type lamps but it is separating the lamp and radio set by at Line radiation can be reduced also by in- felt that as improvements are continued in least 10 feet. serting a filter in the line at the lamp. This the manufacture of this new light source, If separation by 10 feet is not feasible procedure shunts the noise to ground before material reductions can be expected in the then it will be necessary to take these pre- it can enter the line and be radiated through problem of radio interference. cautions: the air to the radio reCeiver or antenna This article has been prepared from data (1) Shield (and ground) the lead -in lead -in. supplied by courtesy of Westinghouse Elec- where it passes within 10 feet of the lamp tric & bf fg. Co., Lamp Division. or install a noise -reducing antenna system. LINE FEEDBACK (2) Provide a good ground for the radio. If noise energy is allowed to enter the Watch for Part III, the concluding install- If the radio is of the A.C. -D.C. type, an ex- power lines from the lamp, it may feed ment, of this series of important articles on ground is not required because the Fluorescent Lighting from the Serviceman's ternal *Also see "How to Make a Modern Interference Locator." chassis is usually connected to one side of RadioCraft. January, 1941. -Editor viewpoint.

OPERATING NOTES BOOK REVIEWS

1111111111111111111111111 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 1 11111111 I I I I I I I I I 1 1111111111111111111111 . . . 1 s-T: DET. I;:? I.F. PHOTOTUBES (1940). Published by RCA Mfg. 6A8 61(7 Co., Inc. Size 8% x 11 ins, soft paper cover, .... STEWART- WARNER R136 illustrated, 16 pages. (Single copies available d e Have just finished repairing a Stewart - gratis.) Warner R136 which faded badly and came In " Phototubes," are given detailed descrip- back with a bang. After replacing the 110,- tions and diagrams for the use of phototubes in light-operated relays, for light measurements. 000 -ohm '/4 -watt, and 260,000 -ohm 14 -watt HIFI resistors, the trouble entirely cleared up. and in sound reproduction. Commercial types SCVID/THEROL of one manufacture are illustrated, and working This may aid some Servicemen. CHANGES diagrams complete with electrical values and A. M. HORATER, ADDED design data are given. This booklet is a valuable Bridgeport, Conn. working manual for the electronic specialist and experimenters. AF ÁMé{,MYFqTÉR --- MEASURED- GR,PRtNRNs RCA V -130, HF -I, HF -2: WESTING- IMEG. ñ/JSwITS (STRONG ST,NAI, PHOTO RELAYS. THEIR THEORY AND AP- (1940), by F. H. HOUSE WR -370 .01. 05 .L OA7.MEG. PLICATION Shepard, Jr. MF. by John M. Coffeen. Size 6 x 9 ins.. A rather puzzling and unusual case was ""T MF.Z 30 OHMS 165 OHMS Copyright recently encountered, where the receiver paper cover, well illustrated, 28 pages. Price, 25c. 2.2 The author, n consulting engineer on elec- would cut off if a certain pushbutton set for ..MEGS _ BIAS GT.Pa.e* TRANS. tronic applications and formerly industrial an especially strong signal were pressed. .- WESTINGHOUSE WR -370 electronic application engineer :n one of the This very strong signal, or any heavy burst A.V.C. RCA HF -1, HF -2, U -130^ largest radio companies, has prepared "Photo of static, would temporarily disable the set. OET. Relays, Their Theory and Application," with a It was found that by removing the 1st I.F. view to presenting a description, of photoelectric tube's grid connection, or reducing gain by shown. The 2 -pole, double -throw switch is a devices, graduated from the elements of the sub- using a shorter antenna, or turning the set changeover from normal to high fidelity ject to the eventual conclusion of practical appli- off and on, would restore operation. A band -pass. Apparently the fixed -bias 6K7 cations. vacuum voltmeter the voltages, Essentially practical in its treatment. this book -tube indicated that drew grid current with high input presents a compilation of valuable information grid voltage of the 2nd I.F. 6K7 was -35 cutting off. No further trouble was had when on the use of photocells, exciter systems, and volts. Removing the 1st I.F. tube reduced the change shown was made. The 6K7 then glow discharge tubes. gain and the -35 changed to -3. The was A.V.C.-controlled. Chapter I, Photoelectric Phenomena; Chap. II, changes shown in the diagram were made, WILLARD MOODY, Amplifiers; Chap. III, Glow Discharge Tubes: breaking the lead at X and using the parts New York, N. Y. Chap. IV, Light Sources; Chap. V, Applications. RADIO -CRAFT for MARCH, 1941 525 SERVICING

Radio Service Data Sheet 302

NATIONAL UNION MODEL W -2 5 -Tube Superhet.: 110 -V. A.C. /D.C.; Automatic Volume Control; Tuning Range 528 to 1,730 kc.; Average Sensitivity 35 Microvolts (for 0.05 -Watt Output); Power Output 0.8 -Watt, Undistorted; Power Consumption 28 Watts; Built -in Loop Antenna. 125A7GT 12SWIGT 125QIGT AS 500 35L6GT 1ST- DETECTOR I.F. 2ND: DETECTOR. READ MMF OUTPUT 8. OSCILLATOR / A.V.C.6 IST. A.F. WITH 500.000 OHM METER .O1- 95V MF 15V. SUBJECT lOOV. LOOP ANTENNA VARIATION IOCV. 100V OHMS VOICE COIL

15T 2ND I.FT I.F.T. r- rdf1 I I Q r/ C3 1C7 go iC9f e MÉG - 0.5- á ÇIO Li MEG. YELLOW b cal I I 1 20 °o ó rd Me I oe.k._ I 5 OM ) MEGS. _ r1.6- I L----- L_ _i J ÓM, CONNEC- OHMS 23.1 21.9 HUM - TIONS OHMS 21.9'X194 191 OHMS OHMS OHMS BUCK E%TR OHMS RNAL COIL ANTENNA 2 MEGS. GÁOÚÑO 0.1- MF 110 OHMS 05- MF 50.000 /OHMS MEG. -LT CHASSIS MF GROUND NOT T EXTERNAL 2-GANG b.s- CONDENSER 50 MEG.. (1) VOLUME MMF. r -i CONTROL c IosuLLATOR IJCOIL VOLTAGES AT SOCKETS FOR II V. A.C. LINE. CZ 4 ALL VOLTAGES BETWEEN o SOCKET 3525GT _ (INDICATED BY X). E CEPT RECTIFIER 0 . 4 - 1 HEATERS. OHM I a I OHMS 20 BOTTOM VIEW 125I1(1GT - 35LL6GT 35Z5GT 111V 25 I OF OHMS !(EACH) OSCILLATOR COIL d X 12507GT 125A7GT t OHMS a REDS+ + 12V 12V. 12v 35V, GREEN 0.25- A.C. A.C. A.C. A.C. 9V.,A.C. Á.C2 117V..A.C. MEG. 309 0 1 OHMS. TO.1- SPEAKER MF. FIELD

C Arr 0.25 «DIAL A.C. \ ® OFF OR O.C. MR. SWITCH LAMP I. F..456 KC.N Complete schematic diagram of the National Union Model W -21 Stube, /D.C. Loop A.C. TOP Antenna Receiver. 1.F. -456 kc. VIEW 2ND I.F. ALIGNMENT PROCEDURE ANTENNA ANTENNA TRANSFORMER The following equipment is required for aligning: TRIMMER SECTION Signal generator which will provide an accurately calibrated signal at the test cl OSCILLATOR frequencies as listed. SECTION CZ Output indicating meter; non -metallic screwdriver. OSCILLATOR Dummy antenna-0.1-mf. and 200 mmf. T R Volume control- Maximum for all adjustments. Allow chassis and signal generator to "heat up" for several minutes. Connect ground post of signal generator to "B-" (12SK7GT -prong No. 3) in chassis. SIGNAL GENERATOR ADJUST TRIMMERS FREQUENCY CONNECTION DUMMY CONDENSER TO MAXIMUM 1.I'ST I F. SETTING AT RADIO SET ANTENNA . SETTING (See trimmer illustration) TRANSFORMER 466 KC. Signal grid 0.1 -mf. Turn rotor to full open It I.F. (C7 and Cs) of 1st -det. 2nd I.F. (C9 and C10) Sketch showi g locations of main components and Connect at trimmers. stator of large gang section. 1,780 KC. Antenna clip 200 mmf. Turn rotor to full open Oscillator (C2) 1,500 KC. Antenna clip 200 mmf. Turn rotor to max. output Antenna (C9) NOTE -To obtain dial scale calibration, tune -in an 800 kc. signal. The pointer should be at the 800 kc. mark on the dial. If it is not, first remove the celluloid crystal by taking out the 4 buttons at the corner. Hold the tuning knob and shift the pointer to the 800 kc. mark. Caution The metal chassis is connected to one side of the line through a 0.2 -mf. condenser. Both A.C. and D.C. power lines are generally grounded on one side. If the side of the line not connected to the metal chassis through this condenser is grounded and the metal chassis comes in contact with an external ground, this condenser will be connected across the line and there will be an increase in hum. Therefore, in any service work on the chassis, keep it on a wood or other insulated surface to avoid contacts with ground. The person working on the set should avoid getting in contact with any ground. National Union Model W -2 Receiver.

526 RADIO -CRAFT for MARCH, 1941 HERE'S A BIG SAVING for Any Serviceman Who Makes Frequent Volume Control Replacements

WHAT IS IT? HOW WILL I KNOW WHAT WHAT ABOUT TAP -IN SHAFTS ? This IRC Master Radiotrician's Control CONTROLS TO USE ? IRC Tap -in Shafts make controls easier Kit, factory packed with 18 Type D Included free with your Cabinet is the to install in a crowded chassis by obviat- Universal Controls, 6 switches and 5 latest IRC Volume Control Guide. This ing the necessity for removing other extra shafts of special design (1) Enables indicates exactly what controls to use parts. They won't pull or vibrate loose. A variety of special shafts you to give better, faster service; (2) for practically all sets you may be enables you to make the 18 Controls handle an amazing Saves time and cost by eliminating fre- called upon to repair. quent need for ordering special con- variety of jobs, standard and special. trols; (3) Avoids frequent trips to your WHAT ABOUT OBSOLESCENCE? WHY HURRY? jobber; and (4) Helps systematize your The only things that could become obso- shop by supplying a good -looking con- Well, why postpone getting your Cabi- lete are the shafts and, as fast as new net and starting to collect dividends on tainer that enables you to tell at a glance shaft styles are required, IRC will have just what controls should be re- ordered. a good -paying investment? And don't them -of Tap -in design and constructed forget the re- of broadcast sta- You can actually meet from GO% to allocation 75% for use with the Type D Controls con- tion wave of your replacement needs with this Kit! lengths! Countless customers tained in your cabinet. will want you to re- adjust their pushbutton tuning. Carry your IRC Control CAN I AFFORD IT? ARE "MIDGET" CONTROLS Cabinet on these jobs. You'll be sur- No serviceman who uses controls fre- ANY GOOD? prised how many control replacement quently can afford to be without it. jobs you can also sell -and do the work You pay only the standard net price Don't call IRC Type D Universal Con- right then and there! of the controls, switches and shafts. trols "Midgets "! Actually, they are small - size replicas of the larger IRC Type CS The All -Metal Cabinet (worth $2.50) WHAT'S THE BAD NEWS? Controls only small controls that is included free. -the There is none! Your total investment is are exact mechanical reproductions a of only $14.97 net (List, $24.95). This manufacturer's larger controls. You can DOES IT CONTAIN THE equips you for the big majority of con- use them satisfactorily wherever Type trol replacements -and you get the CONTROLS I NEED? CS or old -style larger controls have been $2.50 Cabinet free. Many IRC jobbers The carefully selected control assortment used in the past. are glad to extend easy terms and other- is based on a nation -wide survey of ser- wise cooperate in making your. IRC vicemen's needs. It includes only popu- Control Kit actually pay for itself in the lar controls, widely universal in applica- time, money and effort it saves during tion, thanks to the Tap -in Shafts. If you the first few months you own it! find by experience, however, that, due to See it at your IRC jobber's today, or write some local predominance of certain sets, to us for folder. you would prefer any other IRC Type D Universal Controls, your jobber will INTERNATIONAL RESISTANCE COMPANY gladly make the exchange at any time. 401 North Broad St., Philadelphia, Pa.

TYPE D UNIVERSAL VOLUME CONTROLS WITH TAP -IN SHAFTS RADIO -CRAFT for MARCH, 1941 527 SERVICING

303 Radio Service Data Sheet CROSLEY "GLAMOUR- TONE" MODEL 26BB (Chassis Model 26) 8 -Tube A.C. Superhet.; 3 Bands (550 to 1,600 kc.; 1,600 to 5,000 kc.; 6 to 18 mc.); Broadcast -band Built -in Adjustable Loop Antenna; Stage of R.F.; Electric Pushbutton Tuning, Variable Bass Compensation; 12 -in. Speaker; Push -Pull Output; Tone Control; A.V.C. 6NTGT R.F. COI l9 `(¡} AMPLIFIER DUU,TOR AMPLIFIER LNn.roOIAL eGa MA MICA. len

M2.

LOCATIONS

OSCILLATOR

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..2?"- CONDENSER PUSHBUTTON UNIT o Ò I.F455KC. aB tvo _ BREED yPt 0`A Soocnev 6FeG ep.TPUT. Complete schematic diagram of the Crosley Model 26BB Chassis. The inset shows how to connect a phono pickup to the ci cuit. ALIGNMENT PROCEDURE Preliminary W 6lFíMPI1ER Po 11CREM sT áM2,x I

Trimmer - Adjust for maximum output. does 6. 900 ohms 5.3 mE Adjust for peak: gang CONNECT To (carbon) Ant. lead (Blue) Police Full open Pol. "OSC" not have to tune through TON AME signal. eOO RN RADNORMAL SOLINO IO RECEPTION 7. 900 ohms Pol. "ANT" Adjust for maximum output TERMINALS (carbon) Police Approx. 5.0 and Pol. "R.F.' h i 1 e rocking gang 'Dimmers through signal. 8. 900 ohms 18.9 Adjust for peak. Gang does (carbon) me* Ant. lead (Blue) S.W. Full open S.W. "OSC' not have to tune through signal. S.W. "ANT" LOW 9. 900 Ohms 18.0 mc. and "ILF." Adjust for maximum output sloe (carbon) Ant. lead (Blue) S.W. Approx. 18 Trimmer while rocking gang through signal. SOCKET -TO- CHASSIS V OLTAGES (117.5 V. LINE; 1,000 OHMS /VOLT METER, ON 500 V. SCALE) --.10% ALL CONHECTNO RES SHOULD 61170T -11.F. Amp. 3 4 5 6 7 8 PHONO 6A8GT NOTES TERMINALS -OSc. -Mod. 7 0 J.B. 6.3 B`COnPERTE° GSKT (REMPO -l.F. Amp. *Measure with A.C. Vm. 187 7T 0 130 6.3 7 6SQ7 -Der. A.V.C. -A.F. J.B. -Junction Block. 2.3 2.3 78 6.3 228.0 BETWEEN 8)5 -Phasc Invert. Max. power output, 117V. 0 0 110 6.3 0 TrentA",Al en-Output line. 8W.; power con- 120 0 J.B. 6.3 5.5 2 3 6F6- Output gumption, 117 V. lino, 220 23 0 J.B. 6.3 14.5 a 5Y30-Rectifier 85 W.; drop across speak- 220 23 0 J.B. 6.3 14.5 Connecting phono pickup to the Drop across speaker field 95 V . er field. 95 V. N 32 .0 J.B. 35 0 J.R. 318 3.11. 329.0 circuit.

S20 RAf)IEl_CRAFT f,.. kAAR9`N leal -SERVICING-

REPAIRING OPEN MAGNETIC COILS lhih eatable BREAN THE INNERMOST ACCESSIBLE TURN, AND TEST

USELESS IN SIOE LEAD aTi,,Ont SPEAKER WITH FIELD MORE than 3,000 SUPREME Model 504 COIL TEST FOR REMOVED Tube & Set Testers in constant and prof. CONTINUOUS CIRCUIT itable service prove it to be the unbeatable value in she test equipment field. There are many combination tube and set testers but SUPREME MODEL 504 WHEN magnetic coils burn out they in- only SUPREME offers those necessary and desirable advantages found in the Model 504. instrument is being set up from the roller variably open at the innermost layer. tube and Take SPEED, for instance. As a multimeter, chart. Tube base connections on future Electric clock coils, A.F. transformers 31 ranges and functions are at your finger tubes may change to any of the many hun- dynamic speaker coils can be made as serv- tips. Only two pin jacks and two rows of dreds of POSSIBLE arrangements and the iceable as ever by making contact with one quick acting push buttons are necessary to 504 will take care -of it- automatically- of the inner layers, inasmuch as the loss of give you complete control. Functional even unknown to the operator. That's why switches are on one side of the panel and the 504 has only one socket for each type the dead end will never be noticed. Magnetic range switches on the other side of the of tube -it is impossible to put a tube in coils will retain their form if one of the side panel. All that is necessary Is to press one the wrong socket. winding forms is removed. button on the left hand row for the function Speed in testing electrolytic condensers desired and one button on the right hand too. All electrolytic capacitors, including With a needle and tweezers, the innermost row for the range desired. accessible turn is broken and the end that high voltage filter capacitors and low volt- As a tube tester, merely rotate the smooth age -high capacity by -pass condensers are makes continuous circuit with the good part acting roller chart to the type desired and checked at their CORRECT WORKING of the coil is determined and unwound "follow the arrows." Leakage tests are equal- VOLTAGE on an English reading scale. enough to make contact with the dead end ly simple. With the same set -up just press These are just a few of the many PLUS on the right hand it is advisable to coat the one button after another advantages you have when you own a Model contact. Sometimes side of the panel. exposed of coil with collodion before 504 Tube A Set Tester. It is beautiful in side the Protection against OBSOLESCENCE is im- appearance, sturdily built, carries a year's the operation is attempted. Often it is easier portant. The Model 504 is built to be mod- free tube setting service, and best of all, it to remove the pasteboard tubing at the cen- ern today, to stay modern tomorrow. It is EASY TO OWN. If you can afford a ter of the coil, and pull out the exposed wire provides for all filament voltages from 1.4 telephone or if you can afford your ciga- until the break is discovered. volts to the full line voltage, of course, but rettes, you can afford the Modal 504. This much more than that-it is the only insfru- complete laboratory, combining a 7 -way C. ELROY, ment having the PATENTED DOUBLE FLOAT- tube tester, a 31 -range set tester and a Philadelphia, Pa. ING FILAMENT RETURN SELECTOR SYSTEM complete condenser analyzer, costs you no which automatically re- connects every tube more than 18c a day on the world's easiest LOCATING "OPENS" IN socket to the proper arrangement while the installment terms.

VOICE COILS THE MODEL 543 is one of those rare values THE MODEL 542 is a regular little pocket laboratory with five multimeter functions in a completely self -contained multimeter. including: AC VOLTS, DECIBELS, DC VOLTS A single rotary switch provides automatic DC MILLIAMPERES, and OHMS -MEGOHMS. operation of the four basic functions, The unit is complete in every respect requiring no external batteries for the ohms and AC VOLTS, DC OHMS, MILLIAMPERES, megohms ranges. A full size 3" DC VOLTS at 1000 ohms per volt meter with a sensitivity of 5000 standard sensitivity. This handy ohms per volt (200 microampere movement) indicates little instrument uses a full the readings for 24 care. sire 3" meter and beauti- fully selected ranges This is a value that is ful bakelite case measur- not being over- ing only 3 "s5)í "s2 ". looked by those who desire an This is truly a u1 tr a portable I WOULD like to take this opportunity of tester that will fit instrument that contributing a small time- and trouble - your pocket and possesses the accuracy and saving wrinkle. your pockt- utility of the This has to do with locating an open - book. larger testers. circuit in the voice coil or voice coil leads of a dynamic speaker, particularly those cones SUPREME MODEL SUPREME MODEL glued to the speaker frame or those with 543 542 wires interwoven with the spider support. MULTIMETER MULTIMETER This open can be determined by a check 5LIFRE111 of continuity but the exact location of the SUPREME INSTRUMENTS CORP. break usually means pulling the cone off GREENWOOD. MISSISSIPPI. U. S. A. the frame and then tracing the wire to the break. Now here's the kink. Place a 60 -watt lamp in series with the voice coil and 110 ASSURE YOURSELF OF GREATER PROFITS BY DOING RADIO SERVICE JOBS volts, and as the cone is moved up and down MORE QUICKLY. USE GERNSBACK MANUALS. SEE PAGE 518. in the speaker, a spark will designate the exact break. In extreme cases a larger lamp UP TO may be necessary to provide a larger arc SAVE 50% but care must then be taken that the voice /DWEST coil is not left in the circuit too long as 5TUBEMRAD /O the wire is seldom large enough to carry I heavy current. VACTORY- 4 STANDARD EARLE B. KIMBLE, TO - YO u TYPES of Amperite Regulators replace Service Manager for PUT THIS CHASSIS III over ZOO types of Pudney Bros., YOUR PRESENT CABINET AC-DC Ballast Tubes now in use.... Has London, Ontario, Canada Puls-BUT patented automatic starting resistor. TUNING FOREIGN RECEPTION OIBECT UP TO 51.00 Liberal trade -io allowance List ONLY on new models shown WRITE FOR REPLACEMENT CHART "S" in FREE catalog -from 6 to $251 Amperite Co. 5E1 Broadway, N. Y. C. NEXT MONTH: IK tubes -up to s bands- including automatic record- TRADE -IN Part I of the CLASSIFIED RADIO DIRECTORY 11995 changing radio phonos ... AUOWYMKE completely revised. Home Recorder, tc) Reserve your copy at COMPLETE User- Agents Warned, EASY reams your local newsdealer today. (See listing of emASS,5 N /rM rasa MIDWEST RADIO CORPORATION classifications, by months, on page 574.) INAKER oser. OHIO NM 12 CC AMPERITE

RADIO -CRAFT for MARCH, I 9 4 I 529 F. M. r"

O O 8 400 N MEASURED 7 40 350 ó COMPUTED, uì z6 COMPUTED 300 4 .9 5 W MEASURED' 2 250 COMPUTED V O J 4 Z O 4 0 04 ú200 0 2 w 4 '/ ¢ MEASURED a z 3 150 f o z J w NET 1ST 4 - o r 2 CONVERTER ANTENNA GAIN Q 100 4 COIL I- 1ST GAIN 2ND. TOTAL CONVERTER CONVERTER R. F. INPUT INPUT 50 GAIN IMPEDANCES !MN DANCES

I I O O L o 42 44 46 48 50 52 42 44 46 48 50 23 24 25 26 27 28 23 24 25 26 27 28 42 44 46 48 50 FREQUENCY - MC. FREQUENCY -MC. FREQUENCY- MC. FREQUENCY -MC. FREQUENCY -MC FIG.2 FIG.3 FIG.4 FIG.5 FIG.6 RECENT IMPROVEMENTS IN F.M. RECEIVER DESIGN

vi v2 By special arrangement with the Engineering 23.15 - 42-50 4.3 Department of the Radio Manufacturers' Asso- MO. 2MC.5 eywt MC ciation an engineer here analyzes new develop- 1 `\ ments in Frequency Modulation embodied in a late -model F.M. set.

SOLVING J. A. WORCESTER, JR. r f Tl fn f -F V3 56.+ 8+' 4 The G.E. model feedback through the plate -to -grid capacity JFM -90 is an F.M. de- f-FeFL "double superhet." utilis- of the tubes themselves. Formulas for 18.85 - ing only 1 oscillator. termining the maximum gain of single and 2M85 fl-fo F ',SIGNAL FREQUENCY multi -stage amplifiers before oscillation AIII I.F. fo405CILLATQR FREQUENCY from plate -to -grid tube capacity occurs have FIG.1 F2iot.F. been developed in the literature. Experi- ence indicates that 2 stages of intermediate frequency amplification prior to the limiter NOW that the Federal Communications mately 4 volts r.m.s., is required for 20 is thus are capable of supplying all the amplifica- Commission has permitted Frequency db. (or 10 to 1) noise reduction. It tion that can be obtained with stability. The Modulation on a nation -wide commer- seen that a minimum voltage gain of 4,000,- input theoretical maximum stage gain of such cial basis, it is important that certain 000 times is required to the limiter an amplifier is given by the equation improvements be made in F.M. receiver de- and since a limiter amplification of at least sign, from 2 important standpoints: 5 is required for adequate deviation sensi- (1) to ade- tivity, the required total voltage gain, ex- Gain - Greater sensitivity, permit 2>ccff quate quieting on all signal inputs down to clusive of audio amplification is 20,000,000 the ultimate limit imposed by receiver tube times. where gm is the mutual conductance of the tube noise; and, The on the voltage gain that limitations c is the grid -to -plate capacity of (2) More satisfactory quieting, by effect- can be realized at the intermediate frequen- ing better limiter operation. the tube cy will be investigated followed by a study and f is the intermediate frequency Both of these receiver improvements are involved in completing the of the difficulties It will be noted that the gain factor of necessary if the full noise-reducing proper- required total gain at the signal frequency. ties of F.M. are to be demonstrated and The the as incorporated the tube is g,,,/c. The 6SK7 is somewhat solution to problem superior to the 6AB7 (1853) in this respect effectively employed to permit the realiza- in the JFM -90 General Electric Frequency tion of satisfactory full -range reproduction. Editor) and hence will be considered in the com- Modulation Translator (or adapter- putations. The 6AC7 (1852) is will described. This, incidentally, slightly su- then be perior to both, but is not preferred due to SENSITIVITY is a complete frequency modulation receiver, its high cost and somewhat questionable for audio amplification and is de- It is proposed to initially the re- except reliability. consider signed to plug into the phono jack of an quirement of adequate sensitivity. It can receiver. The remaining factor influencing the am- be shown that the receiver inherent noise ordinary plification is the intermediate frequency. level is approximately 1 microvolt r.m.s., The amplification that can be realized at Since the voltage gain per stage decreases when referred to the antenna input. This is the intermediate frequency is, of course, as the square root of the intermediate fre- determined by computing the thermal agi- limited by feedback tending to cause in- quency it is desirable to employ as low a tation noise in the grid circuit and the stability or oscillation. Feedback may occur value as possible. It should not, however, shot noise in the plate circuit of the first in any or all of the ways enumerated. be reduced to the point where image diffi- tube. The shot noise is referred to the grid (a) Through common plate, screen -grid, culties are encountered. For a 42 -50 mega- circuit by dividing by the first tube gain. A.V.C., or heater circuits. cycle frequency modulation band, the in- These 2 noise voltages are then combined (b) Overall or stage -to -stage stray intermediate frequency should preferably by taking the square root of the sum of ductive coupling. equal or exceed 4 megacycles in order to pre- their squares. This total noise voltage is (c) Overall or stage -to -stage stray ca- clude the possibility of images occurring then referred to the antenna input by pacitative coupling. within the frequency range covered. Another dividing by the antenna coil gain. All of these feedback paths can be theo- factor to consider is direct I.F. pick -up. It can also be determined experimentally retically eliminated by filter networks and This renders 4 megacycles undesirable since that a signal at the limiter input of approxi- extensive shielding except the capacitative it would pick up the 80 -meter amateur 530 RADIO -CRAFT for MARCH. 1941 F.M.

The use of 2 type 6SJ7 tubes as in the G.E. model JFM -90 Frequency 30 IIIu Modulation receiver, af- F.M.I ECEIVVERu fords better latitude of grid -bias control and also increases the effec- "i tiveness against impulse E noise. 20 D IlUU1 LIMITING SIGNAL f N 1 50% AMPLITUDE 15 MODULATED AT L000 CYCLES

phone band. Many other considerations are 4,000,000 was necessary. This leaves a gain involved in the selection of a suitable inter- of 200 to be supplied by the R.F. amplifier. 0 mediate frequency which are outside the 0 10 100 1000 10,000 scope of this article. Many of these factors R.F. GAIN have been considered by the Radio Manu- 70r The antenna coil gain that can ordinarily Association and they have as a I I I facturers' be obtained can be computed with a fair CHANGE IN QUIETING result recommended an intermediate fre- SIGNAL INPUT FOR degree of accuracy from the formula 60 LP SENSITIVITY quency of 4.3 megacycles. REDUCTION Ant. coil gain =.707 z. 50 V zp EFFECTIVE I.F. GAIN With this as a basis it is found that a where Z. is the equivalent secondary 40 theoretical I.F. gain of 122 per stage is pos- impedance ORDINARY 2 Zp is the primary transmission sible. This figure is, however, subject to 30 1ORECEEIIVER revisions. line impedance of 100 ohms. The first of these is a factor of 2 required The factor of .707 is necessary since the 20 to prevent oscillation during the aligning reactance in the primary circuit is not nor- Z, is represented by the process. This assumes the use of critically - mally tuned out. 10 coupled, 2 -coil transformers and comes about parallel combination of the tuned circuit JFM 90 impedance and the input impedance of the from the fact that until tuned to the same o frequency the individual circuits of each tube. At 46 megacycles, the former is about 0 1 2 3 4 5 6 transformer have approximately twice their 16,600 ohms with a well -designed antenna FIG.9 SENSITIVITY REDUCTION FACTOR normal impedance and hence represent a coil and the latter about 6,650 ohms for a a net im- +10 condition much more susceptible to oscilla- 6AB7 tube. This gives secondary OSCILLATOR pedance of 4,600 ohms. tion. This then reduces the theoretical gain +5 to 61 per stage. Hence I-u; The second revision is to provide some Ant. coil gain =.707 707 X 6.8 =4.8 LL >. 0 factor in tubes, in- 1 4100 = EMI= safety for variations (Y ductances, line voltage, power transformers, 200 O rectifier drops and tolerances in other corn - The required R.F. gain is then =41.6 Y -5 ponents. The difficulty in obtaining useful 4.8 information from this formula lies in the The theoretical voltage gain of a single - -10 10 15 '30 60 120 of second factor. sources of 0 5 proper evaluation this stage R.F. amplifier when all FI G.10 TIME -MINUTES Indications are that it should be at least 2, feedback except that due to plate -to -grid thus resulting in a theoretical stable gain tube capacity have been eliminated can be +20 per stage of approximately 30. Hence, the computed in a similar manner to that pre- gain of the I.F. amplifier prior to the limiter viously employed for the I.F. amplifier. The +15 is 900 exclusive of the converter gain. a single -stage amplifier is DISCRIMINATOR about formula for CURVE The converter voltage gain is normally given by +10 included as I.F. amplification, but since the converter input represents essentially zero G.,.= I +5 impedance to I.F. it is not involved in sta- act bility considerations. It is obvious, therefore, G.,= Mutual conductance of tube= 0 FREQUENCY that the converter gain should be made as 5,000 X 10-e DEVIATION large as possible. This indicates the use of Grid -to -plate capacity of tube= c= 5 a high -g,,, pentode such as the 6AB7. Oper- .015 X 10 -" ated under suitable conditions as a converter f =Radio frequency =60 X 10--e this tube will provide about 1.25 times the A 6AB7 tube is assumed in this instance 10 gain of a 6SK7 operated as an amplifier. since the computed gain can not be readily Thus the converter voltage gain should be obtained with the lower gm, 6SK7, tube. A IS about 37.5 providing a total theoretical I.F. frequency of 50 megacycles is assumed since voltage gain of 33,800. the highest frequency would be most sus- -20 -150 -100 -50 0 +50 +100 +150 It should be emphasized at this point that ceptible to oscillation from this feedback FIG.11 the above voltage gain figure assumes that source, therefore all sources of feedback except that through 5,000 the plate -to -grid capacity of the tubes have Gain= = V2,120 =46 Y X .015 x been eliminated. This is never entirely true 3.14 50 especially when an additional I.F. ampli- As in the case with the I.F. amplifier this fication of 5 exists subsequent to the limiter. figure is subject to revision. There are no Practical experience dictates that I.F. volt- coupled circuits in the R.F. amplifier but age gains at 4.3 megacycles appreciably in a reduction in amplification is necessary excess of 15,000 to the limiter input are to take account of variations in tubes and decidedly risky from a production stand- other components, variations in line voltage, point. It is possible that receivers made on etc., as enumerated previously. a custom -built basis could be designed with As before, the factor should be at least a total I.F. voltage gain lying somewhere 2 to prevent manufacturing and field diffi- between the theoretical 33,800 and the maxi- culties. This reduces the theoretical gain to mum practical production value of 15,000. 23. Again, it should be emphasized that this Suppose for the sake of argument that the gain figure assumes that all sources of feed- maximum I.F. voltage gain permissible back except plate -to -grid tube feedback -100 0 +100 +200 +300 ahead of the limiter is 20,000. We previously have been eliminated. In an R.F. amplifier FIG.12. FREQUENCY OEVIATION have found that a total amplification of it is even more difficult to approach this

RADIO -CRAFT for MARCH, I 9 4 I 531 F. M.

condition. The actual plate -to -grid capacity megacycles, and the oscillator from 18.85 to is considerably enhanced by the capacity 22.85 megacycles. YOU'RE THE DOCTOR between the antenna and R.F. sections of The oscillator voltage is inductively the gang condenser Z.3 well as by the leads coupled to the grid of the first tube V1. Al- associated with the same. These leads also . a a and you can prove it! ternatively this coupling may be accom- provide inductive coupling which is difficult plished capacitatively. This produces by to entirely eliminate. Indications are that heterodyne action a signal to which the plate even with considerable shielding the effec- circuit is tuned. The tube also provides a tive plate -to -grid capacity is more than gain of approximate unity for the oscillator doubled by these external contributing frequency. Accordingly, oscillator voltage sources. An an approximation, therefore, we is also applied to the grid of V2. This can assume that the practical stable gain operates as a 2nd converter and produces is reduced to a value of not more than 10. in its plate circuit the I.F. of 4.3 mega- The realizable gain is reduced still fur- cycles. ther by an additional source of feedback To illustrate the action by an example in the gang condenser of the conventional consider the signal frequency of 42 mega- common rotor type. This results from com- cycles. The oscillator frequency of 18.85 mon impedance coupling in the ground - megacycles produces a new frequency in the returns and cannot be eliminated at these 1st converter plate circuit of 23.15 mega- frequencies by the expedient of employing cycles. This, in turn, beats with the oscilla- individual wipers for each gang section. In tor voltage on tube V2 producing the I.F. practice this feedback source reduces the of 4.3 megacycles. Formulas for determining stable R.F. tube gain obtainable to a value the oscillator frequency and 1st I.F. for of approximately 6. It is possible, of course, any signal and 2nd I.F. may be obtained to eliminate this latter source of feedback as follows: by using a gang condenser construction with insulated rotor sections and individual Let wipers insulated from the frame. This con- f= signal frequency, f, =1st I.F. struction is difficult, however, from the con- f,= oscillator frequency and F =2nd I.F. denser manufacturer's standpoint and re- then - sults in a considerable cost increase. f -fo =f, and f, -fo =F It is evident that the R.F. tube voltage f +F f -F gain of 6, which appears to be the highest solving f- and f,- obtainable with conventional gang construc- 2 2 tion without inviting production difficulties from oscillation, or the gain of 10 obtain- The performance of this circuit as used in able with a special gang rotor construc- the JFM -90 will now be considered in some HERE IS Sylvania's latest tion falls far short of the 41.5 figure we detail. Figure 2 indicates the computed in- sales -builder ... a radio chas- found necessary to complete our required put impedance of the 6AB7 tube and the sis chart that will discourage the gain. computed tuned circuit impedance both most optimistic home tinkerer. plotted against frequency. The input conductance of the 6AB7 was first com- More clearly than any other pro- DOUBLE SUPERHET. (2 oscillators) puted as an amplifier using the formula A possible solution that suggests itself is g = .3f + .065f'. This conductance was then motion piece we've ever seen, the double superheterodyne. In this circuit halved since the tube operated as a con- "What Is Wrong with Your Radio" the R.F. tube becomes the 1st converter verter has only half its normal mutual con- convinces your customer that only which may Lc designed to produce an I.F. ductance. The reciprocal was then taken to an expert can make radio repairs in the neighborhood of 10 megacycles. The obtain input impedance and the result original converter tube now heterodynes plotted. The tuned circuit impedance was ... and YOU'RE THE EXPERT. this 10 megacycle signal to the normal I.F. computed knowing the inductance to be of 4.3 megacycles. 0.45 -microhenry and the effective circuit Q Write Hygrade Sylvania Corp., It is thus seen that the oscillator section to be 120 with the primary loaded with 100 Dept. RC31, Emporium, Pa., for a of the 2nd converter operates at a fixed ohms. The net result of these 2 parallel free copy of this mailing piece .. . frequency while the oscillator of the 1st impedances is shown and is seen to be near- and for full information on the 25 converter must be ganged with the antenna ly constant at 7,000 ohms. other silent salesmen Sylvania offers tuning condenser in the usual manner to The antenna coil gain can now be cottt- produce the fixed 1st I.F. of 10 megacycles. puted in the manner previously discussed you either free, or at substantial Herein lies the main difficulty with this and the result is shown in Fig. 3. The actual savings. circuit. We have 1 variable oscillator and measured antenna coil gain is also plotted. 1 fixed oscillator whose fundamentals and The computed gain is nearly constant at harmonics produce innumerable beats, many 5.8 while the actual gain varies from 5.2 Sylvania's Silent Salesmen of which will produce I.F. signals. If these to 5.6. The agreement is seen to be reason- 1. Window Displays, 15. Service hints book- are than ably dummy tube cartons, lets spurious I.F. signals greater the close. It should be noted that the an- timely window 16. Technical manual equivalent of a 3 or 4 microvolt signal on tenna gain computed previously assuming streamers. etc. 17. Tube base charts the antenna they will seriously affect the the 6AB7 tube to be operated as an ampli- 2. Counter displays 18. Price cards usable sensitivity. It is generally possible fier was 4.8. The difference, of course, is due 19. Sylvania News 3. Electric Clock signs to substantially eliminate this difficulty by to the higher input impedance of the tube 4. Electric Window 20. Characteristics signs Sheets choosing the 1st I.F. so that none of the when operated as a converter. 21. Interchangeable tube of fixed oscillator fall within 5. Outdoor metal signs charts harmonics the The impedance of the 1st converter tuned 6. Window cards 22. Tube complement the frequency band covered; and by employ- circuit and the 6AB7 2nd converter input 7. Personalized postal books ing rather exhaustive shielding and isolation impedance are plotted against the 1st I.F. carde 23. Floor model cabinet of the fixed oscillator to minimize second 8. Imprinted match 24. Large and small and are shown in Fig. 4. The net equivalent books service carrying kits and higher order heterodyne effects. The of these 2 impedances is plotted and seems 9. Imprinted tube 25. Customer card in- complication involved in this latter precau- to be approximately constant at 15,000 ohms. dex ales stickers tion unfortunately prevents its utilization The first converter gain can then be com- 10. Business cards 26. Service Garments in the small chassis space permitted by the 11. Doorknob hangers 27. 3 -in -1 business puted assuming the ge of the 1st converter forms usual commercial receiver designs. to be 2,500 micromhos. This is shown in 12. Newspaper mats 28. Job record cards 13. Store stationery (with customer re- Fig. 5 along with the amplification as ac- 14. Billheads ceipt) DOUBLE SUPERHET. ( I oscillator) tually measured. It is again seen that the This brings us to the variation of the agreement is good, the computed voltage double superheterodyne circuit employed in gain varying from 36 to 38 and the actual the JFM -90 which utilizes only 1 oscillator. voltage gain from 34 to 42.5. SYLVANIA Figure 1 is a schematic diagram of the The total voltage gain ahead of the 2nd circuit employed. The tuning condensers for converter is shown in Fig. 6. The computed SET -TESTED RADIO TUBES antenna, R.F., and oscillator are ganged gain is seen to vary from 210 24_ and together as usual. The antenna circuit tunes the actual gain varies from 182 to 228. It Also makers of Hygrade Lamp Bulbs, Hygrade Fluorescent Lamps, and Miralume Fluorescent the F.M. band from 42 to 50 megacycles, is readily evident, from this, that we can Light Fixtures. the R.F. circuit tunes from 23.15 to 27.15 essentially realize the amplification of 200 532 RADIO -CRAFT for MARCH, 1941 TWNWWWWNTNNI F. M. which we found necessary to provide the total required voltage gain of 4,000,000 prior BLOWER OUTER to the limiter input. AS CHIEF CONDENSER Having disposed of the problem of ob- OTTO OOMPH WAS A FLOPPEROO taining sufficient voltage gain to produce a Ever since Otto Oomph In a massive oven, dozens signal large enough to provide adequate was a boy, he suffered from of units were undergoing limiting on any input down to the actual a strange disease. Smasho- life tests at'200° F. Else - phobia, the doctor called it where, Television condensers receiver noise level we are in a position to -the horror of breaking were telling their story under undertake the 2nd required improvement things -but there was noth- 3,000 to 10,000 volts of DC; of more satisfactory limiting. ing to be done about it. tiny electric razor condens- When he broke a Christ- ers were getting the equiv- mas tree ornament one J L alent of 14 years of the SINGLE -TUBE LIMITER year, poor Otto cried for hardest kind of use; and, The limiter used in previously available two days. When he grew almost every minute some up, he wouldn't shoot as condenser gave up the ghost production receivers is the conventional "sin- fact was added gle tube grid-bias" type. As is well known, much as a clay pigeon and and another even the thought of dent- to.the science of construct- this merely consists of a grid condenser - ing the fender of his car ing condensers that excel in resistor combination in conjunction, with a would make him sick. the rough and tumble usage sharp cut -off pentode such as the 6SJ7. The Eventually, however, of the field. - limiter also generally operates at reduced Otto became an electrical expert. That got "I can't stand it-4 can't stand it," wailed screen -grid voltage to provide as small an him a job in the Sprague laboratories and Otto at last, weeping over the remains of active -grid voltage swing as possible. By Otto was really happy for the first time - an 8 mfd. 450 V. Atom midget dry elec- "active -grid voltage swing" is meant that is, until someone made him Chief Con- trolytic. grid denser Blower Outer in the Test Division. "Gosh, Otto," consoled an engineer. "What voltage variation active in changing plate Now, voltage in the electric chair at Sing you worrying about? That condenser is only current. Sing is 1,200 volts. In contrast, controllable rated at 450 V. We had to smack it with a The control -grid bias limiter though sim- AC voltages in the Sprague lab run as high surge of almost 700 V. before it went. ". as 7,200 (and much higher in the special "Sure," sobbed Otto. "But I can't stand ple in appearance is somewhat complicated things. ain't fair Its is high voltage lab) for here is where Sprague this business of busting it in operation. purpose, of course, to condensers really get "the works." They are to treat such swell condensers so downright remove amplitude modulation. In order to torn apart, blown apart, tortured and blast- mean. It makes me sick. I -I wanna, quit. describe its operation, first assume a con- ed, not only to see how good they are, but And quit Otto did. stant- amplitude signal applied to the limiter how to make 'em even better. 'Twas a year before we heard from him grid having a peak -to -peak amplitude sev- WHAM! Poor Otto jumped six feet when again and then he wrote: eral times the active voltage swing of the a can condenser, deliberately loaded with "On,' Bon: Maybe you think I was silly to gull MY -Flown lob. but it Just isn't my nature to bust things up. I'd tube. The positive peaks of this signal will supercharge to determine its break go home nights and dream about condensers on those then charge the condenser sufficiently to point, exploded in a cage. torture racks -the finest condensers in the world lust BAM! SNAPPETY- CRACK. Otto shiv- waiting to be blown up even if it took all the power in provide the required negative bias which ered as another condenser gave its life under Massachusetts to do it. is "But all's well that ends well. I'm in the radio service nearly equal to the peak amplitude of 4,000 volts of DC:.. . business and doing fine. I use Sprague Condensers- the signal. Since the condenser discharges and boy, are they real! Not a blow -uul in a carload. CLICKETY -CLICK in monotonous regu- No failures from moisture -or anything else In fact. I relatively slowly through the grid resistor larity as AC refrigerator motor starting e l:re it's largely because of the work you guys are condensers were switched on and doing back there in the lab, but I still say blowing up which may have a value from 50,000 to tortuously condensers is a helluva lob for a sensitive man Ilke me. 250,000 ohms and charges rapidly through off 150 times an hour. Love and Kisses. SIZZ- SIZZLE and SISS as vapor streams OTTO OOMPH" the tube grid resistance which is of the mois- SPRAGUE PRODUCTS COMPANY 2,000 ohms, it is played on condensers to prove their order of only evident that ture -proof ability. North Adams, Mass. only a small portion of the signal is required to drive positive and draw grid current. The smaller the grid leak the more to permit the desired balance for normal positive the signal has to go since the con- amplitude modulation as previously ex- denser then discharges more rapidly. plained which requires grid resistance of It is seen that with a limiter operating in the order of 125,000 to 200,000 ohms. this manner the plate current flows in pulses produced by part of each positive grid cycle. CASCADE LIMITER The remaining part of the positive grid cycle as well as the entire negative half These difficulties are essentially removed by the use of a cascade limiter. Figure 7 You'll save money. Here's drives the grid beyond cut -off. Now assume you need to build your own versa- in shows the cascade limiter employed in the everything that some amplitude modulation the form tile, modern multitester typical Lafay- an in signal amplitude occurs. JFM -90. It will be noted that 2 6SJ7 limiter -at of increase ette low prices! Rush your theck or money It is evident that the grid will be driven tubes are employed in cascade utilizing re- more positive by this increase in signal sistance coupling between the stages. This order today! Ask for FREE 196 page Lafay- and the plate current will tend to increase. produces a gain in the 1st limiter of ap- ette Catalog No. 82 when you order. However, the plate circuit pulse also be- proximately 3. It will be noted, therefore, comes slimmer since a smaller percentage that the maximum signal that can be ap- LAFA200TE of the total positive grid cycle produces plied to the 2nd limiter is only 3 times the 0.200 active grid voltage swing of the 1st limiter. plate current. This tends to reduce the MICROAMPER If the active grid swings of the 2 tubes average plate current. The trick is to select FOUNDATION are equal, the 2nd limiter only has to handle K1054ó a value of grid resistor so that these 2 METER 1i547 a 3 -to -1 signal ratio. This permits the to 5000 effects:produce no net change in the funda- AC IS DC volts choice of a grid resistor which will provide ample s. m ,lliomP,s mental component of the plate pulse. The pares, ehm.. Cup - an excellent balance of increased e hem difficulty is, however, that this balance will peak cur- ocily and inductance only hold over a small input range. If a rent vs. reduced transit angle for all signal chmt. furnbhed. signal having 10 times or 1/10 the ampli- inputs. The grid resistor of the 1st limiter tude of the one considered is applied to is 50,000 ohms and picked to provide a short LAFAYETTE HARDWOOD CASE. Finely eei.hd$142 II the limiter this balance will no longer hold time constant and consequently good limit- Open-lace eo,.e ..Ah leather handle. 1(10530 I and a new value of grid resistor will have ing on impulse noise. . NSW YORK. M. T. to be found for each case. The large reduction of impulse noise in IN Leath A... CHICAGO. ILL. This is one of the major difficulties with the 1st limiter makes time constant con- WI W. ,eel,.. n.d. siderations for the 2nd limiter much less ATLANTA. GA. the single -tube grid bias limiter. The other 215 rwehtm Street cohcerns its operation on impulse noise for important, and the 2nd limiter grid resistor SOSTON. NASS. can be chosen substantially without regard MONT. M. T. which it is notoriously ineffective. This is g1 - - NtWARR. M. J. - L. I. -I - -- JAMAICA. due to the time constant of the grid con- to time constant. A value of 180,000 ohms LAFAYETTE RADIO CORP. denser - resistor combination which is too is chosen in this instance. On direct listening I Dept. 3C1 -901 W. Jackson Blvd., Chicago. III. ' slow to properly follow short -duration im- tests this 'cascade grid bias limiter has been I or 100 Sixth Avenue, New York, N. Y. pulse noises. The grid condenser can only found superior on impulse noises to the non - 1 I enclose S . Rusk my order. be reduced to a point where it begins to grid bias and direct -coupled limiters that seriously affect the sensitivity. In practice have been tested. Please rush FREE catalog. the grid condenser is reduced as much as The combination of greater sensitivity ' NAME ..__...... _...... ___.._.._.._...... ___. »..._.. »...... - ..... ». ' possible and then a severe compromise made and better limiting can be shown by a sin- by reducing the grid leak from 20,000 to gle curve showing the amount of limiting ADDRESS. 50,000 ohms. This is much too low a value in decibels 'plotted against signal input. LCITY------STATE - - J RADIO -CRAFT for MARCH, 1941 533 Figure 8 shows such a curve for the JFM -90 image frequency fixed at the same frequency receiver and also includes a curve for a as the 2nd I.F., namely 4.3 megacycles. Al- representative receiver of last year's pro- though this means that the 1st tuned circuit duction which employs an R.F. amplifier, 2 alone is effective in providing I.F. rejec- stage I.F., and single -tube grid bias limiter. tion a value of 800 is obtained in the JFM - The tremendous improvement in the new 90. It is felt that this is entirely adequate receiver on both counts is immediately from a commercial standpoint. evident. OSCILLATOR DRIFT "COMMERCIAL" SENSITIVITY The importance of good oscillator stability It will be noted that it requires approxi- requires no comment. This problem, normal- mately a 4- microvolt signal to produce 20 ly quite serious in an F.M. receiver, has db. quieting. This is due to the presence of been alleviated in the JFM -90 by the re- peaks of random noise which have about duced frequency at which the oscillator op- 4 times the r.m.s. amplitude of 1µv. The ques- erates, namely, 18.85 to 22.85 megacycles. tion might be raised of whether a 4- micro- The oscillator circuit is shown on the sche- volt sensitivity might not have been just as matic diagram, Fig. 1. good as the 1- microvolt value we were en- To further reduce drift a 7A4 loctal -type deavoring to obtain. It is felt that this lat- tube is employed using a mica -filled Bake- ter sensitivity is desirable to take care of lite socket. Hard - rubber stator insulation is the variations of sensitivity in production used on the gang condenser, and the oscilla- and possible later misalignment. Manufac- tor coil is wound on a ceramic form. Trim- turing final test limits are generally about ming is accomplished with an air condenser 3 times that of a representative normal re- and the grid condenser is of the zero - ceiver and additional reductions in sensi- temperature- coefficient ceramic type. The re- tivity are likely to occur in storage, ship- maining drift is substantially removed with ment and normal use. It is thus evident that a shunt ceramic condenser having a suitable some receivers in actual use will be deficient negative coefficient. The resulting drift is in sensitivity possibly by a factor of 3 to 5 indicated in Fig. 10. times. Drift precautions are maintained through- The effect of such sensitivity loss on quiet- out the remainder of the circuit. The I.F. ing signal input was determined for the trimmers are of a composite construction JFM -90 by adding adjustable bias to the having the major portion of the capacity I.F. amplifier to reduce the I.F. sensitivity in a fixed silver -mica unit and only that by the desired amounts and then the quiet- necessary to compensate for manufacturing ing signal input measured. The result of and tube tolerances in the adjustable unit. these measurements is shown in Fig. 9 and All R.F. and I.F. coils throughout the trans- for comparison a similar measurement was lator are wound on ceramic forms. The dis- made on an ordinary type of F.M. receiver criminator has wider peak separation than requiring a quieting signal input of 10 mi- in some previous designs to further allevi- crovolts. It will be noted that the required ate the effects of drift and to provide less quieting input does not change for the critical tuning. The discriminator curve is JFM -90 with gain reductions of as much as shown in Fig. 11. 5 to 1 while that of the ordinary receiver The I.F. selectivity curve of the JFM -90 is MODEL 1600 -E increases in linear fashion. shown in Fig. 12. It will be noted that approximate critical coupling is employed with IMAGE REJECTION 75 Ice. deviation down about 2 times from DEALER NET PRICE '2 1100 It is obviously impossible in an article normal input. The I.F. system was some- DC scales of the instrument read: Vol- of this nature to cover in such detail all what over- designed to cope with the situa- tage 0- 10 -50. 250 -1000 (25,000 ohms the features of the JFM -90 translator. In tion existing until Jan. 1 where adjacent - per volt); 0- 1- 10 -50- 250 -500 milliam- view of the new type of superheterodyne channel operation of F.M. stations was peres; Resistance, low ohms, backup cir- circuit used a brief review of its perform- prevalent in the same locality. Eight tuned cuit, 1 to 500 high ohms, 20,000- ance as regards image rejection may be of circuits were provided in this connection by 200,000 ohms and 2 and 20 megohms. interest. making the first 2 transformers of 3 -coil Batteries included for all ranges but 20 In the usual double superheterodyne 2 construction. megohms. 221/2 'volt battery for that sets of images have to be considered, one Concluding, the writer wishes to express range can be mounted inside the tester differing from the signal by twice the 2nd his appreciation to Messrs L. M. Ewing and case; brackets provided. AC Voltage I.F. and the other differing by twice the W. W. Moe for the various performance data 0- 10 -50- 250 -1000 at 2000 ohms .per 1st I.F. In the common-oscillator double - prezented and to Mr. R. B. Dome whose lec- volt. A plug -in copper -oxide rectifier, superheterodyne circuit used in the JFM -90, ture material was utilized in the computa- easily replaced in case of overload, is however, the 1st I.F. is variable making the tions included in this article. used to obtain AC readings. Model 1600 -E, less case for mounting in panel. Dealer Net Price $21.00 In case with handle for portable use - Dealer Net Price $25.50 RECOLLECTIONS OF BROADCASTING'S EARLY DAYS MODEL 1620 Versatile was the word for a radioman going to pin a big, bright star right over This is a counter type, lever switch oper- back in the early days of the broadcasting your house. ") ated tube tester. Four business recalls announcer John B. Garn- . When mike fright was so common that "quick change" non - bling, for 15 years a familiar WOR voice. a famous actress "froze" and couldn't utter obsolescent features, John likes to remember: a word, and when in the midst of a com- including RED DOT ... When he was often announcer, engi- mercial program a speaker got so frightened Lifetime Guaranteed neer, newscaster, physical training instruc- she fainted in his arms. Instrument. Speed Roll tor, all in the space of an hour and a half. When he interviewed the late Queen Chart, New socket . When he used to go out on "remote" Marie in her boudoir in a special train en panel and Switching assignments to hotels and night clubs, with route to New York from Washington, D. C. Section can all be re- an amplifier under one arm, "B" batteries When he took two parts in WOR's first placed should unantici- under the other, a coil of wire on his neck, dramatic show, "Step on the Stairs," a mys- pated changes make it and huge batteries in his hands which tery thriller, announced and engineered as necessary. dripped acid on his Tuxedo pants. WOR had well. He would monitor the program, then Dealer Net Price only one set of remote broadcast equipment dash out for his lines, then rush back into $37.84 in those days, so John had to lug his load the control -room again. WRITE FOR CATALOG -SECTION 163 HARMON AVE. to as many as three places during a night. When most programs consisted of When he was pinch- hitting for "The either /and /or a pianist and singer, and the TRIPLETT ELECTRICAL INSTRUMENT CO. Man in the Moon," the first kiddie's broad- staff pianist used to do four consecutive caster ( "Little Sylvia of 999 Newark Ave- fifteen minute programs under four dif- Bluffton, Ohio nue has been a very good girl, so Sylvia I'm ferent names. 534 RADIO -CRAFT for MARCH, 1941 TEST INSTRUMENTS

A GENERAL UTILITY TESTER Eat Satvici zy Ll e tE.!ca 1)npIiancei Radio men looking for new fields to profitably explore, will do well to consider the possi- bilities afforded by Electrical Appliances, as Mr. Litt here capably shows. The design and use of an A.C. -D.C. "appliance tester ", measuring up to 100 amperes, 1,000 volts and 5,000 watts, and down to 1 /50th ohm, and especially devised for this service, is described in this article. Circuit features incorporated in the instrument are diagrammed and analyzed. SHEPHERD LITT

ADIO SERVICEMEN in recent years ment but with a half -wave rectifier across have been looking for newer equip- it. A current -limiting resistor is placed be- F ment so that fields associated with tween the half-wave rectifier and the meter. radio, which their knowledge of elec- This resistor determines the amount of tricity and radio covers, could be serviced. linearity of the A.C. scale. The higher this Appliance repairs, a field very close to radio resistance, the more linear the A.C. scale. repairing, has been sorely neglected. It is An 800 -ohm resistor is used in this instru- true that most radio Servicemen have fixed ment to give a fairly linear scale and at small defective equipment such as toasters the same time eliminate needle vibration. and electric irons. However the larger elec- The multiplier resistors are placed between trical appliances have been usually neglected. the source of voltage and the rectifier. This is not because the Servicemen do not Because of the amount of current taken know how to repair such appliances but by the rectifier, the A.C. sensitivity of the rather because of a lack -of suitable equip- meter is approximately 400 ohms /volt. This ment. With a simple tester such as described relatively low sensitivity is of no importance below, motors, electric ranges, heaters, irons, since most A.C. voltage readings are taken washers, sun lamps, vacuum cleaners, electric of low- impedance lines. Therefore the meter refrigerators and even air conditioning movement need not be as highly sensitive as equipment may be successfully serviced. for D.C. use. The A.C. ranges are taken Further, the cost of operation of these vari- from the lower deck of the 7 -point 2 -deck ous appliances may be easily computed and switch. Six voltage ranges are available, estimates given, all based on the prevailing viz., 0/1/10/50/100/500 /1,000 volts. This price per kilowatt -hour rate. allows a very wide range of voltage meas- Illustration of the completed General Utility Tester. The Utility Tester here described (see Fig. urements. (See Fig. 1.) 5 for circuit diagram) operates on simple ance a very simple ammeter can be had. electrical laws and is basically a multi -range AMMETER This resistor will have to be of high watts voltmeter reading both A.C. and D.C. By The ammeter circuit (Fig. 2) is also un- rating so that the high current passing taking each section of the instrument sep- It consists of a single shunt through it will not burn it out. The volt- of the in- conventional. arately, a better understanding across which a voltage drop is measured. meter across this resistor should have a strument can be had. The ordinary ammeter uses multiple resist- high resistance so that the amount of cur- ances placed across the meter movement it- rent drawn from the circuit will be small. D.C. VOLTMETER self. These resistances carry a large current The voltmeter section uses a simple volt- necessitating a switch with very large con- WATTS meter circuit known to every Serviceman. tacts which is impractical on ranges over 1 If the amount of current flowing through It consists of a 0 -1 ma. meter and a group ampere. The circuit used here eliminates the the circuit is multiplied by the voltage of series resistors to give the proper voltage need of a large switch since only a small across the circuit, watts or power consump- ranges. Six D.C. ranges are available, viz., amount of current flows through the switch tion results. Since this instrument contains 0/1/10/50 /100 /500 /1,000 volts. They are se- contacts. It makes use of the fact that the both a direct -reading voltmeter and an am- lected by 6 positions on a 2 -deck, 7- position voltage drop across a resistor rises in pro- meter, the watts drawn by any appliance rotary switch. The sensitivity of the meter portion to the current through that resistor, can easily be measured. (See Fig. 3.) The is 1,000 ohms /volt. (See Fig. 1.) in other words, Ohm's law. If this resistance scale of the instrument has all the necessary is made 1 ohm, the voltage drop across this computations on it, but since there is a A.C. VOLTMETER resistance will be equal to the current pass- power loss in the 1 -ohm resistor, this power The A.C. voltmeter is not so conventional. ing through the resistance. By connecting loss must be added to the scale reading to It makes use of the same 0 -1. ma. move- a multi -range voltmeter across this resist- indicate the power drawn.

0-1mA.4ANGE0 -- O-I.MA. 0 -I.MA. bOOn (100 ONMSI MULTI- i- 100 n. 100 JL RANGE 1 INT. RES. RECTIFIER VOLTMETER 0.9n / RECTIFIE0. (UNIVERSAL( tOp mA SNUNT IOn 800A. 4.C. I.000A / IO.00Dn. AC. SO,DOOA MEG. Ln 1 1 GANGED / 0'9 ,O 1 -MEG `- - ADJUST GA. L.MEG - 1 TIGLOwSMA. (A R 1 T L$V Iy / / r,000J1 I A -' PERVOLT 1 /11 /1 /MV TNROUGN - I i i OC. SOURCE LOAD CIRCUIT T '

/' 1 Qi O (iv,1A., I 10 50 100 500 1.000 -AMMETER- -HIGH -RANGE OHMMETER -= LO. A.) DC. ® AC (UNIVERSAL) O-1. MA. 1 10 50..100t500 (000 IOn MOLTMETE H VOLTMETER I.A. In LO A. V AC. (CALIBRATED / IN WATTS),V. / 6n I.n 1 Ip00n , NtTIÓIAIf f . ADJUST TO ) 1 1.SV. 5.:i --I- TILL LAMP 6A. - POWER PVÑC11ONS S (A l - +SUPPLY Q UO / - OO 0 OROA \ WATTS LOST HERE1 FLOWS (ZERO V LOAD THROUGH IS AT ,,5 R * VIA SOURCE EQUAL TO APPLIED J CIRCUIT COM VOLTAGE AT SOURCE f W O O t VONLY O 7.) `¡ RECEPTACLE -- D.C.ANDA C VOLTMETER- ® .- WATTMETER ^ ® -LOW- RANGEONMMETER- - COMPLETE UTILITY TESTER- RADIO -CRAFT for MARCH, 1941 535 vserown

TEST INSTRUMENTS

If a toaster is connected to the appliance tester and the meter scale reads 440 watts, BUILD and the applied voltage to this toaster is the RADIO CITY PRODUCTS CO. 110 volts, the sum total will be 550 watts drawn. Since the power loss in the resistor is equal to the voltage applied, then the ap- MULTI -RANGE plied voltage can easily be added to the scale for correct readings. This is true ir- TESTER respective of the line voltage used. An out- Complete Kit of parta as de- .99 let on the front panel of the tester facili- scribed 1 tates measuring the power in watts drawn Special sale on Radio City Products #446. and you'll enjoy building by any appliance having a standard plug as featured in December issue of RADIO -CRAFT, Complete Kit of á8.32 at its end. All other tests including the Parts your own test equipment watts drain of equipment not having stand- Both Kits now ready for Immediate delivery. ard plugs are made by inserting the test leads into the proper tip -jacks. The A.C. ADSON RADIO with 118077' Kits readings on the wattmeter are read the 201 Greenwich St., New York City same way as the D.C.; however, the accuracy Save money on on up -fo -the- minute fester in on A.C. will be slightly off if a large induc- few -hours just o spore lime. It's instructive, and tive load is in the circuit. This is due to the you'll gel a kick out of it. too. These RCP Kits out -of -phase relationship of the current and have every latest feature in test equipment. voltage. For ordinary work this can be dis- They're complete - no extras to buy! regarded. The cost of running equipment 110 VOLTS AC ANYWHERE can be computed by multiplying the power With KATOLIGHT. Furnish standard 60 -cycle drawn by the amount of time the appliance AC for operating sound truck equipment, MODEL L is used. This in turn is changed to kilowatt - AC radios, transmitters, flood lights. motors, 4IIK hours by dividing by 1,000 and then multi- moving picture projectors. etc. plying by the prevailing rate per kilowatt - SUPERTESTER hour. COMPLETE KIT

'., . OHMMETER $17.35 se The high -range ohmmeter (Fig. 4A) uses a conventional circuit and consists of a 1.5- SPEC FICATIONS volt drycell, a zero -adjusting resistor and a 0/10/100/250/1000 /5000 volts 100- milliampere meter. The 100 -ohm, zero DC; 0 /10 /100 /250/1000/5000 to 1 ma. movement is shunted by a 0.9 -ohm volts AC; 0/200 microamperes resistor to obtain the 100- milliampere range. DC; 0/ 10/ 100/1000 milliamperes By using this method, a value of 15 ohms DC; 0/1/10/25 amperes DC; appears in the centér of the scale and the 0/500 milliamperes AC; 0/2.5/5/ scale reads up to and including 3,000 ohms. 25 amperes AC; 0/400/40,000/4 This is more than enough for all appliance A complete line of light and power plants megohms: (40 mega with extra work. ranging up to 10,000 watts capacity. Also 6, 12 and 32 volt battery charging plants. Diesel battery); Db. meter, 5 ranges -IO The low -range ohmmeter (Fig. 4B) is un- plants, rotary converters, and frequency to +69; Capacity from .002 to I conventional as it consists of a 0 -1.0 volt changers. Inductance Mfd.; from .3 to 70 voltmeter across which a 1 -ohm resistor is List prices $50.00 and up Henries; (direct reading from placed. A current of 1 ampere or less is Jobben and Dealers Write for Latest Catalog charts); 41" square D'Arsonval passed through this 1 -ohm resistor and the meter; Hardwood carrying case; corresponding voltage drop is read. With Kato Engineering Co., Inc. All necessary parts. this method a center -scale reading of 1.5 ohms can be had. The useful range of this MANKATO. MINN., U.S.A. low -range ohmmeter is up to 300 ohms. A feature of this circuit is that 1/50 of an MODEL ohm is the first scale division and can easily 446K be read. This is a "must" as windings on transformers and motors often approach this value of resistance. ELEMENTARY This article has been prepared from data supplied by courtesy of Superior Instru- MULTITESTER $8.49 ments Co. COMPLETE KIT MATHEMATICS SPECIFICATIONS 0/5/50/250/500/2500 volts DC; EASY - SIMPLIFIED - PRACTICAL 0/1 /10/100/1000 milliamps DC; AGAIN, HEARING -AIDS 0 /IO amperes DC; 0 /10 HERE Is a book for the business man. the tech /100 /500/ Dear Editor: nldan and craftsman explain inp and answering 1000 volts AC: 0/500/100,000/1 every operation and meaning with Interpreting In the May, 1940, issue of your magazine Illustrations and examples. megohm; (will read as low as It is the key to a simple understanding of many ohm); Four Db. ranges, -8 to you have an article on hearing -aids in which Perplexing problems In daily life. I am very much interested, as I am very In clear, positive and definite language. the author +55; Output meter four ranges; pnnularlres and clarifies every subject and helps the hard of hearing (so- called "deaf "), and have reader to overcome any apparent difficulty In the study 3" square D'Arsonval meter: Wal- mathematics. a great deal of with hearing -aids as of nut finish case; All necessary parts. trouble A real home .tudtourse In mathematics for the I am classed in group 4 with 85% deafness. student or the man who enta to achieve proficiency YOU NEED a modern meter that or desires to brush -up on whis knowledge. I do not believe the circuits you have de- Entire Chapter on Special tests Television and FM sets, fluo- scribed will be strong enough for me, and - emetics for the Radio Technician lamps, neon signs, rescent household if you can send me the more powerful lay- CONTENTS OF BOOK equipment, motors and lots of other out spoke of in the article will be you I CHAPTER t. Arit hmetie-Addition- Subheetlo>MUltlO1I money- making service work. See very grateful. cation-Don.II. Faring and Cancellation-Fractions -DSat both of these latest type, valuepriced la- Percentage-Kano -and Proportion. Thanks for this favor. CHAPTER Ill. The Metric System. RCP Kits at your CHAPTER IV. How to Measure Surface. and GPaity EDW. J. GEAR, tceomelrys. Jobber -or send for RCPp CHAPTER V. Powers and Involution -Roots and Evolu- Los Angeles, Calif. tion. ,Catalog 124 Today! [ItyenOable CHAPTER VI. Mathematle for the 'Man- ual and Technical Craftsman-Ther- instruments e1etnornofPlotig-Lo`lNma-Ü e ONLY the Slide Rule. Mr. Shaney advised in this connection CHAPTER VII. Mathematics for as Speciat 50e below. CHAPTER VIII. Commercial Calculations - Interests Discount. short Cut POSTPAID A higher -powered hearing -aid can not be Arithmetic.- - CHAPTER IX. Weights and Masan. conveniently made wearable. If you would Useful Tablas. CITY be read: peel. RADIO Elamentory M.thmnatits- carried v i. voue have no objection to having this unit de- SendStamps. Cash or Money Order PRODUCTS COMPANY, INC. signed to fit a space of approximately a 4 -in. 88 PARK PLACE NEW YORK. N. Y. cube, I shall be pleased to present such a TF:t:11 I FAX design in a future issue of Radio -Craft. 1917 S. State St. RC -341 Ch,tago, III. 536 RADIO -CRAFT for MARCH, 1941 *TEST INSTRUMENTS

Vacuum -Tube Voltmeters are of many different types, and in commercial designs present quite different appearances, as here illustrated. The instruments in the above photo layout are identified as follows: (I) RCA Junior VoltOhmyst; (2) Supreme Instruments Co. model 549 Electronic Voltmeter; (3) Radio City Products model 660 Electronic Multitester; (4) Superior Instruments Corp. Dynarometer; and, (5) Weston Electrical Instrument Corp. model 669 Vacuum -Tube Voltmeter. V. -T. VOLTMETERS 'Meaty and Ptactica

AGREAT deal of material has been A Serviceman casts an expert eye over published descrip- printed with reference to the basic design and use of the V.-T. Voltmeter, tions of vacuum -tube voltmeters, discusses their pros and or "V: T.Vm.," so that now it may cons, and concludes with the construction details of a be in order briefly to review what we have "V.-T.Vm." he finds exceptionally suitable in his everyday learned and to take stock of the methods available to those unable or unwilling to service work. pay the prices asked for such equipment, prices which range from about $20 to over $100 of hard- earned money. (A number of WILLARD MOODY V.-T. voltmeters have been described in construction articles in past issues of Radio - electrical quantities, is that of the slide - cathode of the tube. Also, it measures the Craf t.- Editor) back type of voltmeter depicted in Fig. 1 ('). peak value of an alternating current, a Fundamentally, as has been so often re- This type, while accurate, is apt to give useful feature in determining, for example, marked, the "V: T.Vm." is a detector of al- trouble, since a stable source of bias supply the overload point in an audio amplifier grid ternating current, or in other words, it is a is required, and, in addition, stray currents circuit. direct current amplifier. There is an essen- may flow through the grid- circuit meter. The connection from the voltmeter to the tial difference in the operation of the in- Also, it generally has low sensitivity unless receiver circuit being tested should, of strument according to whether it is to be an expensive galvanometer is used in the course, be shielded, and the shielding in- used on A.C. or D.C. and there is a further plate circuit at a sacrifice of ruggedness sulated to prevent the possibility in the case classification possible of the A.C. instru- and maintenance of calibration. Of course, of an A.C.-D.C. receiver of shorting the ment, which is one concerned with the fact a D.C. amplifier could be used, but there power line; or in the case of an ordinary of its mode of operation on (a) peak, (b) still would remain the necessity for adjust- A.C. receiver of shorting, through allowing effective or (c) mean values of alternating ing the meter for every single voltage test. the cable to touch the wiring, of any sec- current. The main advantage of such a peak volt- tion of the set: meter is its very high input impedance, For stability, a high resistance, of the SLIDE -BACK which is essentially that of the grid to order of 10 megohms, should always be The classic example, and one which you connected across the input circuit to provide (s) A.1111.1. "Amateur Handbook." 1940 Edition. will find in many texts on measurement of p. 268. a constant path for the flow of direct cur-

30 I0.1-MF 45 NEGATIVE FILTER V/ y SPKR FEEDBACK /\ INPUT Q © sj . = o. c. + NN , _ o.c. INP T 22.5 Sw, STABLE g5 y ll / ! =V' BIAS D.C.VOLTMETER i y + (FILTERED INPUT) ^ /\ SW. -PUSHPULL - 10MEG51 `Q7 `T + MATCHING- M. 955 FILTE0. (EACNJ s= CONTROLLED ít -- 1 + 0-1. ' DIODE - t3V. MA ?w DIODE _ rvWy BIAS : h CONTROL SW. INPUT \` \( i fJ CATHODE + + 100 + / RESISTANCE IIII---III MME. M 50 MEG9 © IMPROVES - -((DER 1 ^ SLIDE-BACK --' _ REGULATION 3V.9 4.5V. = CIRCUIT^ PEAK -GENERAL DELAYEO- f v. VACTION' 5w. Wall VOLTMETER 0001 RADIO 726A- 'III FI .4 RADIO -CRAFT for MARCH, 1941 537 TEST INSTRUMENTS'

1.000 205. 50 1.MEGJ 6ABG al MEG. OHMS 64 MIXER GN7 ai MEG. 0.1- 2-' MEG. MECS 1 MEG. ÍJ MEG. _ L 1 I MEG. D.C. A.C. V.T. VM. MEG 6 D.L. il VOLTS CONNECTION 5 al MEG. 4 300 .05 MEG. 3 VOLTS, MF. i1 21 WELL 0.5MEG REGULATED 0.1- 0.1- 10.000 i 0.1-MEG. MEG. - DELAYED -ACTION (SEE FIG.S (EACH -- MEG. OHMS V. -T. FOR METER 10.0000HM5 f VM.^ A.0 1T 0-- (ADJUST ON Nil SCALE .NO INPUT. READINGS CIRCUIT) FIG.7 ARE NEGATIVE, FROM I TO ZERO MA.) 0. 1MF.' 8MF.-"" 30.000 OHMS o 1-MEG. TEST C. RESISTOR PROD SHIELDED SUPA.PLY I.MEG. / WIRE VT VM. CALIBRATOR AMP. I--- 1 M I -CONNECTION OF UNHNOWN V. -T. VM. C. V. -T.VM. VOLTAGE -O. METER TO RECEIVER - FIG.5 ALLIGATOR CLIP (AND PROBE) -- CALIBRATION A.V.0 rent from the grid of the tube in the meter as a very sensitive output meter, is also to the measurement of resistance at V: T.Vm. to its Marnent or cathode, depend- available(') and will be of assistance to low current values. This is a distinct ad- ing on the type tube used. This will remove the beginner in servicing. vantage, as you can get knocked on your ear the possibility of meaningless fluctuations with some of the present -day equipment of the meter in the plate circuit. In the case "DUAL- TRIODE" BALANCE V: T.Vm. using high voltage on the Megohm ranges of the instrument designed to work on D.C. An easy -to- understand analysis of the of the tester. a condenser across the input will filter out V: T.Vm. is given by Terry in his "Ad- the A.C. with a resultant stability, precau- vanced Laboratory Practice." This discus- REFLEX V: T.Vm. tions being taken of course that the design sion involves a slight acquaintance with For measurement of A.C. the V: T.Vm. of the instrument is such that if the integral calculus. A less mathematical treat- may consist simply of an amplifier with V: T.Vm. is connected to a circuit in which ment is given in the "Radio Engineering" output meter calibrated in volts or db. and A.C. is flowing there will be no disturbance of F. E. Terman. a suitable source of calibrating voltage un- of its value, except as concerns the meter In the "Communication Engineering," by der control, which may be checked against and not the circuit itself. This is clearly W. L. Everitt, there is given a splendid the unknown, as shown in Fig. 6. A less shown in Fig. 2. chapter on the subject of detection, a real complicated circuit is shown in Fig. 7. This The 'grid leak and power detector have aid to complete understanding of the circuit is of the reflex type, using the gain their counterpart in the family of vacuum - V: T.Vm. since it is closely related to rec- of the triode to supply the A.C. voltage tube voltmeter circuits. The first has great tification of alternating current as in the necessary to allow current flow in the diode sensitivity, but slightly loads the circuit. The detector of a receiver. which in turn supplies a negative bias for second has negligible loading effect upon In the "Radio Engineering Handbook," the triode grid, reducing the plate current the tested circuit, but the sensitivity is not chapter by R. F. Field on Measurements, by the amount or in accordance with the as great. At present, most commercially - there is given a circuit which is of par- value of the unknown applied voltage. This made V.-T. voltmeter circuits are of the ticular interest, since a form of it is today circuit appeared some time ago in the pages "plate detection" type, although in the case being used, with some improvements, in of Electronics magazine, and has been of one expensive instrument(') a "diode - the Rider VoltOhmyst, a very good com- slightly modified. type" rectifier is used in conjunction with a mercially -made. V. -T.Vm. Turner, and Mc- D.C. amplifier arrangement. Namara, in a 1930 issue of the Proceedings TESTING A.V.C. CIRCUITS In this circuit advantage is taken of the of the Institute of Radio Engineers, first One of the most useful features of the fact that a condenser will charge up to the published the data. The circuit is of the V. -T.Vm. is the ability it has for checking maximum value of an applied voltage, in a "dual- triode" balance type, and is similar in the A.V.C. circuit of modern radio re- relatively short instant of time, and thus principle to the old -style test circuit used ceivers. This is shown in Fig. 8, where we there will be only a momentary loading of for checking the matching of type 45 tubes have a typical A.V.C. circuit. The test prod the circuit. The further advantage is that in in push -pull, as shown some years ago in may be placed across the circuit consisting the diode rectification circuit, independence Popular Mechanics. The modern circuit, by of the 0.05 -mf. condenser to ground, to of frequency variation is achieved with con- Rider, uses a high resistance in the cathode check the amount of A.C. across it. If siderably greater accuracy of operation. lead, as shown in Fig. 4. audio voltage appears here, it indicates that This is shown graphically in Fig. 3. the condenser is open or leaky and should SERVICING -TYPE VACUUM -TUBE D.C. VOLTMETER be replaced. If with the instrument INVERTED TRIODE the bias to the controlled tubes does not There is still another type of voltmeter, The circuit which I am using, while not vary according to the strength of the re- the inverted triode, used for high power so complicated, is satisfactory for my pur- ceived carrier, being low off resonance, in- measurements. This is shown in Fig. 4. The pose, as it will be for most other Service- creasing to the maximum value of perhaps flashover voltage of the tube should be high men or amateurs. See Fig. 5. The ampli- 20 volts when tuned to a strong station, enough to prevent damaging the meter, in fication, as given in the Prod., I.R.E., is in then the A.V.C. supply is at fault and may the case of high voltage tests. This type may the vicinity of 100. This high value in com- be checked by the usual routine resistance be used for not -too -high (television) re- bination with modern high -mu tubes ren- measurements. sistance circuits, or for amateur transmitter ders unnecessary the use of complicated For the final result, the resistance meas- checking. bridge circuits or D.C. amplifiers to achieve urements must usually be made; why, then, There are also a variety of other circuits, sensitivity. should we use the V.- T.Vm.? Because, it most of them having no great importance, Also, the instrument can be made to check saves the time that might so often have been which it is necessary to inspect to get a accurately voltages and conditions which are spent in checking the separate parts of the clear picture of the entire field of this not so well dealt with by employment of network; by localizing the trouble it en- type instrument ('). A study of the opera- the oscilloscope with its manifold problems; ables the tester to service only that part tion of these circuits again reminds the the V: T.Vm.'is a time saver, not time con- of the A.V.C. which is likely to be at fault. Serviceman or amateur of the basic prin- sumer. For flat -top alignment the oscillo- The first condenser, in the A.V.C., might ciples of vacuum -tube operation (') which scope is best in adjusting the I.F. as far have been shorted partially, without affect- are vital to the complete and useful under- as receiver servicing goes. For checking ing to any extent, the rest of the circuit. standing of the procedure to be followed in A.F.C. or A.V.C., the V: T.Vm. is my The V: T.Vm. confirms this, before allowing testing with the V: T.Vm. as well as grasp- favorite instrument. Eventually, I believe, you to rip the parts out for test. ing its fundamental design principles. portable instruments of this type will super- It is also useful in determining dynami- An elementary explanation and a simple sede and thereby render obsolete our present cally if the controlled tubes are receiving circuit, depicting chiefly the use of the volt- antiquated meters of 1,000 to 20,000 ohms/ proper bias, a point particularly important volt. where dctuning is experienced as the result (') General Radio Co. The advantage of the T.Vm. extends 1T) Sylvania News, January, 1938. V: of a change in the input capacity of A.V.C: (I) "Vacuum Tubo Voltmeters," R. Lorenzen, Service, January, 1939. (5) "Modern Radio Servicing," (Mardi, p. 155. controlled tubes. In this connection, refer- 538 RADIO -CRAFT for MARCH, 1941 TEST INSTRUMENTS

GREAT NEWS!! . THE NEW UTILITY TESTER The Utility Tester is a new kind of instrument for testing all electrical appliances- WASHERS, IRONERS, REFRIGERATORS, RANGES, VACUUM -CLEANERS, TOASTERS, PERCOLATORS, HEATERS, SUN LAMPS, AIR -CONDITIONING, MOTORS, etc. The Utility Tester enables every possible measurement necessary to service any electrical appliance. Mr. Radio Serviceman, here is a new source of revenue for you. The UTILITY TESTER will enable you to accept and economically service electrical and industrial jobs you have been compelled to pass up in the past. You already possess the fundamental electrical knowledge necessary to service electrical and industrial utilities, and now you can have the instrument which will enable you to apply this knowledge to a new and lucrative source of extra income. SPECIFICATIONS: 3 WATTAGE RANGES: A.C. AND D.C. 0 -100 Watts, 0 -1000 Watts, 0 -5000 Watts. The UTILITY TESTER reads the actual wattage consumption of any appliance, motor, etc., while it is in operation. Thus you can actually prove to the layman the actual consumption of any appliance and compute the actual cost per hour operation, basing your calculation on the local current cost. This is a feature never before obtainable in any instrument selling for less than $50. 6 VOLTAGE RANGES: A.C. AND D.C. 0 -I Volt, 0 -IO Volts, 0 -50 Volts, 0 -100 Volts, 0 -500 Volts, 0 -1000 Volts. 4 CURRENT RANGES: A.C. AND D.C. 0 -1 Ampere, 0 -10 Amperes, 0 -50 Amperes, 0 -100 Amperes. As far as we know, no instrument selling for less than $50 has ever enabled current measurements up to 100 Amperes. The UTILITY TESTER provides this service on both A.C. and D.C. 2 RESISTANCE RANGES: 0 -300 Ohms, 0 -3000 Ohms. The UTILITY TESTER reads all resistances commonly used in electrical appliances and in addition reads extremely low resistances. For instance, I1/2 ohms appears on the center of the low ohms scale and resistances as low as 1/50th of an ohm are easily read. This is a feature never y}. ^ r before obtainable in an instrument selling for less than $50. +x! uJ`1J1 The Utility Tester comes complete with portable cover, self- contained battery, test leads, and all necessary instructions. Shipping Weight 11 lbs.

SUPERIOR INSTRUMENTS CO., 136 Liberty St., Dept. S.T., New York, N. Y. once may be made to RCA Patent Note the work on A.V.C. and power circuits. For green shadow of the tubes. In the meter No. 101, which deals with the subject ex- one thing, the input impedance is higher, scale, there are definite points to which one haustively. The main point is that for very and because of the meter scale the precision may refer. For R.F. tests the oscilloscope large values of bias, due to the non - greater. The oscilloscope has the advantage is useless, while the V: T.Vm. comes into linearity of the tube characteristics, and of enabling you to see the voltage being its own. In the Rider Chanalyst, in the to cathode lead inductance within the tubes, measured, but the scale on the tube affords Supreme Audolyzer or the Meissner Analyst, 3rd -order demodulation effects and changed only qualitative measurement and there- some form of vacuum -tube voltmeter is em- input impedance may result, with consequent fore is not as accurate as a meter scale. ployed to check the various stages in the detuning and distortion.(") In this regard, let us say that the tubes such receiver, while in the Weston V. -T.Vm. one The V: T.Vm. is also useful for checking as the 6E5 and 6U5 are not, in our opinion, instrument serves all functions. The choice the amount of hum voltage across filter desirable as indicating instruments in the that may be made is limited only by your condensers, or the A.C. across any con- V: T.Vm., as the zero setting is none too willingness, or your ability to spend. I denser, which is a positive indication of the clear and there is the disadvantage of hav- should say: if possible, buy commercial efficiency of the particular condenser under ing no intermediate points between the equipment; but it is more fun building your examination. It gives illuminating knowl- widest opening and the narrowest of the own. edge of the function of parts, refreshes the lagging memory with constant evidences of how a circuit should operate, refers you continuously to basic theory and radio fundamentals, allowing you to service all makes of radio receivers with mere certainty, since knowing tube characteristics, you become SOUND IS BOOMING! . ever more concerned with the heart and soul of the receiver: its tubes. Less dependence . is thereby placed upon circuit diagrams, . . so )24dio -et4P yoei to town which while extremely convenient and de- not be sirable, may always available. This The May issue of RADIO -CRAFT will be a "Sound Special." Home Record- is particularly true in the case of the ing and Phono -Radio Combinations have taken the public by storm, so Serviceman who does not live near the "big RADIO -CRAFT is going to town! The May issue will be devoted mainly to city" and does not have access to as many Sound. This, of course, includes public address as well as home recording diagrams as his more fortunate city dweller. and phono -radio combinations. If he will concentrate on basic circuit data, and tubes, he will be able to service In addition to the usual departments on this topic, there will be special radio receivers with a good deal more pre- articles and construction projects which will be of considerable value to cision than would be expected under the Servicemen, Sound Specialists, and radio men in general;-not the ordinary conditions described. run of articles but specially -prepared material for this issue.

ACCURACY In addition to this, there will be the usual departments devoted to Servic- ing, Test Instruments, Electronics, Radio Developments, etc. The V. -T.Vm. is also a satisfactory if not a better substitute for the oscilloscope in (el Radio Today. Service, end RCA "Patent Note Reserve your copy NOW! No. 101." RAr1IA_CRAFT ; n. AAARC:1-I SIO *TEST INSTRUMENTS

Exterior and interior appearance of the completed Modern Multi -Tester built from kit parts.

Build rout Own getilitila MODERN MULTI- TESTER In the December, 1940, issue of RADIO -CRAFT the author described a simple multi -range meter which even a novice could easily construct. This month another such unit is described for the benefit of readers who desire to construct for themselves a somewhat more ambitious multiple test meter-one with even more ranges and greater convenience of operation. A 200 -microampere basic meter affords a sensitivity of over 2,000 ohms /volt.

MILTON REINER

THE meter to be described provides Output meter: Same ranges as A.C. volts. eluding resistance), the test probes are a number of unusual features. First Second, the inclusion of high current and plugged into the pair of D.C. tip -jacks and of all it serves the purposes of 27 in- voltage ranges -both A.C. and D.C. -per- any desired range is then selected by means dividual meters as follows: mits measurement of values utilized in of the switch. For A.C. measurements it is D.C. voltage: 0- 10/100/250/1,000 /5,000 cathode -ray and television equipment, trans- only necessary to shift the probes to the A.C. voltage: 0- 10/100/250/1,000 /5,000 mitting equipment, neon and fluorescent pair of jacks marked "A.C.", then select any D.C. microamperes: 0 -200 lamp installations; starting surge currents A.C. range by means of the switch. D.C. milliamperes: 0 -10 /100 of motors, and the high values encountered The circuits and discussion which follow A.C. milliamperes: 0 -500 in many industrial as well as miscellaneous will enable anyone to duplicate this meter D.C. amperes: 0- 1/10/25 radio applications. Because of practical con- unit. To make this entirely practical, and to A.C. amperes: 0- 2.5/5/25 siderations -and safety- separate tip -jacks make possible an instrument of highly pro- Decibels: -10 to +15, 10 to 35, 18 to 43, are provided for these higher ranges. fessional appearance, the entire kit of parts, 25 to 65 For all normal measurements the ranges including the embossed panel, all resistors, Resistance: 0- 400/40,000 ohms /4 megs. are selected by means of the main selector jacks, switches, the meter (with its A.C., Capacity: 0.01- to 1.0 mf. switch. Thus for all D.C. measurements (in- D.C., High -Ohms, Low -Ohms and Decibel scales), and a sturdy wood case with carrying handle, have been made up in the form of a coordinated kit which is both ÓÑMS 01:1ÉG CAPACITY NORMAL ADJUST simple to put together and low in cost. 10V 362 The R.C.P. model 411L meter employed is I i 100V. Í OHMS 1, of the square type, 4',2 ins. wide x 4 ins. high, with the outer scale approximately 250V. UMW 32.000 CAP. OHMS // 3'4 ins. long. A 200 -microampere d'Arsonval "0 525- ----M1 1441Y'OÑMS MEG. movement is utilized, its readings at full - í000V BLACK x1 (10x.5 1515 MÉGx42$ scale accurate to within 2 %. All resistors MEGS. IOMCA REDS MÉSGS) supplied with the kit are accurate to within D. 2% of their rated values. 100MA. D.C. ti The complete circuit is shown in Fig. 1. 118 But to facilitate matters for the student or IAMP. OHMS D.C. D.C. novice who may wish to construct such a

I A.C. 500MA 10 unit -and do it with a full understanding of AMPS. O 5000V.. the functioning of every circuit -the indi- 2.5AMP .012- A.C. OHM vidual circuits for the various types of i _. 2.5 5.000V NM AMPS O measurements are shown in the other 400 GANGED NANGE D0B- 25A PS OHMS OHM OHMS SELECTOR ADJUST _ OHM .02-OHM illustrations. 0.C. 40.000 COM. o DJ VOLTS, OHMS TWIN MA, A.C. R x10 21000 JACK OHMS COM. 1.5VT+ CIRCUIT BREAKDOWNS OHMS Ci PACITY 4 MEGS 505' O VOLTS BATTERY Fig. 2.- Figure 2, for instance, shows the Rx1.000 U< OHMS MA. complete circuit utilized in measuring direct FIG .1 A.C. -D. C. SWITCH COMBINED WITH -OHMS ADJUST- RHEOSTAT. current. In these measurements the 3rd deck

540 RADIO -CRAFT for MARCH, 1941 TEST INSTRUMENTS

(C) of the 3 -deck, 12- position selector In order to use the same meter scale and switch is not employed and is therefore not multipliers for both D.C. and A.C. voltage ARM A' 111LOU 1GANGED OHMS shown. measurements it is necessary to shunt the (VOLTS 1 " ARM`B" eCICURRENTO IS Considering the meter circuit alone for meter during D.C. applications, to make its LOHMS the moment, it will be seen that it represents sensitivity the same as when the rectifier MIAMPT PT a closed loop of 1,000 ohms, consisting of the is in the circuit. It is for this reason that `OHMS 500 -ohm resistance of the meter itself, and the 362 -ohm shunt is employed in the D.C. the sum of 7 other resistors in the circuit. voltage measurement circuit of Fig. 4. As svifa CC..QQCC -OHM O There are actually only 6 such resistors 2 before, the small resistors in series with 10AM' r shown but the A.C.-D.C. switch has a re- the 362 ohms have no place in the circuit but ".012- OHM } sistance of 0.02 -ohm which must be included are left in as a of OHMS. matter convenience. 2$AMPS, 200 in the calculations. With the meter shunted to sensitivity of L OOS- MKROA. COMMON OHM (M) When current is applied across any por- 476 microamperes (2,100 ohms -per -volt in D.C. tion of this resistance part will flow directly voltage measurements) the multiplier values FIG 2 ^-CURRENT RANGES (DC), through this shunt and the balance through work out as shown in Fig. 4, - the meter. Where the resistance of the In the A.C. circuit, for voltage measure- CVRRLTSENT }AC /.-..-.. meter branch is high as compared with MA. ------._i the ments, Fig. 5, the ohms /volt sensitivity is (.0...4i.(8. /r0.8- C' B shunt branch, then the current through the the same as for. D.C. measurements. Here, OHM 'meter will be small. In the 10 -ma. position however, there is no shunt across the meter AMPS. 118 of the switch, for instance, the shunt is 20 for reasons OHMS already explained. It might be r-0.1- ohms while the resistance of the meter well to point out here that the full -wave 5AMPS OHM branch is 980 ohms. Only 1 /50th of the total rectifier is conductive through the meter A.C. current will flow through the meter and only on one -half of each cycle, the other "'OM; 10 ma. would therefore have to be applied half-cycle being bypassed around the meter 25ACPS, to the circuit to drive the meter to its full by - the other side of the rectifier. The pur %o2- A.A.C. D.C. 200 -microampere limit. pose of this latter branch is to prevent high OMMON OHM BLACK SWITCH The divisibn of the current is inversely inverse voltages developing across the recti- O proportional to the ratio of the resistance fier during the inoperative half -cycle -volt p FIG .3 CURRENT RANGES(A.C.y. OOHM OHM of the two branches. A more simple way to age which on the higher ranges would be determine 'the extent by which the meter ._._._._. sufficient to cause the rectifier to arc over. : Ó-.Z1W15 5á _, MEG. range is multiplied by any given shunt, is / EOV find - MG.MEG. to the ratio of the shunt to the total OHMMETER 100V. B . circuit resistance, then multiply the normal In Fig. 6 are shown the ohmmeter circuits. meter range by this value, inverted. Thus 250V' OHMS In the 40,000 -ohm position of the switch we 1.000V. in the example cited the ratio is 20 /1,000ths have the standard ohmmeter circuit. In this or 1 /50th. Inverting and multiplying we case the meter is 5.05 ohms, L.515 A.C. -D.C. shunted by re- MEGS. SwiTCH have 200 microamperes x 50 equals 10,000 ducing its to 20 ma. The VOLTS sensitivity internal NT microamperes, or 10 milliamperes. In the series resistance is 275 ohms plus approxi- D.C. LOHMS 1- ampere position of the switch the re- ¡.012 mately 5 ohms represented by the meter and Á000V. OHM M sistance included in the shunt js 0.2 -ohm. its shunt, plus whatever is added from the The ratio is 0.2/1,000 or 1 /5,000. This gives variable "Ohms Adjust" resistor. With the COMMON MEGS. coos- 200 microamperes x 5,000 equals 1 ampere. 7.5 -volt battery this results in a total of 375 While there is no marked switch position ohms but as the battery drops the variable utilizing the maximum sensitivity of the resistor provides means for compensating FIG4 ....VOLTAGE RANGES(O.C.) meter, 0 -200 the microampere scale can nev- the drop in order that the ohms scale still , ertheless be used. This is accomplished by will remain accurate. This will hold true OHMS setting A.C.-D.C. switch in the the A.C. po- until the battery has dropped to 5.5 volts. - 0.21 - sition and Range Selector in iOV icyv MEG. the switch the Beyond this figure the "Ohms Adjust" knob Aeve. "1 Amp." position. With the prods in test will no longer permit full -scale deflection OM,SG - the D.C. jacks the measurement range will and the battery should' be discarded. 4000v z50v '`+ ' be that of the meter itself. While there is The 4- megohm circuit is similar to the some resistance in - 1.575. series with the meter. one just described except that the shunt is MEGS, with this arrangement, its effect is neg- eliminated, allowing the meter its full sensi- ligible. tivity in order that high resistance values A.0 KRENT(VOLURTS In the A.C. ranges (Fig. 3) the principles may be measured without resorting to high- .008 . and arrangement are similar except that in er battery voltage. SOOOV, OHM this case the normal current range of A,G -DpC. the The Low Ohms circuit varies materially :MADE UP OF SWITCH is no 200 EG. meter longer microamperes. Due from the others in that the resistance under MATCHED to the rectifier in series efficiency is reduced measurement is COMMON RESISTORS) shunted across the meter, A.C, BLACK nearly 60 %, the sensitivity of the meter instead of being in series with it. In this becoming 476 microamperes as a result. RED 012- instance the meter is again also shunted OHM Further, in this instance, the meter is shunt- with 6.05 ohms, making its total resistance FIG.5 - VOLTAGE RANGES(A.C.) ed with a fixed value 178 of ohms, so that 5 ohms and its sensitivity 20 milliamperes. aoO .50000 the effective OHMS OHMS sensitivity of this meter and The battery, its variable series resistance os fixed shunt combination decreases to about and the fixed 275 -ohm series resistor, also 11M5 O A., .0 1.8 ma. constitute another shunt across the meter. VOLTS Because this latter combination will be ad- CURRENT D.C. ME OHMS A.C.-D.C. CONSIDERATIONS OHMS justed for a resistance of about 375 ohms it OHMS ADJUST Calculations become a little complicated has no material bearing on the overall re- where a rectifier is employed and for that sistance of the meter circuit. OHMS reason it is often considered more simple to When the resistance to be measured is select some M convenient value for the shunt connected to the input jacks its shunting COMMON III' network, dividing this up into units in in- effect will decrease the meter current. If it D.G R..- BATTERY verse proportion to the desired current is 5 ohms, for instance, it will cut the meter o ranges. Then if the fixed shunt is selected reading to hillf- scale. Thus very low values FIG.6 -OHMS RANGES"- to provide the correct meter reading for of resistance can be measured with accuracy any one of the desired ranges it will be 1 GúRRÉNT }A -G sOH ADJUST -down to less than /10th -ohm. -A' / correct for all. In this case, the shunt network totals 1 ohm. The correct fixed shunt CAPACITY METER **I L I.; 2sov was found to be 178 ohms. The capacity measuring 7 OU CAPACITY % range of Fig. TO / It might be added here that the 2 low - utilizes the ability of condensers pass 105- CONDENSER 0.EO. to 130 V., TOR MEG. value resistors in series with the meter have A.C. TTEESS alternating current and the fact that the LINE no part in the functioning of this circuit. amount of current passed varies with the Their value is too small to influence the capacity. For this measurement the usual BLACK ,012- .006` } COMMON total series value appreciably. They are ac- A.C. tip -jacks are connected across the A.C. A.G. OHMJ MÌ tually used in the D.C. positions and for line as though this line voltage were to be RED A.C. measurements it was more simple to measured. The switch is set in the 250 V. FIG.7 "'CAPACITY RANGE^' leave them in than to arrange to switch position with but the separate "Capacity" Elements of the complete schematic circuit, of the. them out. switch in the circuit the 250 -volt multiplier Modern Multi -Tester, shown in Fig. I.

RADIO -CRAFT for MARCH, I 9 4 1 - 541 prWtrww-e."z.-.." ,

TEST INSTRUMENTS

resistor is -shorted out and one of 32,000 BUY DIRECT FROM THE MANUFACTURER AND SAVE ohms substituted. At the same time this THE NEW MODEL 1240 "Capacity" switch cuts in a variable "Cap. Adjust" shunt across the meter so that full - TUBE TESTER scale deflection is obtainable for any value of line voltage by a simple adjustment Instantaneous snap switches of reduce time this shunt. When this adjustment has been actual testing made, the condenser to be measured is con- to absolute minimum. nected by means of another pair of test Tests all tubes 1.4 to 117 probes across the "Capacity" jacks. These volts. - jacks are a special circuit -closing type which connect the condenser in series with the Sockets for all tubes - circuit, when No but no tips are plugged in Adapters. automatically close the circuit. Capacity Superior is proud to offer the new- readings are made on the regular 0 -50 est and most practical tube tester volts scale in conjunction with a conversion ever designed. Unbelievably low in chart provided in the instructions which price -unbelievably high in per- accompany the kit. Another such conversion formance. chart permits inductance measurements with *Tests all tubos. 1.4 to 117 Volts, In- this same circuit. cluding 4, 5, 6. 7. 7L, octal,. loctals, To Bantam Jr. Peanut. single ended, float- obtain readings in decibels the instru- ing filamen,t. Mercury Vapor Rectifiers, ment is used exactly as when measuring the new S serles. in fact- every tube designed to date. A.C. Voltages, except that the values are * Spare socket Included on front panel read from the for any future tubes. separate "Decibel" scale on Tests by the well -established emission the face of the meter. The decibel calibration method for tube quality directly read is for a 600 -ohm line. For lines of other on the GOOD t BAD scale of the meter. impedance, a table Jewel protected neon. of correction factors for lines of from 5 to 1,000 ohms is available. * Tests shorts and leakages up to 2 meg In Tests and shorts in all elements AGAINST all elements * Testa BOTH plates in rectifiers. in all tubes. LIST OF PARTS Testa individual sections such as diodes, triodes- pentodes, etc., * latest type voltage regulator. In multi- purpose tubas. BRIGHT STAR BATTERY COMPANY * Features an attractive etched aluminum panel. One 4% -V., No. 51 -17; * Works on 90 to 125 volts 60 cycles A.C. Model 1240 comes complete with instructions and tabular data for every known One 3 -V., No. 50 -1. type of receiving tube. Shipping weight 12 pounds. She 6" Our Net Price x 7%" x 10Y". AMERICAN PHENOLIC CORP. Portable cover $1.00 additional Eight Amphenol tip -jacks (6 red -2 black); Two Amphenol high -voltage tip -jacks (red). THE NEW MODEL 1230 WIRT COMPANY One D.P,D.T. slide switch. SIGNAL YAXLEY MANUFACTURING CO. GENERATOR One twin series closed- circuit jack. RADIO CITY PRODUCTS COMPANY WITH FIVE STEPS of One copper -oxide rectifier; One tapered rheostat (and switch), 18,750 SINE -WAVE AUDIO ohms; SPECIFICATIONS One 3 -gang 12- position selector switch; RADIO FREQUENCIES from 100 ICJ'. to 90 One tapered rheostat 2,250 ohms; Megacycles in 7 bands by front panel switch manipulation. All direct reading and accurate to One wire -wound molded resistor, 100 ohms; within 1% on I.F. and Broadcast bands. 2 % on One large bar knob; higher frequencies. The R.F. is obtainable separately or modulated by any one of the five Audio One 41/4 in. microammeter 0 -200 microA., Frequencies. model 411; AUDIO FREQUENCIES: 5 steps of SINE -WAVE L audio 200, 900. 1000. 5000 and 7500 cycles WITH Eleven flexible wire -wound resistors, 2%% OUTPUT OF OVER I VOLT. Any one of the above frequencies obtainable separately for serv- accuracy, 1 each of the following resist- icing P.A., hard -of- hearing aids, etc. ance (ohms) values: 275, 5.05, 480, 18, ATTENUATOR: Lote design. full-range atten- uamr used for controlling either the pure 1t.F. 1.8, 0.18, 0.8, 0.08, 10, 362, 178; er Three 1 CIRCUIT: The Model 1230 employs an improved electron coupled oscillatorcircuit for the R.F. affording positive shunt resistors, 2% accuracy, each Protection against frequency drift and a Hartley oscillator circuit for the A.F. section. of the following resistance (ohms) values: DIAL MANIPULATION: large 5A" dial etched directly on front panel, using a new mechanically perfected drive for perfect vernier control. 0.02, 0.012, 0.008; APPEARANCE: The front panel is etched by a recently perfected process which results in a life -long attractive Four metallized resistors (2 matched finish and the Instrument comes housed in streamlined shielded cabinet. pairs, CURRENT SOURCE: The Model 1230 operates on 90 to 130 volts A.C. or D.C. any frequency. 5.25 megs. per pair), 1% accuracy; The Model 1230 cornea complete with tubes, shielded cables, moulded carrying Four special molded carbon resistors, 2% handle and instructions. Size 14" x 6" x 11 ". Shipping weight 15 pounds. ONLY $i;t85` accuracy, 1 each of the following resistance (ohms) values: 20,500, 210,000, 136 S.T. 525,000, 1,575,000; SUPERIOR INSTRUMENTS CO. NEW YORK, Ne Y. One carbon resistor, 5% accuracy, 32,000 ohms; One carbon resistor, 5% accuracy, 27,600 Amazing Dew "WI1L5I0" ohms; Two bakelite resistor mounting PICTORIAL strips; THE STAPLE DRIVER One drilled and etched panel model L 411K FLYING REVIEW size; Brings you all the phases for radio mew electrician et anyone doing ,,.pang. Mei« rin end of World aviation and able in/alb/ions twice at .,y -'noeh ne.tet -u +e, hall the time. One hardwood case (with battery compart- aeronauticstics i,, a no Wino can be ,(.pled in cameo, behind pipe.. inta meklnq. -p4mc yet educational -n enibl. with hammer staples. Dri.Dried. tbph. ment and handle). ,citing articles oven inle , which catch your breath. wee brill. mode.. c. M.g.riMogan., .orh .utomeliully and yet give you the (undo. held. drip. of tiepin .hid come in several colon. Ad yes. ¡ebb.. Misc. for demaeb.sen and cabbgue,4lRol as WALSCO PRODUCTS ALL 'related suhJaecta. One small round knob; FLIGI1T or write WALTER L. SCHOTT CO. abreast of all the major One small round knob with pointer. developments as fast 5264 W. Pico Boulevard, Los Angeles, California they any- (A kit of parts for the Modern Multi - ca t Nów,.9ywhen planes Tester can be supplied by leading Parts job- vital Partial Contents of the March Importance bers and radio mailorder houses.) Issue: Stratosphere Fighting! to all Armament M Modern Bombers. highly absorbing This article has been prepared from data The Secret of the Rocket pub- :if011 }:1)- A 11 S Plane. AIR WAR sa Seen lication. You( musts be supplied by courtesy of Radio City Products Through German Eyes. The "in the know. Smaller Diameter Dry Electrolylics HE 111.10 Nast Bomber. De Co. taus of the ItAF Snitare." attraetiVe 1a Bombing by Stnpp- Watch. So thrcover, 15Vw SPE E Dog. Flight Digest. BomaÌers vs. Submarines. Formation ens. PY Due to unforseen circumstances, a number of Flying. interesting articles scheduled to appear in this Wrue ter ee.emg FLIGHT MAGAZINE 50a r year, CaCanada issue of RADIO -CRAFT had to be held over for 20 -R Vesey St., New York. N.Y. 51and foreign 52.00. the next issue. WATCH FOR THEM IN THE SOLAR MEG . CORP. Bayonne. New Jersey APRIL NUMBER!

542 RADIO -CRAFT for MARCH, 1941 1-1011JARD 941 COMMUNICATION RECEIVER 7111H FIRST TIME: a`veyó and $39.95 "Ham" Receivers With Tuned R.F. on All Bands

Again HOWARD leads the field with a new line of communication receivers that are outstanding in both performance and value. Foreign and weak signals are tuned in with surprising ease. Selectivity, sensitivity and signal -to-noise ratio are equal to radios costing twice as much. All models tune from 540 K.C. to 43 M.C. (556 to 7 meters) on four overlapping bands. Designed and built in the famous HOWARD factory, the oldest in America. The HOWARD Progressive Series Pion permits you to start with the Model "435 -A" 7 -Tube Receiver, and later add to it in easy stages until you have MODEL 43-A -7-TUBE communication receiver, built for a complete 15 -tube receiving station that will rival laboratory equipment. amateurs and short -wave listeners who desire reception from all parts of the world. Has highly efficient stage of tuned R.F. on all your bands, iron core transformer L F. stage, broad band spread tuning that can be logged. Has built -in 14 61/2" Howard -Jensen electrodynamic speaker, with connections "490" -Tube Professional for extra speaker. Front panel has headphone jack, AVC "Off -On" switch, BFO "Off -On" switch and pitch control, AF Gain volume control and Main Tuning and Band Spread tuning dials. Supplied complete with tubes. Net Price to Amateurs $2995- Terms: $5.99 Down Payment, 52.12 per month for 12 months.

MODEL 436 -A_8 -TUBE receiver. Identical to above Model 435 -A, but has a built -in automatic noise limiter that practically eliminates auto ignition interference and greatly reduces static. Model 436 -A also has the famous HOWARD Inertia Tuning Knobs for fast, fly -wheel action on both main and band spread tuning dials A Net Price to Am at 3975- Terms: $7.93 Down Payment, $2.83 per month for 12 months

The finest receiver built for either communication or entertainment reception. Has two stages of tuned R.F., large callibrated band spread dial, air tuned I.F. transformers, variable I.F. selectivity, temperature compensated oscillator, split stator tuning condensers with ceramic (steatite) insulation, variable audio fidelity, 8 watt 1 push -pull output, automatic noise limiter, and every other worth while feature. The Model 490 is the result of years of engineering and development. Never before, outside of laboratories, was a radio of this quality available. Foreign and weak signals whip in with ease. On broad fidelity the reception of music is equal to reproduction by finest home radios. Complete with 14 tubes, large external speaker in matching cabinet, and complete crystal filter. Net Price to Amateurs $14950 Terms: Down Payment, $10.56 per month for 12 months $29.90 MODEL 437-A_9- TUBES. Has all the features of Models 435 -A and 436 -A, plus an additional stage of I.F. and Crystal Phasing Control to eliminate all unwanted Write me for any amateur or shortwave radio equipment in any catalog signals. Complete, less crystal. or advertisement. Or send me your order and I guarantee that you can't Net Price buy for less or on better terms elsewhere. Write and tell me what you to Amateurs $542 want and how you want everything handled. Your inquiries invited. Terms: $10.90 Down Payment, $3.85 permonth for 72 months MODEL 437 -A complete with crystal. (Note: It is recommended that crystal be purchased with receiver ...11enry, W9ARA to assure proper alignment.) Net Price to Amateurs $62.00 BUTLER, HENRY RADIO SHOP (W9ARA) MISSOURI

RADIO -CRAFT for MARCH. 1941 543 SOUND SOUND ENGINEERING 7-taa !%¢siyn and Pdvisoty S'atvica `Tot Radio-etatt SáGsetiGats

Conducted by A. C. SHANEY

This department is being conducted for the benefit of RADIO -CRAFT subscribers. All 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, Electronic mixing is also employed in order or a copy of the circuit should be supplied in order to facilitate reply.) to avoid the possibility of hontrols developing noise when used ahead of the 1st stage, No. 15 as in your original model. When the 10 -meg. feedback resistor is connected from the 500 - ohm tap of the output transformer to the MOD,ERNIZED AMPLIFIER circuit that can be modernized by simply in- grid of the 6SC7 inverter, the gain should terchanging tubes. be reduced by approximately 5 db. If the The Question . . . One of the reasons the 42 (triode connect- gain is increased, is I am enclosing a (Fig. 1) or oscillation encoun- circuit diagram ed) did not operate satisfactorily as a 59 tered, the plate leads of the power output of an amplifier which I obtained in 1935 or triode -connected, is that the latter is capa- stage should be reversed. 1936. This unit is of course quite obsolete, ble of delivering much more undistorted high -drain being used, such as With 300 volts available at the "B+" due to tubes driving power (a 59 triode delivers approxi- point, the amplifier should deliver approxi- a 59 driver which is a 21/2-volt tube and re- mately 1.25 watts; a 42 triode delivers ap- mately 19 watts. A 5,000 -ohm plate -to -plate quires 2 amperes for its heater. proximately 0.8- watt). In addition, the driv- transformer should be used. Your I would appreciate it very much if you present er transformer originally designed for thé class B transformer is probably 4,000 ohms would send me any information on reducing 59 driver will not operate as well with a 42 and improving the amplifier as a plate -to- plate, and I suggest you try this the drain driver because of differences in recommend- unit before purchasing a new one. The low- whole. ed plate loads. Assuming that you were will- er impedance will reduce power output Could a 59 be changed to a 42, triode - ing to replace the driver transformer, sub- I but there seems slightly. connected? have done this, stitution of a 42 in place of the 59 would Thank you for your commendatory re- to be too much distortion. save approximately 1.3 amperes, but the marks. I am a subscriber of Radio -Craft, and like driver transformer would still undoubtedly it very much. Please continue to run your be the limiting factor in the operation of Sound Department, as I have learned a the amplifier. Your present amplifier draws 8- CHANNEL ELECTRONIC great deal from it. approximately 4.8 amperes at 6 volts. The MIXER ED CORRELL, revised circuit draws approximately 2 am- The Question . . . Silverhill, Alabama peres, which is a saving of nearly 59 %. Preamplifiers and mixers for several high - The Answer . . . Furthermore, the performance of the latter impedance microphones are common and A recommended circuit is given in Fig. 2. amplifier will greatly exceed that of your easily obtainable, but little need has ever You will note that quite a drastic revision original model. been found for a mixing system for several has taken place, not only in circuit; but You will note that the driver transform- high- output, high- impedance inputs such as in tubes, as well. er has been completely eliminated and an used for phonograph and other electronic You will rarely find an obsolete amplifier electronic inverter substituted, instead. devices.

41"mP 6C6 o.F- 797 59(TRIOOE) 6AG 65J- E 3 05 1/ OF. ' NF NtG ` o r L°re>v TRANS -^., tiltn c.,.--- á N.1 ° r f ° Ell- km - Ei Soo (4CN/ 0.1-MP. G7% MFGS i ` ...w5 I- 250 < .: iFIIi` uF D I ° ' é4 Ma. F -- 2 t_ G + - - 15 _ N.3 6x7 óf : W6 : : i _ I . íM ppp [ :. ao05' G I` _ 2 J -w.)i,/ O. La 10úcMN)4 muG ¢iNV1ER1 . i 000 EoM. ON,.S 65C7 I I MF mÉG . MÉÿ A} _r .}' eÉÇ 4 . M G5.7fJ níiv. N.3 _/ IP L- C 1 \ C L F Al , ' /'R . M%jr a ^ a°ÓM$ \ $ió GCG 1 45 MÉG ORIGINAL CIRC-Úi-r OF OLD F 'B. MP ` (1935-36)AMRLIFICR+. ' a MCn)CC 2000 miG II 65F5 GLGG 7 T réi 5 N LJACK gg i0EG5 m[G MF MÉG ,.0.iF- ó - 0i10 +1 Mf G- 14 FCIj M[IMV FA (CKN) Pi?:II(S uC f / G ¡ 6SC7 I $ M 3 \ MP r 33 é5- `ÚO.CiiY /.C+1 ÓNms.. L/ , O.N MF iij or. M[ - o-250 I GX9 i 1 o 3 .e.F u i I- M,en c` 16 x 1t o N,< J 01 , F , -( FKN) o i ans _ 4 n ,i- r3.iF. r INS . pwMS / 11 - - ` 1 .000 _ ( 1 ONM9 g COM 14000 r°n-[4 . MfG M EG. SYlG - lOr: ISOV. ÑEG ?AIRS O.EG MF I 1 'LOiÉ CN.2 CN.1 o00 V ;^ G6LGGT/~ ' `°O0 2o iow ca OW t000W MF. 4F ? Bi - T M ú ú°I 'ICY' iu5! ó 6RECOMMEINEDCIRCUITTOREFUCE AGA,. MF 1Ow . M8 FIG.3 '8CuANNEL ELECTRONIC MI%ER^ .-/(,-----

544 RADIO -CRAFT for MARCH, 1941 1 SOUND

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The growth of the electronic musical in- circuits of the 6SC7, so as to avoid undue strument field has brought forth a need shunting between channels. All resistors for such a system, and I would like to have may be of the carbon 1 -watt type, except- Keep a Weather Eye Peeled! ... your assistance in designing one for an ing those otherwise indicated. Reasonable for the May Issue of RADIO-CRAFT. Electronic Orchestra which I am organiz- care should be exercised in placing the pow- ... ing. er transformer and filter chokes away from It is the big issue of the year, devoted in the I intend to use this with a standard am- any of the input circuits so as to avoid hum main to Sound. In addition to the usual ma- plifier. I will need 3 microphone inputs and pick-up. The terial, it will contain special theoretical and electronic mixer should feed constructional articles on Home Recording, at least 6 input channels for high- output into a voltage amplifier which employs a Phono-Radio Combinations. Public Address electronic instruments. Each input must be tube having a comparatively low input ca- Systems. Amplifiera, etc. Sound is booming! . . . so RADIO controlled separately without having any pacity. Otherwise, appreciable loss of high -CRAFT is going to town! effect on the other input channels. This is frequencies may result. A 6C5 is excellent RESERVE YOUR MAY ISSUE NOW necessary, as foot -control units will be used. for this application. I intend to build it on a separate chassis so a power supply can be included with it, if necessary. CHARLES FREY, MAI LBAG Ottawa, Ohio (Continued from page 517) The Answer .. . frequencies, and so changed his mind about in some method of suppressing all harmonics The type of circuit you require is illustrat- their being rebroadcast from local broad- above the fundamental of the H.F. oscil- ed in Fig. 3. You will note that electronic cast band stations, as he previously claimed lator. mixing is used throughout. Four twin tri- they were. I hope this may prove of some help to. odes (6SC7s) are employed to provide 8 Now I'd like to aid Mr. Ettinger with his some one, and that I may receive some word grids, each one of which connects to its in- troubles, and I believe this will explain them. on how to cure this trouble. dependent volume control and associated But I'm at a loss as to how to go about J. W. DEMISE, channels. Three 6SC7s are used as pream- correcting the trouble. It would lie, I believe, Portland, Ore. plifiers for the .microphone input channels. While independent volume controls for the high -level inputs are connected in this cir- NEWS SHORTS cuit, these may be eliminated if the foot controls of each electronic instrument are to be Requests for F.M. licenses last month in- (a National Association of Broadcasters es- used only. On the other hand, it might be cluded Muzak Corp. (New York), and Sea- timate). desirable to use both controls. The one on board Broadcasting Corp. (Glenside, Pa.), the instrument for the musician thus bringing the total of applications for to adjust, New York City is contemplating the and the one on the preamplifier for some station licenses to 58; 7 construction per- use pre- mits for F.M. stations in the of 2 -way radio equipment aboard ferries as determined maximum. setting. New York a convenience Some economy could area have been granted by the F.C.C. to the boat -travelers, Mayor be effected by using LaGuardia acknowledged last month. 1 common cathode resistor and bypass condenser for all 6SC7 tubes, this would require The 20th Anniversary of Radio has come a 500 -ohm resistor and a 100 -rnf. bypass and gone. It leaves in its wake this indelible The $9,500,000 Edison Memorial Bridge condenser. You will V note that /, -meg. fact: as of Jan. 1, 1941, there are in the over the Raritan River at Trenton, N. J., isolating resistors are employed in the plate United States a total of 50,100,000 radio sets was dedicated last month. RADIO -CRAFT' for MARCH, I941 545 THE FINEST RADIO BOOK 4 WE EVER OFFERED :- the 1940 -41 Radio -Television Reference Annual With $/.00 su3ctietcon to FREE RADIO - CRAFT / WITH our compliments, we want to send a copy of the 1940 RADIO -TELEVISION REFERENCE ANNUAL to you FREE, If you will simply take advantage of RADIOCRAFT magazine's special Reed the summary of contents subscription offer NOW. This offer Is being made for a limited time only. 8' /r a II'/r. with The 1940 RADIOTELEVISION REFERENCE ANNUAL has 68 pages, large sire in this FREE BOOK! In handy book form. Its pages over 170 illustrations. The contents of this book has never appeared before of radio sound, public address, servicing. television, construction articles cover practically every branch circuit Informa- for advanced radio men and technicians, time and money- saving kinks, wrinkles, useful THE 1940 RADIO -TELEVISION REFERENCE. tion, "ham" transmitters and receivers, and a host of other data. ANNUAL contains a collection of the best and of radio regarded as a standard reference work for every practical branch most important articles. Covering as they do The Annuals have always been man wants a copy and service. This 1940 edition ably' sustains this reputation. Every radio of radio, they form a handy operation value to you. so. too. will every nearly every branch of this valuable book- Just as this book will be of unquestionable reference worka. In addition, many time and labor- CRAFT. This magazine brings you big value every month. It keeps you monthly Issue of RADIO- the news, want it saving kinks, circuits and wrinkles. tried and tested Intelligently informed about new developments In radio and television. You want should read RADIO -CRAFT regularly. by practicing Servicemen, experimenters and radio fully but concisely, want It first -that Is why you be we want youl subscriber. Annual. fans have been included. This book cannot This very made now. any price. Yet It is yours by appears aat he right,I notesoId, but a COPY in FREE to bought anywhere at whose contents Is merely subscribing. Use the convenient coupon SAME SIZE AS below. RADIO -CRAFT BEGINNER'S SIMPLE INEXPENSIVE CONSTRUCTION ARTICLES Beginner's Breadboard Special - a 1 -Tube High -Gain All - Wave Receiver- Wiring Pointers for Radio Beginners-A Watch. Charm Size 1 -Tube Set -Beginner's Simple Volt Mllllammeter- Melting a 1 -Tube Broadcast Loop Recetrer -A.C. -D.C. Power Supply for Battery Portables -A 1 -Tube Short -Waver with Band CALL Switching. MORE ADVANCED SET CONSTRUCTION The "High -Seas 4" Broadcast Lamp Radio -How to Build a 6 -Tubo 1.4 -volt Short -Wave Superhet for the "Ham" or Short -Wave Fan -Build the "Lunch Boa 5" Super Set - a Broadcast Battery Portable -How to Build a Plug - Together 8 Tube Broadcast Sot-The "5-in-4" All -Wave Radio for A.C. Operation -An Easily -Built 3 -Tube Midget Broadcast Superheterodyne Receiver, THE SERVICEMEN'S. SECTION Ban Tone Control amplified Variable Selectivity-Prac- tical Servicing Pointers- Servicing Universal A.C. -D.C. Re- ceivers-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 SereenGrld T.B.F. Receiver -Iron Particles in Speaker Air Gap. TEST INSTRUMENTS A Useful Noon Lamp Tester -An Inexpensive Output Meter -Making Mllliammoter Multipllere -Home -Made Frequency Modulator -The Buey Servicemen's V.T. Volt -Meter. PUBLIC ADDRESS AND AMPLIFIERS Build thle Combination A.C. -D.C. Radio and Inter -Com- 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 fiors-How to Build a High- Fidelity 5 -Watt Versatile Amplifier. "HAM" SECTION Ultra -High Frequency Antennae -The Beginner's LowCost Xmittor- Modulator Meter-Phone Monitor -The Begtn- er'e "Ham" Becelver -2;¢ Meter Acorn Transceiver, TELEVISION How to Build a 441 Line T.R.F. Television Receiver-Use- ful Notes on Television Antennas. MISCELLANEOUS Simple Photo -Cell Relay Set Up- Making a Burglar Alarm -How to Build A.C. -D.C. Capacity Relay -How to Make a Modem Radio Treasure Locator. USEFUL KINKS, CIRCUITS AND WRINKLES Making s Flexible Coupler -Two -Timing Chime -A Simple Portable Aerial -An Improvised Non -Slip ScrewDrivsr. NOTE: l'ho book contain. numerous other useful Kinks, Circuits and Wrinkles, not listed here. (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 to RADIO -CRAFT Magazine for Eight Months. Send me ABSOLUTELY FREE 1 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-341 1941 546 RADIO -CRAFT for MARCH, SOUND

Representative Phono-Radio -Recording sets for 1941. Shown above are newest products of the following companies: A, Emerson Radio á Phonograph Company; 8, Lafayette Radio Corp.; C, Radolek Co.; D, Allied Radio Corp.; E, General Electric Company; F, RCA Mfg. Co.; G, Wilcox-Gay Corp.; H, Howard Radio Co. HOME RECORDING 71eoty and Ptactice oá Sound -on- Disc

Sound recording equipment introduced in 1940 enabled radio men generally- Servicemen, experimenters, etc. -to "feel their oats" in this new field. Radio manufacturers finding wide acceptance of modern sound recording facilities have gone to town in incorporating sound recording equipment in their new lines for 1941. Mr. Queen draws on his wide practical experience as a sound recordist to tell RADIO -CRAFT readers short -cuts and recommended procedures for obtaining best results with sound recording equipment. A useful bibliography on sound recording concludes this article.

I. QUEEN

MANY of the current lines of radio PROSPECTS tant relatives and friends take on a new sets are featuring a sound -on -disc The progressive radio salesman and Serv- personal meaning. There is no surer way of recorder as part of the combination, iceman would do well to gain a firm knowl- checking on code -sending ability or musical so that it is possible to make record- edge of the principles which are involved so study than liy listening to oneself over and ings either from the radio set's output, from as to be able to solve difficulties which may .over again. a microphone, or from both simultaneously. arise in this new branch of radio. An en- The business opportunities involved are There is also available on the market sep- terprising technician will find dozens of many. Sales messages may be sent from arately various types of cutting heads, screw practical ways in which to profit by selling headquarters to branch personnel, and store feeds, motors and pickups so that the ex- accessories, and repairing and setting up demonstrations become far more effective perimenter may assemble his own recorder apparatus for recording enthusiasts. when accompanied by a spoken sales mes- utilizing his own ideas in the building. The The first sounds of the baby, a child's sage. Small sound - effects records may be response from the public this past year musical accomplishment, and family har- made up and sold to dramatic groups or shows definitely that home recording is here mony groups, may be recorded and placed parties. to stay and is becoming an entertainment away in an album to be brought out time To aid the radio man to take advantage and educational necessity. This has been and again for entertainment or to refresh of these opportunities, only a few of which made possible by modern developments the memory. The historic broadcasts of have been enumerated, this article will de- whereby a result may be obtained comparing these critical times will become invaluable scribe the principles involved, the systems favorably with many professional discs and in the future, while favorite broadcasts may used, and how to surmount the difficulties with the expenditure of far less time, effort entertain again and again. "Special occa- which may be encountered. It should prove and money. sion" greetings recorded and sent on to dis- of interest to both beginner and to those

RADIO -CRAFT for MARCH, I941 547 SOUND

who may have had some experience with cording since the lower frequencies will cut home recording. over the grooves long before the higher I ones, and the space available will be wasted THEORY when recording the latter. To solve this, in low - Thomas A. Edison found when he spoke cutters are purposely restricted their in assembly and made into a horn directly connected to a needle, frequency response the latter vibrated in accordance with to follow a "constant voltage" characteristic that is, in this his speech. He wound a metal foil about a from about 350 cycles down, that GEM and placed the fixed range, the amplitude is governed only by the revolving cylinder In the play- needle in contact with the foil. The vibrat- voltage and not the frequency. ing needle scratched -in lines in the foil, back, of course, means are taken to raise the and when the needle was again allowed "lows" considerably to make up for their to move over the foil, the original sounds deficiency. In cutters there is also a delib- Q were reproduced. Because the cylinder was erate cutting down of the extreme high fre- inconvenient to handle and difficult to make quencies since it has already been shown use of when duplicates were required, the that such frequencies at high amplitude can- Man disc is now commonly used (except for ma- not be cut by a needle. A.F. CHOKE chines such as the Ediphone). Also, the disc Crystal cutters are also used to some ex- allows recording on both sides. The grooves tent. These are worked on the same princi along which the vibrations take place are in ple as crystal microphones and have the the form of a spiral from the outside to- same limitations as to humidity and tem- wards the center of the disc. perature. They cannot stand much over- The usual cutter takes the form of Fig. 1 load, but have good frequency response. Un- which shows the scheme of a magnetic cut- corrected crystal cutters follow a constant ter. The soft -iron armature is placed be- voltage characteristic and the input must be -V.4. VOLUME INDICATOR - tween the poles of a powerful permanent corrected electrically if an ordinary cutting IM,. magnet on the pivot P. Turns of wire are is to be made. wound about the armature and on passing audio currents through the winding. the DISC SPEED COPPER movement of the armature is passed on to There are 2 general speeds now in use, - -ss- OXIDE the needle at the end, causing a lateral vi- 78 r.p.m. and 33 1/3 r.p.m., the former be- Z--e METER bration of the latter about its central posi- ing common for home recording. Diameter tion. Damping is required to bring the sizes are usually 10 ins. and 12 ins. although -COPPER -OXIDE VOLUME INDICATOR needle back to its neutral position when no smaller ones are available. Considering modulation is applied, arid this may take the linear speed along a groove, it can be seen G.3 form of rubber or oil damping, the latter that near the edge of the disc the diameter 5 eg E COIMBIHEO being more efficient but expensive. is much greater than near the center. From PuTS Assuming for the moment that the un- the previous discussion, it is readily under- modulated or "silent" groove approaches a stood that the greater the linear speed, the yyppI, O\` straight line such as at the edge of the better will higher frequencies be cut, so that as I record; a high frequency will look like near the center of the disc there is a falling - L PADS... Fig. 2A while a low frequency of the same off of fidelity. This is usually not very power level will be as in Fig. 2B. noticeable unless the grooves are very close IN It is seen at once that the amplitude of to the center, and could be remedied by / the lateral movement depends directly upon gradual manual control as the arm moves our the voltage applied to the cutter and that along. An ordinary tone control could be the limit is reached when this is sufficient utilized. IN for the needle to swing from its groove is the experimenter While it unlikely that H PADS - into the adjacent one, ruining the record. or home recordist will encounter 33 1/3 There is also a limit to the high frequency r.p.m. recordings as often as the faster we IN c:3 )r1 which can be recorded, since the higher ones, a description of the system used will go more the tendency of the needle to the be given. OUT move right -angles to its groove, which is at is used for This slow speed extensively IN ,C3 impossible. movie work. Edison's invention used the vertical cut transcriptions and formerly for A 16 -in. record rotating at 33 1/3 r p m in which the needle vibrated up and down FIG.4 -T PADS - common gives a full 15- minute recording when cut along its groove as against the -inch. Be- lateral cut which is being described. While at approximately 125 lines -per 2PRI. HIG5EC. DANCE spacing, the maxi- CARBON PRI. SEC. the first was unsuitable for common electrical cause of the close groove MIKE mum modulation applied must be below that ì recording, its one big advantage was that fact that its volume level was not limited by the of home recordings, but due to the ..: low surface - Mr@ the discs are made of a special - proximity of the grooves. It is desirable to lateral swing noise -level material, more amplification may X put on the disc the maximum slow speed be used in playing back. The FIG.5 'L SAT'''. possible; and, (In the other hand, it is eco- poorer nomical and practical to place as much sound shows that with the same equipment will be obtained. However, proper XTAL APPROX. 50,000 APPRO %. 60.000 on one record as we can. For ordinary home fidelity MIKE ONMS. PRI. OMMS,SEC. up I use a cut of equalization of the "highs" brings them recordings it js customary to high fidelity /I LINE approximately 100 lines or grooves per when playing back so that inch. The spacing is determined by a screw results. feed which carries the cutter slowly while Near the center of the disc, however, the T due to very slow the turntable revolves. fidelity is decidedly poorer 500.014M A magnetic cutter needle assembly pos- speeds. To overcome this, several steps must FIG.6 Siff" sesses a fair amount of inertiá and so tends be taken.. First, the equalization of the to move at a constant speed along the highs must proceed progressively while the L L groove. For example, let us apply a given disc is in motion; that is, while cutting, the Ry R power at different frequencies to the cut- highs must be boosted far above normal ting head. At 100 cycles then, the needle while the inside is being cut and not so will have half the amplitude as at 50 cycles, much as the grooves nearer the edge are since at the former frequency it is changing cut. Secondly, since the needle will dull after `f direction twice as much. The distance trav- a few minutes' use, and since it cannot be eled therefore will be the same for both. This changed while the recording or playback is is called a "constant velocity" characteristic. taking place, it is started at the inside and P E. CELL -back with a will allowed to work out towards the edge. While LIGHT EEO Playing magnetic head P BY R.F. be normal since the higher frequency, caus- the needle is new and can best follow the ..-Á1 ti OSCILLATORR it is near the center ing a more rapid fluctuation, will develop high frequencies, N VIBRATING MIRROR off AMPLIFIER \ /. twice the voltage, but since the amplitude is grooves; after the point has rounded N ON PIVOT ATTACHED nearer /.J/ F TO PLAYBACK NEEDLE half, the voltage for both recordings will slightly, it is following the grooves t . outside, thus balancing the result. Prop- be equal at the playback output. the MD - PHOTOELECTRIC REPRODUCING ELEMENTS-. A serious difficulty will take place in re- er equalization may take place automatically

548 RADIO CRAFT for MARCH. 194! SOUND

(as governed by the position of the arm), or manually. 15 WATT AMPLIFIER at9 " GIVES WAX VS. INSTANTANEOUS Professional and commercial recordings entail intricate processes, which are avail- 3100 HOURSe01105SER VICE able only to manufacturing concerns which specialize in them. A brief description will be given. GOING The cutting takes place on a heavy, thick AND STILL STRONG! disc made of a wax -like material. The wax is then sent to be processed as follows: It is "painted" with an exceedingly fine copper powder which makes it conducting. 1?aJ&9 On immersion in a copper -plating bath a thin copper layer is deposited upon the wax and the two are then separated. The copper layer is backed up with suitable metal and is known as a master. It is the reverse of the wax, and every fine ridge in one has a corresponding depression in the other. The master may be used to stamp out playback records in a press. If records are required in large quantities, the master under- goes additional, similar processes which give MUELLE a "mother" similar to the wax and a "stamp- O'N@¡L er" similar to the master. This safeguards ëpMPHNY the master against damage. The home recordist on the is %~Dilr V other hand vs. roñ co. lc`` é. sra interested in only one or possibly a few CHECK THESE FEATURES onel.a playback discs. There are several types of rr EXTRA HEAVY CHASSIS > blanks available for such instantaneous re- Dt>.., >ovr COMPLETELY tnaen.°°1 f,2j DOUr ID cordings. The oldest type is the aluminum SHIELDED ALL OVERSIZED COMPONENTS deyéa"á;°u°[n::. reá'°it1n;¡ryir1.. disc which is sometimes pre- grooved, that vDao.s°N°t1J SIX TUBE CLASS A PUSH -PULL e «° sir>l a; ;1°O!D,Mr¿IOa is, it _squires no feed screw. The cutter la.. n ass ° Dethó FIFTEEN WATT OUTPUT °M ° a ala simply widens the groove and modulates it. °r á éiej, 4m [o ée ^es THREE INPUT POSITIONS ésr.iv°- j>ré1°;. m eese , The present -day and most satisfactory 2 Microphone, 1 >sem Phono Input á° Hi:1°;lti.[ñ éhv,sé,j, tw blanks are those made either of heavy card 2 -4 -8 -500 OHM OUTPUTS sere i,ls or thin metal and coated on both sides HIGH GAIN, WIDE FREQUENCY RESPONSE tDl°ve!M]J with celluloid. The latter may be either CONTINUOUS, °ltDat[Ns eDllrM1,Ito, VARIABLE TONE CONTROL tals j,Ic`p Na h lr Dan nitrate or acetate. The former is highly in- n tñ, o°e t FOUR STAGES OF AMPLIFICATION 1hj ° w s > ' ° ° flammable and should be handled with care, TUBE LINEUP 1 -68]7, 2 -SC7, 2 -6N6, 1 -81V rn4j..ac while the iqo-:t.nra a é latter being absolutely safe is OPERATION ON 110 -120 Volts, 50 -60 CYCLE 7ww , n. sD%:. i°at> t widely. used. Both are excellent materials; LIST PRICE 224.50 -YOUR COST ONLY ° Yours , , $9.75 (leas tubes) they have low surface noise, and they cut > [ easily, thus requiring less needle pressure. With good care such records may be played - BUY THE BEST FOR LESS! gustier Ne614, 0 a back hundreds of times. In cutting celluloid - Don't let our low price fool you! When you buy a TokFone Am- coated discs, a thin thread of material is plifier you're buying QUALITY. cut from the surface and means are pro- Mr. O'Neil's letter and many FOR AMPLIFIER vided with recorders to have this pushed others like it prove that you need Less Tubes F.O.B.. N.V. not pay high prices to get High (lilt of 11:nched Tunes add $4!fI out of the way of further cutting. Because Quality. no additional processes are involved with Regal Amplifier Mfg. Co. these type discs, the quality is excellent and A COMPLETE ALL -PURPOSE á325o 14 West 17th ft. noise low. SOUND SYSTEM FOR ONLY L New York City watt amplifiers Three general types of needles may be Tho Send mo 1i at $9.75 amplifier described aboyo may be purchased alone loess tobes) used with instantaneous recordings: (1) nr as part of the Complete TokFone Sound System. Here's what you pet: LIST PRICE Send me 15 watt sound systems steel, (2) alloy, and (3) sapphire. The 15 Watt Amplifier as Described $24.50 $32.50 (loss tubes) first is very inexpensive, but wears quickly, 2 12- Speakers @ $7.50 each 15.00 Send me kits of matched tubes @ 2 Wooden Speaker Baffles @ $10.00 sash 20.00 $4.50 so that the beginning of the record is I better Crystal Microphone with Desk Stand 12.50 Semi me screen corers @ $2.23 I Kit of 6 Matched Tubes 9.30 than further on, though good results may Send me completo Illustrated catalog and price list. be obtained. The alloy needle is long -lasting TOTAL $81.30 and can be resharpened inexpensively, giv- For amplifier screen cover add $2.25 Name ing economical and satisfactory service. The Address sapphire is the most satisfactory in service MAIL COUPON TODAY! since it may be used a comparatively long City State time before resharpening is in order. It i should, however, be handled carefully because it is brittle and therefore susceptible For WIRED MUSIC OPERATORS POPULAR PRICE WITH REAL MUSICAL QUALITY! to damage. Breastplate "Dispatcher" tY ne. , Additional copies of instantaneous Leaves hands free. Handsome dielec- discs tric black finish. Adj. fabric neck- are best made by re- recording the first from band. Choice of single or double a second turntable, the output of the play- headset. high or low impedance. Available total of 12 dif. types and back being fed into the amplifier and the Imp. Incl. 71/n ft. flex. cord. Wt. 8 output of the amplifier supplying the cutter. oz. Most attractive, lightweight Because rugged, practical chest mike yet de- of the fact that the noise in the vised for operators of wired music "master" will be present in all the others, units. At your dealer or jobber. it is advisable to make these duplicates be- UNIVERSAL MICROPHONE CO, LTD. fore the first has been played more than a INGLEWOOD, CAL.. U. S. A. few times. If quite a few copies are wanted, it is -best for the individual to decide wheth- IT PAYS TO USE er to make all the discs from óne, or after to.. * THE BEST! University's "Non- a while, to choose one of the duplicates for Resonant" high ef- le has everything you n d to bring customer+ into further re- recording. With ficiency Reflex" your store for records d keep them coming back care, and the Loudspeakers for more. Quality crystal pickupD.' self- starting client will rim drive motor (also In 25. 30 cycle and ACDC) use of new needles all along the line, very always prove most uilt in high fidelity amplifier end Speaker. Even little additional economical in the though Model IllstrateÁ Carts at 814.95 the ex- noise will be introduced. long run. cellence of tone is en good that dealers use It as Or counter or SEE The booth record emonstrtor and HER turntable used for both cutting and UNIVERSITY the MUSIC MASTER. Dealers write for proposition. playback should be free from slight varia- LABORATORIES MUSIC MASTER MANUFACTURING CO. St. 508 South Dearborn St. Chicago, Illinois tions of speed under varying load. For in- a NewGYoí22íCCity

RADIO -CRAFT for MARCH, I941 549 SOUND

stance, the cutting stylus when fed high - latter would interfere with the original level sounds must cut through more disc sounds (if a microphone is being used), the material, and unless the turntable can sup- headphone method is recommended. Inci- ply this load, there will be momentary varia- dentally, the latter excludes sounds which tions. In playing -back, these changes of may be present but which are not being speed will manifest themselves as "wows." picked up by the mike, so that only the A momentary decrease in the recording sounds actually recorded are heard. Most turntable will result in a momentary incomplete recorders do not come equipped for crease of frequency in the playback, and headphone operation. It is possible to place a vice versa. The average ear will detect a high- resistance 'phone across a low -impe- 1% change in frequency. dance cutting head (assuming the D.C. is ex- cluded from the circuit) for there will be MICROPHONES only slight change in resultant impedance; or, a pair of headphones may be connected The recordist will in general use either into the amplifier at the detector output, of 3 types of microphones: (1) the crystal, and some switching arrangement made for (2) dynamic, or (3) velocity. The crystal shutting off the speaker. is a very good talking mike and has a high output so that it requires no special When using the microphone in anything preamplifier. Certain models come in direc- but a small, well- furnished room it may be tional types and are valuable where room noticed that a distinct echo or reverbera- reverberation is likely to be met. Being a tion is present. This is due to the fact that high- impedance mike, it cannot be used very the sound is being reflected from walls, far from the amplifier unless transformers floor and ceiling. A heavy rug on the floor are used to and from the line. They may will decrease the difficulty while curtains be susceptible to humidity and high tem- and drapes will help as far as the walls are peratures. concerned. Since close mike talking increases the sound input without producing The velocity microphone is a very low a corresponding increase frequency in reverberation, For the Best of Service level device but has an excellent this may be tried, although with some mikes and directional characteristic. It may be it is not good policy to talk too closely, spoken to from either front or back, its breath noises being accentuated. sensitivity dropping off gradually and at the sides it has practically no response. Its It must be understood that what we nor- low impedance makes possible long lines to mally hear in a room and what a mike will the amplifier (which must be equipped with hear in the very same room may be two a matching transformer). The velocity type entirely different things! With 2 ears, we RESISTANCE UNITS cannot be used out -of -doors due to wind. have the faculty of being able to concentrate on wanted sounds, subconsciously is re- The dynamic microphone probably the jecting interfering noises. We may, for in- be used under most rugged of all and can stance, be able to carry on a conversation It's for is extra assurance the job practically all conditions. It somewhat in a room filled with other voices, even when when you use these famous Ohmite directional especially to voice frequencies. Parts. Servicemen and Engineers every. the latter are loud compared with the first. It is usually of low impedance, and though A mike, however, not having where have standardized on Ohmite Re- low, its output this charac- its sensitivity is somewhat teristic, picks up sound only in relation to sistance Units for dependable, trouble. can easily be amplified to proper level. free performance. their strengths. A room which may seem The power level of electrical devices such correct for microphone use may give poor See Your Jobber. for: as microphones is measured in decibels results when actually monitoring on the Cordohms- replace internal voltage (db.). The definition of the decibel is 10 'phones, and on the finished record, due to dropping resistor in A.C. -D.C. radio sets. times the logarithm of the ratio between reverberation or outside noises. A direc- Tapped Cords for pilot light also avail- 2 given power levels. In practice one level tional mike will greatly decrease reverbera- able. Dividohm Resistors -Easily ad- is chosen as reference or zero decibel and tion troubles. with it. For justed to resistance you want -or tapped the given level is compared As stated above, we wish to cut the record where needed. Sizes from 10 to 200 those little acquainted with mathematical of at as high a level as possible for best re- watts in complete range of resistance procedure it may be stated that tables sults. For this it is best to have a visible values. Brown Devils -10 and 20 watt logarithms are readily available and require means of control, the eye being more sensi- we wish to know vitreous-enameled resistors for voltage no calculation. Suppose tive to intensity changes than the ear. It 10 than dropping, bias units, bleeders, etc. Re. the level of a power times greater is common practice to utilize a "tuning eye" sistance values from 1 to 100,000 ohms. that of the reference value. The logarithm or electronic visual indicator for this pur- 10 is 1, and 10 times Also Power Line Chokes, Rheostats, and (from the tables) of pose. Several tries will determine how far other Ohmite Units. this value is 10, resulting in an answer of for it may be the eye closes maximum modulation and 10 db. To simplify calculations amount must not be exceeded any every time we multiply this at NEW! remembered that time. A more precise arrangement would be a power by 10 we add 10 to the db. value. OHMITE or minus one using a meter to show the power level. The level may be so many db. plus Two general methods are in use: (1) the LAW upon it is higher or lower OHM'S depending whether vacuum -tube voltmeter; and, (2) the cop- CALCULATOR than the zero value. In most instances the Because a vacuum per -oxide rectifier. One of the figures shows zero level is 0.006 -watt. connections involved. tube is a voltage- operated device, when the Solves any Ohm's Law problem with one -tube voltmeter is setting of the slide! No slide rule knowledge microphones are concerned, it is usual to The vacuum biased al- required! All direct readings. Only 10e to choose reference value as 1 volt per bar, most to cut -off, and as a result, the D.C. cover handling cost. At your Jobber or send a unit of air pressure (created meter in the plate circuit will indicate rela- coupon. the bar being by the sound). The bar is equal to a mega - tive voltage inputs. Its advantage is that it dyne per square centimeter. takes no power from the input, but on the OHMITE MANUFACTURING CO. other hand, it requires a filament and plate 4896 Flournoy St.,Chicago,U.S.A. voltage supply. MONITORING -MIXING 10e enclosed. Send Ohm's Law The other method uses a rectifier in con- Calculator. (Please Print Clearly) There 3 of monitor- are distinct purposes a D.C. milliammeter. The ing the sound input as the recording is tak- junction with Name -up on audio frequencies are changed to D.C. The ing place. First, we wish to check the usually takes the form of copper Address quality of the sound and make sure that rectifier nothing has gone wrong as far as mike and washers, one side of each of which is City State amplifier are concerned. Second, we wish to oxidized. The pure copper is connected to side of the output. Occupation make sure that the level is as high as pos- the positive Radio -Craft -Mar. sible for high ratio of sound -to -noise with- The bridge connection shown in the dia- out overcutting. Third, we must obtain gram will give the greatest output with proper balance between the several sound least strain on the rectifier elements for a sources (assuming more than one). given voltage input. The elements are some- ©flllMllTE, To accomplish the first purpose it is what sensitive to temperature and humid- at about 150 RHEOSTATS RESISTORS TAP SWITCHES necessary to listen to the sound either ity, breakdown occurring on headphones or on a speaker. Since the deg. F. The diagram shows a tapped sec - 550 RADIO -CRAFT for MARCH, 1941 SOUND

ondary in each case, so that maximum modulation on the meter will be obtained at a convenient scale setting (somewhat past half -way). The needle is unable to follow the peak of each individual frequency and will simply follow the average contour of the envelope. A little practice will enable the recordist to obtain maximum cutting SOUND SYSTEMS stylus vibration without danger of over - cutting. To obtain proper balance between several ezedr 7 4a 6e4 óa f.ee1 inputs, it is an absolute necessity to listen - in to the output of the amplifier. It may ...Say Sound System Men be necessary to increase or decrease the If you want the most for your money in a sound system, note these few expressions, radio set's output in relation to the micro- typical of hundreds, about the Ward Airline from men out on the firing line: "Far phone sounds. If two or more performers better than others!" "Exceeds expectations!" "Best I ever heard, and I have owned several!" "Compares with others twice ita price!" "Easily the best for the money !" are being used on the microphone their "Surpasses other equipment that costa much more!" WHY? They say it's because relative positions from the mike may have of Airline's marvelous tone quality, its volume without distortion, its adaptability to be adjusted until they are nearly equal to any use, indoors or outdoors, its low upkeep! (unless one is simply an accompanist). Only monitoring will determine this. Get new Catalog for more of the Facts The Airline Sound System Catalog is packed with additional facts you'll be inter- Varying the power levels of electrical cir- ested in knowing. Shows sound systems for every purpose, and how to select the cuits until they can be combined at the proper amplifiers, speakers and mikes for your own needs. Offers you tremendous desired volumes is known as "mixing." The savings because of Wards direct selling plan . savings PLUS performance. devices used for this purpose are known as Send for this FREE Catalog NOW !I Mail the Coupon! pads. The levels are not increased but the PROFIT BY WARDS stronger ones are brought down to the Time Payments 15 -Day Trial Money -Back Guarantee level of the lower ones in every case. The 3 - - general types, in the order of their effectiveness, are the L, H and T. The diagrams show pads arranged for 2 inputs, but more may be used, of course. 9 GREAT MAIL ORDER HOUSES In following their hookup it can be seen M O R E T H A N 6 0 0 RETAIL STORES that only a portion of the input voltage is -__'1 applied to the output. The 2 horizontal arms MONTGOMERY WARD & CO. shown in the T -pad are varied simultaneous- Dept. RZ43, Chicago, Ill. ly. Only in the latter is the impedance of i either circuit unchanged by variation. Please send me your FREE Sound Systems Catalog at i i once! MATCHING IMPEDANCES Name The impedance of all electrical circuits must be matched as to impedance for maxi- Address mum power transfer and minimum distor- 1 tion. For example, having a 200 -ohm micro- City State phone, we cannot connect this directly to the tube input, since the latter is of very marked value on the primary we must do cially good, thus bringing out needle high impedance. Figure 5 shows the pro- scratch,': the same at the secondary, and so on. and a cedure. The mike is connected to a 200 -ohm It scratch filter is sometimes used in is not advisable for most transformers to this connection. Since this filter eliminates' primary and the tube input is connected to more than double the marked value as not a very- high -impedance secondary. The only scratch but also the higher sound above, for best response. When choosing a frequencies, it is a question whether it is' transformer then would be known as a 200 - transformer, its frequency characteristic desirable where ohm -to -tube input transformer. high fidelity is a requisite. should be kept in mind. Since a crystal assembly is much lighter A high- impedance crystal mike could be than a magnetic'one, it is possible to manu- connected directly to the tube but since a EQUALIZERS facture such a device with a pressure on the long line entails electrical losses, we would An equalizer as its name suggests is used disc of only 1 oz., or so. This light pressure in the latter case use the procedure of Fig. to equalize the frequency response when, results in exceedingly long life for both 5. Long lines may efficiently carry energy due to inherent characteristics, such need records and needles, and in fact, the life of when at low impedance such as approxi- is necessary. It is simply an elaborate tone a sapphire needle in such a device will be mately 500 ohms. Two transformers will control. The calculation of constants for indefinite. thus be needed. Crystal cutters being of high specific equalization is very complicated, so When steel needles are used in the aver- impedance require a high -impedance transit is best to judge by listening to what is age pickup, it is advisable to change needles former secondary with the primary match- proper equalization in any given case. Fig- often, since a dull needle will wear the ing the impedance of the output tube. ure 7 shows the fundamental circuit in- grooves down quickly besides greatly adding Magnetic cutters are usually (a) 8, (b) volved. When the circuit is tuned to the de- to the noise level. 500, or (c) high-impedance, and should sired frequency range, a high voltage is Several models among the pickup arms be connected to the output tube accordingly. built up at this frequency band and the available feature a device for securing A high impedance may be connected directly others more or less bypassed. Variation of tangent tracking of the groove no matter across the output -tube transformer primary the resistor determines the amount df what the position of the arm is with respect using merely a large condenser in series equalization. Figure 8 shows another method to the record. This is desirable from the with the cutter to keep D.C. out. An 8 -ohm whereby a band of frequencies may be by- standpoint of long life of needle and disc cutter may be substituted for the voice coil passed when the circuit is tuned to it and and a minimum of noise. The arm must of a speaker, since the latter is also 8 the other frequencies are passed on without always be free to move easily from side ohms. Both cannot be connected at once much attenuation. Both circuits may be used to side, as it follows the grooves.from the because the resultant impedance is then 4 to simultaneously drop some frequencies edge to the center, or otherwise more wear ohms. If the speaker transformer secondary and bring up others. will occur on one side of the groove and has a tap fox 4 ohms this can be done, how- needle. ever. PLAYBACKS If trouble is had from an "echo" at cer- One principle not well understood even The finished record is the only test as to tain places, it is due to the needle pushing by some technicians in regard to impedance how our best efforts have resulted, and cer- the walls of the groove from one groove matching is the following. Suppose we have tain precautions and care must be taken to the next as it moves, that is the varia- a transTormer marked 500 ohms on the so that the discs may be played back a great tions along one groove will be partly re- primary and 200 on the secondary. It is number of times faithfully. Just as in reproduced along the next. This may be due perfectly permissible to connect to the pri- cording, there are 2 general types of play- to excessively high modulation applied to mary a device with a 1,000 -ohm impedance back apparatus in use: the crystal; and, the cutter which, however, has not quite if we also double the impedance connected the magnetic. The crystal pickup is in wide overcut into the next groove. Improper to the secondary (400 ohms). Likewise, if use, offering very- high -fidelity results and depth of cut will also cause this. Insufficient we use an impedance of '11/2 times the a large voltage output. The highs are espe- (Continued on page 560)

RADIO -CRAFT for MARCH, I 9 4 I 551 SOUND MODERN MICROPHONE TECHNIQUE This is the 2nd article in a series of 3 designed to answer many questions on the choice and use of microphones (and on amplifier input considerations) in Public Address work, and Home and Semi- Professional Home Recording. Sound specialists in every branch of the field were consulted during the preparation of this article in an effort to present concrete, applicational information on this topic. Part I, last month, analyzed Crystal, Dynamic, Velocity and Cardioid microphones. PART II -The Microphone and Its Relation to the Amplifier H. S. MANNEY

Microphone lines may also be shielded or unshielded. If shielded, the lines may be composed of 2 wires and a shield, or a single wire with a surrounding shield. The shields of such lines may or may not have an external insulating cover. Microphone lines may further be classified as high impedance or low impedance. While no official line of demarcation differ- entiates either type, popular terminology Recording the children's has restricted the use of "low impedance" growth audibly in rec- to all lines up. to and including 600 ohms. ords for the family album is the latest use All other higher impedance lines are simply made of home recording classified as "high impedance." They may equipment. Junior and range up to 100,000 ohms. sister are shown here preparing for a record- Most popular high -impedance velocity ing with Philco's profes- microphones are at 10,000 ohms; sionally- designed home terminated recording apparatus while others at 5,000 ohms, and some as low as mother sets the blank 2,000 ohms. The relative importance of these disc in place. Note P.M. terminal impedances will be discussed after dynamic microphone (arrow). the various characteristics of lines have been covered.

LINE RESISTANCE Microphone lines display 3 electrical characteristics: (1) Resistance. (2) Inductance. (3) Capacity.

THE basic requirements outlined in Part which the prime moving element is inductive I of this series may help the technician in nature. This is particularly true of dy- to select a particular type of micro- namic microphones, wherein a moving coil phone for his application. The next is employed. Its impedance is practically step involves the technique of connecting equivalent to its inductive reactance. Its the microphone to the amplifier. Specific D.C. resistance usually is negligible. When types of installation will necessitate the this moving coil is coupled to a transformer, selection of a particular kind of basic micro- the output terminals of the microphone are phone. The academic conception of "connect- inductive, because of the reflected inductance ing" a microphone to an amplifier simply connected to its primary. means running the two wires from the mi- Capacitative microphones are those types crophone output to the amplifier input. In in which the prime moving element is capaci- actual practice, however, a number of fac- tative in nature. This is particularly true tors tend to complicate this apparently sim- of the crystal -type microphone. Its im- ple procedure. pedance is equivalent to its capacitative reactance. When this crystal unit is coupled BASIC CLASSIFICATIONS to a transformer, the output terminals of the Electrically, microphones may be classi- microphone become capacitative, because of fied into 3 distinct groups: the reflected capacity connected to its (1) Resistive primary. (2) Inductive (3) Capacitative LINE Resistive microphones are those types in THE MICROPHONE which the prime moving element is resistive Although microphone lines, per se., may in nature. This is particularly true of the appear to be a prosaic item for discussion, carbon -type microphones, wherein carbon a brief analysis of the types and their granules are employed. Its impedance is ex- characteristics will disclose some unusual actly equal to its resistance. When this problems. microphone is coupled to a low- impedance Microphone lines may broadly be classi- transformer, the output terminals of the fied into long and short. While there is no microphone are resistive because of the re- arbitrary classification of the two, 100 flected resistance connected to its primary. feet is popularly regarded as the dividing When the carbon unit is coupled to a high - line. In other words, microphone lines up impedance transformer the output terminals to 100 feet are usually construed as short of the microphone become predominately in- lines. Those exceeding 100 feet are conductive because the coefficient of coupling is sidered long. This terminology, of course, is usually low (in high- impedance tranforma- confined to microphone lines only as dis- tions). cussed within the scope of this series of Brush "Sound -Cell" Crystal Microphones: AR 26 Inductive microphones are those types in articles. (with transformer); AR 43, R43; BR2S, R22; BI.

552 RADIO -CRAFT for MARCH, 1941 SOUND

The quantity of these characteristics is ductive microphone. It may, under some determined by the length and type of line. conditions, actually resonate at some audio The relative importance of each of these frequency, and thereby produce a very un- 3 characteristics will greatly affect the desirable peak. Furthermore, it will nearly selection of the output impedance of the always introduce an appreciable frequency - zLr microphone as well as the input circuit of discriminating characteristic, usually a pre- r the amplifier. dominant loss of high frequencies. The resistance of a line is proportional to Therefore any high -impedance inductive its length, and therefore, actual resistance or resistive microphone will lose high fre- of any microphone line can be found by quencies when coupled into a long, capacita- FIGI - EQUIVALENT CIRCUIT OF LOW- IMPEDANCE either direct measurement or by referring tive line. Capacitative microphones, on the V MIRE LINE AND RESISTANCE LOSS to copper -wire tables. This resistance plays other hand, will not display frequency dis- no important part in high- impedance lines. criminating characteristics when coupled to In a low- impedance line, such as 60 ohms such lines, but will suffer reduction in a. or 25 ohms, the resistance of a long micro- output. 2x phone line can introduce a considerable loss. This is illustrated in Fig. 1 where E is LINE INDUCTANCE the voltage generated by the microphone, When a twisted pair of wires are run for E ZL, its terminal impedance, RL, the resist- an appreciable distance, the line may dis- ance of the line, and ZL', the input trans- play, in addition to resistive and capacita- former. Although ZL may equal ZL', the loss tive characteristics, an inductive reactance, -- OF CRYSTAL becomes appreciable when RL approaches ZL. which is effectively placed in series with the FIG.2 EQIC VALEN ECIRCUIT The loss in db. may be expressed mathe- generator, as illustrated in Fig. 4. If the matically as follows: microphone is of an inductive nature and ZL+RL+ZL' the amplifier input of an equivalent induc- Loss db. = 10 Log tance, no frequency discrimination will oc- Zx ZL cur, but a drop in effective voltage will be It will be noted that the loss becomes noticed at the amplifier input. jzC smaller as Zr. and ZL' become large, with It will be noted that this nicety of fre- a given fixed value of RL. This simply means quency balance is only maintained when the that the line resistance may be neglected characteristics of the line are similar to in high -impedance circuits. In calculating those of the microphone and the amplifier the line resistance, 2 wires should be taken input. When variations exist between these FIG.3 -MOINE AND LINE CAPACOTYRYSTAL into consideration, that is the one going 3 elements, some form of discrimination will from the microphone MINE LINE to the amplifier, and occur. The usual end result is a loss of high IMPEDANCE its return lead, so that the actual wire or low frequencies. REACTANCE TRANSFORMER length would he double the distance of the These phenomena are outlined for the microphone cable. technician so that he may affect suitable Another point to remember in ZL employing remedial measures and correct any notice- ZL3 long low- impedance circuits is that fre- able discrimination in the coupling link be- quency discrimination will occur when line tween microphone and amplifier. losses become large. This phenomenon is we brought about by the fact that the inductive AMPLIFIER INPUT TERMINALS generator is feeding the resistive -inductance Input terminals of all amplifiers can INDUCTANCE OP network. The FIG.4 -EQUUiIIV LENT .SERIES resistance displaying a non - broadly be classified into 2 groups: frequency discriminating characteristic while (1) High Impedance the load may display a frequency discriminating (2) Low Impedance characteristic. This condition would The high- impedance type may be further bring about a loss of low frequencies, which classified into resistive or inductive. may sometimes be desirable. 7 All low- impedance inputs employ trans- INPUT formers for matching the line impedance to LINE CAPACITY the input grid circuit. Some high- impedance OUTPUT It is apparent that a shielded wire will inputs similarly employ transformers. This have some capacity. It is also obvious that is particularly true of bridging amplifiers, I j longer the shielded line, 5,000 the more the wherein a -ohm input is bridged across FIG 5 -BASIC H.F. ACCENTUATOR- total capacity. Likewise, the less the distance a 600 -ohm line so as to provide minimum separating the wires (the center wire and loading effect. All ordinary high- impedance its shield or each of the twisted wires), inputs are terminated directly into the grid the smaller will be the capacity of the line. circuit of an amplifier without any inter- This line capacity is of a negligible value in vening component. 1 low- impedance lines, but may assume an an If amplifier employs an input trans- PUT appreciable value in a high -impedance line. former, the characteristics of this latter i The capacitative characteristic of lines is unit are just as important as those of the OUTPUT/A of great importance when dealing with transformer employed within the micro- T crystal microphones, because the crystal mi- phone. The frequency response of any in- 1 1 crophone is a capacitative generator, as il- ductive microphone can be no better than lustrated in Fig. 2. This device has effective- the frequency of the transformer into FIG.6 --BASIC H.F, ATTENUATORti ly no series resistance. Any capacity con- which it feeds. As most input transformers nected in parallel with it will only reduce must be built small to avoid excessive hum the voltage output, but will not introduce pick -up, an appreciable amount of loss is CH. any frequency discrimination. usually encountered because of transformer This can easily be analyzed by referring inefficiency. INPUT to Fig. 3 wherein a crystal microphone is When it is difficult to decide whether or connected to a cable having measurable ca- not to use high- or low- impedance lines, pacity Zc. The voltage which appears across the disadvantages of an additional input OUTPUT Zc transformer within the amplifier should al- 2c will be proportional to . As Zc ways be taken into consideration. Its re- Zc + Zx sponse and efficiency are of vital importance. FIG.7 'BASIC L. F. ACCENTUATOR- and Zx are both capacitative in nature, Furthermore, a low- impedance microphone their relative impedance will remain pro- necessitates the use of 2 transformers, one portional through the entire audio spectrum within the microphone and one within the thereby accounting for the fact that no dis- amplifier. On the other hand, high -impe- crimination occurs when long, capacitative dance crystal microphones require no trans- lines are used in conjunction with crystal former, while high- impedance velocity or INPUT microphones (which do not employ internal dynamic microphones require a single trans- CH. ouTPuT/ step -down transformers) former within the microphone itself, and This capacitative nature of a long, high - none in the amplifier. impedance line, however, will greatly im- For a non -frequency- discriminating match, pair the original characteristics of an in- it is important that the inductive micro- FIG.8 '-BASIC L.P. ATTENUATOR."

RADIO -CRAFT for MARCH, I941 553 SOUND

response of a complete system. In all practical work, however, a competent technician can easily judge what type of discrimination is taking place, so that fundamentally, the problem evolves itself into incorporating an equalizer within the amplifier, which will attenuate or accentuate either one or both the high or low end of the audio spectrum. A simple high -impedance acceatttating circuit, which can easily be interposed between 2 high- impedance stages, is illustrated in Fig. 6. Likewise, a high- frequency attenuator is illustrated in Fig. 6. Basic low -frequency accentuation and attenuation circuits are given in Figs. '7 and 8, respectively. The degree of equalization desired will determine the values of the various resistors, inductances, and capacities. Some experimentation will usually provide the desired degree of equalization. Where a complex frequency discrimination occurs, as when the frequency response characteristic is composed of predominant hills and valleys, the design of a suitable equalizer becomes involved, and unless absolutely necessary, should not be attempted A Two -Way by the layman. Ì System Complete EVALUATING THE FREQUENCY with Integral Dividing Network DEFICIENCIES When a system is being judged for lack or presence of any portion of the spectrum, Providing faithful wide -range reproduction obtainable only with a Two -Way System care should be taken not to be misled in the presented for the first time in a com- wrong direction. For example, a system that pact UNIT including PM high- and low frequency sneakers. frequency- dividing net- has a predominant bass boost can sound as work and impedance matching facilities . . . though high frequencies were lacking. On at remarkably low cost: For high quality phonographs wherever a the other hand, a system that accentuates BETTER speaker is needed, use Jensen high frequencies, may appear to be lacking JHP -51. List Price S46.50. Also available in complete Reproducers with Jensen Bass in lows. It is obvious that the best corrective Reflex. Write for free Data Sheet 119. method is to eliminate the source of trouble and not introduce an additional source of discrimination. For example, the system which has excessive highs and appears to lack lows may W." RADIO MFG. CO., 6601 SOUTH LARAMIE AVENUE, CHICAGO be subjectively corrected by introducing a bass accentuating circuit. This is not the phone feed into an inductive input having most desirable procedure to follow, for it similar impedance -frequency characteristic. is usually much simpler and more economical RADIO This general rule holds true for all ideal to reduce the excessive high frequencies. coupling circuits between microphone and This latter method will not introduce any amplifier. When a cross -match is made, that secondary troubles, such as increase of hum is, a capacitative, microphone coupled into when low frequencies are accentuated. It DIAGRAMS a resistive input, or a resistive microphone is hoped that this discussion will bring to coupled into an inductive input, some form the attention of technicians, many condi- MOST -OFTEN- NEEDED of frequency discrimination is sure to occur. tions with relation to the use of micro- Under some conditions, this type of dis- phones which affect the overall response of crimination may be desirable and used to the system and that better judgement will ALL MAKES 1926 -1938 full advantage. In most cases, however, be exercised in the selection of various ' MOST In this one low- priced manual the technician is unaware of, and therefore components in view of the characteristics you have all the circuits you does not control, the discriminating charac- OFTEN - really need. 427 diagrams of outlined. most -often serviced radios is the teristics introduced by the link whicL cou- help you want for easier. faster. ples the microphone to the amplifier, The following, concluding article will NEEDED nod bettor repairs. You will and outline several points which should be con- 4 out of 5 diagram 95 needed In this manual. sidered when actually using the micro- RADIO 244 pages.. large 8%x11 MICROPHONE EQUALIZATION 1n. site. Special price phone. DIAGRAMS Frequency discrepancies which may exist HOW TO SAVE TIME in a microphone, its coupling link, amplifier Service hints, diagrams, align- and its acoustic environ- ment data, test charts. and part: input, or speaker, Feature Articles in the MARCH 4OUT5 lists included will prove lime ment may be compensated -for by suitable OF savers and money- makers for RADIO C TELEVISION you. Oat then handy "on -the- selection of equalizer circuits within the CIRCUITS job" handbook.. No need to amplifier proper. CBS Demonstrates Color Television with work hlind- folded. Tho time "Live" Subjects YOU saved in two days will more For varied applications, it is usually ad- New Frequency Modulation Transmitter and NEED than pay for these manuals. visable to provide a variable set of equalizers Receiver for Amateurs- Ricardo Muni.. frequency E.E., Donald & Warren Oeatreicher 1939 -1940 DIAGRAMS so that any predetermined re- Electronic Music Through Your Radio Set be from - This single niJimal will give you sponse characteristic may obtained H. G. Clain. M.E. over 80% of all 1939 -40 circuits the entire system from microphone to speak- Adapting Mobile Amateur Equipment to the MOST POPULAR ever needed, acquaint you with New Regulations- Howard G. McEntee, recent radio developments. and er or recording head. The design of equal- W 2FHP teach you how to service quickly both varied and complex. Design ar izers is "CQ "- Latest News of "Ham Doings" - millions of sets sold last year LeKaahman, 1940 Models of 43 manufae' details are beyond the scope of this discus- Larry W2IOP turers. 212 large pages, $1 Some fundamental principles, how- Principles of Frequency Modulation Explained 81x11 inches. Laniard sion. -F. L. Sprayberry RADIO >t Quantity at ever, will be outlined in the hope that tech- International Radio Review, Including Circuits nicians may be able to correct for some fre- of Foreign Receivers An FM Receiver for the "Home Constructor" DIAGRAMS FREE EXAMINATION quency discrepancies. L. M. Dezettel, W9SFW form of discrimination "Question and Answer" Box SUPREME PUBLICATIONS. Room 645 The most distorted 3727 W. 13th St.. Ch,easio, Illinois occurs when the character of the original Latest Radio Patents Ship thq uals checked. 7 must be motioned or you Radio Hook -Up Department will refund n my money In fun. sound is altered to a noticeable degree. This Experimental Radio Section Most Often -Needed Diagrams, 1026 -1038. n 31.05 usually occurs when the system attenuates Interference Prevention in Television Recep- D Most Popular 1040 Radio Diagrams. e 81.50 tion-Thornton Chew, Television Engineer D r a loalnt3...... d poatpald or accentuates either or both high and low D S end C.Ü.D. I Ill Pm' ihe'mnliman. A Simple "Signal Tracer" frequencies. Ordinarily, elaborate equip- NYA Do Fine Radio Job in Maine HAASE ment would be required to check the overall (tIte ..a. w and this comer. . - 554 RADIO -CRAFT for MARCH, 1941 SOUND

INDEPENDENT POWER SUPPLIES

PUS WULL improve -audio Output STAGE Ti Fixed bias, an important feature in audio amplifiers, has been thus far supplied by either expensive or inconvenient devices. The author of this article has developed very unusual and A.F. economical circuits to be used in their stead. INPUT

JOEL JULIE R3

IN MANY receivers and in many audio amplifiers it is often advantageous to have more than one independent power supply. This circuit by elim- C4 'Changes of current in one part of the inating the extra circuit affect the voltages of other parts of winding of the trans- the circuit. Generally in radio receivers all former, makes possible the voltages are obtained from one power the use of a standard - type transformer. It sug- (EAUTI ON: supply, since this is the cheapest method of gests a less expensive CT CHASSIS equivalent TO LINE EXCEPT obtaining the desired result. However this of the circuit THROUGH situation has its advantages for the Service- shown in Fig. 2. man inasmuch as it affords him an opportunity to suggest to customers improvement FIG 3 in operation through the addition of a separate power supply, as for example one of rangements are known as self -bias those here described, since ratings with self -bias as compared with 60 to achieve greater op- the plate current is fed through a resistor, erating efficiency (primarily, greater with fixed -bias. The same ratio of power am- providing its own bias. Fixed -bias is a bias plifier power output -greater dynamic outputs holds true with almost all the out- range voltage supplied by an independent source. put tubes. Strangely enough -for a given input), and hence, improved The there are some great majority of output tubes will tubes, like the 6F6, operated as a pentode, tone quality. work with practically the Let us same degree of that will work as efficiently with self -bias concern ourselves in this article efficiency with fixed -bias or self -bias only with the factors affecting under as with fixed -bias even in class AB. The the power class A operation. Significantly, most tubes, number of these output. The power output of an audio stage tubes, though, is very small. though, operate more efficiently if fixed -bias For those cases where an independent depends largely upon the plate supply and is applied, even though grid supply voltage operated in class A power supply for grid bias is necessary, of that stage and the only. various stability of those voltages arrangements were used in the past, which were either inconvenient or expensive, under different loads; this SELF -BIAS EFFICIENCY stability is what is usually or both. These are still being used today- In class AB operation, bulky "C" batteries or expensive, complete- called the regulation of the where power supply. the operating point is ly independent "C" power supplies. In Figs. chosen near the cut -off point 1, 2, and 3, is shown a convenient and cheap of the method of - REGULATION characteristic, the obtaining a fixed "C" supply plate current of the output voltage, which is adaptable to many condi- As far as class A operation stage varies considerably tions of service. is concerned where the oper- with the variation of the sig- ating point is chosen on the nal strength. If self -bias SINGLE -ENDED OUTPUT straight part of the charac- were used the variations of In 1 teristic we would Fig. we have the design applied to have no the plate current would cause a condition trouble with the regulation of tranaformerlesa operation variations of grid voltage, (A.C. only). We use a voltage doubler oper- of the power supply, since the plate current thus causing displacement of the operating ated remains practically constant as 2 independent power supplies. One under varying point of the output stage. A class AB stage section of the rectifier supplies signal strength. In class A then, we get the plate can operated in such a manner would not work and screen -grid voltages; the other section, along successfully with one power supply, very efficiently. In fact obtaining a pair of 2A3s will control -grid voltage. The field of the speak- the grid voltage as a voltage drop supply 15 watts output at 300 volts plate er is utilized on a cathode bias resistor as a filter choke for the con- or on a resistor voltage with fixed -bias as compared with trol -grid voltage. Provided that placed between the minus ( the capaci- -) terminal of only 10 watts output with self-bias; a pair ty of condenser Cl is large enough the plate supply and the ground. These ar- of the plate 6L6s will supply 40 watts at its maximum voltage of the output tube can be taken

SINGLE- T { PUSH -PULL ENDED OUTPUT CHOKE T2 OUTPUT STAGE + VRl STAGE RECTIFIER - R3 vvvvvv- C2 f RECTIFIER ` T I Cl ) SEC' _

CHOKE

3V R4 X (fir J la C3 Il --- 5 sect - FIG. 1 SF AKER SPEAKER 115V,A.C. FIG.2 FIELD- i.. VR2, RECTIFIER® 115V ,A.C. RADIO -CRAFT for MARCH, I 9 4 I 555 SOUND

using, for example, a pair of 6A3s as the NEW FM AUDIO AMPLIFIERS power tubes, a 5T4 rectifier, and an 84 grid Designed by A. C. Shaney and field supply rectifier -the following: RESISTORS FREQUENCY RANGE: 13. 30,000 c.o.s. db R1, R2, 50,000 ohms, 1 -W.; POWER RANGE: 0.003 to 30.000 Milliwatn MUSICAL RANGE: I I Octaves R3, 20,000 ohms, 15 W.; DYNAMIC RANGE: 80 db R4, 600 ohms, 10 W.; Outstanding inin their performances construction. and appearance. amplifiers were pecifically designed CONDENSERS for with frequency modulation tuners. standard modulation iv and absolute fidelity Cl, C2, 8-mf., 350 V.; añamplitudeono reproducers. Lead, bye a wide margin the very resistance. impedance orO transformer -coupled C3, 30 inf., 150 V.; amplifiers. incorporate two basic and DC balancing circuitsits (Pat. app. for) which provide greater Circuit C4, 30 mf., 100 V.; than conventionalamplifiers. Misc. Guaranteed for FIVE YEARS Field, 750 ohms; Write for literature describing our FM Amplifiers Choke, 100 ohms, 12 hy., 125 ma.; Transformer T1, output 3,000 ohms plate - AMPLIFIER CO. of AMERICA to- plate; 17 WEST 20th STREET NEW YORK. N. Y. Transformer T2, power, 5 V., 2 A.; 6.3 V., 4 A.; Sec. 1, 125 ma., 275 V. r.m.s.; Sec. 2, 100 ma., 125 V. r.m.s. from the cathode of the rectifier. That arrangement will provide for better PUSH -PULL PENTODES regulation and also will snake available to Fig. 3 is almost identical with Fig. 2, the the output stage, the maximum voltage ob- only difference being that here we do away tainable, or 120 volts. with the extra winding of the transformer The appropriate values of resistance and and make possible the use of just one or- capacity when using a type 43 power am- dinary -type transformer. The bias -supply plifier and 25Z5 rectifier, for example, would rectifier VR2 gets the A.C. plate voltage be about as follows: directly from the A.C. line. Here too .we RESISTORS use the field as a filter for the "C" supply. Rl, 75,000 to 100,000 ohms, 1 -w.; Those who desire to build a 60 -watt am- R2, 400 ohms, 10 W.; plifier will find the following data useful. Use this Simpler CONDENSERS The values are approximate, as a result of Cl, 40 mf. or more, 150 V.; calculation. Tubes used are taken to be 2 Better Selling C2, 16 mf., 150 V.; 6L6s in the output; as a plate voltage recti- C3, 30 mf., 150 V.; fier an 83 is used; the bias voltage rectifier Record Changer C4, 25 mf., 25 V.; VR2 is an 84. Misc. CONDENSERS to operate better. easy -sells 8 950 GI-C1 20 Record changer is simple and Field, 2,000 ohms; Cl, mf., V.; ONE lever adjusts for it or it records or Choke, 400 ohms, 12 hy., 30 ma.; C2, 16 mf., 350 V.; for manual playing. Easy to install -saves Transformer T, output, 9,500 ohms (im- C3, 30 mf., 125 V.; labor. Complete unit (changer, turntable, motor, tangent -tracking crystal pickup) pedance). C4, 25 mf., 25 V.; mounted on base plate, ready for your cab- A type 43 tube operated in such a manner RESISTORS inet. Order one to test, from your Jobber. would deliver about 1% watts; a 25B6 R3, 20,000 ohms, 20 W.; would deliver as much output as a 6F6 hav- R2, 240 ohms, 10 W.; 'GENERAL INDUSTRIES CO, ing 250 volts on its plate. It can readily be Misc. Dept. 20 - - Elyria, Ohio seen that in small A.C. receivers, the cost Transformer Tl, input, for class AB, for of the power transformer can be saved 6L6s; while we may still obtain as much power Transformer T2, output, 3,800 ohms plate - l as we could with the transformer. As com- to- plate; UDIOGRAPH pared with the regular voltage doubler this Transformer P.T., power, 5 V., 3A.; 6.3 circuit has many advantages, the most im- V., 9A.; 490 -0 -490 V. r.m.s., 250 ma. NE Sound Catalòg portant of which is better regulation and The value for resistor R1 can not be de- AUDIOG APH Sound Systems repre- of course, the welcome feature of a fixed termined without the exact knowledge of "C,, bias supply. the taken from sent the atest in Sound Engineering current off the point "B +.'t This circuit makes possible for the first Its value should be calculated to deliver 300 and Desig complete line plus pre- -a time, the attainment of fixed -bias in trans - volts at the point "B +." tested accesso formerless- operated apparatus, without the The circuit of Fig. 3 means something necessity of using batteries. special to the Serviceman who builds his NEW LOWER RICES own audio amplifiers, and to the amateur Outstanding quality and erform- PUSH -PULL TRIODES who wants an efficient plate modulator. You once at prices that help you n eet any can actually get 60 watts out of a pair In Fig. 2, a circuit of 2 independent power of competition. 6L6s without the need supplies is shown using a single transformer of using 2 power transformers or 1 special of exactly the same size as if 1 power supply transformer ex- WRITE FOR FREE OPY pensive for were used. The only difference is that the its extra windings. JOHN MECK INDU RIES There is a very high -voltage winding is divided into 2 parts; important item to be 1313 W. Randolph St., Chicago, IIL remembered in one that supplies 315 volts for the plate making such a change. That voltage, and one that supplies 140 volts for is, whenever fixed -bias is used the total re- the control -grid and field excitation-if for sistance in the grid circuit should under no example we are considering a pair of 6A3s. circumstances exceed 50,000 ohms. The rectifier VR2 is heated from the same The application in Fig. 3 combines most source as the receiver tubes. Its cathode efficiently the factors of economy, simplicity DEAL DIRECT . and versatility that typify our new circuit. FACTORY PRICES is connected to ground. As a result we may 60 As a means of obtaining satisfactory, fixed 1s increase the output of the amplifier from Portables $8.08 "C,, bias it is far in advance of previous tubes.Farm 10 to 15 watts without increasing the size up. sets 88.9P methods, and those designs presented here D. 4 of the transformer. Foreign bande be S8.013 up. Sample, As a 2nd advantage the lower operating can used to good advantage in the con- 506'e off. Quantity dia. most receivers counts. Free 1941 Bar- voltage for Cl may be mentioned. Ordi- struction of and power am- tlil, of 10 -day FREF. case field, plate and con- plifiers. tr1o1. gent's proposition d discounts. Mall postcard narily for this if s QOLDENTONE RADIO CO., DEPT. RC, DEARBORN. MICH trol -grid voltages were to be obtained from 1 power supply, the operating voltage for It should be mentioned as a precaution Cl would have to be about 455 volts, neces- that no direct ground connection should be FLMGR'E\PH sitating the use of a high- voltage condenser, used in sets employing circuits of Figs. 1 lÿ VOICE AND MUSIC RECORDINGS or better yet, 2 condensers in' series. A 3rd and 3, since one terminal of the line is con- Lengthy or continuous recordings now possible with newly advantage is better regulation since the field nected to the chassis. If grounding is neces- patented ' FILMGRAPH." Over 13 hours of indexed voice, radio, code, telephone recording on a single 500 ft. reel of excitation is obtained from the bias voltage sary, it should only be. done through a film costing $3.00 and up. No other expense. INSTAN- thus making the resistance of the condenser. TANEOUS and PERMANENT play-back. Can easily be supply, synchronlred with Motion pictures. Bulletins free. plate supply circuit as low as possible. Note: The author reserves all rights to MILES REPRODUCER CO., INC., Dept. RCS Under these conditions we would have the commercial application of the material 012 Broadway New York City for the values of the component parts- contained in this article.

556 RADIO -CRAFT for MARCH, 1941 ELEC:TRONICS

L L2

I 1 1 1 1 a rCgc Cpt v

Rg Rp

WWI The Oscillator may fake any one of 3 basic circuit arrangements: A, shunt feed, arate coils electrically connected; and C, series feed, by means of separate coils. using a tap on a single winding or autotransformer; B, shunt feed, using 2 sep- Compare these working diagrams with the theoretical oscillator circuit, Fig. IA. VACUUM -TUBE OSCILLATORS 19ná 7!yow 1 ey Woeh What are the factors which enable a vacuum tube to generate alternating current, i.e., function as an oscillator; and, frequently of more immediate importance to Servicemen, which may cause an oscillator circuit to cease operating? These fundamentals are here given microscopic examination. Any radio man reading this article, if he takes care to absorb the information it presents, cannot fail to, have a firmer grasp on one of the basic building blocks of modern radio transmission and reception. This article, by the Chief Instructor of a well -known radio school, has been reprinted by special permission from National Radio News. J. A. DOWIE

N every radio transmitter, in every super- oscillators which maintain oscillation by In an oscillatory circuit the tube does not heterodyne receiver and in radio servic- ionization of gas and by the projection of become an oscillator-it continues to act as ing equipment, we find oscillators pro- electrons through chambers where the rate an amplifier -amplifying the voltage which ducing the signal. It is this oscillator of travel of the electron determines the is applied to its grid circuit and sending it that supplies the signal that is so essential frequency of oscillation. In this discussion through the circuit coupled to its plate. in carrying out our work. Since it is so im- I am going to cover only the operation of When the plate circuit is properly coupled portant in radio, let's study in greater detail the better -known oscillator circuits. to its respective grid circuit so that it con- how it works. That is, how does an oscillator The oscillators that are used most exten- tinues to amplify the signal it excites itself, operate in generating the signal and how sively in the radio field are, for example, the circuit and the tube become an oscillator. does it continue to develop a signal after the tuned -grid, the tuned -plate, the Arm- Since the tube continues to operate as an it is placed into operation? strong, the Meissner, the Hartley, the Col - amplifier even though it is in an oscillatory pitta, the ultra -audion, the push -push and circuit let us study some of the important OSCILLATOR CIRCUITS the push -pull types with either the tuned - characteristics of vacuum -tube amplifiers. There are a large number of different grid or tuned -plate, or both. types of oscillators in operation. There are In my discussion I will cover these circuits BASIC CIRCUITS and their operating characteristics. It will In Fig. lA is shown a triode having elec- be pointed out that when you understand trode supply voltages. Its operating point the characteristics of oscillator circuits being at a on the Eg -Ip characteristic curve which depend upon capacitative or inductive shown at B. feedback that you will understand the oper- It can be shown that as the grid voltage ating characteristics of all of the conven- of the tube is driven in a positive direction tional types of oscillator circuits mentioned by some force that this will result in a de- above. crease in plate voltage between P and X. This is due to the increase in plate current, PHASE RELATIONSHIPS the voltage drop being in the plate load It can be stated that the primary require- and the polarity or phase of the voltage ment in order to sustain oscillations in in this circuit being in a negative direction. either an inductive or a capacitative feed- Now when the grid is driven in a negative back circuit is that the applied grid -to- direction in the grid circuit the plate circuit cathode voltage must be approximately voltage goes in a positive direction. 180° out -of -phase with the plate -to- cathode This can be proven by Fig. 1B. Point 1 voltage. on the grid voltage moves positive to point This means that when the grid -to- cathode 2 and the plate current increases from point voltage is rising in a positive direction the 3 to point 4. An increase in plate current plate -to- cathode voltage must be dropping means a drop in plate -to- cathode voltage; in a negative direction. That is, the tube and from a high positive value to a less itself acts as an amplifier. Then, too, if positive value with respect to the cathode. the reversal is of a sine wave character the It is therefore evident that the voltage ap- waveform of the signal generated will be plied to the grid- cathode circuit must always a pure sine wave. Remember that the volt- be 180° out -of -phase with the change tak- age applied to the control -grid of a tube ing place in the plate circuit of the tube which is not overloaded controls the plate in order to have the tube excite itself and circuit output waveform and that the thus maintain oscillation. triode tube is easily adapted to the inductive So long as the signal voltage on the grid or capacitative feedback types of oscillating of the tube does not swing beyond points circuits. b and c on the Eg -Ip curve there will be

RADIO -CRAFT for MARCH 1941 557 ELECTRONICS no waveform distortion introduced and if the coupling between the grid and plate Ip circuit permits uniform waveform changes, then a sine wave will be developed in the plate circuit and consequently at the output of the oscillator. This condition of oper- is known as "class A" amplification. ation IIII¡IIIÌ1illi__ tie AMPLIFIER CHARACTERISTICS .- -E9 1 The efficiency of an oscillator is dependent Ip upon the claim of opera- 1 to a large extent CLASS"A"CYCLE tion. As in the case of the various classes 1 of amplifiers used, the class A, B and C, the efficiency of the oscillator tube is the same Ip as if it were an amplifier insofar as the CLASS 'B CYCLE tube is concerned. Figure 2 shows the rela- bias voltage, grid tionship between the grid Ip swing and plate current for the 3 funda- may mental types of amplifiers all of which CLASS "C" CYCLE be used in the operation of an oscillator. The outstanding operating characteristics of a properly- operated class A amplifier is Fig. 2. Relationship between control -grid bias voltage, grid swing and plate current for class A, B and C the fact that the variations in excitation amplifiers. In class A. the grid never swings positive; In class B the grid swings positive only ove+' the linear region of the plate current characteristic; in class C the grid swings beyond the plate current do not produce a change in the average D.C. saturation point. plate current. That is, the increases in plate current are equal to the decreases and for this reason the average current taken from is confronted with the job of connecting the FEEDING POWER TO OSCILLATORS the power supply does not change. The grid unmarked leads of an oscillator coil to pro- Figure 3B shows how the power or elec- excitation signal never drives the grid posi- duce oscillations. trode voltages are supplied to the tube so tive with respect to the cathode of the tube. In order to connect the coils of an oscilla- it can amplify by what is known as the In the class B amplifier increases in grid tor so the phase will be correct, refer to shunt or "parallel" feed method. The signal excitation produce proportional increases in Fig. 3B. Note that a and d are at opposite voltage generated is in parallel with the the average D.C. plate current, that is, an ends of the oscillator coil. If lead c is con- path taken by the power to the tube increase in excitation raises the output of nected to the plate coupling condenser Cpc electrodes. the oscillator. The grid excitation is suffi- then to insure proper polarity lead b must the grid positive but not off condenser In Fig. SC the same circuit components cient to drive be connected to the grid coupling us the the straight portion of the Eg -Ip curve. difficult to remember this re- are shown but connected to give Cgc. It isn't feed method of supplying power to The class C amplifier is operated so that quirement. I always says that "when the aeries grid excitation show the tube electrodes. Note that the coupling further increases in grid is at one end of a coil form having and no further increases in the average plate must be at the condensers are now bypass condensers 2 windings then the plate the cathode of the tube. current. This condition of operation can other end of the coil form when the 2 coils are connected to only exist with the flow of grid current. are wound in the same direction." That is, It is, of course, possible to use the series The grid is driven positive and far enough these 2 leads are always on the opposite feed in the grid circuit and the parallel or to cause plate current saturation. It can ends of the 2 coils or at the 2 inside shunt feed method in the plate circuit or also be stated that an oscillator employing terminals. shunt feed in the grid circuit and series a class C amplifier has very high harmonic This rule holds good regardless of the feed in the plate circuit. The method of feed content as the plate current exceeds the placement of the tuning condenser or con- selected by the engineer in the construction saturation point as can be seen at the upper - densers or the method used in supplying of the device may be any one of these com- right in Fig. 2. power to the oscillator circuit. The tuning binations. The series plate feed method being condenser or condensers do not shift the somewhat more efficient than the shunt feed HOW PHASING IS OBTAINED phase of the voltage across the coils suffi- method as this method prevents Rp from As stated there must always exist a 180° ciently to stop oscillation. shunting the plate circuit of the oscillator. phase shift in the voltages between the grid and plate circuits in order to use a triode as an amplifier tube in an oscillator circuit. VT (A.C. TANK CIRCUIT VOLTAGE) This required phase shift can be obtained by means of a or through the TIME .-1 transformer PLATE w aid of a phase- shifting network or phase VOLTAGE r?

inverter consisting of another tube. MAXIMUM 1 V (PLATE SUPPLY VOLTAGE) vP Most oscillatory circuits use a transformer O J 1 1 IFI consisting of either 1 winding having a I MINIMUMYP tap on it or 2 separate windings. For ex- G Fig. 3A a y2c,cLE I ample, shows tapped transformer, OR 190° 1CYCLE often referred to as an autotraneformer. OR 3600 The position of the tap being selected to MAXIMUM POSITIVE give the required excitation voltage for the Fig 4. These plate and .1 ZERO GRID GRID VOLTAGE VOLTAGE class of amplification desired. grid currents and volt- TIME ages represent operating The transformer winding gives us the conditions in the oscilla- GRID r because one end of tor circuit of Fig. 3. Re- .GRID BIAS VOLTAGE desired phase shift the VOLTAGE will be of opposite polarity member that graphs like winding always these are always read ---- with respect to the other. No coil or winding from left to right. When O on a transformer can have the same polarity comparing 2 voltages, r--i when the winding is wound in one direction. that one which reaches a positive peak closest while A.C. GRIO I One end will always be positive the to the vertical reference 1 line is said to lead the VOLTAGE l other is negative. This is the condition I other; thus, VT. in A PG when are linked together by the I all turns leads ea in B. = I Ip field. 1 AVERAGE same electromagnetic PLATE a IP we oscillator coil having 2 wind- CURRENT ¿I If use an I V ings then the windings must be connected 11; so that the grid end of one winding will O O I f TIME -Y be of opposite polarity with respect to the , I /2 ,1 plate end of the other, thus keeping the CYCLE I I 180° phase shift. The connections will be I I GRID Ç I IG AVERAGE 1G as shown in Fig. 3B. CURR E NT I I e V V COIL POLARITY O O t Oftentimes the Serviceman is required to TIME make an oscillator coil replacement and he FI .4 1941 558 RADIO -CRAFT for MARCH, ELECTRONICS

AUTOMATIC "C" BIAS voltage across winding Ll should be high GENERAL DISCUSSION Although the circuit shown in Fig. 3A has and naturally the greater the number of In discussing how oscillations are main- a "C" battery to enable class A operation turns in coil Ll, the higher the voltage de- tained we stated that the veloped. plate current in- of the tube at a given point on its Eg -Ip This will mean more excitation volt- creased to a value established by the emis- curve, it is possible to obtain class B and C age and also a greater plate current as more sion characteristics of the tube. An oscilla- power will be required to operation by omitting the battery. supply the extra tor tube functioning in this manner will not This latter is possible because the upper excitation. These facts also apply to the operate very long as it will lose operation of its emis- end of the resistor Rg will become negative the circuit shown in Figs. 3A sion and become defective. It is for and B. this when the grid is driven positive by the ex- reason desirable to The provide a self- biasing citation signal. The grid serves as the anode turns ratio factor is also present resistor having a value of resistance which and the cathode of the tube as the cathode, and holds true when the interelectrode causes the production of the automatic "C" of a rectifier tube. The positive end of the capacity of the tube is used in tuning the bias voltage will entire circuit that give class B or C resistor Rg being connected to the cathode and when the tuning con - operation of the oscillator tube. Lower effi- Rg may be considered the load on the rec- denser is connected between terminals a and ciency of operation is obtained when d in using tifier. The voltage across Rg is dependent Figs. 3A, B and C. When the tuning either class B or A condenser operation. upon its current and resistance. is connected across either coils The self- biasing grid voltage thus de- Now that we know how the proper polar- Li or L2 then the coil without the con- veloped should limit the peak plate current ity of the winding can be ascertained, how denser across it has the least number of rather than the emission characteristics of power may be fed to the tube and how the turns. This is due to the fact that the con- a tube in a well- designed oscillator circuit. grid bias can be obtained automatically, let's denser tunes the circuit to resonance and The ability allows of the self bias voltage de- determine how oscillations are developed a higher voltage to exist across the veloped to limit the plate current flow is coil and naturally with a larger and maintained. magnetic . often referred -to as field. a "braking action" that limits the grid A.C. voltages for a fixed GENERATING OSCILLATIONS amount cf excitation and prevents them EXCITATION REGULATION Assume that the cathode of the tube in from reaching unsafe values of operation. For a given plate supply voltage it is I will add that if we get a clear picture Fig. 3B is at its operating temperature and possible that the "B" battery voltage is applied to find the correct excitation of what takes place in an oscillator, the instantly. voltage by either selecting the proper num- effects of changing any factor in the cir- Upon application condenser Cpc will start cuit can be explained very easily. Let us to charge up to the value of the D.C. volt- see what is the basic action in an oscillator age dropped in the resistor Rp. Plate cur- circuit. rent will start to flow through winding L2. WARNING! When the oscillator reaches its final oscil- This causes a magnetic field to be present lating condition, we know that the grid is about coil L2. This field would appear to be Unless you reserve your copy of the May driven sufficiently positive to produce grid of a steady value because the flow of the issue of RADIO -CRAFT NOW, your dealer current which in turn develops across the may be all sold out. This is because the grid resistor a definite negative "C" bias D.C. plate current is assumed to be con- May issue is going to be a special one on stant. This is not, however, the case. The SOUND. voltage. This voltage establishes a new moment the plate voltage is applied the In addition to the usual material, this operating point on the Eg-Ip characteristio magnetic field about coil L2 starts to expand, issue will contain special theoretical and curve. The A.C. grid voltage drives the grid constructional articles on Home Recording, positive and negative with respect to the which according to the electromagnetic law Phono -Radio Combinations, Public Address, would link the coil Ll (due to its inductive Amplifiers, etc. It is going to be an im- operating "C" bias value as shown in Fig. relation), and would consequently induce an portant issue for Sound Specialista, radio 1B, always sufficiently positive so it creates e.m.f. or a difference of potential across it. Servicemen and radio men in general. this "C" bias voltage. The plate current Sound is booming! ... so RADIO -CRAFT flows only during that portion of the grid If then, the coils Ll and L2 are wound is going to town! RESERVE YOUR MAY cycle when the grid voltage as above where ISSUE NOW. is less than stated coil Li would pro- the cut -off value. This is the point where duce a positive potential at the terminal a the grid voltage stops the flow of plate cur- and a negative potential at b, the grid which relit. The higher the excitation the smaller is connected to a would receive a positive ber of turns or regulating the coupling, or the operating angle charge. This for the plate current. immediately partly neutralizes both, in an oscillator circuit. The excita- For class B operation the operating the "space charge" between angle; the cathode and tion voltage is also affected by the auto- for the plate current will be less than 180 °. plate and allows more plate current to flow matic bias voltage placed on the oscillator and at the same time causes the production tube and the load coupled to the output WAVEFORM ANALYSES L of a negative grid bias. This causes a greater circuit. field to exist around coil L2 and results in In Figs. 4A and B we find the plate and For efficient operation of the oscillator grid voltage curves a greater positive charge on the grid. The circuit and for a given power output we respectively. Note that plate current then increases and in turn the A.C. grid voltage decreases to a maxi -I must select the correct amount of excitation mum while applies a greater positive potential to the class of operation consistent with the A.C. tank circuit or plates to give the voltage increases a maximum. grid. the type of performance we desire. This to This is the Of course this action continues until the correct phase relationship between the in- value will usually be for the least amount put and output voltages plate current is limited by the emission char- of plate current that will give the most of a tube used in acteristics of the tube or by the automatic an oscillator. rl'he plate current as shown. power output. There are other factors such in Fig. "C" bias voltage which is developed by frequency waveform 4C, and as pulse ip represents the as stability and that driving power to sustain the rectified grid current which is across must be taken into consideration in the oscillations, it is, the resistor Rg. The turns ratio and am- this change in current that is fed back selection of the circuit values. It is the work into the circuit plification factor of the tube will also affect of the radio engineer to select the proper tank to set this resonant cir- the peak value of plate current. operating characteristics of an oscillator cuit into natural oscillation. When the peak plate current value has circuit. The area of this pulse when we view it as been reached, the magnetic field collapses The output of the oscillator is affected by a graph represents available oscillating and as a result the grid is driven negative. a change in the oscillator plate voltage for power, the greater the area of the plate This causes a reduction a given turns ratio or coupling between current pulse the more the power avail- in plate current able. which tends to aid in making the grid more the grid and plate circuits. It is also a fact Technically speaking any increase in . negative. The grid may be that an increase in the D.C. plate voltage peak current, any increase in the operating driven so far angle, and negative that the plate current is completely causes an increase in the D.C. plate current, any trend to make the size of cut off as the generated R.F. tank voltage, the R.F. this pulse steeper and more flattened on top shown in Fig. 4C. No further indicates changes will then occur in the negative tank current, the R.F. grid and plate cur- more operating power; for all of direction and rent as well as the self -adjusting grid bias- these factors increase the area of the plate again the magnetic field col- current lapses. Then the complete cycle of operation ing voltage. pulse ip. will be reversed and as before the opera- These factors are all related to the power The amount of power consumed by the tion will start all over again. supplied to the oscillator for a fixed amount oscillator has a number of important func- Thus it can be seen that the polarity of coupling. It can also be stated that for a tions to perform. It must overcome the given of the coils Ll and L2 must be correct to supply voltage it is impossible to losses in the tank circuit (resonant circuit), cause the proper changes in plate current. change any of the other currents or voltages overcome the power lost in the grid resistor, in the oscillator circuit without changing the power lost in the grid cathode of the all other values. This means that an increase tube, overcome the power dissipated in the TURNS RATIO in the coupling of the load to the oscillator plate cathode circuit of the tube supply It should also be evident that the greater circuit will affect all of the values of cur- power to the load and any other incidental the turns ratio of L1 to L2, the higher the rents and voltages, that is, their relation- circuit losses as well as to develop enough voltage across terminals ab. That is, the ship to the other values. excitation to drive the grid circuit of the

RADIO -CRAFT for MARCH, 1941 559 ELECTRONICSa

tube in order to produce the correct amount biasing grid voltage can be measured with of plate current. a voltmeter having a "high- resistance per volt" rating. When there is any increase voltage for O MAINTAINING OSCILLATION in the automatic D.C. grid a given value of grid resistance we have an G If we assume that there is a tendency .._-1 indication of more A.C. tank voltage. This 1 A.C. voltage to increase, then for the grid fact should be remembered and taken into immediately, the grid current increases and consideration when servicing oscillators. MODEL consequently the bias voltage becomes great- This in turn reduces the operating angle 860 er. The author of thla article Is on the teaching staff of of the plate current pulse, even though the National Radio Institute. current peak may tend to rise. Less power will then be available for oscillation and the braking action takes place preventing more power from reaching the circuit and consequently preventing the grid excitation HOME RECORDING to increase. If the grid A.C. voltage drops, Theory and Practice the "C" biasing voltage is automatically reduced as the grid current is reduced and of Sound -on -Disc in turn the plate current flows over a greater (Continued from page 551) portion of the cycle, resulting in the application of more power to overcome losses depth of cut may cause difficulty in tracking and again drive the grid up to a point and the playback will slide from groove to where all losses are supplied and the grid groove. If the cutter has adjustments for excitation is sufficient to sustain the oscil- varying the angle of needle and depth of lating condition. cut, experiment will show that one adjust- The basic braking action is the inability ment will give a cleaner cut and a minimum ' of the oscillator circuit to draw enough of scratch. The best way to check -up on fin- power to take care of all current demands, ished records is to examine the grooves by a high Performance . . Eye and as a result the circuit sets itself to a means of -power magnifying glass. on Appeal . . Value . á;q"--1! definite operating condition and balance. Alight coming at an angle the disc will show the grooves as dark and the surface Sensationally Priced at For example, if we increase the grid re- $17.85, Dealer Net Price. or "lands" as white. Unusual wear on sistor value from a low value to a slightly records may be detected in this way before Here Is an AC -DC VoltOhmMllliemmeter with higher value the initial action results in an all the ranges you want . . . easily readable on the discs are entirely ruined. the large 7' Instrument wih eatralong 6' scale. increased "C" bias voltage. As this takes in a new up -to- the -minute three -tone case. DC An ingenious device for playing -back Volts O- I0-50. 250.500 -1000 at 5000 Ohms per volt place the operating point on the Eg -Ip curve DC; 1000 ohms per volt AC. AC Volts 0- 10 -50- of the tube is further negative. The grid, records, due to Philco, is the photoelectric 250.1000 at 400 ohms per volt; DC Ma. 0.1.10.100; cell reproducer. The assembly consists of Resistance ranges; 0.1500 Low Ohms; 0- 150.000 however, must draw current to supply auto- Ohms and 0.7.5 and 0.15 Megohms. Maroon case matic "C" bias voltage, and to do this the a bulb, a vibrating mirror attached to the with red and silver panel. attached handle. A.C. grid excitation increases. Because of needle, and a photoelectric cell as shown Dealer Net Price, $17.85, in the diagram. The vibrations of the mirror Fer Catalog Write -- Section 316. College Drive this grid circuit action the peak plate current goes up slightly but at the same time modulate the light passed to the cell. The READRITE METER WORKS, Bluffton, Ohio the operating angle decreases. The power light is supplied with an R.F. current well drawn by the circuit depends on both the beyond audibility. The result is that the EVERYTHING operating angle and the peak plate current. needle assembly possesses very little inertia, If we increase one and decrease the other having no work to do but move the tiny IN RADIO e4A` by a small amount the circuit will draw mirror. more power increasing both the grid ex- The principle of creation of sounds by citation and "C" bias voltage. Again the a vibrating mirror modulating a steady light peak plate current increases but it is per- source is in a few respects similar to the d - This big book serves your fectly possible for the operating angle to galvanometer method of recording on film t tire needs It includes sets, 10 i of power which in a 3 -part ar- 09 OP, parts end upplies, Dpublic d decrease so much that the amount the writer described ,A ( drkietm okuaupm t drawn starts to decrease at the point where ticle in Radio -Craft beginning November, %S rt 1937. is a full 'B l w/Nationally known favorites at maximum power is drawn from the supply; In these articles there also rOU i lowest prices, t balance then occurs and the circuit condi- account of monitoring, mixing and studio today for your copy of this stabilized. Of course we can make procedure which the reader will find helpful ig,, tions are rr7/ E, BIG FREE the grid' resistor so high in its (ohmic) for recording on disc. It is hoped that this ^° CATALOG ,..:::::::::M: value that this condition of maximum power present article has been of help to all is far below any condition which would exist readers who now own recorders or who BURSTEIN- COMPANY for normal circuit values, and a large -value contemplate acquiring such apparatus in the APPLEBEE grid resistor may actually produce less near future. 1012 -14 McGEE STREET, KANSAS CITY, MISSOURI power in the oscillator circuit than normal low grid resistor values. Increasing the grid Technicians interested in sound recording excitation (using a given grid resistor), may also wish to look up one or more of may also decrease the power developed, be- the following articles which have appeared Fau? !' cause the operating angle is decreased more in past issues of Radio -Craft. than the peak increase in plate current. "Correct Playback of Spot Recordings." Part I. D.C. plate voltage, ; '37. ' If we increase the Oct. '37 Part II, Nov. ' cvsaafa".,,,no HAMMARLUND , instead of being 6.- `a..`°° NEW "41" the Eg -Ip characteristic "How to Conduct a Sound -on -Film Recording r held at the operating point as shown in Studio," Part IA, Nov. '37 ; Part IB, Dec. 17; RADIO CATALOG Fig. 1B will move toward the operating Part II, Jan. '33. for an increase in plate I, May '38; The latest Hammarlund catalog with point b. Therefore "Phono Pickups on Parade," Part complete data. illustrations, draw- voltage the grid current will be greater as Part II, June '38. ings and curves on the entire Ham - the grid voltage is increased, and conse- "A Modern Amplifier for Recording and Play- marlund line. Address Department a higher negative "C" bias will be back," April '39. RC -3 -1 for your free copy. quently produced, as it will be required in order "Simple Technique for Making Home Talkies," HAMMARLUND MFG. CO., INC. to cut off plate current. Since the grid A.C. Part I, March '39; Part II, April '39. 424.438 West 33rd Street. New York City voltage must always drive the grid positive "Scratch Filter Design." Feb. '40. to produce the automatic "C" bias voltage, "A Low-Cost Amplifier for Recording and Play- and as this "C" bias voltage is greater than back," April '90. the result is a much stronger the cut -off bias, "Profits in Recording." T.' -rt I, May '39; Part current pulse; the plate current increases, II, June '39. as explained above. Under this condition "Constant Groove -Speed Recording." Aug. '40. D U. M O N .T more oscillating power is available and Precision Condensers "Recording - Playback Amplifier Has Direct - Built greater power will be received from the Coupled Output Circuit and Equalized 30 -Watt at your nearest jobber or write to oscillator. Output." Nov. '40. DUMONT ELECTRIC CO., INC. With the usual testing instruments avail- "Recording Pointers," Jan. '41. Ls. }iG BROADWAY NEW YORI(. N Y. able to Servicemen, only the D.C. plate volt- PAPER - MICA - ELECTROt-Y TIC age, the D.C. plate current and the self - *See "Photoelectric Phono Pickup." Radie- Craft. Sept. '40 660 RADIO -CRAFT for MARCH, 1941 RADIO DEVELOPMENTS

THE "ACCELETRON"

Çanetatal £natyy o f 2,300,000 Volts/

AN Induction Electron Accelerator, a new device which gives electrons the smallest negatively charged particles of matter known to science, almost the 186,000 -mile -a- second speed of light in a glass doughnut of less than a foot in diameter, was described to the American Physical Society last month by Dr. D. W. Kerst of the General Electric Research Laboratory at Schenectady, N. Y. In the course of their whirling the electrons gain 2,300,000 volts of energy, something hitherto requiring much larger apparatus and great insulation, Dr. Kerst Electroscopic study, of the radiations by the "Acceletron," or Induction Electron Accelerator, by Dr. disclosed. The device is expected to make D. W. i

ROBESON TECHNIQUE OF ACOUSTICS CONTROL

politan Opera Association, Stevens Insti- tute of Technology, The Rockefeller Founda- tion, and Theatrical Protective Union Local 4 Paul Robeson, concert vocalist, is shown here No. 1. They are being conducted under the (and on Radio -Craft's supervision of Harold Burris -Meyer of cover) with the equip- Stevens Institute of Technology, who pio- ment he uses to control concert -hall acoustics. neered much of the sound control technique Photo - Courtesy The now used in radio, motion pictures, concert Evening Bulletin (Phil- and the legitimate adelphia, Pa.). theatre. The Robeson Technique has yet to be tried out for recording or radio but the desirability of its use seems probable. Concert singers.and instrumentalists per- SOUND control apparatus developed at in a small, highly reverberant room. The form by choice in small, highly reverberant Stevens Institute of Technology has audience is totally unaware that the Tech- rooms since in them they are able to hear been u=sd experimentally during recent nique is in operation. rehearsal periods at the Metropolitan Opera, according The experiments which have been in to an announcement made last progress since October are being undertaken month by Edward Johnson, General Mana- ger. as a cooperative enterprise by the Metro- The experiments have been devoted primarily to creating acoustic conditions on o IMII111=111111= the stage which are as satisfactory to the LOUD- SOUND parU artists as the acoustics of the theatre are 1Il;iiiM\'20111II1 SGEAKEq to the audience. Through the use of sev- - o 11111111111. er l elements of this "Robeson Technique," /IIIIIIIVIIi is now ó it possible for offstage choruses and Mr1111In1111111111

themselves easily. However, they deplore the acoustic conditions of most large concert OPPORTUNITY AD-LETS Advertisements in this section cost 15 cents a word STEP UP YOUR halls and auditoriums. The nature of the for each insertion. Name, address and initials must complaint is that the artist cannot hear be Included at the above rate. Cash should accompany all classified advertisements unless placed by SHOP PROFITS with himself. an accredited advertising agency. No advertisement of not being able to hear are for less than ten wordi accepted. Ten percent dis- The results count sir issues. twenty percent for twelve issue.. the catalogue of the artist's woes: tension, Objectionable or misleading advertisements not ac- Q.tz& EQUIPMENT cepted. Advertisements for April. 1991, Issue most inability to relax, a feeling of being ill at reach us not later than February 7th. voice ease, of low vocal efficiency, forcing the Radio -Craft 20 Vesey St. New York. N. Y. in an effort to project, using a higher key than is best for the song in an effort to get out more volume and fill up the house. BOOKS AND MAGAZINES Several years ago, Mr. Paul Robeson dis- if he stood in front of the ASSURE YOURSELF OF GREATER PROFITS BY covered that doing radio service jobs more quickly. Authentic [fenie. speaker of a public address system which guides show you the way to locate and correct troubles In any radio receiver. Gernsback Official Radio Service was being used in the concert, he enjoyed Manuals show you how to complete more repair jobs in some of the desirable acoustic conditions Iesa time -how to earn more money by faster servicing. usually associated with the small studio. Raderait Publications. 20 Yetey St.. New York City. Last winter, on the occasion of the stereo- WE HAVE A FEW HUNDRED RADIO ENCYCLO- Scene $ate98.by sold phonic recording of the first Forest Book GA as 352 pagdweiight3 lb.. sire from The Emperor Jonte8, technicians of 12 inches. Red morocco-keratol flexible binding. Send 52.49 in stamps. cash or money order and book will be Stevens Institute discovered the possibility forwarded express collect. Technifar, 1915 So. State Street. of using this phenomenon to surround the Chicago. Illinois. performer by an "acoustic envelope" tai- WHAT 00 YOU KNOW ABOUT AMPLIFIERS AND to his demands. Experiments were con- Sound Systems? Tho Amplifier Handbook and Public lored Address Guide covers P.A. from A to Z. Most complete ducted in the Maplewood (New Jersey) end authentic book published on the subject. Contains many acoustic limita- 80 pagos of vital Information on Amplifiers, P.A. Systems. Theatre which has Speakers. Accessories. Pickups. Microphones. etc. Printed tions. A simple set of equipment was then on fine coated stock, with numerous photographic illustra- EASY TO tions and explanatory diagrams, and only 25c. See OPERATE devised for Mr. Robeson and used by him Imo 570. It's easy to turn out your own machine on a concert tour. work on an Atlas Lathe -and make for The first step in devising the system was EDUCATIONAL COURSES Yourself the profits you now have to Pay to find out what it was about the acoustics CORRESPONDENCE COURSES AND EDUCATIONAL small, reverberant room that was books, slightly used. Sold. Rented. Exchanged. All sub- others. of the jects. Satisfaction guaranteed. Cash paid for used courses. is FREE. Write Nelson ' Radio Servicemen in all sections find that significant as far as the artist concerned. Complete details and bargain catalog Dept. C-242, Chicago. the Atlas Lathe makes quick work of dial It was found that the artist hears himself Company. 500 Sherman, shafts and drums, knobs, special screws and if he can perceive a difference in any char- MANUSCRIPTS WANTED of sound between the original studs; service tools, microphones, special acteristic WANTED -MANUSCRIPTS, POEMS. SONGS FOR dies and molds. Operating instructions show sound as it leaves him and the reproduced publication. Fortuny'e, 87 Fifth Ave_ New York. It is the difference correct gear set -ups for winding R.F., choke. sound as it comes back. PATENT ATTORNEYS and short wave coils, transformers. which counts. Time differences are most useful. If the INVENTORS -TAKE PROMPT STEPS TO PROTECT Your invention. Delays are dangerous. Oet new FREE Send Coupon for FREE 1941 Catalog artist hears the reproduced sound later than book, 'Row to Protect Your Invention" and 'Invention the original one, he is perfectly satisfied Record" form. Preliminary information free. Reasonable the many operations you can do in fees. Conscientious counsel. Easy payment plan. Learn See that he is hearing himself, and he is able how to protect and sell your invention. Write us today. your own shop with Atlas Equipment. Send Meaforrow and Berman, Registered Patent Attorneys. the coupon below today for full details. to do this even though the reproduced sound 176 -C Barrister Building. Washington. D. C. be of much less intensity than the original one. It seems entirely logical that time PHOTOGRAPHY UNIT FOR difference should be satisfactory since time 1 /100.000 OF A SECOND SPEED FLASH Stroboscopic Photography. $200.00. Apt. 63, 782 West difference is a characteristic of long rever- End Ave.. New York City. beration or room resonance. Time difference is achieved by placing a RADIO WE BUY AND SELL USED RADIO TESTING EQUIP - ARBOR PRESSES directional speaker 60 feet or more from LATHES 00111 PRESSES a ment. Time payments if desired. Harold Davis. Inc.. METAL SHAPERS VISES CIRCULAR SAWS the artist, or by pointing it at surface Jackson, Mise. which will reflect the sound to the artist so WANTED: ELECTROLYTIC DETECTOR. SLIDEPLATE ATLAS PRESS CO. that the path from the speaker to the riablo condenser (preferably United). Magnavox model Mich. 50 See Fig. 1. Tick -5 act. early studio-type carbon microphone in case, 345 N. Pitcher St., Kalamazoo. artist is more than feet.' rotary spark gap and Thordareon "Flexible- transformer. Please send me your 1991 Catalog on ID 6" Metal Low frequencies lack directional. charac- Tusks "Superdyne." Adams -Morgan wooden case brass- Lathes O it Metal Lathes O New Milling Machine teristics; are not readily absorbed by wall plate condenser, Grant" loudspeaker. Will swap home D 7" Metal Shaper ODOR Pressee D Arbor Pressee. radio set. car -radio set. meters, etc. R. Bernard, 90 surfaces or audience; and, when a footlight Manning Ave.. No. Plainfield. N. J. microphone is used, the system will pick -up RADIO KITS Name low -frequency sounds transmitted by the responds to low fre- RADIO KITS --$3.95 UP. SINGLE BAND: ALL WAVE. floor if the system 5 -10 tubes. Fluorescent lighting. Save 50%. DtcOee Address quencies. High frequencies, on the other Radio. 1'-2055. K.C.. Dlo. hand, are directional enough to be kept TECHNICAL ART SERVICE away from the audience and are absorbed City and State below back- DRAFTING AND ART SERVICE -A COMPLETE readily enough so that they are Service for the industrial and Commercial Marketers. a ground if they ever do get out. If your business or plant can't afford a designing or I. drafting staff, don't let this stop you from going ahead The response curve is not particularly with that new product you intend marketing. or that 2, is off catalog of mechanical or electrical Items which Seeds Turn to Page 570 critical, and as shown in Fig. cut fine detailed drawings and highly retouched photographs. 500 cycles, has a flat peak at 2,000 Any mechanical, electrical or radio problem can be solved for the BEST BOOK ON SOUND! below for you by our associated staff of designers, draftsmen cycles from which it drops off slowly, and and artists. and technical copywriters. Write for any 6,000. Thus only the additional information as to methods and price for this is down 10 decibels at service. Tee-Art Drafting Service. 228 Charlotte Terrace. significant harmonics are projected to the Roselle Park, N. J. artist. DRAFTING SCHEMATIC DIAGRAMS SEND US A The Technique is fully effective when the rough sketch of your draft. Estimates by return mail. Our prime are moderate: our work guaranteed. No Jobs sound level, at the position of the artist, too big or small. Wm. Kadlecek, Jr.. 440 East 85th SL.. is not measurably affected by turning the New York. N. Y. system on or off. A level set well below the TEST INSTRUMENTS regeneration for the empty house point of SUPREME 590 -$24.00. TRIPLETT 1177 OSCILLATOR is safe, and more than adequate for the and Tesler, $14.50. 138 Vino St., Plymouth, Pa. full house. In the first concert in which the Technique was tried at Carnegie Hall, Mr. Robeson If you subscribe now to RADIO-CRAFT was able to sing "Water Boy" in a lower you receive valuable premiums absolutely key than he had ever used before for that FREE I A Genuine Electric Dry Shaver -see number in concert. "The enthusiasm of the page 567. The Radio -Television Reference artists who have tried it beats anything of Annual -see page 546. the sort I have encountered," comments Professor Burris- Meyer. MARCH, 1941 562 RADIO CRAFT for LATEST RADIO APPARATUS

1941 SUPER SKYRIDER so that 4 additional remote stations may be .c connected to it. A 6th button marked The Hallicrafters DEALERS SERVICEMEN "Quiet" leaves the master station in a 2611 S. Indiana, Chicago, III. ¡ i. "standby" condition so that any message Z. c. BUILDERS AMATEURS from remote station is instantly received.- Radio-Craft NEW AUTO ANTENNA Ward Products Corporation ¡ 1523 E. 45th St., Cleveland, Ohio gigged/¡,n THE "Flex Angle" antenna is (j ., of the 2 -bolt single- mount, 3- i section telescopic type with an THE latest Super Skyrider has a tuning extended length of 68 ins. It is designed range of from 500 kc. to 42 mc. in 6 bands. to fit all types of cowl contours. A simple adjusting Other features include 6 degrees of selec- OD lfs nut at the base permits the an- tivity-3 with crystal, 3 without,; 2 high - gain R.F. stages; front-panel antenna trim- tenna to be adjusted through a mer control; headphone and phono jacks; range of 16 deg., permitting the temperature-compensated high- frequency os- vertical antenna position to fol- cillator; provision for mobile or battery low the design of any cowl. The K i operation; remote standby control; noise antenna proper is shielded from J w1 noise and moisture. The anten- limiter circuit; beat oscillator; free- wheel- GET ing band -spread dials, and a main dial hav- na lead is shielded from noise as IT NOW! well as ./, protected against under - ing an auxiliary micrometer scale.- Radio- 212 RRj¡ Craft fender water and slush.- Radio- PAGES! Craft EVERYTHING . IN RADIOI RECIPROCATING ELECTRIC BALANCED PHONO PICKUP ,r.>7 TOOL Fairchild Aviation Corp. 85 NEW/ H & H Research Co. 88.06 Van Wyck Blvd., Jamaica, N. Y 1925 W. Buena Vista. Detroit, Mich. RpOS Hiu:. Models Sor 1941's Radio See them all- every puce. Persona and every purposatworld -wide uts: mantel models; Recorders and Radios; Ama- Portables.Auto Sets; priced See Receive; nettnew low rloes1at of Rocelvers- n low teurtear them Ratlio Catalogs.

mow- r* 4

MODEL 209 -3 phono pickup has an extended frequency range of from 40 to 6,000 cycles. Its needle pressure is adjusta- ,___.=,..1.01 ble from 1 to 3 ozs., and is set by means of a calibrated scale. It is a crystal cartridge EVERYTHING IN RAD10 fil unit with a sensitivity of -31.6 db. /500,000,- 24 NEW SOUND complete P.A. SYSTEMS, ohm load with 0.0004 -in. groove at 1,000 cy- Amateur lletln g e; receiver, all new t cles /second. Because of the natural charac- Ham gear and complete tpole teat tlonu; Dart:- ° I° teristics of the crystal, very little mechan- more 55"Ipóment, ical damping is employed. All mechanical Radio trou'115Md ÉverYthlkng joints ride on ball bearings. -Radio -Craft at Lowest h¡ oO'J.o ALLIED Catalog) Price"ver Tpgt. THE tool looks like a portable electric drill but instead of the usual rotary mo- HIGH- CAPACITY MERCURY tion, it has a reciprocating motion. By inserting files, hones, saws, and other tools SWITCHES in its chuck, it can be made to perform a Durakool, Inc. large variety of machining operations which 1010 Main St., Elkhart, Ind. heretofore had to be done by hand. A very handy tool to have around the service shop. -Radio -Craft

I NTERCOMMU N ICATOR Philco Corporation Tioga and C Sts., Phila., Pa.

833 W. Jackson Blvd. Dopt. 2 -C -I Chicago, Illinois ALTHOUGH smaller in size than previous O Send me your FREE 1991 Radio switches, these have greater Catalog. current D I encloua 1Oe for New Radio Dic- handling capacity. Model A -5M will safely encly. handle 10 amperes. It is especially adapted D I encloue ]be for Radio Builder.' Handbook. to snap acting mechanisms as well as tilt Name THE "Philcophone" is an inter -room con- acting mechanisms. Model A -10Z will han- versation system comprising a master dle 20 amperes. Both switches will safely Ad draaa station and one remote station. Master sta- withstand operating speeds of 5 times per tion is equipped with 5 pushbutton controls minute, CitT State 24 hours a day.-Radio-Craf t wminioommwimimrammm ======... -ma.

RADIO -CRAFT for MARCH, 1 9 4 I 5A LATEST RADIO APPARATUS

IMPROVED TRACEOMETER ance drawing up to / -amp. Measures but 264x1fixl 7/16 ins. and designed for 115 - The Hickok Electrical Instrument Co, volt A.C. and /or D.C. lines.-Radio-Craf t 10302 Dupont Ave., Cleveland, Ohio CABINET KIT New England Radiocraffers Brookline, Mass. THIS kit contains 2 aluminum ends sup- porting 4 super -masonite sides, to make a cabinet 6x6x9 ins., easily cut, drilled or stamped with simple tools, or reduced in size to fit compact assemblies. Extremely light weight, but rugged. Extra parts available at low cost for rebuilding. Useful to the amateur, experimenter, Serviceman or custom -builder of radio or electronic equipment.-Radio-Craft GENUINE LEATHER RECORDING BLANKS 81L1fOLD Howard Radio Company without 1731 Belmont Ave., Chicago, Ill. `` HE addition of a self- contained speaker FEATURES of these blanks are: flame- `x r- I increases the versatility of this instru- ' proof; shearing qualities claimed better ment by permitting the monitoring of R.F., than "nitrate" materials, permitting clean- I.F. and A.F. channels. Other measurements er groove cuts without tearing; the special permitted by this instrument are signal coating on the heavy metal cores are very strength in microvolts in the R.F. and I.F. hard, assuring long life and reproduction of sections; oscillator voltages throughout en- high frequencies; there are claimed to be tire range; all D.C. voltages, A.V.C. and no layer definitions, as shown by a cross - A.F.C. voltages; power in watts up to 300 section examined under a microscope. This watts. All measurements do not disturb nor- prevents any stresses being set up between mal operation of circuits under test. May layers which, with time, cause groove dis- be used on F.M., A.M. and television receiv- tortion. Discs are available to dealers in an For the n minal amount of Sac w will send You ers. Known as model 155 Traceometer.- attractive display cabinet. -Radio -Craft the following value 1. One duzeone Imperishably etched Bron. Namee Radio -Cra f t Inches number maenlntyO sampedt ) noonn`IiÌ 2' nbr Billfold.wth MAGNETIC RECORDING HEAD ñ tralu nLeatherbrowycor, four compartments. INTERFERENCE LOCATOR as above. Shure Brothers se Pocketbook is o ub fThi present to you. Abso- lutely pclrs°strings of any We make also Sprague Products Co. c eet to favooryby ing 225 W. Huron St., Chicago, Ill. dO in North Adams, Mass. ordering o el for themselves. That s all. Help us°and You will profit yourself. coupon below enclose ACT NOW! M;n1,w.tThe Plate Leat e Billfold will he forwarded to you at once. r e PREMIUM DISTRIBUTING SERVICE 1 Wrigley Bldg., Chicago, Dept. RC -341 I to the below, my S°odcialaeSecuri ,y 'Bronze late andd`the 1 Genuine Leather Billfold without extra cost. as per I your offer. 1 My Social Security Number fa NAME ADDRESS CITI' STATE MODEL 44A is a wide -range magnetic record cutter recommended for Use with home recording equipment. Operates directly from the voice -coil winding of the 68 PAGES output transformer. Stiff moving element permits recording on practically all record- FREE MODEL IL -2 serves the purpose of lo- ing materials. May be used with almost any 30D Ways to radio set. Impedance 10 ohms at 400 cycles; Make Money cating and isolating radio interference. It operates either from self- contained bat- resistance 4 ohms D.C.; suitable for output teries or from the A.C. and /or D.C. lines. circuits of 4 to 8 ohms. May be used with MARVEL Equipped with a directional loop antenna as steel, alloy- tipped or sapphire recording MAIL ORDER PLANS BOOK OF well as an extensible pole antenna, as il- stylus.- Radio -Craft YEAR! THE 3 ranges are: 500 to TESTED MONEY MAKERS lustrated. Its tuning 40,000 '700 kc.; 1.7 to 5 mc.; and 15 to 32 mc. Its WORDS "PEN -OSCIL -LITE" R.F.- I.F. -A.F. BUSINESS SECRETS is such that an input signal of in TEXT! sensitivity SERVICE OSCILLATOR SUCCESS SCHEMES In "CASA IN" less than 2 microvolts will produce a deflec- trou get ALL the tion of 10% on the output meter scale. In- General Test -Equipment Co. real money-mak- Size, 213 Crosby Ave., Kenmore, N. Y. ers - dozens of dication is both visual and aural. Profitable tested mall 15 x 11 x 8 ins. Weight, 23 lbs.-Radio -Craft order plane, confiden- tisl business secrete, dozens of practical tested formulas. successful -NOISE FILTER tested schemes -actual ex- LINE periences of men uho hate Sprague Products Co. started on a shoestring-pith leas than 810 capital. Pen - Buyers of This Book Tell Us- North Adams, Mass. THE uniqueness of the vest -pocket 'Blggest value I've yet to ace. Doak ta wyorth at -Lite lies not so much in the circu't least s dollar." S. Buda. Bklyn, N. Y. MODEL LF -2 is Oscil 'Your book Is ae of e h an as in the electro- mechanical design that sthelel a multiple AoSrH N e bLaewnFoxh,`vf u ett eetcc iis makes possible such a mechanism in so small , section inductance d eIr fileel dt.h" Broyokyto N. Y. such low power require- "CASH IN" contains only tested Ideas covering every and capacity fil- a space and with typo of full -or spare -time enterprise -It's a "master- ments. piece" in business ventures. ter of the plug -in BOOK CONTAINS NO ADVERTISING. type for use on Circuit -wise, according to the manufactur- SENT FREE TO YOU. very troublesome ers, the Pen -Oscil -Lite consists of an inter- NO STRINGS TO THIS OFFER. a topped wave NO FURTHER OBLIGATIONS TO YOU! sources of radio rupter which creates square Send 3e U. S. stamp to pay for mailing charges interference. followed by an extremely steep wave -front NATIONAL PLANS INSTITUTE Should be installed at the power outlet of pulse. On a peak vacuum -tube voltmeter 246.R Fifth Ave., N.Y.C. any interference- creating electrical appli- this pulse measures in excess' of 125 volts 1941 564 RADIO -CRAFT for MARCH, LATEST RADIO APPARATUS

into a 10- megohm load. Because of the steep- ness of the wave -front of this pulse, transients are created which cover the spectrum from the audio to extremely high radio fre- RADIO quencies. These transients are modulated at COURSE the interrupter frequency of about 700 cycles. How 8,749 Servicemen Obtained Their Training Receiver circuits, to which the Pen- Oscil- You may also get exact reprint of the regular $39.00 Radio Technical Institute course Lite is h for onl 5 $1.95 the full coupled, are shock -excited into oscil- price. This is the latest radio servicing course complete lation or response at their natural fre- in every way and exactly the POSTPAID quency. Can be used in R.F., IyF, and A.F. same as the much higher priced circuits.-Radio-Craft WILL HELP YOU original lessons. GET A RADIO JOB "I think your course AMAZING REDUCED PRICE is tops." Leonard D. Repair all radio sets expertly, learn new speed- tricks of PORTABLE P.A. SYSTEMS Robinson, Toronto, servicing, short -cuts, profit making ideas. Brush up on Webster- Chicago Corporation Canada. latest servicing methods. A single time -saving hint will more than pay for the special $1.96 price for the complete 5622 Bloominodale Ave., Chicago, Ill. FINE COURSE course and all supplementary material. Make certain of "I would like to say your place in Radio. Learn you have a very fine to repair all radios quick- Radio Course." Wil- ly and properly. ford Sanders, Jr., Parrish, Ala. You LIMITED OFFER can get in started Write to us today while Radio with a total this offer is In effect. investment of only Only a limited quantity $1.95. This is the of courses printed to sell lowest priced radio at the reduced price. training. Act today. FOR HOME -STUDY Get ahead in Radio GREAT HELP with this practical train- "I consider the course ing. The lessons are a most valuable addition clear, interesting. easy to my radio library. to understand and use. Also, my diploma Im- Final exam and diploma presses my customers available after course is CONOMY, performance and portabili- and. thereby, helps my finished. Look the course business. I would not over without any risk. ty" is, according to the manufacturer, part with my course for ISM probably the best way of describing this any sum if I could not 'a M 1 - - r secure another. It Is a new economy line of P.A. equipment. Avail - gold mine of useful In- formation." Frank 1 10 DAYS FREE EXAMINATION i able in 3 power sizes, this new line is the Courtney. Augusta, Ge. answer to the smaller band's, SUPREME PUBLICATIONS, Room 635 traveling 1 3727 W. 13th St., Chicago, Ill. show's, carnival's, etc., demand for a com- RECOMMENDED Ship the complete course on approval without any obligation to plete portable P.A. system priced within the FOR BEGINNERS buy. I may keep the course for 10 days. If, for any reason, I am not you guarantee to refund my money. scope of their limited budgets. The entire AND EXPERTS pleased, D I win give $1.95 and 15c to the postman. system, consisting of amplifier, two 124n. "I would recommend postage your Radio Technical D I am sending $1.95. the full price, ship poatpald. speakers, microphone and connecting cable, institute course to any ' is housed in a single carrying case.-Radio- radio man . ." R. J. Relihan. Claremont,' Name: Craft N. 11. Address: 18 -W. BATTERY/ ELECTRIC MOBILE AMPLIFIER Thordarson Electric Mfg. Co. A NEW BOOK TO ADD TO YOUR TECHNICAL (LIBRARY 500 W. Huron St., Chicago, III.

AUTOMOBILE RADIO- Principles 81 Practice by B. Baker Bryant

ACOMPLETE compilation of pertinent data on how to Install and service the modem automobile radio receiver. All of the non -essential details which have crept into the profession have been weeded out. Each topic is treated so as to contain a precise statement of the fundamental principle involved. to assure the reader's clear un derstandtng of this principle, without distracting his attention by the discussion of a multitude of deuils and mathematical expressions. which are primarily for the engineer, and tend to confuse rather than clarify a statement for the auto -radio -technician. A practical treatise based on practical experience by practical radio people for the practical radio- AN 18 -watt amplifier and phono -player technician. operated from either 6 volts D.C. or 115 volts A.C. Suited for all mobile and Brief Outline of Contents- portable applications. Plays either 10- or Introduction -The Auto -Radio Art. 12 -in. records at constant speed with either Features of the Modern Automobile Receiver. battery or A.C. operation. All controls and Installations of Automobile Radios and connections are on the front panel. Has Antenna. The Automobile High and Low Tension phono and voice channels, and provisions for Electrical Systems. Automobile Electrical Disturbances. mixing both. Known as model T- 30W18.- Vibrator Converters and Motor Generators. Radio -Craft Service H ints, Classing d Automobile In- stallation Notes, and Conclusion.

` Send 50e check, money order, un- PROFESSIONAL DISC RECORDER used V. S. stamps. or coin for your 50c copy of "Automobile Radio-Princi- Phonotone Laboratories, Inc. POSTPAID ples & Practice' -it will be cent to Washington, Indiana you postpaid upon receipt of your Sise-O x g remittance. Inches THIS professional disc recorder consists of 04 Pages three units; viz., a motor driven recorder Stie. flexible RADCRAFT with high -fidelity cutting head; .weighted Illustrations PUBLICATIONS, Inc. turntable; crystal pickup and volume con- and trol; 15 watt amplifier for recording and diagrams 20 Vesey Street, New York, N. Y. reproducing and for use as a P.A. sys-

RADIO -CRAFT for MARCH, 1941 565 L'ATEST RADIO APPARATUS

tern; and a P.M. speaker, furnished in 12 or 16 in. diameter. The weight of all three units combined is approximately 65 lbs.- Radio- RADIO Craft 10 BEST 10¢. "ROSTRUM" P.A. SYSTEM Erwood Sound Equipment Co. RADIO FANS EVERYWHERE -these amazed at the wealth of information 223 W. Erie St., Chicago, Ill. fine ten cent text books give you an contained in these handy books. Ex- excellent foundation for the study of cellent for reference -ideal for every ACOMPLETE P.A. unit in all details RADIO. They are clearly written, pro- technical library. YOUR MONEY BACK contained in one portable case: the fusely illustrated and contain over if you are not satisfied. amplifier, loudspeaker, microphone, controls, 15,000 words in each book. You'll be PROMPT SHIPMENTS etc. Removal of the cover gives access to a reading platform illuminated by a miniature lamp. Ideal for hotels, lodges, small churches and other gatherings. -Craft No. I No. 2 -Radio - HOW TO BUILD FOUR HOW TO MAKE THE MOST'. -WAVE I- and T p--. DOERLE SHORT WAVE SETS POPULAR ALL J.., Ho 2 -TUBE RECEIVERS 2 -SPEED RECORDING NEEDLE Do aIË Thiltthe or reste mea nave ,L.yr F 9r AVEeETS D lit the ,.moue UO£RLY- Short Thls hook containssorrá number Of 1-1 Wave Radio Receivers. so in- cellent sea. c of which 4 Recoton Corp. rl latent has been the demand have appeared in f f poet for these Ives, as 11 as AFT. These sets have 178 Prince St., New York, N. Y. } n weuoñaethu. w this been carefully These set. have hook hpe been pub- a t experiments. Not only i ORS ,. IHE Stellite Cutting Needle is, according Ilt are seta in r i£ Contains EVERYTHINOOnhat hoe but hookups.Ìl of the I r 1íl ver been printed these Illustrations, hookups. etc. to the manufacturer, the only needle of 1 /,'' famous receivers. - its type (not being a jewel) which will cut 331/3 and 78 r.p.m. recordings with equal No. 3 No. 4 facility. It is composed of a hard Stellite ALL ABOUT AERIALS tip inserted in a duraluminum shank. It ALTERNATING CURRENT E: .c. FOR BEGINNERS This book ezplaine lee t fort/ noiseless, high -fidelity recordings for underlying the various types f assures This book gives the beginner a aerials; the inverted L, the ALL several hours, and then may be re- sharp- foothold in electricity d Radio. Doubletthe Double Doubled ''''...,...r...°°°°seea Electric circuits are explained. eta. It explains boise-tree reeep- 2 edges, viz.: one C low -impedance trans l'O/nW ened. Needle has patented .. BEGWrrtts Ohm's Law, one of the (Linda. Non. how ` tai law: f radio. Is ex mission lines work; why trans- 11) cutting, and the other polishing; thereby, a ) yL maser the ent; of el: posed are stru an of ' JEW' ternatingthe Unit t: sine.Irae w y et.0 the or Long. of smooth, shining groove is left. -Radio -Craft we aorta lirons, amperes. and aerialsMals nu tree for swave lS 1r+ ana are rs. Condensers. broadcastrr abc lyud forrot non .n.waye 'r'' ;,..: r,-...,_ motarsrand A.C. mswments, lyen and for Ì , receivers. _'... motors and generators. 10- CHANNEL MARINE RADIOPHONE

No. 5 No. 8 Hallicrefters, Inc. ,.s III. BEGINNERS' RADIO HOW TO HAVE FUN WITH ?R 2611 S. Indiana Ave., Chicago, DICTIONARY RADIO eEGIHRwaRRS Are you sled by radio Ian- Stunts for partlns. pnetocal -AYa, jlwerl0 Can you define Ere. joke.. ientrific experiments d I1Nlar gguunngge? T¡!CI'IGF.9// 0'ó 1Ioniz tion? Joule'. expia withusemeisfascinatinan be "YII ADIO ,iI` ode?od Pole? Ionisation^. Joule's explained in this fascinating vet- Lanf Harmonic? Gravity Cell? . It telle how to M 4 \t, , P,s Iry rrou cannot define these very newspaper .1k -how to produce l' radio words and doseras silent music for dances -how to j,.19e,/$ ' M of therQ more tecchhnical. terms make vÚlle music-how to usedM In all gnzlnme ana make Dent radio unit. dO ala$r iA pock', You need Nls usable óy the deafened -how to GIs book In your library. J` - ^, sr (make toys which dance to radio : _ . taste. k., etc. ....was

No. 7 No. 8 ., HOW TO READ RADIO RADIO FOR BEGINNERS .,¡ DIAGRAMS Hugo Gernsback. the Internhtlon 17 > , All of the symbols .mm only ally famous near' author R.tD10spp_^ L. In radio diagrams e pre. and whoampf asnaled In this boo, together sines. RADIO AND TELEVISION I- fYL'DwVi d RADIO.CRAFr are reed b ¡ rppictures of the Impantue scores anotherThor stfr gieothy and million'. triumph anwnt IN Nla new Any be- (, I 1 .5Y method Robert ginner who ads alb Ill get C á ó1Ì them. his grau d work In radio Eichbc the 11 -known radio thorough (ter á; ,d member of they(edl lTeory ticarir erblelnndn ln tonal staff of RADIO.ORAFT Imp é laoneáretags. a mrough, a-w tain: two the O f w iituaauone. YYYJJJJ A,talogles o M to make the plaidaio diagrams of radio clear. simple n setseo that Can myeterlee build. KNOWN as the "Seagoing" Model HT -12, this radiophone is a 50 -watt unit comprising a 10- channel receiver and a 10- No. 9 No. 10 channel transmitter. All channels are ^Ñ which permits the elim- SIMPLE ELECTRICAL TELEVISION IErvIc H' crystal -controlled SIMPLE EXPERIMENTS manual A voice -controlled Every ono le Taking Na lion TELEVISION ination of tuning. ELEfTRIfJ1l Over 100 Interesting and prac- How doms tclevll work? This automatic relay system eliminates manual IXPERIMF.NTS tical[teal rital experiments book explains Il of Ne different I and In this xec k, tine yimpies f tthevlelos from 1.- :. supply is a separate mpl bench f mlcctrltlh from simplest t lust switching. The power _ A -D -C '`i- tee (mente mug; It describes in style plut E ,. now '.(...." unit available in 2 types, viz: operation from . nets to big frequency tun.. the elmaR¢ is scanned. how -l)::kW,' r/ . All o Ne xrpretImonta de pickedÇ P by Mé 12 -volt ship's battery; and, from a 110 -volt Ir 1'. I e thed n be c Icd out IN tclOV talon eInv. andÁ broadcast q(I simple apparatus. toi hich te tour nome. types M A.C. source. The receiver is a sensitive 7- É s0yis can be %tans about the ñomo. ofribteellevision systems are de. tube superhet. with 1 stage of preselection, and with A.V.C. and Q- .A.V.C. systems- Radio -Cra f t BOOKS ARE ALL UNIFORM Every book in the GERNSBACK EDUCATIONAL LIBRARY has 32 pages --with tlluetratlons varying fro.. -PULL VIBRATORS 30 to 66 in number. Each title volume contains over 15.000 words. Positively radio's greatest book buYal If You PUSH do not think these books worth the price asked. return them in 24 hours and your money will be Instantly refunded. The Turner Co. i Cedar Rapids, Iowa OUTSTANDING feature of this RADIO PUBLICATIONS 20 VESEY STREET NEW YORK, N. Y. new line of vibrators is that they do ,e on RADIO PUBLICATIONS, Dept. RC -3 -11 not depend the 20 VESEY STREET. NEW YORK. N. Y. springing action of Gentlemen: Please send immediately, POSTPAID, the book numbers circled below, I am enclosing ^enti -each book being 10e. the vibrator, but 10 1 2 8 1 5 6 7 8 9 instead, employ an NEW NEW Send FREE listing of 48 new 100 publications. equal amount of magnetic power to Name - Addrese push and pull the City Rut. reed and its con- Remit by check or money order- register letter if you send Teh or unused U. S Postage stampe. tacts. This results MAIL COUPON TODAY!. MARCH, 1941 566 RADIO -CRAFT for LATEST RADIO APPARATUS*

in cleaner, more positive contact on each weighs but 9 lbs. complete with heavy -duty swing. Piling and chattering are eliminated, batteries, battery case, cables and head- R.F. hash reduced and mechanical noise low- phones. The size is 6 ins. wide x 4ki ins. DATAP.RINTS ered to a very low level. -Radio -Craft high x 4 ins. deep. The set is a superhet. with a continuously variable TESLA -OUDIN COILS tuning range AI---_ IMPROVED CUTTING NEEDLES of from 198 to 405 kc.-Radio-Craf t 20c Ea. in order for 10 (Data and Drawings only.) Audio Devices, Inc. I .. - 96" Sp'k Tesla -Oudin Coil 40c 1600 Broadway, New York, N. Y. FLUORESCENT DESK LAMP (1 K.W. Exc. Trf. Data incl.) 8" Sp'k Tesla -Oudin 40e CUTTING needles with Stellite Eagle Electric Mfg. Co., Inc. . Coil and Sap- z-. - (Ye K.W. Exc. Trf. Data incl.) phire points further improved to provide 59 -79 Hall St., Brooklyn, N. Y. e` 8" Sp'k Oudin; 110 Vt. improved frequency response and lower -- "Kick Coil" type 40c - FIN_`: 3" Tesla Works Ford noise level. These features should be of on interest Coil 40c to the critical home recordist as ' ' 1' Sp'k Vibrator Hi -Freq. Coi140e well as the studios and broadcast stations NEW! 5 ft. Sp'k. Oudin Coil & Exciter now using the newest type of extremely - Data 75c wide -range cutters. For convenience in Induction PIPE & operation the thread throw has been in- LOCATOR creased and improved. -Radio -Craft - - ORE _ - Induction Type, Data 40e SUPERFINE LUBRICATING OIL -- - Radio Tyne 40e The Davenoil Co. More DATAPRINTS 40c each! 158 Summit St., Newark, New Jersey 5 Meter Superhet. Electric Refrigerator THIS lubricating oil has been expressly % Meter Tr. & Rec. Wheatstone Bridge prepared for delicate and precise 20 A.C. Probs. & Ans. Weld. Transf. 2 K.W. instru- 20 Telephone Hook -ups Rewinding Armatures ments. It will not leave a residue of dirt or FLUORESCENT lighting is going over like 100 Mech. Movements sticky gum. Recommended for laboratory 20 Motor Hook -ups String Galvanometer hot cakes and there is no reason why the Television Hook -up 20 Simple Bell Circuits test equipment, watches, cameras, micro- Serviceman who has a little store of his own 20 Elec. Party Tricks Steel Wire Recorder! scopes, etc. Furnished with metallic ap- or the Serviceman- Dealer should not cash -in Solenoids and Magnets Water Wheels plicator. Radio -Craft by selling such as -get list. Water Turbines units the one illustrated Fry Eggs on Ice! Photo here. This unit is an all -bakelite Cell and Relay desk lamp, Experimental Photo- Ring 4 bells: 2 Wires DYNAMIC "DISPATCHER" complete with starter switch. The base is phone Radio Control for 20 Tesla Tricks MICROPHONE heavy cast metal, lending ruggedness to the Models Polarized Relay Universal Microphone entire unit. Shade has baked white enamel Diathermy Apparatus Induction Balance Co. Inductor Organ Inglewood, Cal. reflector which is adjustable to focus light Electric Pipe Thawer where desired. Known as the Fluralamp Special Prices: 4 prints $1.00; 10 for $2.00; model 552, this lamp uses a No. T8 15 -watt, Single, 40e each. Get New Catalog 100 A. 18 -in. fluorescent bulb. Designed for use on 110 -120 volts, 60 cycles A.C. Measures 15 ins. The DATAPRINT Co. high 18 by ins. wide. Other models also Lock Box 322D, Ramsey, N. J. available.- Radio -Craf t get Ail aectltic ay- fhavet ABSOLUTELY FREE!

JUST THINK OF IT -you can get absolutely FREE, the useful DRY ELECTRIC SHAVER which is shown at the left. This ELECTRIC DRY SHAVER is sent to you by the publishers with a one -year subscription to RADIO- CRAFT. Here Are the Features et The ELECTRIC DRY SHAVER Constructed of metal with attractive red bronze knish. Scientifically constructed to give a perfectly clean shave. 5-foot rubber insulated cord and plug. Constructed to last for many years. Operates from 110 -volt. 60 -pole A.C. electric line. Carries a two -year manufacturer's guarantee. A fine quality, self- sharpening toilet necessity.

Send your subscription to RADIO -CRAFT for One Year (12 issues) and receive absolutely PRIM ono of these remarkable Electric Dry Sharers. New subscribers are accepted or you may extend your ores - OPERATES ON ont subscription another twelve months. Mall your remittance of $2.00 (plus 25c 110 -VOLT, 60 -CYCLE for shipping charges on Sharer) to the A.C. LINE publishers. (Canada and foreign ENGINEERED $2.75.1 You will receive your primarily for operators of DRY ELECTRIC SHAVER im- wired music systems who must have their mediately by return mall. Use coupon below to enter your hands free for operating phono- turntables subscription. and gain controls. This type microphone is being made available in 12 different models RADIO -CRAFT and impedances. The unit includes Tits ft. 20 Vesey Street. New York. N. Y. of flexible cord, weighing a total of but '.4.-lb.-Radio-Craft nr, LIGHT AIRCRAFT RECEIVER RADIO- CRAFT, 20 Vesey Street, New York, N. Y. Gentlemen: Enclosed find my remittance of $2.00 for which enter my Harvey -Wells Communications, Inc. subscription to RADIO -CRAFT for one year (12 Issues). Send me immediately FREE. ELECTRIC DRY SHAVER (Cenada and foreign Southbridge, Mass. WE SHIP $2.75). In U. S. add only 25c additional to corer shipping charges on DESIGNED ELECTRIC DRY Sharer. expressly for use on light air- SHAVER THE SAME DAY O New Subscriber Extend Present Subscription craft, this receiver is designed func- YOUR SUBSCRIPTION Name tionally on the actual requirements of pri- ORDER IS RECEIVED. vate aviation as found through actual flying Add:esa experiences of the company's personnel, City State and by close contact with private pilots. CLIP COUPON (Send remittance by check. money order or unused U.S. Postage Stamps - Register letter if you send or stamps.) Known as AR -2 -A, this 4 -tube receiver AND MAIL! cash RC -341

RADIO -CRAFT for MARCH, 1941 567 LATEST RADIO APPARATUS.

MODEL J -629 is a 6 -tube A.C. rece +ver SEMI- COMMUNICATIONS incorporating a combination phono- RECEIVER graph and recording mechanism. Housed in Radio Corp. a table -model cabinet, the instrument is Echophone complete 201 E. 26 St., Chicago, Ill. compact and an entertainment unit in itself. Both pickup and cutting -head are of the crystal type. Turntable speed is 78 VERTROD r.p.m. The receiver is a superhet. with a Antennae tuning range of 550 to 1,600 kc. and an un- can be mounted anywhere distorted output of 2 watts.-Radio-Craf t. at any angle only a screwdriver is required.

of engineers, employs entirely new principle. Line interference is effectually prevented NEWS OF from reaching aerial. Supplied in convenient, compact package, Vertrod aerial can be TELEVISION quickly set up, wherever 4 ins. of space are accommo- available. Patented rotary base ALTHOUGH air television ac- dates aerial to any surface or angle. Only tivity has been in the dol- a screwdriver is required for mounting. of late,' laboratory parts insure greatest ef- drums EC -1 "Commercial" has features Solid duraluminum have progressed almost un- MODEL and -Craft work seems to many of which are found in regular ficiency durability.-Radio abated. One of the developments having communications -type receivers. For instance, exceptional portent was the installation, its tuning range is continuous from 545 kc. HOME RECORDER by N.B.C. last month, of a special filter to 30.5 mc. The illuminated dial is large and General Electric Company unit which enables the antenna of station fully calibrated for all bands and also in- 1285 Boston Ave., Bridgeport, Conn. W2XWG to transmit both television and chides a separate band- spread scale and Frequency Modulation programs, and the pointer, actuated by a separately -controlled cue signals from a 3rd transmitter, simul- electric band- spread system. Other features taneously and without any interference. include headphone - loudspeaker switch, beat- frequency oscillator switch (which cuts of Commerce re- out the A.V.C. system automatically), and The U. S. Department porta television set manufacturing amount- a stand -by switch. A 5 -in. P.M. speaker is sets, at an average self- contained in cabinet.-Radio-Craf t ing to a total of 4,091 price of $200, during 1939.

NEW ANTENNA Allen B. Du Mont Labs. announced that Alesi & Fener the delay television -tube, which affords 625 - 132 Nassau St., New York, N. Y. line flickerless scanning at 15 frames /sec- THE Vertrod, claimed by manufacturer to ond, now is available with a white screen eliminate most of the man -made static (which therefore supersedes the earlier which has previously defied the best efforts orange- screen type).

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RADIO SERVICEMEN OF AMERICA, INC. RADIO SERVICEMEN 304 S. Dearborn Street, Chicago, Illinois OF AMERICA, INC. $1.00 enclosed for 1941 National Dues in RSA "Reliable Service Assured" Name JOE MARTY, JR., EXECUTIVE SECRETARY Address ILLINOIS 304 S. DEARBORN ST., CHICAGO, City State Radio -Craft -Mar.

-CRAFT for' MARCH, 1941 568 RADIO CLASSIFIED RADIO DIRECTORY

Í1hete toiluyit! SECTION VI 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 publica- There is no charge for regular tion permits the DIRECTORY to be constantly up -to -date since necessary revisions light -face listings in the Classi- and corrections can be made monthly. All names preceded by an asterisk ( *) indicate that fied Radio Directory. This service they are trade names. is absolutely free. However, if dominant bold -face listings are If you cannot find any item or manufacturer in this section or in previously-published desired, we make a charge of 52 sections, just drop us a line for the information. for names $1 concern and for NOTE: Section 1 of this DIRECTORY was published trade names for each bold -face in the .October, 1940 issue, Sec- listing. Please write to the Ad- tion VI, presented here, concludes the 1st Edition of the DIRECTORY. Nezt month: Sec- vertising Dept., Radio-Craft, 20 tion 1, Revised. Vesey St., New York, N. Y., for While every precaution lé taken to insure accuracy, Radio -Craft cannot guarantee against details. 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 I earliest moment to insure corrections in the very next issue.

TUBES (b PARTS) NORTHERN ELECTRIC CO., LTD. 1261 Shearer St. FISCHER DISTRIB. CORP., 22 Fulton St., New York. Montreal Que. Can.-BR C, IN, P RR, TX, V, Pe N. Y. -AV I OFFENBACH ELECTRIC CO., 1452 Market St., San HARRISON RADIO CO., 12 W. Broadway, New Francisco, Calif. -BR C IN, P RR TX, V M York, N. Y.-AV, I PHILCO RADIO & TELEVISION CORP., tioga & HARTMAN ELECTRICAL MFG. CO., Mansfield, C Sts., Phila. Pa. -P, RR Ohio -N PHOTOBELL CORPORATION, 123 Liberty St., New THE HICKOK ELECTRICAL INSTRUMENT CO., York, N. Y.-IN, P 10514 Dupont Ave., Cleveland, Ohio -AV RADIO ELECTRIC SERVICE CO., INC. N. W. Cor. HERBERT H. HORN, 1201 S. Olive St., Los Angeles, 7th & Arch Sts., Phila., Pa. -BR, C, IA, P, RR, TX, Calif.-AV, FV, I Ballast (regulating) BR KAAR ENGINEERING CO., 619 Emerson St., Palo Cathode -ray C RADIO EQUIPMENT CORP. 326 Elm St., Buffalo, Alto Calif. -RT N. Y.-BR C, IN P RR, TX V M LAFAYETTE RADIO CORP., 100 6th Ave., New York, Industrial . IN RADOLEK bOMPANY' 601 W. itendolph St., Chi- N. Y. -AV, FV, I Miniatures (hearing -aid and /or cago, III. -BR, C, IN P, RR TX, V, M FRED M. LINK, 125 W. 17th St., New York, N. Y.- radio receiving) . . . M RAYTHEON PRODUCTIONCORP. 420 Lexington AV Ave., New York, N. Y. -IN, RR TX, M M. & H. SPORTING GOODS CO., 512 Market St., Photocells . . . . P RCA MFG. CO., INC., Front & Cooper Sts., Cam- Phila., Pa. -AV, I Receiving (including rectifiers) den, N. J. -BR C, IN P, RR, TX, V, M P. R. MALLORY & CO., 3029 E. Washington St., RR ROGERS -MAJESTIC CORP., LTD., 622 Fleet St., Indianapolis Ind.-AV, FV Toronto, Can.-C, RR, TX MEISSNER MPG. CO., Mt. Carmel, 111.-AV Transmitting . TX MAURICE SCHWATZ & SON 710-712 Bway. Sche MONTGOMERY WARD & CO., 619 W. Chicago Voltage control V nectady, N. Y.-8R, C, IN, P, RR, TX V, .4 Ave., Chicago, 111. -I SHELLEY RADIO CO., 1841 S. Flower St., Los An- OAK MFG. CO., 1260 Clybourn Ave., Chicago, Ill.

FV, 1 AMERICAN TELEVISION CORP., 130 W. 56th St., geles, Calif.-BR, C, P, RR, V -AV, New York, N. Y -C S.O.S. CINEMA SUPPLY CORP., 636 Ilth Ave., OFFENBACH ELECTRIC CO., 1452 Market St., San AMPERITE COMPANY, 561 B'way., New York, New York, N. Y. -P Francisco, Calif.-AV FV, I N. Y -BR SUN RADIO CO. 212 Fulton St., New York, N. Y.- PHILCO RADIO & TELEVISION CORP., Tioga & ARCO TUBE CO.. 227 Central Ave., Newark, N. J.- BR, C, IN P RR TX, V, M "C" Ste., Phila. Pa. -AV FV BR, C, IN, P, RR TX V, M TAYLOR AIRPI-4ONE PRODUCTS, Hangar IS, Long RADIO ELECTRIC SERVICE CO. INC. N. W. Cdr. CANADIAN MARCONI CO., Montreal, Quebec, Beach Airport, Long Beach, Calif.-M 7th & Arch Sts., Phila., Pa -AV, FV, I Can. -BR, C, IN, P, RR, TX, V, M TAYLOR TUBES INC., 2341 Wabansia Ave., Chi- RADIO EQUIPMENT CORP., 326 Elm St.. Buffalo, N. Y. FV, I CLAROSTAT MFG. CO., INC., 285 N. 6th St., cago ILL. -ttJ, TX -AV Brooklyn, N. Y.-BR TILTON ELECTRIC CORP., 15 E. 26th St., New York, RADOLEK COMPANY, 601 W. Randolph St., Chi- N. Y.-BR cago, III. -AV, FV I CONTINENTAL ELECTRIC CO. Geneva, III -IN P MAURICE SCHWARTZ & SON, CRUMPACKER DISTRIB. CORP., 1801 Fannin St., UNITED ELECTRONICS CO., 42 Spring St., Newark, 710 -712 Broadway, N. I Houston, Tex. -BR, P, RR N. J. -IN TX Schenectady Y. -AV. FV INC., HAROLD DAVIS, INC., 428 W. Capital St., Jackson, WESTINGHOUSE ELEC. & MFG. CO., East Pitts - SETCHELL CARLSON, 2233 University -Ave., burgh, Pa.-C, IN P, TX St. Paul, Minn. -AV, FV Miss. -BR C, IN, P, RR TX, V. M RADIO 6001 Dickens SHELLEY RADIO CO., 1841 5. Flower St., Los An- DOW RADIO SUPPLY CO. 1759 E. Colorado, ZENITH CORP., Ave., Chicago, Pasadena, Calif. -BR, RR, fX 111. -R geles, Calif. -AV ALLEN 8. DU MONT LABS., INC., Passaic, N. J.-C SUN RDIO CO., 212 Fulton St., New York, N. Y.- AV FV, I EITEL- McCULLOUGH, INC., 798 San Mateo Ave., San Bruno, Calif. -TX VIBRATORS TAYLOR AIRPHONE PRODUCTS Hangar 15, Long Beach Airport, Long Beach, ELECTRONIC CONTROL CORP., 2667 E. Grand Calif. -A Blvd., Detroit Mich.-P UTAH RADIO PRODUCTS CO., 812 Orleans St., Chicago, 111.-AV, FV E ÌECTRONS, INC., 127 Sussex Ave., Newark, N. J.- JAMES VIBRAPOWR CO., INC., 341 N. Crawford Ave., Chicago 111.-AK, FV FARNSWORTH TELEVISION & RADIO CORP., 3702 VICTOR ANIMA'TOGRAPH CORP., Davenport, Iowa E. Pontiac St., Fort Wayne, Ind. -C, IN, P, TX FEDERAL TELEGRAPH CO., 200 Mt. Pleasant Ave., Newark, N. WIRE J. -TX (Also see Battery Chargers, Eliminators & FISCHER DISTRIB. CORP., 222 Fulton St., New York, N. Y. -BR C, P RR, M Rectifiers) GENERAL ELECTRICSchenectady, O., N. Y. & Aircraft A Bridgeport, Conn. -BR, IN, P, RR, TX, M Auto -radio AV G -M LABORATORIES, INC., 4326 N. Knox Ave., Chicago, 111.-P Farm -radio FV GOLDENTONE RADIO CO., 15123 Warren Ave., Inverters I Dearborn, Mich. -RR Neon Lighting N HARRISON RADIO CO., 12 W. B'way., New York, Antenna (receiving) . AR N. Y.-BR, C, IN, P, RR. TX, V, M Radio transmitting , . RT HEINTZ & KAUFMAN, LTD., South San Francisco, Antenna (transmitting) . AX Calif. -TX AMERICAN TELEVISION & RADIO CO., 300 E. 4th Antenna, Transmission (receiv- HERBERT St. Paul Minn. -AV, FV, I H. HORN, 1201 S. Olive St., Los An- St., ing) ATR geles, Calif -BR, V. THE BENWOOD -LINZE COMPANY, 1838 Washing- IN, M Transmission HYGRADE SYLVANIA CORP., 500 5th Ave., New ton Ave., St. Louis, Mo. -1 Antenna, (transmit- York, N. Y.-BR, C, RR, M CANADIA N MARCONI CO., Montreal, Quebec, ting) ATX HYTRON CORPORATION, Can. -AV, FV, 1 76 Lafayette St., Salem, Concentric cable - . , C Mass. -BR, C, IN, P, RR. TX, V, M CANADIAN RDIO CORP., LTD., Toronto, Ontario, Cords (attachment) , . . J. F. D. MANUFACTURING CO., 4111 Ft. Hamilton Can. -AV, FV CA Pkwy., Brooklyn, N. Y.-BR CRUMPACKER DISTRIB. CORP., 1801 Fannin St., Hookup H KEN -RAD TUBE & LAMP CORP., INC.-Owensboro, Houston, Ter.-AV. FV, I Insulated cable I Ky. -RR, M HAROLD DAVIS, INC., 428 W. Capital St., Jack-

R. son, FV, I Litzendraht ( "Litz.") . . LW T. McELROY, 100 Brookline Ave., Boston, Mass.- Miss. -AV, BR. P DOW RADIO SUPPLY CO., 1759 E. Colorado, Pasa- Magnet MW M. & G. HEARING dena. Calif.-AV AIDS CO., 30 N. Michigan Microphone cable . . . M Ave., Chicago, III -M ELECTRONIC CONTROL CORP., 2667 E. Grand MONTGOMERY WARD & CO., 619 W. Chicago Blvd.. Detroit, Mich -1 Radio harness RH Ave., Chicago, Ill -BR, C. RR, TX, M ELECTRONIC LABORATORIES, INC., 122 W. New Resistance RES York St.. Indianapolis, Ind NATIONAL UNION RADIO CORP., 57 State -I Resistance cords R ESPEY MFG. CO., INC., 305 E. 63rd St., New York, St., Newark, N. J. -BR, C, P, RR, V N. Y. -1 Shielded SH When writing to companies listed here please mention that you saw the listing in the Radio-Craft "Classified Radio Directory"' RADIO -CRAFT for MARCH, 1941 569 Order your copy NOW the only

D the P. A. HAN A Resume of the Contents of 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 Il- AMPLIFIERS Voltage Amplification Design of resistance -coupled voltage amplifiers Commercial voltage amplifier The Power Stage Class A amplifiers Class AB amplifiers Class AB, amplifiers Class ABt amplifiers Class B amplifiers When to apply class A, AB, and B amplification Power Supplies Half -wave rectification Full -wave rectification Voltage doublers Filter CircuiLs Power supply regulation, etc. Practical Hints on Amplifier Con- struction Microphonism Placement of components Tone compensation Inverse feedback Remote control methods SECTION III -DISTRIBUTION The Loudspeaker Dynamic speakers Speaker performance (frequency response, efficiency) 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 BOOK PUBLISHED SECTION IV- COORDINATION P.A. Input impedance matching Matching speakers to P.A. installa- THAT no book has yet been published Which covenven A MATCHLESS VOLUME amplifiers and sound stems teras (also kindreers. An complete as you would expect to find any engineer- tions PP e radio or P A. man Deievhle. Yet. ills Ìé ing hndbook -thi in how the Phasing speakers print fat, ierel in o booth fn finds the AMPLIFIER HANDBOOK AND PUBLIC AD- which covers Public( Address from An to Z. data compiled to To bridge this wIde.spread gap, RADIO-CRAFT will DRESS GUIDE. With essential technical Effect of mismatching speakers publish omplete, magnificent From large number of Address such volume on Public me overr.tlnearlly a undrtN different subjects amplifier output magnitude-so complete and outherit.. branch Or tubdivslon -that e man engaged In radio can have both very conceivable A typical P.A. installation (in a livetheoretical` and emettes) knowledge function OfdlnstinRAddress.Public d operation of sound systems. The editorial pages THE CONTENTS skating rink) Sr. o filled will° instruction and tete with Il To actually show the scope and magnitude of the USEFUL PUBLIC ustratlons that the volume fully justifies its title AMPLIFIER HANDBOOK AND PUBLIC ADDRESS SECTION V- at the DRESS GUIDE. on of the tents is found ADDRESS DATA AND IN- GUIDE TThiEsRgreeHANDBOOKt HDBOOK On Public Ad right. showing the breakdown of the material featured dress hould be read studied by those who n within thorough FORMATION lstently build. service and sell sound equipment. contents° dhows thsection.mle eness this (book. Speaker matching technique The ABC of Db., VU, Mu, Gm and RADCRAFT PUBLICATIONS 20 VESEY STREET NEW YORK, N. Y. Sm Charts and formulas useful to the a Bs B B BB1 B ara BB1 a ME M r..... - ...... - a practical P.A. sound man to important articles RADCRAFT PUBLICATIONS. INC. * 20 VESEY STREET * NEW YORK. N. Y. RC341 Handy index on public address and sound Gentlemen. Enclosed find my remittance of 25c for which send mo POSTPAID. one cop, of your NEW- 1940 AMPLIFIER HANDBOOK AND PUBLIC ADDRESS GUIDE. 1 Send me others. for friends. also POSTPAID @ 25c each. 1 Order Your Copy NOW- Name Address City State lip &oupon and Remit by cheek or money order: register letter Ì 1 If you send cash or unused U.S. Postage Stamps. /Mail Today! 1 ussss 570 RADIO -CRAFT for MAKLI -1, 1Y41

CLASSIFIED RADIO DIRECTORY

Shielded ignition . . . . S NORTHERN ELECTRIC CO., LTD., 1261 Shearer St., H. W. ACTON CO., INC., 370 7th Ave., New York, Montreal, Que., Can. -AR, AX, ATR, ATX, C, CA, N. Y.-C F, D M. SS Wire shielding . . . . SW WC, GU, HI I MW M RH, RES, SH ADVANCE ELECTRIC CO., 1260 W. 2nd St., Los OFFENBACH ELECTRIC CO., 1452 Market St., San Angeles, Calif.,-C, F, P. 1HE ACME WIRE CO., 1255 Dixwell Ave., New Francisco, Calif.-AR, AX, ATR, ATX C, CA AEROVO CORPORATION, New Bedford, Mass. Haven Conn. -AR. LW. MW - WC GU, H, I, LW MW, M, RES, R, SH S, SW C, HO, F, AR, D, E G M, S, SS SCORN INSULATED WIRE CO., INC., 225 King St., PHILCO RADIO & TELEVISION CORP., ioga & ALDEN PRODUCTS 715 Center St., Brockton, Brooklyn, N. Y. -ATR H, I, SI-1 CO., "C" Sts., Phila. Pa. -AR, CA, H, I M, SH Mass. -C F E M, SS PRODUCTS 715 Center Brockton CO. St., RADIO ELECTRIC SERVICE CO., INC., N. W. ALLEN ELECTRIC & EQUIPMENT CO., 2101.2117 Mass. -AR, C, CA, WC, H, I, M, RH, SH, S, SW Cor. 7th S. Arch Sts. Phila. Pa. -AR, AX, ATR N. Pitcher St., Kalamazoo, Mich. -C, F, D, S 4LLIED RADIO CORP., 833 ATX, MW, M, W. Jackson Blvd., Chi- C, CA, WC, GU, H, I, LW, RH, ALLIED RADIO CORP., 833 W. Jackson Blvd., Chi. cago, III. -AR, AX, TR ATX, C, CA, WC, GU, RES R SH S, SW co o, 111. -C F, A H, I, LW, MW, M, RH, RES, R, S, RADIO 326 Elm SH, SW EQUIPMENT CORP., St., Buffalo, ALLISON BAFFLE CO., 722 Berea Ave., Gadsden, N. Y. AT, ATR, ATX, WC, H, I, 4i-PHA WIRE CORP., 50 Howard St., New York, -AR, GU, MW, Ala. -HO, F, A M, R, SH S, N. Y.-AR, AX, ATR ATX C, CA, WC, GU, H. SW ALPHA WIRE CORPORATION, 50 Howard St., New RADOLEK COMPANY, 601 W. Randolph St., Chi- 1, LW, M , RH S1-1,, S, SW York, N. Y.-C, F, A cago, 111. AX, ATR ATX, C, CA, WC, 4MERICANPHENOLIC CORP., 1250 Van Buren St., -AR GU, AMERICAN COMMUNiCATIONS CORP., 123 Liber- H, I, MW M, RH RES, R, S, Chicago, III. -ATR, ATX, C LW SH SW ty St. New York, N. Y.-C, F, A \TLAS SOUND CORP., 1451 39th St., Brooklyn, N. Y. REX BASSEI INC., 214 Star Bldg Miles Mich. -C AMERICAN CONDENSER CORP., 2508 S. Michigan RHEOSTAT 37 W. New York, -M REX CO., 20th St., Ave., Chicago, III. -C, F, A TANK'S MFG. CO., 5019 N. Winthrop Ave., Chica- N. Y -RES AMERICAN EMBLEM CO., INC., Utica, N. Y. THE RIVERSIDE METAL River- -C, go, 111.-C, H M, SH CO., Pavilion Ave., F, E, D, S, AR IELDEN MFG. CO. 4647 W. Van Buren St. Chicago, side, N. J. -RES AMERICAN GAS ACCUMULATOR CO., 1029 New- A. ROEBLING'S 640 S. Broad 111.-AR, AX, ATR ATX, C, CA, WC, {i, I, LW, JOHN SONS CO., ark Ave., Newark N. J,-C, F A St. Trenton, I, MW M, RH R, Sil S SW N. J. -AR, AX, C, WC, GU, H, AMERICAN LAVA CORP., Cherokee Blvd. & Manu. MW M SH, S, SW .. S. BRACH MFG. CORP., 55 Dickerson St., New- facturer Rd., Chattanooga, Tenn. -C, F, M, E ark N. AX ATR RUPP'S ASSEMBLING & MFG. WORKS, 2341 Semi- J.-AR, ATX AMERICAN PHENOLIC CORP., 1250 W. Van Buren IRUSH DEVELOPMENT 3311 Perkins Ave., nary Ave. Chicago 111. -CA CO., St. Chicago, 111. -C HO, F M, E J MAURICE SCHWARTE & SON, 710 -712 Broadway, Cleveland Ohio -M THE AMERICAN ROLLING MILL CO., Middletown, IUD RADIO, 5205 N. Y. -AR AX, ATR ATX C, CA, INC., Cedar Ave., Cleveland, F M, E WC GU, H. I, LW, MW, M, RFT, RES, R, SH, Ohio -C, Ohio-MW AMPERITE COMPANY, 561 Broadway, New York, :ANADIAN MARCONI CO., Montreal, Quebec, S. Sw SELECTAR MFG. CORP., 30 W. 15th St., New York, N. Y.-C, F, A Can. -AR, AX, ATR, ATX, , H, I, CA, LW, M, AMPLIFIER CO. OF AMERICA, 37 West 20th St., RH N. Y.-M New York N. Y.-C F, A :ANADIAN RADIO CORP., LTD., Toronto, SHELLEY RADIO CO., 1841 S. Flower St. Los An. Ontario, - AMPRO CORPORATION, 2839 N. Western Ave., Can. -AR ATR, H geles, Calif, -AR, CA, H, 1 M SH, S Chicago, III. -C F T :LAROSTAt MFG. CO. INC., 285 N. 6th St., SUN RADIO CO., 212 Fulton St., New York N. Y. ACEVES & IfING, INC., 11 W. 42nd St., New Brooklyn, N. Y. -RES, -AR, C, CA, WC, H, I, MW, M, AMY, York, N. F, M E, D, S WIRE ASSOCIATED R, X,HIR, ASW Y.-C :ONSOLIATED & CORPS. 512 ANSLEY RADIO CORP., 4377 Bronx Blvd., New 17 E. 16thTECHNICAL S. Peoria St., Chicago, 111. AX, ATR AT) , APPLIANCE CORP., St., -AR C, York, N. Y.-C, F D CA, WC, H, I, MW, RH, RES, New York, N. Y. -AR ATR, SH LW, M, k, SH, S, 123 TILTON ELECTRIC CORP., 15 E. 26th St., New York, APPROVED TECHNICAL APPARATUS CO., Lib- erty St., New York N. Y. --C, F, A :ORNISH WIRE CO., INC., 15 Park Row, New N. Y. -R MICROPHONE 424 ARCO TUBE CO., 227 Central Ave., Newark, N. J. York, N. Y.-CA, GU H, I UNIVERSAL CO. LTD., War. -C F A :RUMPACKER DISTRIR. CORP., 1801 ren Lane, Inglewood, Calif. -M Fannin St., ARLAVOif MFG. CO., 430 S. Green St., Chicago, Houston Tex. -AR, ATR, CA, H, I, MW, RES, R, WINCHARGER CORPORATION, Sioux City, Iowa - 111. F, M, E, D SH, S SW GU -C, ASIATIC MICROPHONE LABORATORY, INC., 830 )OOLITYLE & FALKNOR, INC., 7421 S. Loomis Market St., Youngstown, Ohio -C, F, M, E, D, SS, Blvd. 111. Chicago, -C G, AR -AROLD DAVIS, INC., 428 St., W. Capital Jackson, LITERATURE ATLAS CONDENSER PRODUCTS CO., 548 West- Miss. -AR AX, ATR, ATX, C. CA, H, I, LW, RH, chester Ave., New York, N. Y. -C, F, M, D RES, R, SFI, S, SW )OW RADIO SUPPLY CO., 1759 E. Colorado, Pasa- ATLAS PRESS CO., Kalamazoo, Mich. -C, F, A dena, Calif. -AR, AX, ATR, ATX, C, CA, H, I, ATLAS SOUND CORP., 1447.39th St., Brooklyn, N. Y. MW, M, RES R, SH S, SW -C, F, A )RIVER -HARRIS COMPANY, Harrison, N. J. -RES AUDIO DEVELOPMENT CO., 123 Bryant Ave. N., :AGLE ELECTRIC MFG. CO., INC., 59 Hall St., Minneapolis, Minn. -C, F, M, E Brooklyn, N..Y. -CA AUDIOGRAPH SOUND SYSTEMS, 1313 W. Randolph UGH H. EBY, INC., 4700 Stanton Ave., Phila., St., Chicago III.-C, H, F, E, D S, SS Pa. -RH Following is a listing of those companies which pub- D. J. AULD CO., 5t Ave., & 5tl, St., Columbus, HE ELECTRIC AUTO -LITE CO., American Wire lish catalogs, house organs (C, or HO, respectively), Ohio -C F M Div., 3529 24th St., Port Huron, Mich. -AR. H, or both. AUTOCRAT RADIO CO., 3855 N. Hamilton Ave., MW, S SW Whether these publications 'are available gratis (F), Chicago, III. -C, F, A ESSEX WIRE CORP. 14310 Woodward Ave., De- or whether a nominal charge is made (c), is in- THE AUTOMATIC ELECTRICAL DEVICES CO., 324 troit, Mich. -AR, CA, WC, H, I, LW, MW, M, dicated. E. 3rd St. Cincinnati, Ohio -C, F, A RH R SH, S SW Finally, identifying letters signify the particular BAKER & CO., INC., 113 Astor St., Newark, N. J.- =EDERAL SALES CO., 24 -26 S. Jefferson St., Chica- C, F A go, group to which this literature is directed (Engineers, III. -H Dealers, Servicemen etc.). BANK'S MFG. CO., 5019 N. Winthrop Ave., Chica- = ISCHER DISTRIB. CORP., 222 Fulton St. New York, Please mention RADIO -CRAFT when writing to go, III. -C, F, M E, D, S, SS N. Y. -AR, AX ATR, ATX, C, CA, WC, GU, H, these organizations. BARKER & WILLIAIvISON, Audmore, Penna. -C, F, I, LWLW, MW, M, RH RES R, SH S, SW M E, A A. M. & SON. INC., 113 N. Broad St., BELDEN MANUFACTURING CO., 4647 W. Van Trenton, N. J. -AR, SH NATURE OF PUBLICATION Buren Street Chicago, III.-C, F, A "ENERAL CEMENT MFG. CO., 919 Taylor Ave., Catalog C BELMONT RADIO CORP., 1257 ullerton Ave., Chi- Rockford, 111. -H cago 111.-C F, D ì ENERAL ELECTRIC CO., Schenectady N. Y. & Construction Booklet CB THE RENWOOD -LINZE CO. 1838 Washington Bridgeport, Conn. -AR, AX ATR ATX, C, CA House Organ HO Avenue, St. Louis, Mo.-C, F M, E WC H, I, LW MW, M, RH, RES R, SH SW A. BITTER CONSTRUCTIO CORP., 27 -01 Bridge i ENI'RAL INSULATED WIRE CORP., S3 Park Place, Plaza N. L. I. City, N. Y. -C, F, D New York N. Y.-C CA, H I, M, SH, S CHARGES SLAW -KNOX CO., Pittsburgh, Pa.-C, F, M, R :. 1. GUTFIMAN & CO. INC., 400 S. Peoria St., Free F Chicago, III. -LW, MW BLILEY ELECTRIC CO., 200 Union Station Bldg., Erie, Pa.-C, HO (to regular Bliley distributors 4ARRISON RADIO CO. 12 W. Broadway New Price c F, A York, N. Y.-AR, AX, AfR, ATX, C, CA, WC, GU, only), BOND. PRODUCTS CO. 13139 Hamilton Ave., De- H I, LW, MW, M, R, SH, S, SW TO AVAILABLE troit Mich. F, E, ROLYOKE WIRE AND CABLE CORP., 720 Main St., -C D BOONYON MOLDING Co., 376 Myrtle Boon- Holyoke, Mess. -AR, CA, H, I, RH, RES, R, SH, Anyone (being all- inclusive, no Ave., listings are given, ton N. J.-C F, A other if "A" L. S. BRACH MPG. CORP., 55 Dickerson St., Newark, ROPE WEBBING CO., P. O. Box 1495, Providence, is indicated) A N. J. F A R. 1. -AR, ATR WC -C, ALLEN -BRADLEY CO., 1326 S. 2nd St., Milwaukee, RERBERT H. HORN, 1201 S. Olive St., Los Angeles, Amateurs (licensed radio) AR Wisc. F, M Calif. -AR, CA, H. I M, SW -C Consumers CON BRACI-I St., ROSKINS MFG. CO., 4445 Lawton Ave., Detroit, L. S. MFG. CORP., 55 Dickerson Newark, Mich. -RES Dealers D N. J. -C, F, A :. F. JOHNSON COMPANY, Waseca, Minn. -AX, Distributors DIS BRIGHT STAR BATTERY CO., Crooks & Getty Aves., Clifton N. J.-C, F A ATR, ATX C I ES Electronic Specialists BROWNING LABORATORIES, INC., 750 Main St., (ELLOGG SWITCHBOARD & SUPPLY CO., 6650 S. Cicero Ave., Chicago III. -H Engineers E Winchester, Mass. -C, F, A MFG. 403 .AFAYETTE RADIO CORP., 100 6th Ave., New York, General Experimenters G BROWN CO., W. Baltimore, Detroit, Mich. F, A N. Y. -AR, AX, ATR, ATX, C CA C, GU, H, J -C, Jobbers THE BRUSH DEVELOPMENT CO., 3311 Perkins Ave., I LW, MW, M, RES, R, SH, S SW Manufacturers M F =RED M. LINK, 125 W. 17th St. New York, N. Y.-C Cleveland, Ohio -C, HO A BUD RADIO, INC., 5205 Cedar Ave., Cleveland, .DWELL INSULATED WIRE CO. 171 Lincoln St., Marine Supply MS Lowell, Mass. -AR, CA, H, SH, Musicians MUS Ohio -C, F, AR, E, D, G, M, S SS R. McELROY, 100 Brookline Ave., Boston, Mass. BURGESS BATTERY CO., P. O. Box 121, Freeport, -CA Radio Stations R 111.-C, F, E, D, S SS, G A. & G. HEARING AIDS CO., 30 N. Michigan Servicemen S BUSSMANN MFG. CO., Oniversity at Jefferson, St. Louis, Mo.-C, F, M, E, D S Ave., Chicago, 111. -CA Sound Specialists SS A. & H. SPORTING GOODS CO. 512 Market St., CAMBRIDGE INSTRUMENT CO., INC., 3732 Grand Phila., Pa. -AR, AX, ATR, ATX, CA, WC, GU, Talkies Owners T Central Terminal, New York, N. Y.-C, F, M, E, H, I, LW MW, M R, SH S, SW SS, G THE ACME ELECTRIC & THE ALLEN D. CARDWELL MFG. CORP., 81 Pros- .IEISSÑER {.IFG. CO. Mt. Carmel, 111.-LW, MW MFG. CO., Water St., 4ONTGOMERY WARb & CO., 619 W. Chicago Cuba, N. Y-C, F, A, pect St., Brooklyn, N. J.-C, F, M, E, D, G, AR Ave., Chicago, 111. -AR AX, ATR, ATX, C, CA, ACOUSTIC CONSULTANTS INC., 1270 6th Ave. CARRIER MICROPHONE CO., 439 S. La Brea Ave., Y. H, I, MW, M R, SH, W New York, N. -C, F, AR, D, E, G, M, S, SS Inglewood, Calif. -C, F, M, E, D, SS, AR JEW ENGLANb ELETRICAL WORKS, Lisbon, ACRO TOOL & DIE WORKS 2815 Montrose Ave., CARRON MANUFACTURING CO 415 S. Aberdeen N. H.-LW, MW, SW Chicago, I11. -C, F, E, J, M St., Chicago, 111. -C, F, E, D, S, SS, G, AR When writing to companies listed here please mention that you saw the listing in the Radio -Craft "Classified Radio Directory" RADIO -CRAFT for .MARCH, 1941 571 CLASSIFILI) RADIO DIRECTORY

CARTER MOTOR CO., 1608 Milwaukee Ave., Chica- FEDERAL TELEGRAPH CO., 200 Mt. Pleasant Ave., JADUR IMPORT CO., 21 W. 19th St., New York, go 111. -C, F, M, E, SS, G Newark, N. J. -C, HO, , M, E N. Y.-C, F, A CASTLEWOOD MANUFACTURING CO., 12th & FINCH TELECOMMUNICATIONS, INC., 1819 B'way, JANETTE MFG. CO., 556 W. Monroe St., Chicago, Burnett Sts., Louisville, Ky. -C, F, A New York, N. Y.-C, F, E, I, M 111. -C, F, A CHARGIT CORPORATION, Anderson, Ind.-C, F, A FISCHER DISTRIB. CORP., 222 Fulton St., New York, JEFFERSON ELECTRIC CO., Bellwood, III.C, F, A N. F, CHICAGO MOLDED PRODUCTS CORP., 1020 N. Y.-C, A RAY JEFFERSON, INC., 182 Milburn Ave., Baldwin, FISHER REEARCH LABS., Palo F, Kolmar Ave., Chicago, 111.-HO, F, E Alto, Calif.-C, N. Y.-C, F, D, S, MS A CINCH MANUFACTURING CORP., 2335 W. Van JENSEN RADIO MFG. CO., 6601 S. Laramie Ave., A. B. FISHWICH RADIO CO. 139 West 4th St., Buren St. Chicago 111.-C F, M, E, D Chicago, 111.-C, F, A F, M, D CIRCLE F MANUFACTURING CO., 720 Monmouth Cincinnati, Ohio-C M. M. FLERON 113 J. F. D. MANUFACTURING CO., 4111 Ft. Hamilton SE, Trenton, N. J. -C, F, M, E SS & SÖN, INC., N. Broad St., Trenton, N. Parkway, Brooklyn, N. Y. -C, F, A CLAROSTAT MANUFACTURING CO., INC., 285 -287 J. -C, F, D, S N. 6th St., Brooklyn, N. Y. -C, F, A THE FORMICA INSULATION CO., 4614 Spring E. F. JOHNSON COMPANY, Waseca, Minn. -C, Grove Ave., Cincinnati, Ohio -C, F M, E F, A THE CLOUGHBRENGLE CO. 5501 Broadway, Chi- THE FORNSBERG MFG. CO., 125 Seaview Ave., HOWARD 8. JONES, 2300 Wabansia Ave., Chicago, III. F, M, E, D, $, SS, G, AR cago, -C, Bridgeport, Conn. -C, F, M, E, D 111. -C, F, A COLE RADIO WORKS, 86 Westville Ave., Caldwell, FOWLER MANUFACTURING CO., No. 9 Rutger St., KAAR ENGINEERING CO., 619 Emerson St., Palo N. J. -C, F, A St. Louis, Mo. -C, F, A Alto, Calif.-C, F, My D S CONDENSER PRODUCTS CO., 1375 N. Branch St., GARDINER METAL CO., 4820 S. Campbell Ave., KATO ENGINEERINGO COMPANY, INC., 530 N. Chicago, III. -C, F, A Chicago, 111. -C, F, M, E Front St., Mankato, Minn. -C, F, A CONSOLIDATED WIRE & ASSOCIATED CORPS., GAROD RADIO CORP., 70 Washington St., Brooklyn, KELLOGG SWITCHBOARD & SUPPLY CO., 6650 S. 512 S. Peoria St., Chicago, III. HO, F, M N. Y. F, M, D -C, -C, Cicero Ave., Chicago, 111.-C, F, M CONTINENTAL CARBON, INC., 13900 Lorain Ave., GELARDIN, INC., 21 -29 Washington St., Brooklyn, N. Y. F, M, E, D, S, SS KENYON TRANSFORMER CO., INC., 840 Barry St., Cleveland Ohio-C, F, A -C, G. AR GENERAL CEMENT MFG. CO., 919 Taylor Ave., Bronx, N. 1.-C, F A CONTINENTAL DIAMOND FIBRE CO., Newark, KING LABORATORIES, INC., 205 Oneida St., Syra- Rockford, 111.-C, F, M E, D, S, SS, G, AR Dela. -C, F, M E cuse, N. Y.-C F. M CONTINENTAL ELECTRIC CO., Genlva, 10. -HO, GENERAL CERAMICS CO., Plant No. 3, Keasbey, F, KRAEUTER 8 Cb., INC., 585 IBth Ave., Newark, F, D, E, M N. J.-C, M, E GENERAL COMMUNICATION PRODUCTS CO., N. J.-d, F, M, E, D, S CORNING GLASS WORKS, Corning, N. Y. -C, F, A .KURZ- KASCH, INC., 1421 S. Broadway, Dayton, 6245 Lexington Ave., Hollywood, Calif. -C, F, E, 15 N. Y. F, E CORNISH WIRE CO., Park Row, New York, D, SS Ohio-C, M, F, M 100 -C GENERAL DRY BATTERIES, INC., 13000 Athens Ave., LAFAYETTE RADIO CORP., 6th Ave., New York, THE GEORGE F. CRAM CO., 730 E. Washington St., N. Y. F A Cleveland, Ohio -C, F M, E, D, S -C, F, M F, Indianapolis, Ind.-C, D, GENERAL ELECTRIC CO., Schenectady, N. Y. & LAMPKIN LABORATORIES, Bradenton, Fla.-C, CRESCENT TOOL & DIE 4140 Belmont Ave., A CO., Bridgeport, Conn. -C, F, HO D, S 111. F, A MFG. 3918 Monroe Chicago, -C GENERAL INSULATED WIRE CO., 53 Perk Place, LAUREHK RADIO CO., Ave., 405 Mich. F, M, E, D CRUCIBLE STEEL CO. OF AMERICA. Lexington New York, N. Y. -C, F M, J Wayne, -C, York, N. Y. F, E, M Ave., New -C, GENERAL RADIO CO., 30 State St., Cambridge, THE LAUSON COMPANY, New Holstein, Wis. -C, F, M, E D, S CRUMPACKER DISTRIB. CORP., 1801 Fannin St., Mass. -C, HO, F, M, E RELAY 5915 Blvd., Los An- Houston, Tex. -C, F, AR, E, D, S, SS M. A. GERETT CORP., 2947 N. 30th St., Milwaukee, LEACH CO., Avalon geles, Calif.-C, F, A CRYSTAL EAR, INC., 2007 S. Michigan Ave., Chica- Wis. -C, F, A go, 111. -C, F, A GLOBE PHONE MANUFACTURING CORP., Read- LECTROHM, INC., 5133 W. 25th PI., Cicero, DAYCO RADIO CORP., 915 Valley St., Dayton, Ohio ing, Mass.-C, F, M E, D, S, SS, G, AR 111.-C, F, A GOLDENTONE RAMC) CO., 15123 Warren Ave., -C, F, A LeFEBURE 716 Road, Ce- Dearborn Mich.-C, F, D, S, G, AR CORPORATION, Oakland DAYTON ACME CO., 2339 Gilbert Ave., Cincinnati, dar Rapids, F, A GORDON SPECIALTIES CO., 1104 S. Wabash Ave., IowaC Ohio-C, F, A LEOTONE RADIO CO., 63 Dey St., New York, N. Y. TOBE Chicago, III.C, F, M, E, D, S, SS, G, AR DEUTSCHMANN CORPORATION, Washing- -C, F A ton St., Canton, Mass.-C, F, M, E CARL GORR PRINTING CO., 2615 N. Ashland Ave., LETERSTÓNE SALES CO., 2515 S. Wabash Ave., 1111 F, E DeVRY CORPORATION, Armitage Ave., Chi- Chicago 111.-C, HO, M, Chicago, III.-C, F, D S cago, 111.-HO, F, A GRAY RADIO CO., 730 Okeechobee Rd., W. Palm LIBERTY ENGRAVING & MFG. CO., 2911 S. Central DeWALD RADIO MFG. CORP., 440 Lafayette St., Beach, FIe.C, F, A Ave., Los Angeles, Calif.-C, F, A New York, N. 1.-C, F, D, S GUARDIAN ELECTRIC MFG. CO., 1621 -27 W. Wal- THE LIFETIME CORP. 1825 Adams St., Toledo, Ohio DIAL LIGHT CO. OF AMERICA, INC., 90 West St., nut St., Chicago, III. -C, F, M, E, D, S, G, AR -C, F, M, E, D, SS, G, AR 709 -11 New York, N. Y.-C, F, M, E, D, SS, G, AR ROBERT M. HADLEY CO., E. 61st St., Los THE LINCROPHONE CO., INC., 1661 Howard Ave., Angeles, Calif. -C, F, A DOOLITTLE 8 FALKNOR, INC., 7421 Loomis Blvd., Utica, N. Y.-C, F, S THE HALLDORSON CO. 4500 Ravenswood Ave., Buren Chicago, III. F, A JOHN E. LINGE 8 SON INC. 28th St. & -C, Chicago, III.C, HO, E, D, S DRAKE MFG. CO., 1713 W. Hubbard St., Chicago, Ave., Camden, N. J. -C, F, 2611 III.C, F, M, E, D, SS, G, AR HALLICRAFTERS, Indiana Ave., Chicago, LITTELFUSE, INCORPORATED, 4757 Ravenswood DREMEL MFG. CO., Racine, Wis.-C, HO, F, M, . III. -C, F, A Ave., Chicago, III. -C, F, M, E, S, SS E, D, S, G, AR HAMMARLUND MFG. CO., INC., 424 W. 33rd St., LOWELL NEEDLE CO., INC., Putnam, Conn.-C, DRIVER -HARRIS CO., Harrison, N. J. -C, HO, F, M, New York, N. Y.-C, F, A F, D E HAMMOND INSTRUMENT CO., 2915 North West- LUMENITE ELECTRIC CO., 407 S. Dearborn St., ALLEN B. Passaic, 111. F, DU MONT LABS., INC., N. J.- ern Ave., Chicago, -C, HO, CON Chicago, 111. -C, F, M, E, D, S, SS, G, AR C, HO, F, M HAMMOND MANUFACTURING CO., Guelph, On- M. 8 512 Market E. I. DU PONT DE NEMOURS 8 CO., 626 Schuyler tario, Can. -C, F, A H. SPORTING GOODS CO., St.,' Phila., HO, F, A, Ave., Arlington, N. J.-C, F, M, E. S, SS, G HARDWICK, HINDLE, INC., 40 Hermon St., New- Pa.-C, R. 100 Brookline Boston, Mass. ark, N. J. -C, F, A McELROY, Ave., - EAGLE ELECTRIC MFG. CO., INC. 57 -79 Hall St., C, F, D. H. HARRELL, 1527 East 74th Pl., Chicago, III. A Brooklyn, N. Y. -C F, M, D, DIS - MAAS 8 WALDSTEIN 438 Riverside Ave., C, F, E co., EASTERN MIKE -STAND CO., 56 Christopher Ave., Newark, N. J. F, M, HARRISON RADIO CO., 12 W. Broadway, New -C, Brooklyn, N. Y. -C, F, A MAGIC ART PAINT CO., Box 23, Hasbrouck York, N. Y. F, M, E, G. AR HUGH H. EBY, 4700 Stenton Ave., Phila., Pa.-C, C, Heights, N. F, A HARVEY -WELLS COMMUNICATIONS, INC., Box J.-C, F, M, E MAJESTIC RADIO 8 TELEVISION CORP., 2600 W. 100, Southbridge, Mass. -C, F, A EICOR, INC., 515 S. Laflin St., Chicago, 111.,C, F, .111. F, A HEINEMANN CIRCUIT BREAKER CO., Penna. Ave. 50th St., Chicago, -C, M, E, D P. R. MALLORY & CO. INC., 3029 E. Washington 8 Plum St., Trenton N. J. -C, F, A EISLER ENGINEERING CO., 750 S. 13th St., Newark, St., Indianapolis, Ind. F, A HEINTZ & KAUFMAN, LTD., South San Francisco, -C, N. J.-C, F, E D, M MARINE RADIO CORP., 117 -19 168 St., Jamaica, Calif. -C, F, A EITEL-McCULLOIJGH, INC., San Bruno, Celif.C, N. Y.-C, F, A F, AR, E, M HEWLETT-PACKARD CO., 481 Page Mill Rd., Palo MANUFACTURING Mt. Carmel, Alto, Calif. -C, F, A MEISSNER CO., ELECTRIC SOLDERING IRON CO., INC., West Elm 111.-C, F, D, S G, A THE HICKOK ELECTRICAL INSTRUMENT CO., 10514 St., Deep River, Conn. -C, F A MELLOPHONE 65 Atlantic Ave., Rochester, Dupont Ave., Cleveland, Ohio-C, F, A CORP., ELECTRONICS APPLICATIONS, Brunswick, Me.- N. Y.-C, F, M, E, D, SS HO, F, A HERBERT H. HORN, 1201 S. Olive St., Los An- MICA INSULATOR CO., 200 Varick St., New York, ELECTRONIC LABORATORIES, INC., 122 W. New geles, Calif.-C, F, D N. Y.-C, F, A York St., Indianapolis, Ind. -C, F, M, E, AR HOWARD RADIO CO., 1735 Belmont Ave., Chicago, MICAMOLD RADIO CORP., 1087 Flushing Ave.. ELECTRONIC PRODUCTS CO., St. Charles, 111.C, 111.C, F, E, D, S, AR Brooklyn, N. Y. -C, F, D, S, SS, G, AR HYGRADE SYLVANIA CORP., 500 5th Ave., New F, M, E, D S TRANS - York, N. Y.-C, 35c- HO, A CHARLES MICHELSON ELECTRICAL ELECTRO PRODUCTS LABS., 549 W. Randolph St., W. 44th St., New York, N. Y. HYTRON CORP., 76 Lafayette St., Salem, Mass. CRIPTIONS47 -C, Chicago, 111.-C, F, M, E, D, S, SS, G, AR - F, A C, F, A MFG. INC., 1239 MIDWEST RADIO CORP., 909 Broadway, Cincinnati, ELECTRO -VOICE COMPANY, HYTRONIC LABS., 76 Lafayette St., Salem, Mass. Bend, F, - F. A South Bend Ave., South Ind. -C, A C, F, A Ohio-C, MILES REPRODUCER CO., INC., 812 B'way., New GEORGE D. ELLIS & SONS, INC., 309 N. 3rd St., IDEAL COMMUTATOR DRESSER CO., Sycamore, III. York, N. 1.-C, F, A Phila., Pa. -C, F, M F, M E, D, S C. MILLEN MFG. CO., INC., 150 Exchange St., ENGINEERING RESEARCH CORP., 909 Giddens- ILLINOIS CONDENSER CO., 1160 N. Howe Street, JAMES Melden, Mass.-C, F. M, E, D, G, AR Lane Bldg., Shreveport, La.-C, F, M, A Chicago, III.C, F, A RADIO CO., P. O. Box 504, Texarkana, Ark. ERIE RESISTOR CORP., 644 W. 12th St., Erie, Pa- INDUSTRIAL CONDENSER CORP., 4049 Diversey MIMS -. F, F M, E, D. AR C, F M, E, SS Ave., Chicago, III. -C, A C, CORP. 58 W. 25th St., New ERWOOD SOUND EQUIPMENT CO., 224 W. Huron INDUSTRIAL INSTRUMENTS, INC., 156 Culver Ave., MINOR RECORD York, N. Y. -C F, M, E, D S, SS, G, AR St., Chicago, 111.-C, F, A Jersey City, N. J.-C, F, M, E, D, S, SS, G MONTGOMERY WARD & Cb., 619 W. Chicago ESPEY MANUFACTURING CO., INC., 305 E. 63rd INSTRUMENT RESISTORS, INC., 25 Amity St., Little Ave., Chicago, 111.-C, F, A St.. New York, N. Y. -C, F, D, S Falls, N. J.-C, F, M, E ELECTRIC CO., 1583 E. 31st., Cleveland, THE ESTERLINE-ANGUS CO., INC., Box 596, In- MUELLER F. A dianapolis, Ind. -C, HO, F, M, E, SS INSULATION MFG. CORP., 565 W. Wash- Ohio-C, MASTER MFG. CO., 508 S. Dearborn St., EVER -NU PRODUCTS 919 N. Latrobe Ave., Chicago, MUSIC ' ington Blvd., Chicago, III. -C, F. M, E, D, 111. F. D 111.-C, F, D MUS Chicago, -C. 47th St., INCORPORATED, 415 Lexington Ave., S, SS, G MUSICRAFT RECORDS, INC., 10 West New York, N. Y.-C, F, A New York, N. Y.-C, HO, F, M, E, D. S, SS, G INSULINE CORP. OF AMERICA, 30 -30 Northern CARBON CO., INC., 30 E. 42nd St.. Blvd., Long Island City, N. Y.-C, F, A NATIONAL FAHNESTOCK ELECTRIC CO., 46 -44 Ilth St., Long New York, N. Y.-C, F, D Island City, N. Y.-C, F, A INTERNATIONAL RESISTANCE CO., 401 N. Broad NATIONAL DOBRO CORP., 400 S. Peoria St., Chi- Pa. C, F, M, E, D, S, SS, G, AR FARNSWORTH TELEVISION & RADIO CORP., 3702 St., Phila., cago, III. -C, F, A Esst Pontiac St., Fort Wayne, Ind.-C, F, A CHARLES JACK MANUFACTURING CORP., 27 E. CORP., 57 State Philadelphia St., York, Pa.-C, F, A NATIONAL UNION RADIO JOHN E. FAST & CO. 3123 N. Pulaski Ave., Chica- St., Newark, N. J. -C, HO. F, CB, -10c: A go, III.C, F M. E, SS, G THE JACKSON ELECTRICAL INSTRUMENT CO., FEDERAL SALES CO., 24 -26 S. Jefferson St., Chi - 129 Wayne Ave., Dayton, 0.-C, F, M, E, D, NEW ART SPECIALTIES, INC., 816 W. Erie St., Chi- cago, III.-C, F, M, E, SS S, SS, G, AR cago, III.C, F. M, E When writing to companies Usted here please mention that von saw the listing in the Radio -Craft "Classified Radio Directory"

572 RADIO -CRAFT , for MAKGM, 1 94 1 THIS IS YOUR OPPORTUNITY TO SUBSCRIBE FREE: TO RADIO- CRAFT'S SISTER PUBLIICATION RADIO PARTS RADIO & TELEVISION AND ACCESSORIES AND RECEIVE VALUABLE PREMIUMS!

HERE is some real BIG NEWS for you 1 Through a fortunate arrangement which we have been able to make, we can now offer you FREE premiums of such extraordinary value that they over- TELEPHONE JACK shadow anything we have ever offered in the past with PUNCHED CHASSIS long frame to RADIO & TELEVISION Magazine. Substantial subscriptions phone lack. plated nt2-circuito yp Heavy chassis Name closes steel BEFORE, in the I I years' history of the maga- 2tclrcutts. holes NEVER f Dans,- used for with zine, have we offered such worthwhile premiums. All tele- is inserted. radio tubes.bes. porter accessories can be used to when chug Dt,rppses in m et, of these radio parts and of control trans( or or in his satiety weight 4 nz. speaker plug good advantage by the "ham" constructor phone high. Ship. tuning 21sa° 1" 35c. and for experiments. long. Val. dial. Great eon daily 1 (3 Pts.) expert te. Reinforced No. large etc. 3 lbs. Premium sets. transmitters, ,eight mental 13'x7 %'x21 structton. ' Vat 3 lbs. premiumNo- 2 5h10 TWO GANG ;:`e 1' POTENTIOMETER oVaalcpo und tef- gang wirç 2 units H¡ Insulated each These parts are given to you IN ADDITION to the other. 000lurn dual cut -rate subscription prices we list below: ohms. Used s. contr 15.n bias broadcast Ship. ,antenna and circuits.< 75c over the single patrol useful In experimental 7 mos. for $1 (saving you -copy price) weigltu Pts.) Val. 25c. 16 $2 you $2 over the single -copy price) Premium No. 3 (5 mos. for (saving 24 mos. for $3 (saving you $3 over the single -copy price) And, of course, the longer your subscription runs, the more merchandise you obtain FREE. As 1 TUBE CHASSIS we expect a tremendous response to this offer, we eint ehasal' with- Allot for tubes. would suggest that you send your remittance punchhen . c out delay, as our supply of parta is limited and we

1 fer bns ide or mg won't be able to duplicate this offer again. m n eis Metal esse Y a to drill. ea sau 'lotie"x2gx IF YOU ARE A RADIO EXPERIMENTER, 25e. AMATEUR OR SERVICEMAN, TAKE AD- (5 Pta.) Val. Premium No. 5 VANTAGE OF THIS MARVELOUS OPPOR- TUNITY NOW!

ASHORT while ago we were informed that one of the largest surplus houses in the East was ready to sacrifice a huge quantity of radio parts and accessories which cost the original LOUDSPEAKER manufacturers thousands of dollars. We entered into an agreement with this house whereby we suggested to them to allow us to UNIT offer these parts to our readers in connection with subscription offers. magnetic loud- The surplus house enthusiastically endorsed our plan. We-the publishers -pay the surplus house Kellogg fe speaker1 milt Has cash for each of these parts, and you -the reaper of this fortunate arrangement-will get these WWI 1101.11 speaker. valuable radio parts and accessories ABSOLUTELY FREE. adjust ause dlas Pillow used Ddlntr This is positively the first time that we have been enabled to make such an unprecedented ey m c^ uJcra or attached as msltl offer which in many ways sounds too good to be true. Nevertheless, we vouch for it in every way speaker useful i'A Otani ) and we know you will not be disappointed. phone lforphonograph. oduction. 'threaded 2 tbs. deep. Shp. ugt, va to valuable merchandise " diem., I This special arrangement enables offer you this FREE with your iuó 2th Pts.) Val. 75c. subscription to RADIO & TELEVISION magazine, at a price which is already a tremendous PremiumPrat' No. 7 ( 10 saving over the newsstand cost. This is how the plan works :-Next to the premium number of each item, we show its point value. For each 7 months' subscription ($1.00) you receive 15 points' worth of merchandise free. For each 16 months' subscription ($2.00) you receive 30 points' worth of merchandise free. For each 24 months' subscription ($3.00) you receive 45 points' worth of merchandise free. For instance, if you send us a seven months' subscription at $1.00, you prepaid, therefore we show the weight of each piece, packed. If you wish are entitled to 15 points' worth of free merchandise. You may order one your free ports sent by parcel post, please add to your remittance n No. 4 (5 points) and one No. 7 (10 points). Or if you wish, one each of sufficient amount to cover postage. Or, if you would rather have us send numbers 2, 3 and 4 (each 5 points), or any other combination which totals the parcel express charges collect, we will be glad to do so. 15 points. Please remember that we do not sell these articles. You cannot buy them Similarly, if you send us a 16 months' subscription ($2.00) you may from us at any price. order any combination of merchandise which totals 30 points. On a 24 In order to make sure that you receive your parts promptly, ORDER months' subscription ($3.00), any combination totalling 45 points. TODAY. Fill out the coupon, clip and mail to us together with the proper Due to the high cost of the merchandise, we cannot ship the articles remittance. ALL RADIO DON'T MISS THIS RADIO & TELEVISION, 20 Vesey Street, New York, N. Y. RC -341 PARTS ARE NEW OPPORTUNITY! WE Please enter my subscription to RADIO & TELEVISION for AND UNUSED Canadian and foreign coun- ASSURE YOU THAT 7 months-$1.00. Plus 15 points' worth of FREE radio parts. in tries add 32 cents for $1.00 YOU Many are their 16 months -$2.00. Plus 30 worth of FREE subscription; 72 cents for WONT BE DIS- points' radio Parts. $2.03 subscription; $1.08 for Original Packing 24 months -$3.00. Plus 45 points' worth of FREE radio parts. $3.00 subscription. APPOINTED. ORDER

I enclose my remittance for $ which includes parcel post charges on the FREE TODAY! SIMPLY FILL parts I am ordering. OUT THE COUPON. Please send the merchandise to me express charges collect. IMPORTANT 70 PRESENT PROMPT SHIPMENT SUBSCRIBERS L7 I am a new subscriber. Extend my present subscription for months. ASSURED! If you are already a subscriber I am circling the numbers of the parts I wish to have you send me Free. or have recently subscribed to Nos. 1 2 3 4 5 6 7 the magazine. this offer still RADIO & holds good for you. too. We merely will lengthen your sub- Name Address scription for either 7 months. TELEVISION 16 months or 24 months. as the oast may be. There Is a city State 20 VESEY STREET placo on Oho coupon which provides for this. (Send remittance In form of chock or money order. If you sand cash or unused U. B. postage stamps, NEW YORK, N. Y. bo sure to register your letter.) ts RADIO -CRAFT for MARCH, 1941 573 CLASSIFIED RADIO DIRECTORY

NOBLITT- SPARKS INDUSTRIES, INC., Columbus. SENTINEL RADIO CORP., 2020 Ridge Ave., Evans- STANLEY TOOLS, New Britain, Conn.-C, F, M. E, Ind.-C, F, M, E, D, S ton, III. -HO F, D, S D, S, AR OAK MANUFACTURING CO., 1260 Clybourn Ave., SHAKEPROOF LOCK WASHER CO., 2501 N. Keeler STARK ELECTRICAL INSTRUMENT CO., 161A King Chicago, III.-C, F M, E Ave., Chicago, 111. -C, F, M, E St. W., Toronto, Ont., Can. -C, F, M, E, D; 5, ' OHMITE MANUFACTURING CO., 4835 W. Flournoy SHALLCROSS MFG. CO., 10 Jackson Ave.. Coiling- SS. G, AR St. Chicago, 111.-C, HO, F, A dale, Pa.-C F , A THE STATES CO., 19 New Park Ave., Hartford, OLSON MANUFACTURING CO., 362 Wooster Ave., H. 6. SHERMAN MFG. CO., 22 Barney St., Battle Conn. -C, F, M, E, D S, G Akron,Akron Ohio -C, F, A Creek, Mich. -D F, D, E, S STEVENS WALDEN,INCORPORATED, 475 Shrews. D. W. & SONS, 43 Royalston Ave., Minne SHURE BROTHERS, 225 W. Huron St., Chicago, bury St., Worcester Mass. -C, F, A apolis, Minn.-C, F, A 111. -C, F, A F. W. STEWART MFG. CORP., 340 W. Huron St., OPERADIO MFG. CO., St. Charles, 111. -C. F, M, Chicago, Ill -C, F, M E, D E, D, S SS STEWART STAMPING CORP.,P 621 E. 216th St., New OXFORD- tARTAK RADIO CORP., 915 W. Van Buren York, N. Y.-C, F, E M, SS St., Chicago, III.-C, F, S, SS, G , AR STRUTHERS DUNN, INC., 1315 Cherry St., Phila., PACENT ENGINEERING CORP., 79 Madison Ave., Pa.-C F, A New York, N. Y.-C, F, A Preceding Listings in RADIO-CRAFT'S STUPAKOFF LABORATORIES INC., 6627 Hamilton PARAPHONE HEARING AID, INC., 4300 Euclid Ave., Pittsburgh, Pa.-C, F, M Ave., Cleveland, Ohio -C, F, D, RADIO DIRECTORY SUNDT ENGINEERING CO., 4656 Ravenswood Ave., PAR -METAL PRODUCTS CORP., 32 -62 49th St., Long CLASSIFIED Chicago 111. -C, F, 0, S, SS F M, E, D, S, SS, G, AR Fulton St., New York, N. Island City N. Y.-C, Sec. I, Oct. '40: SUN RADIO CO., 212 Y.- PAUL & BEEKMAN, 4250 Wissahickon Ave., Phila., C, F, A Antennas & Accessories Pe.-C F, M SUPERIOR INSTRUMENTS CO., 136 Liberty St:, Tuners & Ports 38 21st St., New Automatic New York, N. Y.-C, F, AR, D, E, G, S, SS PEERLESS ALBUM CO., INC., W. Auto York N. Y. F, M D, -Radio Controls -C Chargers, Eliminators Rectifiers SUPREME INSTRUMENTS CORP., Howard St., PRODUCTS CORP., 6415 Ravenswood Ave., Battery & PERMO Batteries, Dry & Wet Greenwood, Miss. -C, F, A Chicago, 111. F, A -C, Cabinets TALK -A -PHONE MFG. CO., 1219 W. Van Buren St., PETERSEN RADIO CO., 205 N. 17th St., Council III. F, D, J, S, SS Coils IS Transformers (R.F. & I.F.), & Accessories Chicago. -C, Bluffs, Iowa -C F A TAY BERN EQUIPMENT CORP., 135 St., PHILMORE MANUFACTURING CO., 113 Universi- Liberty New York, N. Y.-C, F,' A (special literature PI., New York, N. Y.-C, F, M, E,, S. SS, G, Sec. II, Nov. '40: ty Condensers (Variable) available to Police á Gov't Depts.) TUBES, INC., 2341 Wabansia Ave., Chi- PHONOTONE LABORATORIES. INC., S. E. 15th St., Crystals (Quartz) TAYLOR cago, III. (at their distributors), 5c (from Washington, Ind.-C, HO, F, A Dials & Parts -F C, M E, AR PHOTOBELL CORPORATION, 123 Liberty St., N. Y. Electric Fence Controllers company direct); TELEVISO PRODUCTS, INC., 1135 N. Cicero Ave., -C, F, M, E, D, S, G, AR Electric- Generating Machines 111. F, M, E, D, S, SS, G PIERSOI4- DeLANE, INC., 2345 -47 W. Washington Electronics Chicago -C, TELEX PRODUCTS CO., Minneapolis, Minn. F, Blvd., Los Angeles, Calif. -C, F, AR, E Electronic Musical Instruments & Parts -C, PILOT P.ADIO CORP., 37 -06 36th St., Long Island Frequency Modulation Equipment M, E ELECTRIC MFG. CO., 500 W. Huron City N. Y. -C, F A Hardware- Connectors & Misc. Parts THORDARSON PIONEER GEN -E -MOTOR CORP., 466 W. Superior Headphones St., Chicago, 111.-C, F, A MFG. 1912 N. Ave., Chicago, St., Chicago, III. -C F, A Hearing -Aids TONK CO., Magnolia PIONEER SPEIALTY CO. 5100 St. Jean Ave., De- Hearing -Aid Parts III. -C. F, D THE TORK CLOCK CO., INC., I Grove St., Mt. troit, Mich. -C, F, D S Insulation PITTMAN ELECTRICAL DEVELOPMENTS CO., 127 Intercommunicating Systems Vernon, N. Y.-C, F, M, E, D, S Nippon St. Phila., Pa.-C, F, M, E, D, G, AR Line Filters TRANSFORMER CORPORATION OF AMERICA, POINSETTIA, INC., Pitman, N. J.-C, F, A 69 Wooster St., New York, N. Y. -C, F, M, E, PRECISION APPARATUS CO., 647 Kent Ave., Brook - Sec. III, Dec. '40: D, S, SS G lyn, N. Y. -C, F A Magnets TRANSMARINE RADIO, INC., 1184 Broadway, PRECISION CRYSTAL LABS., Springfield Airport, Metal & Special Fittings (for Radio) Hewlett, L. I., N. Y.-C F, D, S Springfield, Mass. -C, F, A Metal, Ore & Oil Locators TRAV -LER RADIO & TELEVISION CORP., .1036 Van PRECISION PIEZO SERVICE, 427 Asia St., Baton Microphones Buren, Chicago, III. -C, F, D Rouge, La.-C, F, A Noise Elimin'ation Equipment TRICO FUSE MFG. CO., 2948 N. 5th St., Milwaukee, PREMA) PRODUCTS, Niagara Fells, N. Y. -C, F, Peint, Cement & Wax Products Wis. -C, F, D, E, M, S M, E, D, S, SS, G, AR Plastics THE TRIPLETT ELECTRICAL INSTRUMENT CO., PREMIER CRYSTAL LABS., INC., 53 Park Row, New Plastic Molders 286 Harmon Rd., Blufftoo, Ohio -C, HO, F, M, E, York N. Y.-C, F A Radio Logs Maps & Globes D, 5, SS, G, AR PRESTO RECORDING CORP., 242 W. 55th St., New Receiving Sets (including Adapters & Converters) TROY RADIO & TELEVISION CO., 1144 S. Olive York N. Y.-C, F, M, E, , S, SS Records & Record -Playing Equipment St., Los Angeles Calif. -C, F, D QUAtv4NICHOLS COMPANY, 33rd PI. & Cottage THE TURNER CO., 909 -17 Ave., Cedar Rapids, Ave., Chicago, III. F, A Grove -C, Sec. IV, Jan. '41: Iowa -C, F, M, E, D, S, SS, G, AR RACON ELECTRIC CO., INC., 52 E. 19th St., New CHEST CORP., 54 Church St., Le York N. Y.-C, F, A Recording Equipment UNION STEEL Resistors & Volume (Attenuators & Net- Roy, New York F M. D RADE)( CORP., 1733 Milwaukee Ave., Chicago, III. Controls -C, - works) Conn. C, F. A UNITED CINEPHONE CORP., Torrington, - C, F RADIO DESIGN CO., 1353 Sterling PI., Brooklyn, Schools A Service Manuals, Books & Magazines ELECTRONICS CO., 42 Spring St., N. Y. -C, F, A UNITEb Newark F, M, E RADIO ELECTRIC SERVICE CO., INC., N. W. Cor. Servicing Equipment N. J.-C Sound Systems, Amplifiers & Accessories UNITED SCIENTIFIC LAB., INC., 440 Lafayette St., 7th & Arch St. Phila., Pa. C F A New York, N. Y.-C F, 0, S RADIO ENGINEERING LABS., INC., 35 -54 36 $t., UNITED STATES TELEVISION MFG. CORP., 220 E. Long Island City New York, N. Y.-C, F. E Sec. V, Feb. '41: RADIO MFG. ENGINEERING, INC., III Harrison Speakers (& Parts) 51st St., New York, N. Y.-C, F, D UNITED TELETONE CORP., ISO Varick St., New St., Peoria, 111. -C, F, A Switches & Relays York, N. F, A RADIO NAVIGATIONAL INSTRUMENT CORP., 500 Television Y.-C UNITED TRANSFORMER CORP. 150 Varick St., 5th Ave., New York, N. Y.-C F CON Test Equipment-Laboratory & Production New York, N. F, M E. b s, SS, G, AR THE RADIOTECHNIC LABORATORY', 1328 Sherman Tools Y.-C UNIVERSITY LABORATORIES,LABORATORIES , 195 St.. New Ave., Evanston, 111. -C, F, A Transformers & Chokes York, N. Y. F. M E, b, S, SS RADIOTONE, INC., 7356 Melrose Ave., Hollywood, Transmitters (& Equipment) -C, UTAH RADIO PRODUCTS CO., 812 Orleans St., Calif. -C, F A 111.E F, M, E, D, , SS, AR, J RADIO TRANSCEIVER LABS., 8627 115th St., Rich. Chicago, The above back -issues of Radio -Craft are email- VAC -O -GRIP CO., 2023 Detroit Ave.. Toledo, mond Hill, N. Y.-C, F, A 0- able at the regular price of 25c per copy. C, F A RADOLEK COMPANY, 601 W. Randolph St., Chica- month: Section I of the Classified Radio THE VALPEY CRYSTALS, Box 321 Holliston, Mass. go, III. -C, F, A Next - revised, with new classifications, and C F, AR. D E, G, M, SM, SS RAY-0-VAC COMPANY, No. 2317 Winnebago St., Directory, new names and addresses added; and with obsolete THE VEGA CO., 155 Columbus Ave., Boston, Madison, Wis. -C, F S Reserve today, from Mass. F, A RCA MANUFACTURING` dO., INC., Camden, N. J. listings removed. your copy, -C, newsdealer, VERTI -FLEX ILLINOIS SEATING CORP., 2138 N. -C, F, A your regular Racine Avenue, Chicago, 111. F, D, 'S, SS, AR READRITE METER WORKS. Bluffton, 0.-C, F, A -C, JAMES VIBRAPOWR CO. INC., 341 N. Crawford RECOTON CORP., 178 Prince St., New York, N. Y. Ave.. Chicago, 111. F, A -C, F, A -C THE VIBROPLEX CO., INC., 832 B'way., New York, REGAL AMPLIFIER MFG. CORP., 14 W. 17 St., MARK SIMPSON DISTRIB. CO., INC., 16 Hudson N. Y. -C, F. D, A New York, N. Y.-C, F, D. E S, SS N. F, J VIVI TONE CO., 6321 Gratiat St., Detroit, Mich.- REMLER COMPANY LTD., 2161 Bryant St., Sen St., New York Y.-C, ELECTRIC 5216 -18 W. Kinzie St., Francisco, Calif. -C, F, E D SIMPSON CO. III. F, M, E, D, S, SS, G AR WARD LEONARD ELECTRIC CO., 31 S. St., Mount REX RHEOSTAT CO., 37 W. 20th St.. New York, Chicago, -C, Noble and Darien St., Vernon, N. Y.-C F. A N. Y.-C F, A SNYDER, INCORPORATED, F, D, S WARD PRODUCTS CORP., 1523 E. 45 St., Cleveland, JOHN F. RIDER PUBLISHER, INC., 404 4th Ave., Phila. Pa.-C 2525 Ave., F, M E. D S, AR New York, N. Y.-C, HO, F, A SOLA f=LECTRId CO., Clybourn Chicago, Ohio -C, MFG. CORP., 1700 W. Washington THE RIVERSIDE METAL CO., Pavilion Avé., River- 111.-C, F, M, E, D, SS, G, AR WARWICK SOLAR MFG. CORP., Avenue A & 25th St., Blvd., Chicago, III. -C. F, D, S side, N. J.-C, F, M, E Bayonne, N. F, A WEBER MACHINE CORP., 59 Rutter St., Rochester, ALBERT F. ROSS & CO., 2341 Wolfram St., Chi - J.-C S. S. SUPPLY CORP., 636 11th Ave., N. Y. -C. F M, SS cago, 111.-C, F M, D, S O. CINEMA F, M, E, D, S, SS THE WEBSTER CO. 5622 W. Bloomingdale Ave., ROTOPHONE CORPORATION, 26 Journal Sq., New York, N. Y.-C, APPARATUS CO. I50 W. 46th St., New Chicago, III. -C, F A Jersey City, N. J. -C, F A SOUND F (vl E, D. S, SS WEBSTER ELECTRIC COMPANY, Racine, Wis. ROWE INDUSTRIES INC., 3120 Monroe St., York, N. Y.-C, HO, - SPEAK RECORDING & EQUIPMENT C F. A Toledo, Ohio -C, F, D, E, S, SS -O -PHONE CO. 23 W. 60th St., New York, N. Y.-C F; A WESTERN SOUND & ELECTRIC LABORATORIES, WALTER L. SCHOTT CO., 52641/2 W. Pico SPEEDWAY MFG. CO., 1834 S. 52nd Ave., Cicero, INC., 311 W. Kilbourn Ave., Milwaukee, Wis. - Blvd., Los Angeles, Calif.-C, F, A III. -C, F, A C F, A MAURICE SCHWARTZ & SON, 710 -712 Broadway, SPENCER THERMOSTAT CO., 34 Forest St., Attle- WESTON ELECTRICAL INSTRUMENT CORP., Schenectady, N. Y.-C F, S, SS, G, AR boro, Mass. -C, F. M Newark, N. J.-C, HO, F A E. H. SCOTT RADIO LABS., INC., 4450 Ravenswood SPRAGUE PRODUCTS CO., North Adams, Mess. - WINCHARGER CORPORATION. Sioux City, Iowa - Ave., Chicago, 111. -C, HO, F A C, F, A C,F,A SEATTLE RADIO SUPPLY CO., Ih1C., 2117 2nd Ave., STANDARD ELECTRICAL PRODUCTS CO., 317 WIRT COMPANY, 5221 -27 Greene St., Phila, Pa.- Seattle, Wash. -C F A Sibley St., St. Paul Minn. -C, F, A C, F, M, E. D, S. SS, G. AR SELECTAR MFG. CORP., 30 W. 15th St., New York, STANDARD PIEZO CO., Cedar and Louther Sts., X -L RADIO LABORATORIES, 420 W. Chicago Ave N. Y.-C, F, A Carlisle, Pa.-C F, E, M Chicago, III. -C HO, F, A SELF -VULCANIZING RUBBER CO. INC., 605 W. STANDARD TRANSFORMER CORP., 1500 N. Hal- ZIERICIC MFG. CORP., 385 Gerard Ave., New York, Washington Blvd., Chicago, III. -C, F, A sted St., Chicago, 111. -C, F, A N. Y.-C, F, M, E, D, SS When writing to companies Usted here please mention that you sate the listing in the Radio -Craft "Classified Radio Directory"

574 RADIO -CRAFT for MARCH, I 941 SHOP NOTES KINKS -CIRCU ITS

SMALL INDUCTION -TYPE A.C. here illustrated, for bench use. MOTOR REPAIRS An output transformer will frequently serve in this arrangement. The transformer CORE may be enclosed in its own box, as a safety OPEN -CIRCUIT DUD STARTING WINDING X11111 measure, as illustrated. A. MARINO, ® Ili_ GN Ú G cl cl cv cl Staten Island, N. Y. Ci Cl c1 c c. cl <4 Ct Cl cv Cl G Cl cl ct G REPAIRING SPIDERS CORE REMOVED MAY BE USED AS BENCH ANVIL

Al A2 BI B2 wIÑDIfNG Might not occur to some radio experimenters. I made my "anvil" RCA 4 MF, from an 400v. electrodynamic loudspeaker. I find it useful CENTRIFUGAL for clinching rivets by putting a rod in the CH center hole in the top. Of course not all speakers are constructed in exactly the 220V, OLTAGE SUPPL saine way. WALTER C. MUELLER, TO CONNECT FOR 110V.. PARALLEL ALA2 AND 01.02. Chicago, IR. THEN CONNECT CONDENSER FROM LINE THROUGH SWITCH TO CENTER OF PARALLELED COILS. WHEN the spider on dynamic loud- INTERFERENCE ELIMINATION RADIO Servicemen frequently have oc speakers which have the spider located HINT casion to repair washing machine, refrig in the center of the voice coil becomes weak erator and small bench machine motors. The it may be strengthened in the manner here majority of these motors are of the induc- illustrated. ÉTAL WALL tion type using a separate starting wind- Cut a thin pasteboard disc with the same 'LATE TLET) ing of a finer gauge wire than the main or the and Ne 17 diameter as the spider. Coat spider RUBBER running winding. About 80% of the failures one side of the disc with household cement. INSULATED of these motors are due to the starting wind- Place the two together and allow them to WIRE ing burning out because of the centrifugal dry for at least an hour. When thoroughly o.l- 115V LINE switch sticking. To rewind this winding dry, center the voice coil and the speaker 400V (EACH) RAADIO takes time; too, there is always the danger is ready to use. The pasteboard disc serves RECEIVER of damaging the main winding during re- also as a dust cap. (TAPE UP CONNECTIONS ANO CONDEN SERS) pair, resulting in a complete rewind. How- ROBERT ROBINSON, ever, by connecting a condenser of from 2 Silver City, New Mexico mf. to 4 mf. capacity, and of the rated volt- NEXT time you fail to obtain satisfac- age of the motor; and also disconnecting tory reception, try a pair of 0.1 -mf. the faulty starting winding from switch, HANDY ANVIL condensers across the line, as shown in the. the motor will now start as good as new, i.e., HERE is an idea simple enough in its sketch. In a 15 -story apartment house, with converting motor into a "capacitor" type. conception, yet an extremely useful sub- elevator and other noise, a Stromberg -CarI- I have used 4 -mf., radio -type condensers stitute for a bench anvil, the idea for which son table model played very well on a short on several '4- horsepower motors with successful results, saving time. The exact type and size of condenser for any size motor may be calculated from the following formula: RADOIEA<%' Y)Y 1941 E (A) Z = - where "RADIO PROFIT GUIDE" Z= impedance of motor V =line voltage Brings You Hundreds óf I =motor current in . ` BARGAINS Like This One ! amps. Z (B) C ='4 ADLEX THIS FR 2Af- GET BIG where 1 C= Capacity in farads' of re- BOOK OF EVERYTHI quired condenser. 2rif =6.28 x frequency of line. NEW IN Z =from above formula (A). R and Xr, of motor may be neglected. RADIO AT Above, for a Ya -h.p. motor, works out to ap- r.. Ill t^^l prox. 5 mf. but in practice even a 3 -mf. .1 condenser gives sufficient field phase dis- co*gp... Bargain, placement to start the motor. W ANDSW ORTH, Prices. Kotze Road, Shows Mowbry, Cape Town, South hundreds and hua Africa dreds of up -to- the -minute RADIO-PARTS, KITS radio parts, sets, accessories, ham gear, electric appliances ELECTRIC BENCH FLASHLIGHT and supplies. Indispensable Special Value! to every amateur, experimen- Professional Type 11OV., PORTABLE HOME RECORDING DISCS A.C. ter. set builder, sound engi- ELECTRIC VIP 1941 RECEIVERS (Heavy Metal Core -Non Flammable) ANY OUTPUT FLASHLIGHT \r neer and serviceman. Keep up TRANSFORMER) ',v.» with radio and all its phases 10" only 19c each II -send for the big FREE Rado- Made by foremost manufacturer. lek Profit Guide now! DONT Proven equal or superior to any discs WAIT -SAVE MONEY AT of this type regardless of cost. These JACKS blanks have very slight imperfections SOUND SYSTEMS RADOLEK. AddressDept.0 -52. but guaranteed to make perfect record- BOO ings or your money back. Coated on both sides. Big savings! SMALL BOX TO HOLD TRANSFORMER RADOLEK COMPANY 6" Discs -10c 8 "-14e; 1 0 " -19et lc,less in 25 lots. 601 West Randolph Street Send no money -shipped C.O.D. pl us postage. IN order to save on flashlight batteries, I devised the power supply arrangement Chicago, Illinois Order Toda

Auty- I.KArI for MARCH, I Y 4 I 575 BOOK REVIEWS

antenna and ground connection. Without the GEOPHYSICAL filter there was a terrific racket. In a case - - in suburban territory, shortwave reception .5N[., .LG 4fEoP/LLLIPIW. PROSPECTING OUTFITS in the presence of a trolley, as well as house was r apartment elevator interference, --I'ì _ - -- - practically impossible. PUBLIC ADDRESS EQUIPMENT In a second case the filter not only cleared Amplifier Co. of America 566 reception but also raised the apparent signal General Industries Co 556 strength of the overseas broadcaster. In still Jensen Radio Mfg. Co 554 John Meck Industries 556 another instance, where a vibrator -type in- Miles Reproducer Co 556 cna.S,e.s verter was used for supplying power from Music Master Mfg. Co 549 D.C. to an A.C. phonograph -radio, the filter Regal Amplifier Mfg. Corp 549 cut out the vibrator interference on Radio. Universal Microphone Co. Ltd 549 University Laboratories 549 MON( IAEASUN Haar The writer is convinced this kink will pay dividends, and it is obviously cheaper than a regular line filter. Only precaution is this: PUBLISHERS use plenty of tape for good insulation. Data Print Co 567 9 The condensers, in series, are shunted Miller, Wayne 516 National Plans Inat 664 across the power line; the junction of the Radcraft Publications. Inc. 518, 565, 570 2 condensers is connected to ground (the Radio & Technical Pub. Co 515 wall- plate). Radio & Television 573 BLUE PRINTS and INSTRUCTIONS Radio Publications WILLARD MOODY, 566 Supreme Publications 554, 665 For Building the Following Treasure New York, N. Y. Technifax 586. 676 Finders and Prospecting Outfits

Folder No. 1. The "Radiofiectar Pilot " -con- RADIO PARTS eists of a 2 -tube transmitter and 3 -tube receiver. Principle: radiated Wave from BOOK REVIEWS Amperite Co 529 transmitter loop is reflected back to receiver Dumont Electric Co.. Inc 560 loop. visual Hammarlund Emits and aural signals. Tubes 111111I111I111111111111111111111I11IIIIIIII IIIIIIIIIIIIII I I I I1111111I IIIIIIII I11111111I1111IIIIIIIII Mfg. Co. 560 used: two 1A5G-two 1N6G -one IH6G. International Resistance Co 627 Folder No. 2. "Harmonic Frequency Lo- The STUDY GUIDE AND REFERENCE MATERIAL Meissner Mfg. Company 617 cator"- Transmitter radiates low frequency National Union Radio Corp Back wave to receiver. tuned to one of Harmonics FOR COMMERCIAL RADIO OPERATOR EX- Cover of transmitter. (1939). Published by U. S. Ohmite Mfg. Company 660 Using regenerative circuit. AMINATIONS Solar Mfg. Emits aural signals. Tubes used: one 1G6G Government Printing Office. Size W., z 9 ins.. Corp 642 Sprague Products Company -one 1N5G. Flexible paper cover. 96 pages. Price 15c. 533 Folder No. 3. The "Beat -Note Indicator" -Two oscillators so adjusted as to produce beat- Technicians who wish to learn the telegraphic note. Emits visual and aural signals. Tubes code as revised last year in accordance with the RADIO SETS used: Three type '30. a Cairo Conference, should obtain copy of "Study Goldentone Radio Co. 556 Folder No. 4. The "Radio-Balance Surveyor" Guide." Henry -a modulated transmitter and very sensi- Radio Shop 543 tive loop receiver. Principle: Balanced This book contains questions which are repre- Midwest Radio Corp 529 loop. Emits visual and aural signals. By tri- sentative of the scope of questions contained in angulation depth of objects in ground can the various elements of the Commercial Radio RADIO SUPPLY HOUSES be established. Tubes used: Seven type '30. Operator's License Examination -by the Federal Folder No 5. The "Variable Inductance Moni- Adson Radio Single tube oscillator generating Communications Commission. 536 tor"-a Allied Radio Corp 563 o fixed modulated signala and receiver em- This book is divided into chapters as follows: ploying two stages R.F. amplification. Burstein- Applebee Co 660 Works on the inductance principle. Emits Element I- Questions on Basic Law ; Element Lafayette Radio Corp 533 aural signals. Tubes used: six type '30. II -Basic Theory and Practice; Element III- - Radolek Co 575 Folder No. 6. The "Hughes Inductance -Bal- Radiotelephone; Element IV- Advanced Radio- Sears, Roebuck & Company 545 ance Explorer " -a single tube Hartley os- telephone; Element V- Radiotelegraph; Element Montgomery Ward & Co 551 cillator transmitter and sensitive 3 -tube re- Advanced Radiotelegraph. ceiver. Principle: Wheatstone bridge. Emits VI- aural signals. Tubes used: two type '30- SCHOOLS one type '32 -one type '38. ELEMENTS OF ACOUSTICAL ENGINEERING. Capitol Folder No. 7. The "Radiodyne Prospector" - by H. F. Olson (1940). Published by D. Van Radio Eng. Inst 615 a completely shielded instrument. Principle: Coyne Radio School 516 Noatrand Company, Inc. Size 6 z 9 ins., cloth Balanced loop. Transmitter, receiver and Lincoln Engineering School 516 430 Price, $6.00. batteries enclosed in steel box. Very large cover, pgs. National Radio Institute 513 field of radiation and depth of penetration. The sound field at last has a book all its own. National Schools 516 Emits aural signals. Tubes used: two 1N5G In "Elements" the Director of Acoustical Re- New York Y.M.C.A. Schools 516 1G4G-one IH6G -one 1Q5 1G4. -one -one search of RCA, and lecturer in Electrical En- Radio Training Assoc 516 With any one of the modern geophysical gineering in Columbia University, has drawn RCA Institutes 516 methods described in the Blue -Print patterns, upon his wide experience to prepare an excep- Sprayberry Academy of Radio Radio outfits and instruments can be con- useful treatment of acoustical principles Inside Back Cover structed to locate metal and ore deposits tionally (Prospecting); finding lost or buried treas- and their applications -which extend throughout ures; metal war relics: sea and land mines nearly all fields of engineering. Complete work- TEST EQUIPMENT and "duds "; mineral deposits ; subterranean ing methods are given in this well -illustrated water veins; oil deposits (under certain cir- book. Radio City Products Co 636 cumstances): buried gas and water pipes; RCA Manufacturing Co.. Inc. tools or other metallic objects sunken in wa- The range embraces Radio Broadcasting. Radio Inside Front Cover ter, etc., etc. Reception. Public Address, and Sound Motion Readrite Meter Works 660 Pictures. This book offers extensive treatment of Superior Instruments Corp 589, 642 Each set of blueprints and Instructions enclosed In heavy envelope (9 1's' x 121's'). Blueprints 22" x the following topics: Sound Waves; Acoustical Supreme Instruments Corp 629 34"; elghtpage Illustrated 8''2' x Ir fold. 5O,( Radiating Systems; Mechanical Vibrating Sys- Triplett Electrical Instrument Co 534 er of Instructions and construction data . W Add 5e for postage tems; Electrical, Mechanical and Acoustical Analogies ; Acoustical Elements; Driving Sys- TUBES The toml se a tems: Direct Radiator Loudspeakers; Horn Loud- Shippingpweight t2 lbs. (add25e for ship. 53.00 Hygrade Sylvania Corp 532 ping anywhere In U.5. A.) speakers; Microphones; Miscellaneous Trans- ducers; Measurements; Architectural Acoustics. and the Collection and Dispersion of Sound, MISCELLANEOUS Et:IINIF'í1X Speech. Music and Hearing. i 662 RC41 Atlas Press Co 1917 6. STATE ST. CHICAGO. ILL. Classified Section 562 INTRODUCTION TO POLARIZED LIGHT AND 542 N 7 Flight Magazine ITS APPLICATION, (1940). Published by Kato Engineering Co., Inc. 636 TECHNIFAX 1917 So. State. Chicago. III Polaroid Corporation, Cambridge, Mass., size Lancaster, Allwine & Rommel 616 854 illustrated, 46 pgs. Service 664 Enclosed herewith f for which mail to 51 x ins.. paper caver, Premium Distributing address below: Price, 50c. Radio Servicemen of America, Inc 568 Walter L. Schott Co 542 Treasure Finder No. I. 2, 3, 4. 5, 6. 7. and more elec- Experimenters, particularly, Woodstock Typewriter Co 562 Complete set of seven folders. D tronic specialists, will be interested in this new book which discusses polarized light from first principles to its practical application through NAME the medium of Polaroid. Polarized light finds its application in radio (While every precaution is taken to insure ADDRESS as an important element in, for instance. cer- accuracy. we cannot guarantee against the tain types of television operation. For experi- possibility of an occasional change or omis- CITY STATE menters in this field, therefore, the page "Ref- sion in the preparation of this index.) erence on Polarized Light" will be especially RC -341 welcome.

576 Printed In Inc V.S. RADIO -CRAFT for MARCH, 1941 OVER 100 EXPERIMENTS plus Many Other Special Features ALL DESIGNED TO HELP YOU MAKE FAST PROGRESS!

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TWO DRAWER STEEL CABINET Here's a honey of a ecpular steel utility cabinet with the drawers par- titioned to make it easy for storing small CONDENSER CONTENTS - parts. You'll find this ASSORTMENT cabinet a mighty use- KIT CONTAINS: to your 1 WALSCO STAPLER ful addition LIST shop equipment and TYPE QUANTITY 9 59O Mt, Corf.de.r.aeta best of all ... you get IB 8450 4 2oo ciaenol SC 8450 it FREE on this limited AT 8150 1615 offer. Don't delay, EVERY RADIO SERVICE 8250 $1435 4450 of MAN NEEDS IT - take advantage 8450 2 this deal and get your New automatic stapler for 1645 AT 1125 FREE steel cabinet. This fine assortment of pop- quick and easy installation 8845 ular type N.U. condensers of lead -ins-indoor anten- T 601 Cabinet size is - 602 will move fast, give you a nae - running leads and 605 11 ! 2 ", width, length good profit and insure the power cords, P.A. installa- 610 91/2". depth, 5 ". good will of your customers. tions and other shop use. 625 If your already using N.U. Usual dealer price $3.30. condensers, you'll be sure to List Value of N.U. Condensers in Kit, $10.00. Dealee snap up this offer in a hurry. Prise Walsro Stapler, $3.30 (Parked Todethere YOURS FOR ONLY $7.00 pED SFZ If you don't know yet how NO'1 lNbe really good N.U. condens- con- YOURS FREE ON T}NS N. U. CONDENSER DEAL ers are. here's a great op- DEALER PAYS 55.00 FOR CONDENSERS, THE ADDITIONAL bay tot portunity to try them! The cat' assotlme0nt Nt1- 52.00 IS REBATED WHEN DEAL REQUIREMENT IS COMPLETED. assortment you get on this a 9 4oWas HOW YOU GET IT denget las limited offer consists of: Si .50 just order from your N.U. distributor. Your total payment is ponl1ocl to ptes' 3-JB8450 l-A12015 S7.00. You sign an agreement for 75 points and deposit is poor b vaaonaactabtnel I-158845 1-AT8250 refunded when the 75 purchase points are completed. Points N. steel no 1 -SC8450 1-AT4450 can be used on N.U. Tubes, Sound X Tubes, N.U. Radio ent is l-AT8150 3-AT8450 /Tra el condens 1-AT1615 1-AT 1645 Batteries or N.U. Condensers. The National Union Program on get tbnoW' lo e es free equipment has helped thousands of dealers to own the om th 3 -T601 "finest radio shop in town ". sep il- lt e essotltnaksar' With 4 -7602 3 -T605 POINTS ARE COUNTED AS FOLLOWS: 5 -T610 1 Tube = 1 Point. 1 Electro Condenser - I Point, 10 Paper +net.l 2 -7625 ab Condensers - 1 Point, 2 Numite Condensers = 1 Point. 1 Radio Battery = 1 Point.

1840 N.U.R. Corp. fee Your jobber or Write NATIONAL UNION RADI 57 STATE STREET, NEWARK, N. J. ttztation