RADIO GARAGE DOOR OPENER See Page 138

RADIO'S LIVEST MAGAZINE

September 25 Cents Canada 300

HUGO GERN Editor

Describing the New RADIO GARAGE DOOR OPENER See Page 138

A New Triple -Twin Tube - Direct Coupled Amplifiers -A "1- Tube" Super A Quality Audio Amplifier - Design of Test Instruments - Adapters CANDOHM RESISTOR REPLACEMENT CATALOG

MUTER opens a new field for Deal- STANDARD EQUIPMENT ers and Service Men -a plan which IN LEADING SETS enables radio men to do a thorough The Muter Candohm Resistors are service job, to effect proper resistor absolutely permanent in values, and replacements, and to make a good are not subject to "breakdown" in profit. normal service. All Candohms (ex- The selection of Muter Candohm Re- cept type FH), are wire wound on a sistors, since 1929, for use in leading bakelite core with Armite insulation ; receivers proves conclusively, that the type FH is wire wound on a spe- character- cial asbestos core. Candohms de- their design, engineering signed for particular set models are istics, construction and longevity equipped with the required special have, in every way, passed the rigid mountings. Set manufacturers have tests of set manufacturers. standardized on Muter Candohm Re- Muter Candohm Resistors are stand- sistors because of their accuracy, ard equipment in several hundred liberal heat dissipation and absolute receivers manufactured by over fifty freedom from trouble. When neces- Candohm sary to replace a Candohm Resistor, leading set manufacturers. obviously the set will perform much Resistors are heavily armored so better if a genuine Candohm is used, that the Service Man can convenient- made to the set manufacturer's ly carry an assortment without specifications. danger of damage. A supply of stock OUTER PROTECTIVE STEEL INSULATED MOUNTING values of Candohm Resistors, when COVERING MAKING UNITS LUGS FOR alt SCREWS LBSOLUTELY DAMAGE PROOF used singly or in combination, are U. S. PATENT NO. t TN.IY sufficient to attend necessary resistor service work on a large majority of to replace sets. It is advantageous RESISTANCE WIRE WOUND ON GENUINE BAKELITE CORE.

ordinary resistors with MUTER TERMINALS OF ARMRE INSULATION BEST GRADE COKE PLATE CANDOHMS. 'SBB VOLTS A. C FOR EAST SOLDERING

NEW, COMPLETE CATALOG READY FOR DEALERS AND SERVICE MEN Mail Coupon Today! The coupon in the lower left-hand corner, com- CAND0HM pletely filled in, will bring to you the Muter RSSTpR 1933 Candohm Replacement Catalog, and com- .-The Muter Company. Dept. RC. plete information on other dependable Muter ReP/acemen[ 1255 South Michigan Avenue. products for dealers and service men. Write Ca taio Chicago, Illinois today Dept. RC. The Muter Company, Candohm -address Please send me the Muter 1933 1255 Michigan Avenue, Chicago, Illinois. Replacement Catalog listing the seta in South 1933 9' which Candohms are standard equipment. Name MUTER DEPENDABLE PRODUCTS Address

City State Service Man [-] Dealer Jobber OPPORTUNITIES are many for the Radio Trained Man Don't spend your life slaving away in some dull, hopeless job' Don't he satisfied to work for a mere $20 or $30 a week. Let me show you how to get your start in Radio-the fastest- growing, biggest money- making game on earth. Jobs Leading to Salaries of $50 a Week and Up Prepare for jobs as Designer, Inspector and Tester -as Radio Salesman and in Service and Installation Work -as Operator or Manager of a Broadcasting / Station -as Wireless Operator on a Ship or Airplane, or in Talking Picture or Sound Work -HUNDREDS OF OPPORTUNITIES for a real future in Radio: TenWeeks of Shop Trainin Pay Your Tuition After Graduation We don't teach by book study. We train you on a great outlay of Radio, Television and Sound equipment -on scores of modern Radio Receivers, huge Broadcasting equipment, the very latest and newest Television apparatus, Talking Picture and Sound Reproduction equipment, Code Practice equipment, etc. You don't need advanced education or previous experience. We give you -RIGHT HERE IN THE COYNE SHOPS -the actual practice and experience you'll need for your start in this great field. And because we cut out all useless theory and only give that which is necessary you get a practical training in 10 weeks. TELEVISION and TALKING PICTURES And Television is already here! Soon there'll be a demand for THOUSANDS of TELEVISION EXPERTS! The man who learns Television now can have a great future in this great new field. Get in on the ground -floor of this amazing new Radio development! Come to COYNE and learn Television on the very latest, newest Television equipment. Talking Picture and Public Address Systems offer opportunities to the Trained Radio Man. Here is a great new Radio field just beginning to grow! Prepare NOW for these wonderful opportunities! Learn Radio Sound Work at COYNE on actual Talking Picture and Sound Reproduction equipment. don't waste time on useless theory. We give you the prac- PAY FOR YOUR TRAINING tical training you'll need -in 10 short, pleasant weeks. After You Graduate MANY EARN WHILE LEARNING I am making an offer that no other school has dared You get Free Employment Service for Life. And don't let to do. I'll lack of money stop you. Many of our students make all or take you here in my shops and give you a good part of their living expenses while going to school this training and you pay your tuition after you and if you should need this help just write to me. Coyne have graduated. Two months after you complete my is 33 years old. Coyne Training is tested -proven beyond course you make your first payment, and then you all doubt. You can find out everything absolutely free. have ten months to complete your payments. Just mail coupon for my big free book! There H. C. Lewis, Pres. are no strings to this offer. I know a lot of honest fel- RADIO DIVISION Founded I89q lows haven't got a lot of money these days, but still want to prepare themselves for a real job so they COYNE Electrical School won't have to worry about hard times or lay offs. SOO S. Paulina St., Dept.63 -9H, Chicago, Illl. I've got enough confidence in these fellows and in my Mail Coupon Today for All the Facts training to give them the training they need and pay me p back after they have their training. _------tmom -aim you -- If who read this advertisement are really interested H. C. LEWIS, President in your future here is the chance of a life time. Mail the coupon today and I'll give you all the facts. Radio Division, Coyne Electrical School 500 S. Paulina St., Dept. 63-9H, Chicago, III. ALL PRACTICAL WORK Dear Mr. Lewis: - Send me your Big Free Radio Book, and At COYNE in Chicago all details of your Special Offer. ALL ACTUAL, PRACTICAL WORK. You build radio sets, install and service them. You actually operate great Broad- Name casting equipment. You construct Television Receiving Sets and actually transmit your own Television programs over our modern Television equipment. You work on real Talk- Address ing Picture machines and Sound equipment. You learn Wireless Operating on actual Code Practice apparatus. We City State RADIO -CRAFT for SEPTEMBER, 1933 129 (Rdio.af ERVICE MAN - DEALER RADIOTRICIAN

HUGO GERNSBACK, Editor -in -Chief LOUIS MARTIN R. D. WASHBURNE Associate Editor Technical Editor

IN OUR NEXT FEW ISSUES: CONTENTS OF THE WHAT EVERY YOUNG SERVICE MAN SHOULD KNOW ABOUT SEPTEMBER, 1933, ISSUE THE INSTALLATION OF PLAYHOUSE SOUND SYSTEMS. How much does it cost to install an efficient sound system in a theatre? What apparatus will be required for a house with a capacity of VOLUME V NUMBER 3 1,000 people; of 5,0007 What are the probable difficulties one would encounter in installing the system and how could these faults be overcome? These and many more questions of a similar nature Editorial: Our Changing Radio Hugo Gernsback 137 are answered in a practical manner in this multi -article by an authority on the subject. This series alone will be worth the price Describing the Radio Garage Door Opener of many subscriptions to RADIO -CRAFT. R. D. Washburne 138 HOW TO MAKE A UNIVERSAL A.C.-D.C. AUTO RADIO RECEIVER. Latest Radio Equipment 140 A feature of this ultra midget set design is the high gain attained through the use of modern tubes; including the type 6C6. Other A New Deal in the Radio Industry 141 considerations of interest to everyone are its low cost of construction and simplicity of design. Provisions are made for phonograp! A Decade of Progress 141 pickup or microphone input.

The 2B6-A Duplex Triode L. van der Mel 142 THE MAINTENANCE OF CARBON MICROPHONES. Nearly every Constructing the All -Wave Midget "Four" radio technician has viewed the carbon microphone with a sense of awe, presuming that, since the instrument was one of the moss H. G. Cisin 144 expensive, small-size units in his equipment, only a gifted few Constructing A Complete 26 -Watt Dual Channel could successfully service it. In this article the author clearly dis- closes the foibles of the device and the correct repair procedure P.A. System 146 Louis Gancher to be followed by a technician having average ability and good The Design Principles of an All- Purpose Tester judgment. Floyd Fausett 148

Quality in Audio Amplifiers W. H. Hollister 150 RADIO -CRAFT is published monthly, on the fifth of the month preceding that of date; its subscription price is $2.50 per year. (In Canada and Features of a Modern 50 K.W. Station 151 foreign countries, $3.00 a year to corer additional postage.) Entered at the post office at Mt. Morris, Ill., as second -class matter under the act of New Adapters for Modernizing Radio Equipment March 3, 1879. Trademark and copyright by permission of Gernsback Publications, Inc., 98 Park Place, N. Y. C. F. L. Sprayberry 152 Text and illustrations of this magazine are copyright and must not be Designing and reproduced without permission of the copyright owners. We are also agents Constructing Direct -Coupled A.F. for WONDER STORIES and WONDER STORIES QUARTERLY. Subscription Amplifiers, Part II L. M. Barcus 154 to these magazines may be taken in combination with RADIO -CRAFT at reduced Club rates. Write for information. Operating Notes R. F. Lambert 156 Copyright 1933. GERNSBACK PUBLICATIONS, INC.

RADIO SERVICE DATA SHEETS: HUGO GERNSBACK, President J. M. HERZBERG, Vice -President S. GERNSBACK, Treasurer I. S. MANHEIMER, Secretary No. 97- Galvin Motorola Model 77, 7 -Tube Auto- motive Superheterodyne 158 Published by TECHNI -CRAFT PUBLISHING CORPORATION. Pub- No. 98- Galvin Motorola Model 55, 5 -Tube All -In- lication office: 404 N. Wesley Ave., Mount Morris, Illinois. Editorial One Car Superheterodyne 159 and Advertising Office: 96.98 Park Place, New York City. Chicago Advertising 737 North Michigan Avenue, Chicago, III. The Beginner's "1- Tube" Crystal Superheterodyne Office: Western Advertising Office: 220 No. Catalina St., Los Angeles. Francis R. Harris 160 Calif. L. F. McClure, Chicago Advertising Representative. Loyd Readers' Page- Advice to Service Men 162 B. Chappell, Wostern Advertising Representative. How to Construct a Decade Condenser London Agent: Hachette & Cie., 3 La Belle Sauvage, Ludgate Hill, E.C. 4 Harry S. Kenyon 163 Paris Agent: Hachette & Cie.. Australian Agent: McGill's Agency III Rue Reaumur 179 Elisabeth St., Melbourne A Valuable Resistor- Condenser Chart Louis B. Sklar 164 Rewiring the A.K. 70 -Q from 6 to 2 Volt Operation A. A. Janszen 165 RADIO -CRAFT'S Information Bureau 166 Arc Theory -With particular reference to the "Igni- tron" tube Joseph Slepian and L. R. Ludwig 179

130 1

Radio's GREATEST Servicing Book The Most Complete Directory of Radio Circuit Diagrams published! In ONE VOLUME of over 2,300 Pages Extra Heavy Coger-Looseleaf Bound

Huy this Big Volume on our New DEFERRED PAYMENT PLAN Here are two of the most surprising announce- ern, up -to- the -minute, and which contains so Now you can get the ments that we have ever made to the radio trade much useful information as is to be found in and we know that it is such good news that this singleavolume. 1931 OFFICIAL RADIO SERVICE MANUAL, It is a book that will outlast with every radio man will be greatly enthused. any other radio book in print. Look carefully Supplements, FIRST -that the three editions of the OFFI- at the illustration of the complete edition on 1932 OFFICIAL RADIO SERVICE MANUAL. CIAL RADIO SERVICE MANUALS have the top of page. It measures 9" wide. 12" with Supplements, now been combined into one big volume of long, 41/2" thick. and the 1933 OFFICIAL RADIO SERVICE over 2.300 pages. Included MANUAL Complete SECOND -that this new single volume of con- in this volume is a complete radio servicing course. This course covers every step at a big saving. solidated radio circuit diagrams and complete needed to learn radio servicing course can be bought on a de- the servicing business . from THE SPECIAL NEW PRICE FOR ALL THREE ferred payment plan -and at a big saving. starting in business . . . materials needed MANUALS, WITH SUPPLEMENTS, IN ONE and how to go about servicing receivers and VOLUME. WITH It is needless to say how valuable the OFFI- pairing re- HEAVY BINDER IS ONLY CIAL RADIO SERVICE MANUALS have been other radio equipment. This course in to itself, is actually worth the price of the entire members in every branch of the Radio In- book. dustry, and how many thousands of each edition have been sold to manufacturers, jobbers, Our new plan now enables every radio man to $14.00 dealers, Service Men and experimenters. But get this single volume -a Complete Directory of You buy this book this way - we must emphasize this one fact: Service Men all Circuit Diagrams, of over 2,300 pages, on Send $3.00 with order- J now realize that they are tremendously handi- deferred payments. You can order this book Pay $5.00 to Express Company upon receipt of capped without the full set of Gernsback Man- immediately -get it in a few days, and use it book. uals. So much so, that those who have pur- while you are doing servicing work. You can Send $3.00 thirty days after receipt of book. chased only one or two volumes, are NOW OR- make the first few calls. pay for the entire cost Send $3.00 sixty days after receipt of book. DERING THE MISSING BOOKS. They want of the book. Total $14.00. their files to be complete. For you to get this is IF THE ENTIRE r The book quite simple and it AMOUNT IS SENT WITH complete book gives you a volume of over is sent to you as soon as your order is received. YOUR ORDER, WE WILL ALLOW YOU A 2,300 pagas with over 5.500 diagrams, charts You pay for it in small monthly amounts which 10% DISCOUNT. THIS CAN BE DEDUCTED and photos. There are absolutely no pages or can be taken from your earnings. If you were FROM YOUR REMITTANCE. illustrations or diagrams duplicated. There is to buy the three volumes separately, the total no radio book published today which is so mod- cost would be $17.00, including the supplement -. IMMEDIATE SHIPMENT .flail Coupon Today! 2,300 Pages GERNSBACK PUBLICATIONS. Me- 96-98 Park Place. New York. N. Y. Ile t lumen: 5,500 Illustrations In accordance with your Special Offer, I emir.. OVER herewith $3.00 as first payment tot and the (i Volume Radio Manual. Please forward it to i promptly. Upon receipt of the back. I shall i .stress company $5.00. Thirty days later I sl,.. ..n l you $3.00, and sixty days after receipt took. I shall send you my last payment of $3.00. If gnu want to take advantage of the Special Dis. TITIS IS TIIE GREATEST SINGLE 1111 lilt of 10%. remit only $12.00 with this coupon.

VOLUME RADIO BOOK IN PRINT TODAY Name

Address GERNSBACK PUBLICATIONS, Inc. 96 -98 Park Place New York, N. Y. f'itr .. State ////////////////////////,e////////////////////////////////////////////////////////////////////// / / / / / / / / / / / / // / / / / / / / / / / / / / /// RC -9â8

RADIO -CRAFT for SEPTEMBER, 1933 131 The Radio-ft Library Series corers accurately erery branch of Radio -anal thoroughly, too

Presented on this page are the new books of in these books will increase your knowledge; you familiar with the field which he represents. the RADIO -CRAFT LIBRARY -the most com- will find them a real help in your work and they This is perhaps the first real opportunity that plete and authentic set of volumes treating indi- will cons ibute to your money earning capacity. you have ever had to build a radio library of vidually, important divisions of radio. Each book Read these books during your spare time at home. books that are authentic, right-up -to- the -minute has been designed to give radio men the oppor- The au hors of these books are well -known to and written so that they are easily digested and tunity to specialize in one or more of the popular everybody. Each one is an expert radio man; clearly understood. Mail coupon below for your branches of the industry. The material contained an autho icy on the subject-each is thoroughly books.

TO THE RIGHT Beek Ni. I Book Ne. 4 Book Ne. 7 Book Ni. 10 ,/ WILL BE FOUND Radio Set Modern Radio Radio Kinks and Home Recording and A SHORT RESUME Analyzers Hook -Ups Wrinkles All About It f OF EACH BOOK And How To Use Them The Best Radio Circuits For Service Men and Experi- A Complete Treatise on Instan- menters taneous Recordings, Miero- With Full Instructions end De- A Complete Compendium of the phones, Recorders. Amplifiers, scriptions of Set Analyzers. Most Important Experimental A Complete Compendium on the Commercial Machines, Serv- Tube Cheeken, Oscillators. Etc. and Custembuilt Receivers Latest Radio Short -Cuts and icing, etc. Money -Savers By L. DER MEL R. VAN By D. WASHBURNE By GEORGE J. By C. W. PALMER SALIBA book explains thoroughly This It Is fascinating to the experi- If there is one subject that the operation of set analyzers. menter, ore n to the up- to-date It often becomes necessary for Is fascinating to tube checkers. and rvire Marl. every radio oscillators to take a ereial experimenters Service to man, It is that of Home Re- of her tea hug equipment, l'or let and to change it into none us- callca theirssmemry some cording. every book Of course, this volume radio man this is ex- ing a famous hookup that is not short rut or radio wrinkle that is not all on "Homo" record- tremely helpful. It covers every found in any ma nufact sired set. will solve a problem quickly. In ing. the of and you but information con- phase testing sires Irony excellent circuits have nev- business. "short tuts" mean time tained therein is important to va wild,. cuts; completely short i been t ol nmerrbdlzed, but lim- and money saved. and to the Serv- commercial radio men, studio Illustrated with photographs and ited only to hone set builders. ice Man "time saved-' means operators. engineers diagrams to facilitate the use of Thousands and others of these popular cir- money earned. interested In this phase of ra- modern testers. Recently reprinted. cuits have been requested from dio. time to time, and in this book The art of recording and re- we have included over 150 cir- Book No. 0 producing broadcast selections Is cuits. Book No, 2 which Include the famous becoming more important every Peridyne, Cash -Box A.C.D.C. Radio Questions day to radio men. experiment- Modern Vacuum Set and others. ers and Service Men. Equip- and Answers ping dance halls, auditoriums. Tubes churches, restaurants and homes A Selection of the Most Impor- And How They Work Book No. S sv i1 is public address systems and tant of 5.000 Questions Submit- amplifiers brings many extra complete Technical Data ted by Radio Men During the ollar, and often an excellent With on How to Become a Course of One Year All Standard and Many Special income. Tubes Radio Service Man By R. D. WASHBURNE How to Get end How By ROBERT HERTZBERG Started to There have been collected a wide Make Money in Radio Servicing Book No. Il MODERN VACUUM TUBES variety of questions which have describes the fundamental elec- By LOUIS MARTIN come Into our ',Mortal amtes dur- Point -to-Point tron theory which is the basis of ing the past two years, and only Resist- all vacuum tube operation, and 'The ambition of many men in those whose answers would benefit ance Measurements the of Is engaged goes progressively from the sim- radio today Is to become a first - majority In plest two- element tubes right up grade Service Man. It Is not as radio have been incorporated In The Modern Method of Servic- this amazing and an- to the latest pentodes and thyra- difficult as one might believe, but question ing Radio Receivers Irons. It is written in clear, it cannot be done in a few short swer hook. A tremendously long simple language and Is devoid of months. Following very carefully list of topics la treated. By CLIFFORD E. DENTON the advice of Mr. Martin, who the mathematics which is usually Of the difficult problems which so confusing. Valuable rrterence has dealt with the problems of thousands of Service Men. this Service Men fare today when charts and characteristic curves repairing receivers. the of standard and special tubes are hock deals very r refully with the Book No. 9 greatest is that eof replacing proper y to be found. also diagrams of essential stages In the prepara- . sockets and pin connections. tion for qualifying as a Service Automobile Radio ru pre difficult when the )fan. of unknown; and manu- and Servicing facturers ofmInany . and.rd ut. do n his information on to Service Men. A Complete Treatise on the Sub Iarn this new hook rada, mm wile find the Book No. 3 information needed to a Book No. 6 beet Covering All Phases from quickly place Installing to and ul tutti Servicing nenni av r... u .m1Ìy The Superheterodyne Maintenance M tocudiutn he Bringing Electric Sets sr°tthei e nnetbeen derdevoted red i the Book By LOUIS MARTIN elem cry problem. d th. of Up to Date electricity . . few. Wied re.ú e All About Superheterodynes Automobile radios are up and hat the.ne licevi..` t5I. With Pentodes, Multi Mus. Dy- will have : comprehensive to how coming. and someone has to sen - How They Work, How to Build namic Speakers -Complete In - to e hi. problem. and How to Service Them formation How to Modernize ice them properly. It therefore you will find partial list al the n which will appear in ter new A. C.. D. C. and Battery Oper- behooves you to read this Im- menely important hook on cboonok. By CLYDE FITCH ated Receivers new INTRODUCTION. Advantage. of Re- the art of .automobile Radio. The Measurement Method of Serv- There is no more fascinating a By CLIFFORD E. DENTON hook is concise. and full of Illus- nxforne itadio Work: Ravie Principle.: subJeet In the Targe array of radio trations, photographs, diagrams Method. of Reabtnne \Ira.arement: circuits than the famous super- In this country there are over hookups. Resistors in Radio Receivers and Ann. and Other.: i'int.to- P.,in, Reú.nee- heterodyne circuit. Whether you ten million elettrlcally operated A few of the really interesting aees m R are a Service Man or experiment- receivers that c dd be modern - chapters: Introduction ; Automo- an 4'4 loeeel e MdRno .t.on. er. first -hand knowledge about the ized -by placing oin them new type tive Radio Installations; Complete Modern Teeter: Routine construction superheterodyne new Testing where Circuit Dúaram ú Avatl- of re- tubes, speaker equipment and Descriptions of Commercial Auto- ble endnt here Reútnnrn are Eno.n; ceivers Is very Important. The other modern improvements. This motive Receivers; Servicing Auto- itoutine Tenting where Cire t Dúaram book on Superheteroolynes gives business of improving old sets motive Receivers: The Ignition i. Not Available .rad bereuRe.iaaneee underbing principles of their eon- can go to the experimenters and System; General Service Consider- e Uak nenni Ise R.Ietion of voltas. struetlon. right from the very tiret Service Men they Effects MPIeEchAPPENDIX. ReReiú. M If will quickly ation.; of Temperature on AP PENDIX. tn.epe a Ceuhuurt set made. Jump Into action. l'Ower Supply: Conclusion.

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132 RADIO -CRAFT for SEPTEMBER, 1933 I will Train You at Home in your spare time to fill a GOOD JOB in Radio -4 Get away from disagreeable job: with no future. From skinny, little pay envelopes. From skimping Special Free Offer along, Free Book Art moww ee i e inn ad. just barely getting by, but dili to fey lig e free book, not getting ahead. DON'T PUT UI' "Rid, Reward. Radio." WITH THEM ANY LONGER. Gel Tells How this Service Manual on into a field with a future. Act to- D. ('.. t'.. t t Bette, 'Pun* meta. day to put yourself ahead. aerated Only sus . Mail Mail Coupon! dente mull have this book the coupon for my free 64 -page book in the past. Now readers that tells how you can train at home of this magazine who 111161 in your spare time to be a Radio the mnaon will r Expert; about my Course that doubles and triples the pay f r Overcoming t Mr s, of many who take it. MAIL noises Of all rkinds, fading THAT COUPON NOW and ib, broad toning, howls lake the first step toward a real future. eiII oneillations. Ingo din - reception. distorted or llyd signals. /IOW' Audio and Real Opportunities Ahead in Radio for risdio Frwueer pnlification and other. t.i.rr leridor Service Manager Trained Men ]i n here, 'PNiíß:,ei1 n'îNO, Earns $Foe Month It's hard to find a field with more opportunity awaiting the trained man. Why in 1932 -the worst year of the de- As Radio Service Man- pression -the Radio Industry sold $200,000.000 worth of ager for Sterchi's four sets and parts! Manufacturers alone employed nearly 100,- SPECIAL Radio Equipment Nashville Stores, my earn- 000 people! About 300.000 people worked in the industry. ings are around $200 a 1932 broadcasting revenue was the biggest in history. It's for Broad month. My N. R. I. train- a gigantic business, even in the worst business years! And Practical Experience ing enables me to keep look what's ahead! Millions of sets becoming obsolete an- our customers satisfied." nually. 17,000,000 sets in operation that need servicing Given Without Extra Charge from time to time! Over 600 great broadcasting stations I E. H. LEFTWICH, My Cour .ors, I'll show i lal furnishing entertainment and news to 100.000,000 people. yon, Sterchi Bros. Stores Inc., Radio equh , experimen,. . note Nashville, Tenn. These figures are so big that they are hard to grasp! Yet, illtnarote m they are all true! Here is a new seta Ñf.. i1 l., Sneed I.L.u¢. industry that has grown itr11. A.. \'irt ., M onentie and of here. You into a commercial giant. No wonder great business leaders ,with your n hood many of the read lessen predict a brilliant future for this great and whanks. ñh;', uvaa , .t hod f growing busi- lag ekes learning at Mg. ness. io n lypractical. You learn how why they work. and how to make them worrk Get al en they a of order. 'fronting like Into This Field With a Future oin shows HoI rM There's opportunity for you in You graduate you I, .y had trainingt anal Radio. Its future is cer- experience-you're , Ropy tain. Television, short wave. police Radio, automobile Radio, ter get ezptriem.ge talking movies, public address systems. aircraft Radio -in every branch, developments and improvements are taking place. Here is a real future for thousands and thousands $130 a Month of men who really know Radio. Get the training that in Spare Time opens the road to responsibility, good pay, and success! Send me the coupon now, "I'm servicing from 3 and get full particulars on how .,.ht+t to 5 sets daily in spare easy and interesting I make learning at home. Read the time and average $120 a letters from graduates who are today earning real money month from my Radio in this fascinating industry. work. I still hold my regular day job. I owe my Many Make $5, $10, $15 a Week Extra have success to N. R. 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It tells you about Radio's transmitter for Station spare time and full time job opportunities: it tells you WAMC, of which I am en- all about my Course; gineer. what others who have taken it My salary has in- are doing and making. Find out what Radio offers J. E. Smith, President creased $1,000 a year YOU without the slightest obligation. MAIL THE National Radio Institute. Dept. 3JX since entering Radio due COUPON NOW. Washington, D. C. to your splendid train- Dear Mr. Smith: I want to take advantage bt ing." Special Offer. Send me your manual "Trouble shu,t ing In D. I'., Al'. and Battery Sett" and your b,x,k "Rich JULIUS C. VESSELS. J. E. SMITH, President Rewards In 11ad1q" which exploits Radio's Opportunl- Radio Station WAMC ties for bigger pay and your method of training men Anniston. Ala. National Radio Institute, Dept. at home in spare time. I understand this request dues 3JX not obligate me. (Please print plainly.) Washington, D. C.

4. ia

RADIO -CRAFT for SEPTEMBER, 1933 133 4

BUY your radio direct from the Midwest Laborator- Why be satisfied with an ordinary broadcast or ies and save from 30% to 50%. This Super, "dual" wave set when you can have this super- power- Deluxe 16 -Tube ALL -WAVE Radio makes it easy to ful super de luxe 16 -tube ALL -WAVE Midwest secure clear, loud -speaker reception from stations radio? It puts the whole world of radio at your finger 10,000 miles and more distant. It gives you complete tips. It has FIVE distinct wave bands -ultra short, wave length coverage of 9 to 2000 meters (33 mego- short, medium, broadcast and long-all tuned with a cycles to 150 KC)- enabling you to secure almost single dial! You can switch instantly from U. S. magical radio performance! Midwest users regularly programs- Canadian, police, amateur, commercial log such stations as: GSC, London- VK2ME, Sydney, the finest short wave Australia -JIAA, Tokio, Japan -RW50, Moscow airplane and ship broadcasts -to Russia -DJB, Berlin, etc. Never before so much programs from Australia, Japan, Russia, Italy, Ger- radio for so little money! Send coupon today! many, France, England, South America, Etc. 40 New 1934 Features These sensational new features give you amazing performance, perfect realism, new beauty of tone, new wealth of power, fractional microvolt sensitivity, better than 7 KC selectivity. For example -Automatic SELECT -O -BAND (exclusive with Midwest) simplifies short wave tuning by instantly pointing out wave length of station. Amplified AUTOMATIC VOLUME CONTROL keeps volume at predetermined level over wide range of signal inputs, prevents "fading" and interstation "blasting." Some of the other features include: Indicator New and Improved Electro- dynamic Au- All short and Ultra Short American and Automatic Select -O -Band European Bands. All -wave 9 to 2.000 meter tuning range ditorium Speaker (33 megocycles to 150 KC) Latest Type, Higher Efficiency Tubes Fractional Microvolt Sensitivity 7 KC Selectivity. Automatically Adjusted Perfect Tone Quality . . at low veluma Five Full Wave Bands (Low Volume Compensator) Illuminated Frequency Indicator Scientifically Shielded (Coils and Switch levels 16 -Tubes , , . Equivalent to 18 tubes Station Group Locator Catacombed ) e. Calibration in Kilocycles Positive Signal Control New Thermionic Rectifier Dial Frequency R.F. and Megocycles Litzendraught L.F. Transformers, Simplified, Centralized Balanced Unit Super Heterodyne Circuit Coils, and Oscillators Tuning -No Vernier, Slow Motion, Velvety action Tuning Stat -O -Mit Interstation Silencer No Auxiliary Tuning. Volume Super Power Class "A" Audio Amplifier Positive Amplified Automatic Minimum of Control Bias fully Delays 29 Tuned Circuits . . . 10 in Cascade -3 Absolute Variable Background Noises All Police and Airplane Bands Low Operating Cost New Duplex-Diode--High Mu Pentode New Style Consoles The new, big Midwest 1934 catalog shows a ALL - PERFORMS complete line of beauti- The new Super De luxe 16 -Tube Midwest "OUT- ful artistic, de luxe con- WAVE radio positively gives you more features $200.00 SET" soles . in the new and more advantages than sets selling in stores 'Am writing this uns.11oited letter in mull to modernistic designs. fomy hlidarwt radio. It e re than flou claims two to three times Midwest's sensationally r it in many regarda 1, w more nelectl,e than Hand made by Master at any radio that I have with. It Craftsmen, they lend low price! Don't try any radio until you get all will .hip . out-perform shore te., dignity cata- $2m.00 haw t.nd i mut nh,- great when your distinction and the facts! Write for the new Midwest 1934 mpetitor o tira it r to awe to any home. Save 30% low machine.chin that he alla 1 I.. road South to 50% by ordering log. You'll be amazed at the unbelievably . cor Mont ,h..hante at I have n,.in n 1o direct from Midwest direct -from -Midwest Laboratories Prices. They that she Rath. n,.. . oll, three time. what y the ask for it ' -I.. F.. W 'hare 1\Iemher I.R. f.. Laboratories. Mail 50%. 1521 S. W. 7 th St.. coupon today. save you from 30% to MIDWEST RADIO CORP. RADIO -CRAFT for SEPTEMBER, l73 134 ,-` 9fo 2,p tFßs DO

WORLD'S GREATEST

RADIO VALUE ... Midwest guarantees your satisfaction by permitting you to try any Midwest set -right in your own home -for 30 days FREE trial. Thousands upon thousands of delighted Midwest owners all over the U. S. and in many foreign countries are daily en- joying the world's finest radio programs because of Midwest's revolutionary policy of selling direct from the laboratory at rock- bottom prices -and on easy terms. But don't judge quality by price. Even though we offer unbelievably low prices, Midwest Radios are of the very highest quality and positively guaranteed. When you buy from 010' Midwest, you deal with one of the old- established, pioneer radio builders who with New has been selling quality sets all over Terms the world for more than fourteen years. Mail the coupon or write us a postal Deluxe for new 1934 catalog, easy terms and 'ludiforium Type AS LOW AS low laboratory prices. SPEAKER oo rMeiA/IfheFoc/sr DOWN De a/ Dir e ci ivilh !a 6o rufo ri of Got a Liggcr, Letter, nìtuu luvcrlul, clearer -toned radio -at a positive saving of from 30% to 50%. Buy now while you can take advantage of the tre- fFCA COrp., mendous values Midwest offers you. No dio ge c e eaets,l middlemen's profits to pay. Present in- { µ1d 139. ¡o. To and oft flationary legislation is to in Ob 0, tr'cue sure result { Cnloot ob1t1934neáaYoFREE higher prices. Try any Midwest Radio for with FREE slat So. 30 days- FREE -before you decide. As little as äñ $5.00 puts a set in your home. Satisfaction guar- 90"r order- anteed or money back! Just sign and mail s i9 .. coupon -or send name and address on postcard. -same...... ( *Canadian Prices Slightly Higher.) { TA °oeY { Entra DEPT. 231 U. S. { CitY...... -- ...... - CINCINNATI, OHIO, A. ....t....MakeF pets' Established 1920 Cablo Address Miraco. ABC 5th Edition state °r ,Gs Aere { Cb ck RADIO -CRAFT for SEPTEMBER, 1933 135 The Best NEWS of the Year

Announcing the first

Every man connected in any way with the boom- ing auto-radio business will want a copy of this book immediately. It is devoted exclusively to auto-radio service "dope," in complete, understandable f o r m. The OFFICIAL AUTO-RADIO SERV- ICE MANUAL contains schematic diagrams, chassis layouts, mounting instructions, and trouble-shooting hints on all 1933 and many older model auto- radio receivers. This Manual contains a "gold-mine" of information. Over 200 Pages Over 500 Illustrations Flexible, Loose- Leaf Cover

Order Your Copy Today! MAIL THIS COUPON TODAY! I

t. EltNSRACK PURT.ICATIONS. loe RC-9 You have the opportunity to get your copy of 96-98 Park Place, New York, N. Y. AUTO-RADIO SERVICE the 1933 OFFICIAL Enclosed you will find my remittance of $2.50 for stitch pica-e send MANUAL from the first printing of which we me One Copy or the 1933 OFFICIAL AUTO-RADIO SERVICE MANUAL. (Send remittance In check or money order. Resist, have copies on hand. The Auto-Radio Service letter if it contains cash or currency., Manuals are selling so quickly that already another print order has been authorized. We urge you to get your copy now so that it will not be necessary for you to go through the summer Name - without a copy of this manual. GERNSBACK PUBLICATIONS, Inc. Address - 96-98 Park Place New York, N. Y. City State- .s

136 RADIO-CRAFT for SEPTEMBER, 1933 adlo-Caff SERVICE MAN DEALER RADIOTRICIAN "Takes the Resistance Out of Radio"

Editorial Offices: 96 -98 Park Place, New York, N. Y. HUGO GERNSBACK, Editor Vol. V, No. 3, S.pt.mb.r, 1933

OUR CHANGING RADIO An Editorial by HUGO GERNSBACK

THERE is probably no industry in the whole world time, but as yet it is non -existent. Perhaps this is a good that changes so abruptly and so radically as the thing, because after all, radio is too big an art to rely en- American radio industry. It is always a source of tirely upon cigarbox sets. surprise to radio men from foreign countries who visit For better results and for ease in servicing, it is neces- the United States and find most of their radio ideas thrown sary to have adequate space, and this you can only have in overboard. The American radio industry has long been a standard console model. Even the old type midgets were accused of having little or no stability; because one manu- too crowded. One of the foremost radio set manufacturers facturer, in his efforts to beat the next one, seemingly stops never manufactured a midget because their engineers at nothing to gain his goal, provided there are a few dollars claimed that it was impossible to get correct sound value for him in the 6ffing. We have seen it time and again in in small cabinets. the past: first when the $60.00 radio killed all those selling In due time, it is believed that radio manufacturers will for $200.00 or more ; then when the first midget killed the return to sanity and manufacture regulation sets that will legitimate sets; and again last year when the cigarbox be a credit to the industry. While we are on that subject, models promptly smothered what business there was left let me mention one point which has been neglected by most with the regulation midgets. set manufacturers. In Europe, the appearance of the av- That there will be a stop to all this, and that the radio enge American radio set brings forth smiles and guffaws industry will settle down into an unexciting butter -and- of laughter. The European as well as the American artist egg -type of business, no one believes for a minute. Prog- sneers at a radio set housed in the American "Period" style ress, as spelled in radio, simply does not work that way. cabinet. The artist will say, "Why should an ultra- modern Too many radio engineers are lying awake nights figuring article like a radio set be housed in a Louis Quatorze wooden out how they can steal a march on their competitors. While cabinet ?" The idea, he says, is incongruous, and he insists this sort of thing lasts, no one can tell what 1934 will mean you might as well walk the streets today wearing a pow- in terms of radio. dered wig and knee breeches. The effect would be identical. In our May issue we published, purely as an April Fool To me, the Century of Progress in Chicago, translated joke, our now famous (or infamous) Seven -Tube Vest into radio terms, proved an eye- opener. When you look at Pocket Set. The "tubes" in this set were made from ordi- these strikingly, and at first appearance, bizarre buildings, nary pilot lamps. This, at the time, looked like a good joke. you wonder why such an architecture was used. The rea- However, the joke is now on us, because already one of the son is very simple. Science, electricity, radio, etc., have largest tube manufacturers has announced a real radio transformed the world. We live today in a world entirely vacuum tube even smaller than a pilot lamp! We now have different from that of our parents and grand -parents, and the shoe button type of tube, a number of which have al- we should think and act accordingly. To hitch up Egyptian ready been manufactured and demonstrated at the Century art or the art of the French kings with modern progress of Progress in Chicago. Whether we will actually have is a step backward, not forward. If radio is new, as it is, vest pocket sets which, in turn, will do away with the cigar - then it should be new and modern in appearance. box models, no one can foretell at this time. This idea first made itself felt in the cigarbox models, where we already have strictly modern art, and where the Of course, the radio industry did not wax rich on the "period" abortions have been left far behind. There are cigarbox type of set and the dollar volume for 1933 will some very striking cigarbox models which have caught be found to have fallen considerably. When you have to on to the new idea; but so far, there have been hardly run a factory on $7.00 or $8.00 units (some sets sold even any lower) new -art radio sets in the larger models. These are still in comparison with the midget sets which averaged preposterous stilted -leg monstrosities, and they still look about $30.00 or thereabouts, it needs no mathematician to like old -fashioned cabinets instead of expressing themselves predict the result. And, while the actual sales volume of in new terms. these cigarbox sets was fairly large, it was not large Here is a thought that the radio industry enough during the depression to make up for the reduction should embrace, in price. and the quicker it does so, the quicker will it put radio across to the public. There are many new materials which As far as these cigarbox sets are concerned, they perform lend themselves to the working out of these ideas. We a useful function because they give the man who wants a have new plastic materials which, in combination with cheap set a radio, which, perhaps, he could not afford metals, will make strikingly new and modern receivers. otherwise. But, everyone also knows that the sound qual- Wood should not be used, or only sparingly, and the quicker ity from these cigarbox sets is poor; in some sets so poor we get away from the cabinet -looking sets, and take the that voice reproduction becomes almost unintelligible at modern Chicago architecture as a basis, the quicker the times. This is not the fault of the sets themselves, but lies public will approve the idea and buy. in the loudspeaker. So far, because of the exceedingly small Many homes in the United States are undergoing revolu- dimensions of the little sets, no satisfactory loudspeaker tion, and modern furniture is being installed rapidly. The that gives good reproduction has been designed. It is "period" cabinet does not fit into this atmosphere, and conceivable that such a loudspeaker will be made in due ahoùld be replaced by modern designs.

137 THE NEW RADIO GARAGE DOOR. OPENER

A commercial system for the remote control of garage doors, etc. A 100 -meter signal radiated by a transmitter located in, for example, an automobile is picked up by a receiver and, in turn, actuates a door - opening or closing motor.__ A "code" prevents tampering or accidental operation of the system.

Fig. A R. D. WASHBURNE A view from the inside of a garage showing this location of the equipment.

JJ RESTO!" is the "open Sesame" closing and locking of the garage doors. nearby receiving sets. Such slight in- which controls the door of the Literally, the system is a "radio key." terference as may be introduced on ex- really modern garage. Press a A display at A Century of Progress tremely sensitive receivers, or those p button and, lo, the portals of your illustrates this procedure. An idea of operating on short waves, is of little garage swing wide before you, lock open the relative parts arrangement may be consequence as the units operate ordi- while you majestically continue your obtained by reference to the cover il- narily at considerable intervals, and ride; and then, at a second press of lustration and Fig. A. A schematic then only for about three seconds. The the button, close and lock, whether you circuit of the radio transmitter located spark coil unit is contained in a water- are leaving your garage or returning in the car is shown in Fig. 1. The re- tight case and is bolted to the under- to it. We will now (with due apologies ceiver connections are shown in Fig. 2. side of the car chassis. to the ads) disclose the "trick." The door motor, which operates only The transmitter timer, shown only in A radio transmitter mounted in the when a particular set of signals is re- schematic form in Fig. 1, clamps to the automobile transmits a short -wave sig- ceived, connects to the receiver as instrument board, and consists of a nal of "coded" or predetermined dot - shown in Fig. 3. rack -and -pinion arrangement incorpor- dash characteristics, when a knob on As shown in Fig. 1, a simple spark ating a balance wheel, escapement the instrument board is pressed. This coil arrangement is sufficient for the wheel, hairspring, pallet lever, and a signal is radiated by a one -wire an- transmitter requirements of this instal- contact plate and contact springs. The tenna underneath the car chassis, and is lation. The transmission is rather broad, rack -and -pinion mechanism is con- picked up by a one -wire antenna buried on a wavelength of 100 meters. How- trolled by a plunger. in the driveway. The latter antenna is ever, the field of radiation is confined The timer action is set at the factory connected to a receiving set which by the body of the car almost entirely with a combination which is different "de- codes" the signal, and then oper- to an area immediately underneath the for every installation. It is put into op- ates motors which control the opening, car, thus preventing interference on eration by a thrust on the plunger which extends from the lower edge of the instrument board of the automobile. COUPLING GRID MECHANICAL BY PASS Since a similarly -coded action is in- GRID COND. DISCHARGE RELAY COILS stalled at the receiver, it is not possible C for static, or the radiations of a trans- 6V mitter not equipped with the same STORAGE CAR LIGHT/ BATTERY code, to actuate the door motor. SWITCH In reference to the diagram of the LIGHT CAM fSTARTIIe TIMER MTM transmitter, the car wiring is shown in TAIL LIGHT TRANS ADJUSTING SCREW dotted lines; external wiring is shown VIBRATING in heavy lines; and, internal wiring is CAR HAMMER PRIM SEC. IRON FRAME COIL COIL CORE shown in light lines. rG 1 SELECTOR -DRUM SYNCHAONOUS'a-u ..F--RUNNING MOTOR. CONTACT CONTACTS Radio-Controlled Garage Lights! TRANSMITTING 1 ê >^ ê;îr RATCHET COIL ANTENNA 116HT5 'SWITCH It is of considerable interest to note DoolIS4 t-_ CUTOUT SW. 4 4 A¡-ti-4-1 that the lights inside the garage may SPARK be automatically turned on and off by , r-d d ,d ¡ COIL SPARK. LCOND. radio. This is accomplished by an added 6AP impulse in the code, which is transmit- H A 6 C D E I J Fig. I ted only when the lights of the car are A diagram of the transmitter used in the radio - turned on (thus completing a section controlled door opener. Note that the car frame Fig. 2 is used as the radiating system. Diagram of the receiver pictured in Fig. C. of the car lighting circuit which is

138 RADIO -CRAFT for SEPTEMBER, 1933 R

Fig. B, right The illustration at the upper right shows the location of the timer while the ... larger photograph shows the location of the spark -coil transmitter.

Fig. C, above A close -up of the receiver, usually mounted on one of the walls of the garage.

wired to the radio control system). a set amount, and then trips. This per- As the car is driven up the driveway The antenna which connects to the mits the ring gear to run free and the and the door -control plunger is oper- transmitter is strung diagonally under- motor, which continues to run, is dis- ated, the garage, driveway and yard neath the chassis. The receiving an- connected from the driving pinion. The are suddenly flooded with light, pro- tenna, about 150 ft. long, is buried a driving pinion causes the door to open vided the headlights of the car are few inches deep in the driveway. or close. turned on -as for night driving. A The receiver must be in continuous At the end of the door travel a cam conveniently located switch inside the operation; consequently, the amplifier shaft is automatically operated. It house makes it easy to extinguish the tube, VI, shown in Fig. 2, is specially opens the main motor switch and ap- garage and yard lights in case it is de- designed for continuous operation over plies a brake which stops the door. At sired to leave them turned on until the a minimum period of 2% years. For the same time the release mechanism is owner is inside his home. This provi- testing this tube a D.C. milliammeter of locked by a locking lever so that any sion minimizes the possibility of a ma- 0 to 15 ma. range is connected into cir- attempt to force the door will not trip rauder lurking about, since all local cuit at M; for the same purpose an A.C. the release mechanism. Also, the motor areas become flooded with light. Thus, ammeter of 0 to 2 A. range is connect- control switch is shifted and the motor for a few hundred dollars the provi- ed at A. (This tube is of the type prepared to operate in the reverse di- dent person may possess a useful developed for use in automatic train rection on the next signal; an additional "magic wand." control equipment.) The output of V1 switch for controlling the lights also is Installations throughout the country actuates the de- coding mechanism, a shifted. have proved that this "unseen servant" set of relays and electromagnets oper- Radio control of the garage door per- is an absolutely practical mechanism ating a pawl- and -ratchet system that ro- mits the motorist to enter or leave his -another effective member of the radio tates worm gears and a number of discs car under shelter, a boon when it's "robot" family. Whether the Service which close contacts. One receiver can "raining pitchforks," or in blizzard Man will be able to obtain this equip- control, at will, either side of a 2 -car weather. Incidentally, the same princi- ment for private installation cannot be garage. The stock receiver and door ples may be applied to the operation of definitely stated at the present time. To operating units are designed to operate doors within the home. date, all "radio door" installations have on 110 V., 60 cycles, A.C. The com- The radio light control feature of been made only by a corps of techni- ponents are protected by a metal this installation has several points of cians trained by the manufacturer of shield-can; the assembly is mounted particular interest to the car owner. the system. inside the garage, fairly close to the door -operating motor. A split -phase motor is used in the OPERATOR door -opening and closing system, the i L I- circuit STi -?---- -.` of which is shown in Fig. 3. In WIIIOOIO this figure, heavy lines indicate external wiring. Any number of the manual ---T control switches may be placed in convenient locations. Although our major CENT Rif interest lies in the radio components, CUTOUT CONTROL, the action of the door control also is STATION - RELAY described. CUNNING WINDING MOTOR LIMIT SWITCH JUIICTION Power is transferred from the motor RADIODI O RECEIVER i CÉILIÑ6 RADIO -CON - unit, when starting contact is made, i N 6 A O E f J R i to TROLLED LIGHTS

a latch magnet, by means of an arma- _ _I__ 1 CONTROL I ture and spring -operated lever, releas- SWITCHES'SW ing a brake and closing the main motor 1111 switch lever 1 the end. 1 at As soon as r- 1 the electric motor reaches normal I I 30 AMP r - -- J i speed, in about one -half second, a cen- SWITCH BOA Ì l+e trifugal clutch engages and passes the It, -113 AMP motion on to a planetary differential TO 11OV,6O CYCLE SUPPLY FUSE which forms the main par) of the release mechanism. A pawl holds the Fig. 3 Complete schematic circuit of the motor and light -control circuits used in this system. The output of ring gear fixed until the load exceeds the receiver works the works." RADIO -CRAFT for SEPTEMBER, 1933 139 LATEST RADIO EQUIPMENT

TUBE SHIELD AND TUBE -BASE CONNECTION FINDER THE illustration to the left shows a new type of tube shield that may be termed "form fitting." The two units comprise the entire shield, and are installed by placing each half of the shield around the tube. The ring, also shown in the illustration, is then snapped into the groove provided, and the job is finished. The long metallic strip is used for making connection to the shield for grounding. To the right of the photograph is a new tube -base connection finder, a handy little device in these trying times. It is composed of two concentric cardboard discs. To the right of the disc is a small window which indicates the type of tube whose socket connection is desired; in the example photographed, the tube is a 58. The remainder of the disc is taken up by socket holes. When the lower disc is turned to a tube number, the socket connections SHIELD OPEN SHIELD CLOSED appear at a socket whose color corresponds to that of the Tube the c and tube -base connection finder (124) tube number shown at the window.

OUTPUT TRANSFORMER the bugbears in car -radio sets is the AUTO "B" UNIT charging THE universal output transformer, drain on the battery. If the auto "B" eliminator designed is designed to meet the rate is too high, the battery will be ANEW shown below, is too low. for auto-radio use has just been demand for a single unit that will pro- ruined; similarly if the rate The device is compact, be ad- announced. vide the correct impedance matching The charging rate may easily measuring about the size of a device. standard between various types of audio output justed at will with this 45 -volt "B" battery; it is light, weigh- tubes and dynamic speakers. ing but 61/2 pounds; it consumes 2 am- TUNED "AERIAL ELIMINATOR" peres when delivering its rated output of 180 volts at 25 ma.; it is accessible, HERE is a novel little device which since the entire electrical unit may be may be installed on any radio re- removed for testing by loosening two ceiver. There is nothing "mysterious" nuts; and last but not least, the vibra- about this unit -it operates on stand- tor is equipped with two points instead ard coupling principles. Connected to of the usual single point. the antenna and ground posts of the The photograph below shows the in- average radio set, it eliminates the ternal and external views of the elimi- need for an outdoor antenna, for gen- nator. This same company also manu- eral local reception; in many instances factures an "A" power control relay to it even results in improved reception control the "B" power unit from the of distant stations. The ground lead usual switch. affords the necessary pick -up.

Universal output transformer (125)

GENERATOR CONTROL below is a new device that FEATUREDshould find favor among auto -radio users. When installed in your car, it gives remote control of the charging rate of your battery, at will. One of r

e---- _.77714"74-. Above, external view of the "B" eliminator; below, Generator charging -rate control (126) The tuned "aerial eliminator" (127) an internal view of the unit. Note the size (128) Name of manufacturer of any device will be sent on receipt of a self -addressed, stamped envelope. Kindly give (number) in description under picture.

140 RADIO -CRAFT for SEPTEMBER, 1933 THE LATEST TEST UNIT A NEW DEAL IN THE RADIO INDUSTRY unit pictured below is designed organized campaign to THEto operate in conjunction with any AHIGHLYfind a new prosperity for the radio volt- ohm -milliammeter to form a com- industry will be staged this summer PEACH FOP plete voltage, current, and point -to- and fall under the leadership of the point resistance tester. When the volt- R.M.A. This campaign will consist THE JOY OF LIVING meter, milliammeter, or ohmmeter is of two parts: (1) an intensive sales connected to the corresponding posts drive during the month of September; on the test unit, voltage, current, or (2) and, special, spectacular broad- resistance between any two points may casting from October 2 to 7, which will be measured. The unit uses no adapt- be known as Radio Progress Week. ers, except on the plug. The radio industry, from manufacturer to Service Man, is right now bowed down with the hard times. Cut price competition has destroyed profits, and public interest in radio reception is at a low ebb; but the business tide has turned: general prices are rising, and public gloom is changing to confidence and optimism. There are now approximately 6,- 750,000 homes using radio sets that are obsolete, and 13,000,000 homes that have no radio at all; but the radio industry cannot expect to sit back and let the returning prosperity pour new business into its lap. For every other industry is going to be out after these same dollars from the family budget. The test unit (129). Automobiles, refrigerators, travel, clothes, and other strong personal ap- before the public the scope, diversity MORE SOCKETS peals will be scrambling for attention. and richness of modern radio broad- are pictured a number It will now be a competition with other BELOW of new casting, and create a public apprecia- sockets suitable for various mount- industries that will be out energetically tion of the dramatic part it plays in the ing facilities. Center, a group of harn- selling the hone market. life of today as a source of entertain- esses, inserted between tube sockets The Rebuild Radio Prosperity Cam- ment, a promoter of education, a and tube in A.C.-D.C. sets to automa- paign will have two objectives: (1) to liberator of thought and an influence tically connect the filaments for bat- canvass every radio set owner and put for progress. In addition, regular broad- teries. Adapter in upper left, hole -to- his radio receiver into condition, by casting features of the week will be prong connections easily made. installing new tubes, parts or acces- given a Radio Progress flavor and spe- sories, or to replace it with a new set; cial local programs will be arranged (2) to canvass prospects for sets. in many cities. The National Broad- The prime objective will be to casting Company and the Columbia awaken a new popular enthusiasm for Broadcasting Company have pledged the present dependability of radio their hearty cooperation. A colorful equipment, the perfection of its tone program is assured, combining those quality and control, and the perfec- elements of laughter, melody, romance, tion of modern programs. drama, knowledge and news, with Radio Progress Week, especially, which radio is enriching our lives. through the cooperation of broadcast This campaign will benefit the entire studios, advertising agencies and na- radio industry. Prepare to give it your Sockets, adapters, and harnesses (130). tional advertisers, will pass in review complete support.

A DECADE OF PROGRESS R ECENTLY, there was brought to the attention of the editors of RADIO -CRAFT the Rodgers Single Control receiver shown in the figure. Estimates place the "birth date" of the instrument around 1923. It is extremely interesting to note that this radio set incorporates many of the constructional features which contributed largely to the success of receivers designed in the next ten years. Thus, this device, a product of Rodgers Radio Co., Chi- cago, Ill., exemplifies single-dial tuning, resistance- coupled A.F. amplification, combined off -on circuit and volume control, drum -dial tuning scale, trimmer condensers, and metal chassis construction. However, unlike all present-day receivers, which use variable condensers of the inter-leaving -plate type, the broadcast receiver shown in the figure is designed to use three parallel -plate condensers which are ganged in a very novel manner. A hollow shaft extends through the center of the three sets of condenser plates and terminates at one end in a lever and dual -knob control system. By cranking the lever the three sets of parallel plates are slowly drawn together; thus, tuning the figure 8 (astatic) R.F. coils. RADIO -CRAFT for SEPTEMBER, 1933 141 THE 2B6 A DUPLEX TRIODE

Another new tube is now added to the list of power output tubes for radio receivers. The 2B6 described below is an outgrowth of the well -known Triple Twin, with all the "bugs" removed. See its rating, given below. A feature of "triple twin" design lies in the value of the output plate resistance, which is also the value of the output load resistance.

L. VAN DER MEL

IT WAS not long ago when the only over the pentode with respect to qual- output tubes used in radio receivers ity, in fact in most applications it is were triodes, operated in standard worse. Due to its design complications class A circuits. The output of a (particularly the power pack require- class A arrangement is characterized ments) and its high cost, the system is by high quality and relatively low effi- not readily adaptable to receivers. The 266-an improved Triple Twin. is seen that when one wants ciency. Later, the pentode made its Thus, it is secured by the voltage drop across appearance. also quality, the triode class A system is The pentode, while Ro. Since the steady plate current of of the class A type, has a higher power the best, while if one wants power out- with quality as a secondary object this tube is 3 ma. and its self- biasing output and sensitivity for a given plate put resistor has a value of 8,000 ohms, the dissipation class A ; but, the class B system should be used. For than the triode steady D.C. bias is -24 volts. Note unfortunately, the a happy com- promise that this resistor has no bypass con- quality is inferior. of power, denser across it. Furthermore, since This is inherently sensitivity, quality, with THE 2B6 and cost, the pen- the input grid is negative respect due to the mis- to the cathode, no power is dissipated match of the plate Heater voltage 2.5 volts tode has offered in the input grid circuit. impedance to the Heater current.. 2.25 Amp. the best solution to the The output grid connects directly to output load, in or- problem until the cathode as shown, and since the out- der to minimize the INPUT SECTION the introduction of has self -biasing the new 2B6. The put cathode a resistor distortion. Its op- Plate voltage 250 volts 540 ohms, and since the D.C. 2B6 consists of two of steady timum load value Grid bias -24 volts current of the output section is 40 ma., is critical and the Plate current... 4 ma. triodes, and is de- the drop across this resistor, rise signed to provide voltage harmonics R1 is 21.5 volts. The bias, with OUTPUT SECTION high output low actual very rapidly with at no signal at the input grid, therefore, 1 signal changing o a d. Plate voltage 250 volts voltages in is the difference between the voltage 2.5 volts a triode class A Furthermore, the Grid bias across Ra and Rs, +2.5 volts. With predominating Plate current 40 ma. connection. Thus, this small positive bias, the output grid harmonic is third Plate resistance....._ _ .5,150 ohms titis tube when Load resistance.. .5,000 ohms takes approx 1. ma. current. When a which, if large, be- properly used, is signal is applied to the input section of comes disagreeable Signal volts (r. m. s.) 25 volts capable of combin- Power output 4 watts the tube, an A.C. voltage is impressed to the ear. Al- ing the advantages on the output grid which, of course, though pentodes of the high quality swings this grid alternatingly more may be connected found in triode positive and then negative. Since the class A systems the in the push -pull arrangement, the dis- and high power grid is normally a few volts positive tortion still persists, at a somewhat output characteristic of class B systems. more grid power is consumed when it lower level, but this system does not The results are obtained very goes more positive during that part of eliminate the load problems; it is em- economically. the cycle. In other words, more grid phasized because, while the second har- The schematic circuit of this tube is current is required. This grid power monics cancel in a push -pull arrange- shown in Fig. 1. It is seen that a single ment, the third and higher order odd heater supplies two separate cathodes, harmonics add, especially at high out- and that the output grid connects di- puts. rectly to the input cathode inside the Su -h tubes, however, found much tube. That triode section of the tube favor among "midget" set manufac- into which the signal is fed is called the turers merely because they permitted input triode, or section; while that sec- large power outputs to be obtained with tion of the tube which feeds the speak- relatively small signal voltages. In the er is de.ignated as the output section. quest for additional power, class B The respective elements of each section tubes were designed whose main pur- are labeled accordingly. pose is to provide very high power out- An examination of this circuit shows Fig. I put. The system has no improvement that the grid bias for the input section A schematic circuit of the 286.

142 RADIO -CRAFT for SEPTEMBER, 1933 is automatically supplied by the action of the plate current fluctuation, the of the input section. The inherent A.C. voltage developed across Rois 21 compensating feature of this particu- volts. Since this voltage is in phase lar direct coupling provides the A.C. with the signal with respect to ground, voltage across R without distortion the actual peak voltage actuating the irrespective of the changing grid resis- input section is 35 -21, or 14 volts. tance of the output section. It is This corresponds to an effective value significant to note that the D.C. power of 10 volts. Since the D.C. bias is -24 taken by the entire tube with no signal volts, the input grid can never draw is in excess of that required under current. This condition is illustrated Fig. 2 maximum excitation. Therefore, the by the circuit of Fig. 2 in which the in- Feeding the signal from grid to cathode. tube operates under class A condition put section has been redrawn so that and .01- MF 216 no complications in power pack the signal is applied between input - ZO: 5.000 OHMS design Pa ! are necessary- standard parts grid and cathode through the .5 -mf. DET may be used. It should also be noted condenser, rather than between input 0.5-MEG Gla that since the current from the input grid and chassis as shown in Fig. 1. In OUTPUT triode e.DDO\A. L divides, part going through R, this case, therefore, the signal voltage DHM$ and part going through the grid - required for a power output of 4 watts 24 VOLTS 'k titsGib cathode resistance of the output sec- is 10 volts, as calculated previously. SPEAKER tion, the current for determining the Degeneration does not exist in the out- FIELD COIL input grid bias should be measured be- put section of the tube in view of the tween the input cathode and RI, not fact that R1 is RECTI- shunted by a 25 mf. FIER. ` M 26.250V between input plate and "B +:i condenser which is more than sufficient l The resistor Re, in addition to sup- to maintain a constant potential across 4MF plying the required grid bias for the in- the self -biasing resistor, R,. '215V put section, also acts as the load im- Fig. 3 Eliminating the 25 mf. bypass condenser. pedance of the input section and, there- Alternative Connections fore, cannot be shunted by capacitance. The bias voltage for the output sec- OUTPUT SECTION Ip s Ep CURVES In fact, the total load impedance of the tion may be obtained in another man- Eq +IS first tube is the parallel combination of ner which has the advantage EFFECTIVE of elim- +10 OPERATING R. and the grid impedance of the out- inating the 25 mf. bypass condenser. POINT put section. Figure 3 shows the circuit arrangement +5 A particularly significant fact is that which obviates the use of the bypass although the input grid is biased to condenser. The hum level of the tube is -24 volts, a signal of 25 volts r.m.s. is so low that the hum introduced by such required to deliver the rated output of an arrangement is still a negligible 4 watts. Although the peak value of factor. It is down -30 db which is far the signal applied to the tube is ap- below that of more conventional out- -10 proximately 35 volts, this grid does not put tubes. This circuit also has the draw current because of the degenera- additional advantage of having a -15 tion slightly LOAD taking place, due to the lack of better frequency characteristic LINE 5,000 bypass action across Ro. This action than that shown in Fig. 1, even though OHMS may be more fully explained as follows. the 25 mf. condenser was increased, A signal of 35 volts peak is applied in test, to 50 mf. 250 to the input section. As a consequence (Continued on page 167) PLATE VOLTAGE NOTE'- THESE CURVES ARE NOT ACTUAL PERFORMANCE 6UT NAVE MERELY SEEN DRAWN FOR DESCRIPTIVE PURPOSE r.d^-. t..:. g . . Ì Fig. 6 . _... _ :...: R'.. :::::::_ « t_ vs. i Plat. current plate voltage of the 286. . L. li i::: :i , PUSH-PULI 296 ss . ii .: `: MN st i^ : :'»nii.^ 0Tc OHMS :HOP i i i i:i ei»til: : i. i':i ! :;.si g:{. po3-m;i

s"$ l..: 'i OUT- s:: ::R::i ..:t.U::...Rft..f:.i.Da»cf.:.:.i.:.:.: PUT l..: u ' '-'7 . : : :.. . . . :: :i :.ii . .. :L .. _ .ii4fFE_âi;i^a' ..ä-t.°3s,ry i U: i-.:E::f:EE .tii Fi.'.l..:F « ZO s

: i : 10,000 ffiiiiLiçErFI. :::::: iüi si OHMS Mang :3IMOi!g HÍ? PLATE TO : N?ia e.000 PLATE 8 _: s54:Mi?£ OHMS . , ,.:::: __ :i»iliiúff F.'¡ . Fio. 7 RéM ri::-::ñF..1gg111: :::i ::a. : Two 286's in push -pull. Gry rr.::ïi !PTE. l iBB J i f ::::®CR: i:::' Ell...g..?s GRO gg i (iNPUr) J Gil a ' G ïf» (DUTPU"PVr) Gib i » CATNODE rPr.F%f. ; (INPUT) Ka ss.: alai: .d . _ . :.g.:s:.:ii..:i. o' : .....: :. . 1 . L.r -.i.:::: '''i"I 6F.» «^ ':9 *- :t CATHODE ii.so.i.i.*Ei:eitt.. (OUTPUT) Kb 4:T`N ä ësi -: . L P wo.N:e OV'Rri- warA NEATER HEATER

- VIEW LOOKING DOWN ON SOCKET.. Fig. 4 Fig. S Curves showing the relation between power outpu Distortion vs. power output; and signal volts vs. a -,d load resistance. Fig. 8 power output. Socket connections. RADIO -CRAFT for SEPTEMBER. 1933 143 CONSTRUCTING THE ALL -WAVE MIDGET "FOUR"

A description of a novel midget receiver which not only covers the broadcast band, but the short -wave bands as H. G. CISIN well. A switch changes bands, from 15 to 550 meters.

RECENTLY, there has been a considerable demand mended bias of 16.5 volts and a plate voltage of 250, the for an inexpensive A.C. receiver capable of bring- characteristic is substantially linear, resulting in a mini- ing in short -wave as well as the regular broadcast mum of distortion. stations. The All -Wave Midget "Four" is designed The rectifier may be of the conventional 80 type; or, to meet this demand. No plug -in coils are necessary, a 5Z3 may be used in its stead. In the latter case, it because of the use of a new -type all -wave coil having should be kept in mind that the filament requires a cur- enough windings to cover the band from 15 to 550 meters. rent of 3 amperes, necessitating the use of a power trans- The complete set of windings on this new coil, including former designed for this heavy current drain. The field the tickler windings required for regeneration, take up of the dynamic speaker also serves as an audio filter choke. less space than a single short -wave coil of the ordinary The automatic line voltage control aids the attainment type covering the band of excellent performance from 15 to 80 meters. regardless of variations and fluctuations of the sup- Description of Receiver ply voltage. This new receiver is in the "midget" class, being Construction Details mounted on a chassis 8 in. Socket holes and trans- x 5 in. x 2 in. high. It former mounting holes are uses the latest type tubes drilled in the metal sheet and has plenty of "pep." before the chassis is bent. The circuit comprises an R. After the chassis is bent, F. stage with a 58 tube, a the five wafer -type sockets regenerative detector us- are mounted, four on the ing a 57 tube, and a 2A5 "deck," and one for the output, power amplifier. speaker connections at the All three of these tubes rear chassis wall. The are pentodes. The 57 tube, power transformer, 31, may with the special shield ar- now be mounted. rangement in the dome, The small condenser, 17, permits a decided reduc- Is mounted at the right on tion in output capacitance. the front chassis wall, This makes it especially while the volume control, desirable for short -wave 21, is mounted at the left. operation. Moreover, its The three switches, 4, 13, high transconductance, and 32, are also mounted plate resistance, and sharp on the front chassis wall, plate -c u r r en t -grid -bias as indicated in the bottom "cut -off" make it ideal Photograph of the "deck" of the all -wave ultra midget receiver. view diagram. for sensitive detection. The chassis is now turned Grid -leak detection is used. upside down and the all - Resistance coupling to the output stage permits the wave coil, 12, is mounted as shown. The R. F. choke, attainment of high tone quality. Regeneration is con- 18, is mounted next. The two "cardboard" electrolytic trolled by means of the condenser 17. A two -gang con- condensers, 28 and 29, are each fastened to the sides of denser is employed for the two tuned circuits when used the chassis by two thin metal straps; but they should not on wave lengths from 200 to 550 meters. For short -wave be put into place until most of the wiring has been com- reception, switch 4 is thrown to the upper position, cut- pleted; otherwise, they will make it difficult to wire up ting out the antenna coupler, 1; its tuning condenser, 3; certain of the socket terminals. All other parts below and connecting the antenna to the control grid of the the chassis are soldered in position during the wiring. The chassis is again turned right -side up and the dual R. F. tube through a small special type condenser. variable condenser, 3 and 8, is mounted. The two trim- Switch 13 is connected to the various sections of the mer condensers, 3A and 8A, are fastened to the top in- all -wave coil, 12, permitting rapid change -over from one sulating support of the tuning condenser. The grid con- band to another. Volume is controlled by means of a denser, 14, and grid leak, 15, are also fastened to the same potentiometer, 21, connected in the control -grid circuit insulating support. of the 2A5 output tube. This latter tube is a power The set is now ready for wiring. Push -back wire should amplifier pentode of the heater- cathode type. The indi- be used for all wiring. The filament circuits may be rect heating helps to minimize hum, making this tube wired in first. The filaments of 5, 16, and 22 are wired preferable to the 47 type pentode. The 2A5 tube has an in parallel to the 21/2-volt filament winding of the power undistorted power output of 3 watts. With the recom- transformer. The center tap of this winding is grounded

144 RADIO -CRAFT for SEPTEMBER, 1933 to the chassis. If a pilot light is used, many other classes of interesting it should be wired to the 21/2 -volt short -wave transmissions. The circuit winding. THIS ALL -WAVE is regenerative for maximum sensitiv- Grid circuits are wired next. Note MIDGET ity. Three pentodes are employed, in- that the control -grid connections of the - cluding the new 2A5 power output 53 and 67 tubes are at the caps, as Improvements in midget receiv- tube. Change-over from one wave- indicated on the schematic diagram. ers usually mean only a change in band to another is accomplished by The socket connections for these tubes means of tubes. In this midget, however, a double -pole five -point are as follows: Looking down on the switch, connected to a new type coil socket, the two large holes are for the the improvements are real -the having a plurality of inter- connected filament prongs. Then, starting from receiver covers the short -wave windings. This set is compact, inex- the left filament terminal and going bands as well as the conventional pensive, and easy to build. around the socket in a clockwise direction, the terminals are cathode, sup- broadcast frequencies. pressor grid, List of Parts screen grid, and plate, The set is easy to construct, One .000025 -mf. variable condenser, respectively. Note that the suppressor has no special parts, and represents 17; grid terminal is connected externally One dual midway variable condenser, a radical (at the socket) to the cathode term- departure from the .0002 -mf. each section, 3, 8; inal. more conventional sets of the Two Acratest trimmer condensers, 5 Looking down on the socket of the same type. to 25 mmf., No. 2881, 3A, 8A; 2A5 tube, 22, the two large holes are One Find -All antenna coupler, 1; for the filament prongs. Then, start- RADIO -CRAFT is pleased to One Find -All R. F. choke, 18; ing from the left filament terminal present this, the first, description One Find -All all -wave R.F. coil -set and going around the socket in a clock- of an all -wave "cigar box" re- with tickler, 12; wise direction, the terminals are One Electrad 500,000 -ohm volume con- cathode, control grid, screen grid, and ceiver. trol, type RI -203, 21; plate, respectively. In this tube, con- One Electrad Truvolt 1,500 -ohm flexible nection between the sup- resistor, type 2GB 1000, 6; pressor grid and the cath- One Electrad vitreous ode is made within the tube. enameled resistor, 400 After the various grid ohms, type H -897, 24; connections are completed, One Aerovox .001 -mf. mica plate circuits are wired, condenser, type 1460, then cathodes, antenna - 13A; coupler primary, bypass One Aerovox .004 -mf. mica condensers, power supply condenser, type 1460, transformer to rectifier 15A; tube socket, and filter sys- One Aerovox .075 -mf. car- tem. The dynamic speaker tridge condenser, type output transformer and 281, 20; field coil connections are One Aerovox .002 -mf. mica wired to a four -prong plug, condenser, type 1460, 26, to conform to the con- 21A; nections at the socket, 25. Two Aerovox .1 -mf. car- Instead of using binding tridge condensers, type posts, antenna and ground 281, 7, 9; connections are brought up One A e r o v o x .0001 -mf. from below the chassis, us- mica condenser, type ing flexible wire. After the 1460, 14; wiring is completed, the Two Aerovox 9 -mf. dry tubes are inserted, aerial electrolytic condensers, and ground are connected, cardboard container, type and the speaker is plugged An under -view of the receiver. Note the smallness of the coils and their location. P5 -4, 28, 29; in. When current One Aerovox 25- is turned on, the mf., 25 -volt trimmer conden cardboard dry sers are adjusted a VOLu . C 20 CONTROL e 1 e ctrolytic for maximum 55 18 re- 0 irii, d- 2 A 5 e o n de n s e r, sponse on broad- e type PR25 -25, cast signals. The 23; set is 19 then tested 8A One 25,000 -ohm, out on the var- aá IZIA 12 16 21 22 / -watt metal- ó XSX x X ,,71"3A X x ious short -wave lized resistor, J t2 bands. 24 11; This little mid- ID l T3 13A One 500,000 - get covers the en- 11 ohm, 6 9 ISA / -watt tire wave band --T T -r metallized re- from 15 meters sistor, 14A; 550 to meters One 1 0- X 00,00 without changing TO EXT. ohm, / -w a t t coils. Hence, in GROUND 32 X 28, metallized re- addition to resistor, 19; ceiving conven- j25 U6111M, X17 One 1 megohm, tional broadcast- TO 110 v. 1/2-watt metal - ing, it brings in A.G. 30 33 T2.9 ized resistor, police calls, 15; - Atlantic 31 26 SPEAKER trans FIELD Two 10,000 -ohm phone calls, for- (Continued eign stations, and Schematic circuit of the set. There is nothing tricky about if to confuse fhe constructor. on page 167)

RADIO -CRAFT for SEPTEMBER, 1933 145 CONSTRUCTING A COMPLETE 26 -WATT DUAL CHANNEL P. A

A description of a complete portable four stage amplifier for P. A. work. This system is designed to operate from SYSTEM a I IO -volt A.C. power line, or directly from a six -volt LOUIS GANCHER* storage battery.

HISTORY always repeats itself the live -wire radio man will forever in every phase of industry, and it is, -the radio boom days of 1921 revere the fortunate day that he de- therefore, no great wonder that many to 1926 brought fame and cided to enter this new industry. Its radio dealers and Service Men turn fortune to many radio busi- profit making possibilities are really to P. A. work, which they find yields ness men. Right now, a new industry enormous and limited only by the in- a much more lucrative income than -that of P. A. amplifier sales and dividual's aggressiveness. the sale and repair of radio receivers. rentals -is in its embryonic stage, and A large number of new applications are found for public address systems A Modern P. A. System President, Coast -to -Coast Radio Corp The compactness of the modern P. A. system to be described has not im- paired its over -all efficiency, quality, or power output. In fact, the employ- 110 VOLTS,A.C. ment of high grade components and design and layout of the STORAGE SPEAKER AND CASE the careful TONE- SPEAKER AND CASE BATTERY system has resulted in the perfection CONT. a has the /PO W ER of P. A. amplifier that all OUTLET desirable features of a portable system, such as light weight, high output of good quality with fairly small tubes operating at relatively low plate voltages and an unusual overall economy of power consumption. Although present operating requirements might only call for exclusive use from 110 -volt A.C. light sockets, this system is the logical one to own, A C.EXCITER A C. PHONO a VOL CON? one at SPEAKERS MOTOR MOTORGEN. A.C. PHONO. for it enables to secure, any FOR MOTOR EXCITER CONTROL 26 W. AMPLIFIER POWER PACK later date, a suitable 6 -volt, storage - BOX UNIT battery- operated motor generator, which may be bolted to the chassis in Fig. A View showing the complete system unlocked. The tuner is not shown. the space left vacant. In the same

09 T2 53 CHANNEL N9 2 1, 73 e1.6 Gm NOTE C7.C8.C9.C10 .00035-MF. - OP WNEN EMPLOYING A C POWER OyHMS CIt,C12.C13 3, 4 MF 500V SUPPLY, GROUND C.7 RESISTOR BP C14,C13,C16. 3. 8 MF 500V. ON FILAMENT WINDING BPS ,I5 WHEN EMPLOYING BATTERIES, OHMS BP 2 GROUND ONE SIDE OF FILAMENT V4 ó.l49 BATTERY C6 o- s tOMF,35V- --t- RIO q4 PI oHMs 1.000 OHMS .5ONM 3w R4 C2 C4 37 0.25+IEG .02.F 37 02-MF 51 89 r 53 R7 INPUT o.25- C3 MEG CS $ MF Y IOMF,35V 35V RB 0.25- 0.3- V3+ MEG 71 1 L V2 MEG + _+ R5 1 . R9 0.25- Loy G T -Cl2 Ip00OHMS MF OHM$ T R3' / RII R13 C13 R2 / Cii `1,500 OHMS, 3W R12 / 10.000 ËG WNW CNt, G OMMS PLUG au PL 30.000 OPTIONAL FOR ONE OHMS TONE CONTROL + CH 35 l N ( ) -MF) (.00G T- r H2T FL F r GROUND yT CI4 Cls _i C16

Fig. I Schematic circuit of the dual -channel system using two type 53 tubes. Ground BP. 4 to BP. I.

146 RADIO -CRAFT for SEPTEMBER, 1933 manner, you can start with the motor generator alone, and then, later on, add the 110 -volt A.C. Power Pack. However, before discussing further 0. VY CD details of this system, it might be best ID ID ® to outline the series of articles to follow monthly. This series will describe at length the complete system, giving full constructional details on all the essential units that comprise a complete installation. Here is the ideal arrangement for a public- address system capable of meeting every application arising in the P. A. field, regardless of whether such applications require operation from a six -volt storage battery in an automobile, sound truck, boat (wherever 110 volts A.C. is not available) or from any commercial 110 -volt A.C. IA power line. Another exclusive feature incorporated in the design of this highly efficient system provides for the simple and rapid change -over from any one of the sources mentioned previously to any other.

Portable Inter- Locking Feature Fig. B An under -view of the -To The unique method of housing the Coast -Coast amplifier showing the location of all parts. individual units that comprise the complete P. A. is System meeting the ap- MICROPNONE proval of all P. A. Engineers, and is 110 V. .0 ! E shown FOR in Figs. A, B, and C. From Fig. 13 WATT 13 WATT CHANNEL SPEAKER. NE.1 C, it is clear inasmuch CHANNEL N2.2 that, as each N2.1 portable case and associated cover is exactly identical in size, and as the I 1 snap-on draw DUAL- SPEED -Y -J bolts and catches are all PICK -UP 26 WATT OUTNR fastened to each case in identical posi- AMPLIFIER- - CONTROL I WPM tions, it is possible to "nest" or "inter- -MIn e." a M01011 1 6V lock" BON any one, two, three, etc. cases 6 PHONVOLT C GEN POWER SPEAKER MOTOR 1BATOR PACK N2.2 together, thereby simplifying the (DUAL-SPEED) (A.C) 1LO V.,A.C. carrying around of complete systems. EYCITER I 1 Obviously, two men are required to FIELD FOR. I SPEAKER. conveniently I NE .2 carry three or more 6 VOL D.C. 11Ó V. amplifier units. i1 AND 110V.,A.0 AC 110 V.. A C 7 TUBE Separately removable handles are INCITER SUPERNET FOR TUNER. another feature. The illustration of PHONO. Fig. C clearly shows how a complete MOTOR. amplifier system -composed of the amplifier, phono. turntable, and two 6 VOLT + L- speakers -are inter -locked into one STORAGE 00 óúroitrt unified, easily transported compact BATTERY unit. The three great advantages offered by this system are: L=.7= ----f (1) Ability to change the size of Fig. 3 the system to suit any particular A block diagram of the entire system from microphone or turntable to the dual -channel output system. method of transportation. Thus the entire outfit may be interlocked into cases also retain the valuable inter- described. This tuner represents an one unified case (as illustrated) for locking feature and may, in themselves, advanced design, incorporating such auto or, .w use; it may be interlocked in be employed in pairs, forming a versa- improvements as automatic volume groups of two or three cases for carry- tile- purpose carrying case for housing control, inter -station noise suppression, ing by hand; records, cables, etc. visual meter tuning, push -pull power (2) Each of the P. A. components, Described in this article is the univer- detection, 10 k.c. tuning separation, ordinarily housed in a separate case, sally- operated, power amplifier deliver- four -gang oscillator "tracker," band may be separately removed and placed ing up to 26 watts of audio output. In pass pre -selection, and has a sensitivity at some remote point to effect proper the second article completing this better than 1 microvolt per meter. sound distribution or to provide for the series (scheduled to appear in next The control of the introduction of the twin class complete system from month's issue), there will be described B, 53 tube has heralded the advent of any strategic position. In fact, the the dynamic speakers equipped with most difficult of P. A. installations economically operated amplifier sys- are dual fields, permitting 6 volt D.C. and tems, wherein the plate easily handled by this system; 110 will requirements -volt A.C. operation; there also are low enough to permit (3) Each of the varied units may be be described the separately -removable the use of built, or purchased, separately to meet input "mixer" control box as well as low drain D.C. motor generators. present requirements, with the assur- the 110 -volt A.C. exciter, which per- Heretofore, the only other class B tube was ance that regardless of when additional mits operation of the 6 volt D.C. that capable of producing 26 units are built or purchased, the entire phono. motor from both sources of watts were two 59's, requiring 450 system will retain both its unified con- current. The universally- operated 6- volts of "B," at 125 ma. Compare struction and all of its portable fea- volt D.C. and 110 -volt A.C. super- that to the 53 tube, two of which also tures. The covers of the individual heterodyne receiver will also be fully (Continued on page 170)

RADIO -CRAFT for SEPTEMBER, 1933 147 THE DESIGN PRINCIPLES OF AN

ALL - PURPOSE TESTER

This article is a bit different from the average run of tester articles in that the author describes the electrical details of a commercial instrument. This article will give you an idea of how the brain of a chief engineer works.

35 .1 OHMS 9 FLOYD FAUSETT* 0100. .5M F. OHMS + S.56 =61V. PROFESSIONAL radiomen are OHMS - T- While the condition of radio tubes 5 V. IIIo ltov always interested in professional A.C:. may be easily checked with this tester equipment, is no test- sockets and there 10 K from the tube of operative ing equipment as professional in OHMS radio sets, are for K provisions made appearance as that which incorporates TO Tu6E testing tubes with separate A.C. power all of the essential testing elements 001-A TEST SOCKET supply potentials on a meter which in one compact design; such a tester O.C.METER, is provided with a colored quality dial may be conveniently carried into cus- OHMS -ß- OHMS 0 -A- divided for "Bad," "Doubtful," and tomers' homes for preliminary tests, Fig. I 'Good" classifications. This meter is or used in laboratories for the de- Fundamental elements of the meter circuit used in associated with a new circuit which tailed testing procedure required for the new tester. eliminates the necessity of a "bucking effecting necessary repairs and adjust- 25111E current" rectifier, so that the meter ments. It is the purpose of this dis- 9719.86 needle cannot back violently off -scale OMMS 356300 OHMS cussion outline the design principles 8595.67 when tube is removed from to 668.21 WES a a tube of a modern tester which completely OHMS OHMS testing socket before the tester is 90.000 514E6. fulfills these desirable requirements. OHMS turned "Off." This arrangement per- The rapid changes in the tube and 0-7000 200 OSMIO mits the radioman's customers to ob- circuit designs involved in new radio OHMS OHMS 500M serve the meter indications of tube developments have made it necessary 109.52 OHMS conditions in terms which they can that the design engineers of radio 50M understand, instead of referring to a testers anticipate such changes as far 5M chart of electrical terms which the as possible by designing equipment .00032-A r customers cannot understand. The new Oj p 96.6 OHMS 6AL+ -4.5V. -45V -250V. which is readily adaptable to test- OHM COMMO test indications are based on the prin- ing procedure. This has resulted in Fig. 2 ciples of the well -known transconduc- the development of the new "free Circuit of the ohmmeter ranges for values fo be tance (or mutual conductance) char- reference" point -to -point system of measured above 500 ohms. acteristics of amplifier tubes, and pro- current, potential, and resistance an- 2500V. visions are included for indicating .5 MI6 V alyses and tube testing, so that the 00032 50.000 OHMS shorted elements, against which the -A 250V. asks D.C. Mersa 50.000 OHMS is professional radioman naturally 100V. tube testing meter fully protected. whether or not the new equipment 330 OHMS 15.000 OHMS In addition to the usual tube test- 15.000 OHMS 25V. 10V. which is offered to him enables com- 7.500 OHMS ing provisions, a special cathode -heater 5000 2.5V. leakage circuit is incorporated plete "free reference" tests. OHMS 500 OHMS testing in this tester. The usual "cathode - Description of the Tester 2000 OHMS 1600 i 2.5M4 short inadequate 'OHMS heater test" is for This new portable laboratory is so 1000 OHMS practical requirements it is 10 MA because designed that any circuit may be used 3,333 i 700 OHMS seldom found that the resistance be- for reference purposes for potential DHM3 MA. 100 OHMS tween the cathode and heater elements or resistance analyses or for tube test- ' NOMA. is low enough to be indicated by such ing from the sockets of operative 300! i 20 OHMS MA. tests. It has, therefore, been found - OHMS radio sets by the operation of plainly 1133 OHMS advisable to develop a sensitive meter- 650 /' marked switches which are designed OHMS COMMON ing circuit for indicating leakages as especially for this tester. well as shorted conditions between the of the "free refer- The principles Fig. 3 cathode and heater elements. The ence" system of point -to -point analy- Circuit of the meter movement with The rectifie fundamental elements of this testing ses through an analyzing cable may be included. circuit are shown in Fig. 1A. compared to the principles of the subject of this discussion is, funda- The milliammeter which is used for modern telephone switchboard through mentally, a miniature switchboard to tube testing is also used, in conjunc- which any subscriber may be connected which all of the circuits of a radio tion with a small flashlight battery, with any other subscriber, and which tube socket are extended for any de- for a low resistance -measuring range is easily adaptable to changes in the sired measurement by connections up to 500 ohms, so that the meter list of subscribers. The fundamental made with plainly-marked rotary needle will be deflected about half switchboard principles are practically switches of a special circuit- breaking scale when measuring a 15 -ohm re- the same whether the connections be type, so that it is not necessary to dis- sistor. A resistor of unknown value, made manually or by dialing switches. mantle the radio chassis as is the case when measured on this range, is con- The portable laboratory, which is the when the usual point -to -point tester is nected as a shunt to the meter, so Chief Engineer, Supreme Instruments Corp. used. that the resistance calibrations range

148 RADIO -CRAFT for SEPTEMBER, 1933 from zero on the left end of the scale to a maximum on the right end of the scale. The circuit for the 0 to 500 - ohm range is shown in Fig. 1B. A circuit diagram of the ohmmeter ranges above 500 ohms is shown in Fig. 2. It will be observed that unknown resistors to be measured are to be connected in series with the ohmmeter circuits, so that the meter calibration for the "OHMS" scale reads from zero at full -scale deflection to a maximum at the left end of the scale. The variable ohmmeter, zero- adjust- ment rheostats for both meters are mounted on a single shaft, so that one control knob serves to adjust the ohmmeter functions of both meters. The 0/500 /5,000/50,000 /500,000 -ohm ranges are powered by a small 4.5- volt flashlight battery contained in the tester. The 0/5/25- megohm ranges are operated from the A.C. power supply system through a rectifier tube inserted in one of the panel sockets during the test. The ohm:.,eter ranges This "laboratory," the new Supreme Master AAA -I tester, permits "free reference" or point -to -point tests. are selected by a simple switching arrangement and may be applied through the analyzer cable to radio circuits without the necessity of using test leads or jumpers. The higher ohmmeter ranges are about five times as high as those obtainable with a meter of one milliampere sensitivity. The meter employed for these higher ranges has a sensitivity resistance of approximately 3,000- ohms-per -volt. A meter of high sensitivity is required for effecting the necessary compensation of crystalline rectifier characteristics for current, capacity, and potential measurements. The meter employed in this tester has a full -scale sensitivity of about 320 microamperes, Fig. 4 Here which is less than one -third of a mil- is the oscillator circuit used in the new Supreme Master AAA-I tester. liampere. The meter movement is shunted for D.C. measurements so D.C. potential and current measure- pacity of paper capacitors, provisions that the full -scale sensitivity becomes ments, in ranges of 0/2.5/10/25/100 /- are made for applying the 250 -volt 400 microamperes. Part of the re- 250 milliamperes and 2.5 amperes, D.C. output potential of the tester for sistance connected in series with the and 0/2.5/10/25/100 /250/1,000 and measuring the leakage current of elec- meter movement is composed of an 2,500 volts. The meter ranges which trolytic and paper capacitors, so that alloy which has a temperature coef- are used in radio tube socket analyses such capacitors can be discarded when ficient opposite that of the rectifier, are selected by a multi -gang rotary the leakage current exceeds one milli- so as to "balance out," or compen- switch, one gang being used for cur- ampere per rated microfarad. The sate, the effect of temperature varia- rent ranges and one for voltages. arrangement whereby capacitive val- tions on the rectifier. ues are directly indicated on a meter The Multimeter scale which is also A study of Fig. 3 used for A.C. and will show that The sensitive Multimeter is ideally D.C. potential and current measure- the total resistance of the meter move- suited for output measurements, ment combined with that of and ments is unique in radio tester de- the recti- provisions are made for such meas- signs, as no separate chart is required. fier and two series resistors is 5,000 urements without the use of trouble- ohms. A divided, or tapped, 3,333 - some output adapters which are dif- The Oscillator ohm shunt resistor reduces the effec- ficult to tive attach to tubes in close- fitting The oscillator circuits of this tester meter resistance to a value of shields. Output measurements are are shown 2,000 ohms. The current then re- in Fig. 4, and are tuned accomplished by inserting the analyzer by a tap switch arrangement so that quired for full-scale sensitivity is one plug into one of the power output tube calibration milliampere, so that the multiplier charts are not required, re- sockets and setting a switch for out- the frequency values being marked on sistors must have a resistance of 1,000 - put indications. ohms- per -volt. Output measurements the panel. Eleven fundamental fre- may be made within any of six ranges. quencies between 130 and 1,8'i5 kilo- By the use of a very sensitive high The 3,333 -ohm shunt resistor of the cycles are provided, with a tuning resistance meter circuit, the resistance Multimeter is also tapped for three ca- signal in each of the 20- meter, 40- variations of the rectifier, owing to pacity- measuring ranges of 0/0.01/- meter and 80 -meter short -wave bands. temperature and current density va- 1.0/10 microfarads for direct read- The oscillator may be operated with riations, are made a comparatively ings on the 100 -scale of the meter. either A.C. or D.C. power supply, and negligible factor when compared to These taps are not indicated in Fig. is completely shielded with a variable the total resistance values of the met- 3. The capacity measurements are output attenuator. er circuits. This circuitual arrange- made in series with the ordinary A.C. When operated with A.C. power ment enables a universal single -scale power supply system. In addition to supply, 100% modulation is auto - calibration of the meter for A.C. and these facilities for measuring the ca- (Continued on page 173) RADIO -CRAFT for SEPTEMBER, 1933 149 QUALITY IN AUDIO AMPLIFIERS

The author describes below a novel audio amplifier, used in a commercial receiver, which makes use of the new 2B6, described elsewhere in this issue. Two output tubes are used, each feeding into a separate audio channel.

W. H. HOLLISTER*

IT IS an underlying trait in human Lincoln, like other custom -built sets, was necessary in order to, eliminate nature to follow the common herd. has been catering to the appeal of the additional stages of amplification with Radio manufacturers are today so exclusive who want the best in music their attendant distortion. busily engaged in imitating each and DX. The audio system is the best A quick summary of the existing other that it is not surprising that the that the design of present-day tubes tubes will indicate their shortcomings. average radio set, instead of being the makes possible. However, an ever in- The type 45 tube in class A delivers marvelous musical instrument it should creasing number of inquiries and re- only 1.6 watts, and 35 r.m.s. volts be, has degenerated into a "cigar box," quests for something new and better must be applied to the grid for this which cannot cover the eight and a half in sound effects and tone led Lincoln power; it is evident that the power octaves that are possible in the audio engineers to search further for the un- sensitivity is low and additional stages spectrum, and that are necessary for usual and exceptional in tonal repro- would be required. The type 50 tube, the production of good music. duction. This search extended over of course, was not considered because who once took pride the greater part of the last year, and of the high plate voltages necessary Manufacturers make in the quality and tone of their prod- has finally terminated in the develop- for its operation, which would ucts hang their heads in shame as they ment of the new Bin -aural Duo -channel necessary the use of expensive trans- look at the red figures on their books audio system. This is not a trick name formers, condensers, and rectifier tubes, after a year in competition with "cigar designed to arouse your curiosity; so that the list price would become al- box" manufacturers. rather, it is an exact description of most prohibitive; then, too, the power This tendency toward extreme econ- what this system accomplishes: "Bin- sensitivity is low, requiring 60 r.m.s. omy and small size has brought about aural" means to hear from two direc- volts applied to the grid to secure the a rapid development in the tube art. tions, and "Duo-channel," as its name rated power output. The new 2A3 was Tubes having tremendous amplification implies, means two channels. also tried out and discarded because at R.F. and I.F. have been developed, However, the outstanding feature of of its internal construction, having a but practically little or nothing has this new system lies in the use of a new multiple filament; furthermore, it re- been done toward the development of super -power output tube, which deliv- quires 42 r.m.s. volts for rated output, tubes for the audio end of the set. ers four watts at less than five per and has a very high plate current -60 The commonly used pentode is famous cent distortion. The realization of this ma. This tube is rated at 3.5 watts. for its high distortion, but is used be- new Bin -aural Duo-channel audio sys- A study of the characteristics of the cause of its high gain. The distortion tem was made possible largely through new 2B6 tube will plainly indicate why is not so noticeable when the frequency the use of this new output tube, the it is superior in every way and why it range covered by the small speaker 2B6. A study of its characteristics was selected: rated watts output, 4 and baffle area is only about 25 per will indicate why this is the case. watts; total plate current, 44 ma.; cent of that possible; but when used (See article on this tube elsewhere in r.m.s. input volts to the grid to secure with a large, well designed speaker and this issue. Editor) First of all, at rated watts output, 24; plate volt- baffle, the objectionable harmonics least four watts output was required; age, 250; plate battery, 274 volts; per make its use prohibitive. second, triode quality was imperative; cent distortion, less than 5 per cent. third, a greater power sensitivity than By less than 5 per cent, we mean that be- President. Lincoln Radio Corp. was possible with any existing triodes at onlp 4 watts does the distortion come 5 per cent, and that at less than 4 watts, the distortion is less than J 0OwcR per cent. WUNDERLICM .5 -MP 56'3 IN PARALLEL 256 OETECTOR T1 OUTPUT Using the 2B6 YOL. CONTROL LO WATTS: / TRIODE QUALITY The study of Figs. 1 and 2 will ,T2 50.000 0.25 - plainly indicate just how this tube is 014MS MEG. circuits. In Fig. 1 used in two different LP 1 the two type 56 tubes are connected .004- / MF in parallel to increase their power ti handling capacity and, also, to reduce 1 MF. 2.700 DMMS 1 ML their plate impedance which is normally quite high. This latter adds TO IMF. 50 MF OMMs LOUD- very materially in the transformer de- SPEAKER_ sign for low frequency response. The LOW FREQUENCY 5+ 280 V y transformer, T1, is a COMPENSATION AT LOW /VOLUME push -pull input specially designed transformer having MIGM FREQUENCY RISE AT 4.000 the rising characteristic from 20 to CYCLES COMPENSATES FOP. SELECTIVITY, RUT SHARP CUT OFF ASOVE 4.500 4,000 cycles, as shown in the figure. It CYCLES ELIMINATES NOISE is extremely good at low and high LOO 1000 4.000 10,000 high -frequency rise FREQUENCY frequencies. The compensates for the extreme selectivity Fig. I of the Lincoln receiver. Incorporated A circuit illustrating one manner in which the 2116 tubes may be used. for SEPTEMBER, 1933 150 RADIO -CRAFT in the volume control is a low -frequency compensator to make up for the deficiency of the ear on low frequencies TRIODE CLASS A AUDIO SYSTEMS

at low volume. The high frequency Many a good receiver was made obsolete when the pentode and class B tubes cut off at 1,500 cycles eliminates noise, were first announced. They were made obsolete simply because new tubes were hiss, etc. available, and not because the new tubes made reception any better. During the This is a big improvement over the past few months many reputable manufacturers have returned to the triode. class A standard design, but by no means com- systems, and have discarded entirely the pentode and class B output tubes. pares with the new Bin -aural Duo - The general censensus of opinion among these manufacturers is that pentodes channel system which is shown in Fig. are good where high power /sensitivity is desired; class B systems where economical 2. Reference to Fig. 2 will show how operation, such as in portable sets, is required; and triode, class A audio systems the two channels split at the detector where high qualify is essential. plate circuit into a high and low chan- This article by Mr. Hollister treats the audio system used in his latest receiver, nel, being roughly divided at a thou- and is self -explanatory. sand cycles, which is the apex of the average ear-pressure curve. Each of these channels operate directly into its own speaker, and each speaker is de- and fundamental than any other con- eign broadcasts, but how? Of what signed for the best reproduction of the tribution. As one well -known engineer use is any receiver if the reproduction frequencies above and below a thousand so aptly states: "It is no trick to de- produced by its operation is not enjoy- cycles in their respective channels. It sign a receiver which will receive for- able?" can readily be seen, therefore, that exact adjustment of the bass or treble may be secured for any ear under any N c vol. CONTROL conditions, as the entire level above or 56 below a thousand cycles is raised or 05 F 05-MF lowered at the will of the operator. WINDER 25/ + LICH `EC ,,, 50.000 Many startling and beautiful effects OIEC,CR OHM5 may be secured by placing of the the 25. bass and treble speakers in different MEG HIGH FREQUENCY 1MF CHANNEL locations in a room so that a spread, 1 ur 1700 1 000 CYCLES UP diffused, or orchestral effect is secured; OHMS L.F vet. CONTROL the sound coming from two different 1 MF directions and in the two different S0,000 halves of the frequency spectrum creat- iF -- OHMS 1 MF ing a naturalness not heretofore pos- ós zs- sible. Likewise, it has a wide applica- iOHMS .25- 8.000 tion in the tuning of short waves, a, MEG OHMS LOW FREQUENCY 1 MF excessive noise or interference may be . 1MF CHANNEL 2.700 1,000 CYCLES DOWN diminished by reduction of the high - SO MF frequency range. OHMS B+ A strange paradox exists today. Broadcast studio managers bend every z GRAPH SHOWING APPROXIMATELY ul effort for the production of the entire MOW LOW AND HIGH REGISTER. MAY SE CONTROLLED, WITH EAR astioqiimm 14 F audio -frequency spectrum, and their CURVE DOTTED IN AT VARIOUS ,,, L o RESPONSE RESPONSE use of the highest type of orchestra VOLUME LEVELS n and vocalists seems to be an empty f0 loo 1000 10.000 100 000 gesture when one views the "two by FREOuENCV four" boxes now displayed as receivers. It has long been Lincoln's belief that Fig. 2 A circuit superior to that of Fig. I, and which is adaptable to twin -speaker operation. The response is music is more necessary and lasting adjusted to suit the selectivity of the R. F. stages.

FEATURES OF A MODERN 50 KW. STATION THE General Electric Company is installing at South transmitted by the service telephone excepting that the fre- Schenectady, N. Y., one of the most modern 50 kw. broad- quencies present include those in the approximate range cast transmitters in the United States. This transmitter from 30 to 10,000 cycles. The signals arrive at the trans- is designed for improved operating characteristics particu- mitter building via a telephone wire line which is specially larly as regards frequency stability, quality of transmis- adjusted and balanced to permit the transmission of all sion and continuity of operation. Many of these improve- these frequencies without discrimination. This is necessary ments are being incorporated as a result of the company's to insure that the full range of essential frequencies is experience in operating and maintaining broadcast trans- made available to the radio audience. mitters for the past ten years. The company also has wide At the transmitter building the signals are sent to the experience in the commercial field. This experience has transmitter control room where audio control, metering and been continually used as a basis for continued improve- amplifying apparatus is located. Here the signal is ampli- ments up to the present time. It has been the company's fied to compensate for the losses sustained in the telephone policy to incorporate new design features at WGY for line and sent on to the transmitter proper. thorough operating tests under actual service conditions The signals next pass through a power amplifier to before such features are included in commercial transmit- first stage of which employs a 50 watt tube. The sec- ters. This policy has been applied to the new transmitter ond stage consists of two 250 watt tubes operating in and it is confidently expected that many important improve- push -pull. After passing through this stage, the audio ments will result. signals attain a voltage level equivalent to ten times the It may be interesting to follow the audio signals which voltage of the ordinary lighting circuit. The power are sent out from the studio for transmission to the radio developed is greater than that r e q u i red to o p e rate audience. three ordinary radio r e c e i v e r s. In the above audio These signals consist of electric currents similar to those (Continued on page 174)

RADIO -CRAFT for SEPTEMBER. 1933 151 PHONE-TIP FIL. CENTER TAP CONNECTORS RESISTOR NEW ADAPTERS FOR MODERNIZING CONTROL GRID EQUIPMENT !II RADIO MANMIW. CONTROL ÌÌÌk GRID CLIP In view of the availability of adapter "blanks," there are de- F10 i FIG.2 scribed below twenty -two new adapters especially useful FIL CENTER 62 TAP RESISTOR for using and testing new tubes in old sets and test instru- !c ments. F. L. SPRAYBERRY*

EVERY time the Service Man New Set Adapters 62 changes his testing equipment, or Now, for some of the very latest obtains the required number of adapters. No. 9G1T, Fig. 1, is a unit adapters, along comes another which Service Men have long wanted. flock of new tubes to be dealt with. As It permits an oscillator, microphone, Fl 0.3 one Service Man has expressed it, his phono pickup, etc., to be connected in test equipment is "just one piece of ap- series with the control -grid circuit of FIL CENTER is " TAP RESISTOR uaratus that never paid for -in- a screen -grid tube. To use this adap- stallments are always due in the form ter, remove the CG clip from tube and of adapters and other additions to the attach to CG stud on adapter. Then, test apparatus. However much new place the adapter CG clip on CG of tubes may be needed by the set indus- tube. Finally, connect microphone, try, to the Service Man they are just pickup or other device to the phone tip another evil. To the writer, therefore, connections on adapter. it seems that the only thing to do is to So much for a "convenience" adap- make the best of conditions, and keep ter. We will now describe a few adap- our test equipment up to date in the ters that the Service Man may use in most 3 convenient and inexpensive man- demonstrating to a set owner the actual ner. improvement which may be effected in A series of articles by the writer, his receiver by incorporating one or on the subject of adapters, appeared in more of the new types of tubes. FIG. 4 the October, November, December, No. 964KSPR, Fig. 2, permits the FIL CENTER 1932, and January, 1933, issues of use of a 2A5 tube in a 45 socket. Place GTAP RESISTOR RADIO- CRAFT. The purpose of those ar- adapter in the 45 socket of the receiver MEDIUM GS 61 r SEVEN ticles was to help the Service Man and then place tube in adapter. After K 7)P choose the adapters for his test equip- this, you are ready to use the 2A5 tube ment so that tests might be made on in place of a 45. H4 new tubes and circuits. The present No. 965GKR, Fig. 3, permits the use article is intended to cover some of the of a 2A5 tube in a 47 socket. more recent adapters which permit the No. 974GGR, Fig. 4, permits the use use and test of the new tubes in old of a 59 tube in a 45 socket. Remove receiver circuits and test equipment. 45 tube from socket and insert adapter We suggest that you read this article in socket of receiver. Then place 59 through carefully, if you are interested tube in adapter and operate the re- in keeping your equipment modern. ceiver in the usual manner. Sprayberry Radio Data Sheets No. 975KSPR, Fig. 5, may be used FIG 5 GRID CLIP GRID CLIP G G 0 0 G, 62 K P Pr

GRID STUD

P F

FIG.6 FIG.7 FICa.8 FIG.9

152 RADIO -CRAFT for SEPTEMBER, 1033 ADAPTERS We suppose that everyone knows of the new tubes and circuits that have appeared during the past few months. "What shall I do with my test equipment ?" is the cry. Of course, if you can afford it, buy new ones; but if the wolf has been making scratches on your already dull door, then use adapters.

FIG 10 FIG 11 in any receiver to replace the 47 tube Table B GRID CLIP- -a. 6 with a 59 tube. The adapter is in- Type Tube Fil. Volts G serted in the 47 socket and the 59 tube A22 15 placed in adapter. This adapter has the correct center -tap 14 14 filament connec- 291 tion taken from the cathode circuit so 12.6 that bias is automatically provided. Table C While these power tubes may im- Type Tube Fil. Volts prove the quality or volume of repro- HZ50 12.6 duction in models, older set the Service 12Z3 12.6 Man is primarily interested in means 25Z3 25 for determining the relative worth of i F vacuum tubes. The following descrip- 25Z5 25 tions of new adapters for test purposes, 262A 10 therefore, are given. 96 10 FIG 12 No. 950TR, Fig. 6, may be used to bring any old tube tester up to date. Testing New Tubes The only requirement is that the tube No. 964GL, Fig. 7, is used to test tester must have a socket regularly the 2A6, 55, 75 and 85 tubes in almost used to test the type 24 tube. This any type of tube tester which has pro- unique adapter incorporates a trans- visions for testing the 45 or 50 type former winding and three "composite" tubes. This adapter tests the triode sockets. These sockets are made so as section; it is rarely necessary to check to take four- five and six -prong tubes. the diode section. When testing the The table given below lists the tubes 2A6 or 55 tube, place adapter in the that can be tested in sockets A, B and 45 socket and connect the control-grid C of the adapter. leads. When testing the 75 or 85 tubes, place adapter in the 10 or 50 socket Table A and connect the control -grid leads. Type Tube Fil. Volts No. 975 -AB7, Fig. 8, is used to test AE 12.6 the 2A7 and 2B7 in the 24 socket of FIG 14 FIG.15 A26 15 tube testers. This adapter will also 6A7 A28 test the and 6B7 in tube testers 15 employing a 36 socket. Place adapter G3 Gt A30 15 in proper socket and test tube in the K_ A32 15 usual manner. A40 15 No. 975 -6F7, Fig. 9, is used to test A48 15 the 6F7 tube in the 36 socket of any 17 tube tester. Place adapter in the 313 14 socket and make tests as if you were 18 14 testing a 36 tube. Make sure that the SERIES 43 25 control -grid circuit of the adapter is SOCKET 48 30 correctly connected before tests are 272A 10 made on the tube. M RA1 15 (Continued on page 175) FIG.16 FIG.17

P7 K K K1 P2 K

P1 P2

S.P.O.T

SPOT

I II PZ

Fi i

FIG.22 FIG.21 FIG.20 FIG.19 F1G.18

RADIO -CRAFT for SEPTEMBER, 1933 153 DESIGNING AND CONSTRUCTING DIRECT - COUPLED A. F. AMPLIFIERS

This article is the second, and final, of the series giving PART II complete theoretical and constructional details of direct - coupled amplifiers.

L. M. BARCUS

IN last month's issue of RADIO -CRAFT we touched briefly upon the construction of a two stage amplifier and gave enough details of the calculations to enable anyone to design his own particular amplifier. It was remarked, at that time, that the two stage amplifier had too small a voltage gain to have extensive uses, and that the plain, three or more stage circuit had drawbacks which limited its applications with ordinary materials. Therefore, this article will touch upon more elaborate types which give high gain and output without demanding other than standard components in universal use today. In order to derive the benefits of multi- stages without resorting to special Typical converted receiver using the circuit of Fig. 4 constructed by the author. apparatus in the voltage supply -which would mean high cost and possibly of the first -audio socket in the receiver 160 volts for V2 of which about ten trouble -a double powered amplifier is not individually wired, the power will be required for its bias. was developed, as shown in Fig. 4. By tube winding is usually adaptable, pro- For those desiring a straight ampli- using this method, the number of vided that a 45 tube is used. In case fier of the type in Fig. 4, for P. A. sys- stages may be extended indefinitely 5 -volt filaments are used, the voltage tems, phonographs, and the like, the without relying upon excessively high may be dropped to 2% volts by suitable only changes are in the first stage potentials; in addition, it does away resistors or, if the winding is center where the proper tube is substituted with some of the bias bypass condens- tapped, one -half of it may be used. for the 55 and means for its bias taken ers, which naturally results in an addi- As a general rule, any audio trans- care of as explained previously. If four tional advantage- better tone quality. formers in the receiver may be used as stages are wanted, the second power The layout of Fig. 4 is the one pre- audio chokes in the revamped set. The section can be designed to accommodate ferred for all receivers, including tele- primaries and secondaries should be another tube between V2 and V3. The vision. Outside of the power units, wired in series to obtain the best re- effect is, in general, that of two, two there is only one audio bypass condens- sults. It is preferable, however, to use stage amplifiers placed in series. er employed. This gives the lower fre- good audio chokes if the added expense It must always be remembered that quencies a chance to show themselves, is not objectionable. the second power unit is at a very high and their strength and clarity are The removal of the heavy drain of potential above ground and its parts amazing. Yet, there is absolutely no the power tubes from the tuner power must be insulated from the tuner chas- trace of the hollow barrel effect usually pack will necessitate readjustments of sis, or first section. For this reason, associated with receivers that produce the voltages. In some cases, particu- it is always preferable to build it as an the lower notes by artificial tone con- larly those where the power section and individual unit in conjunction with the trol methods. speaker are separate from the tuner, it power tube and speaker. For Service Men or others who desire may be advisable to use the new power The fact that a bleeder current flows to remodel old receivers whose tuning supply for the tuning section and to re- through the series of resistances in Fig. units are satisfactory, the layout of tain the power section of the set as it 4 does not complicate the calculations Fig. 4 is especially convenient. It per- stands. A few changes are necessary to any extent. The only requirement mits the use of practically all the parts to adapt such a unit for its new pur- is to add the desired bleeder current to in the receiver, and only requires the pose. the normal tube currents in each case. addition of a power transformer, a filter Whatever voltage supply is used for In Fig. 4, a bleeder current of 10 ma. choke, and two filter condensers. Be- the tuner, it must be capable of giving was used in the calculations. The 5 cause the power stage requires but a fairly high potential, since VI and ma. of V2 and the 10 ma. bleeder cur- 250 volts, the 50 -volt bias being ob- V2 derive their operating voltages, in rent thus flow through Rl, while only tained from the first power unit, and addition to the bias for V3. 300 10 ma. passes through R2. V3, of because the current drain is small, the volts is usually sufficient for this pur- course, has no bearing on any of the power transformer may be of any of pose. As 50 volts are required for V3, current flows, being an entirely sepa- the now obsolete types. They all have this leaves 250 volts to be divided be- rate unit. a 2%-volt filament winding which is tween VI and V2. Inasmuch as the tri- Choke 2 of Fig. 4 may be mounted on suitable for the 45. ode half of the 55 is diode biased, 90 either unit, depending entirely on me- The second audio stage (a 27 or 56) volts on its plate will tend to accommo- chanical convenience. However, three requires a separate filament winding date the inequalities of bias and give lead wires are necessary when it is since the filament is at a much higher better results than if the maximum po- mounted on the power tube unit, the potential than ground. If the filament tential were used. This will leave some leads running from the points marked '54 RADIO -CRAFT for SEPTEMBER, 1933 DIRECT -COUPLED AMPLIFIERS Look through your files of diagrams of commercial radio receivers and notice how many of them use transformer coupling in the audio stages -practically none. Resistance coupling is at the wheel, and it certainly is doing its stuff. Direct coupling is an improved form of resistance coupling; it has all of its advantages and few of its disadvantages. In fact, it's the only "perfect" coupling to use.

with an x. R1 should preferably be beauty and mellowness of tone. It will amplifiers will become la mode in a placed in the second unit with choke. make any speaker sound like a new short time. The technician is referred thing; yet that vital part should be to the following articles in past issues One for the Experimenter chosen with the greatest of care, and of RADIO-CRAFT, for interesting data on For those of an experimental turn of one should be sought which is capable amplifiers of this type. "Bureau of mind, the circuit in Fig. 5 may provide of performing over the extended range Standards Audio Amplifiers," by S. R. an interesting and instructing amplifi- of frequencies. The input transformer Winters, September, 1929, pg. 112. er. The cost of construction is practi- should be carefully examined. Usually "Constructing the Loftin -White Ampli- cally the same as that of a two stage they are small and totally unfit to step fier," by M. W. Sterns, September. system, yet it has the added advantages down the lower frequencies. If nec- 1930, pg. 156. "A Direct -Coupled Pen- of much greater gain and output. essary, it may be wise to purchase a tode Amplifier," August, 1930, pg. 100. Unfortunately, the auxiliary power separate transformer of the best qual- "Servicing Direct -Coupled Amplifiers," tube is not directly coupled to the ity and of generous size. Further, the by Sidney Fishberg, January, 1932, pg. source of its signal input, but must cone should be so mounted that it has 403. "How to Build a Direct -Coupled make use of the usual stopping con- a wide range of unrestricted movement Type 45 Amplifier," by S. H. Burns, denser. However, this condenser is and is not stiff. Finally, a baffle -board December, 1930, pg. 354. preferably of a large size and the usual of generous size should be used, one Additional information concerning bypass condenser from the power tube that will properly bring out the lowest direct -coupled amplifiers, has appeared filaments to ground is eliminated, so notes. in the Information Bureau of past is- any impairment of tone is more than (Unquestionably, direct -coupled A.F. sues. Technical Editor.) counteracted.

The use of such an amplifier with Es. 135 V. Es 2513V. Is3.7MA. 0.5- EgÌ35V. Eq 50V. power tubes of high gain is somewhat R F doubtful, although it has been operated o MEG. IP. SMA. I Iv 34 MA. R.FC. S5 135V. 27 180+148 5 328.5V 45 OUTPUT with great success with standard low .r. 4 mu tubes, such as the 45. When used 300 l OHMS OMMS with a radio tuner, such an amplifier is MA. -s 3.7 S MA - Ì sometimes obstructed in its operation ..\ (K1 CK2 I by residual R.F. currents which go into L V 135+ 135V VI 1,1 V. I a regenerative cycle in the power 148.5V 328.5+ 50 stages. Such an action is easily over- 379.SV fi x x V I z come by the use of a small bypass con- R4 R3 vR2 denser from the plate of the first power 11.3 MA. 15MA. 10 MA. T I tube to ground. tsMA. While only a few circuits have been w 135 V. --.j -- 1.1 V-.- 12.4 V. -.. ..L lei .sv --1-148.5v,- u9470H14 970HMS eat OHMS 18150 OHM5 "RI I presented in these articles the system 3253 -+ OHMS of direct -coupling must not be con- s MF. ` strued to be limited to them. This cou- (EACH) t pling method can be adapted to prac- SECTION TO RIGHT tically any situation where superb tone OF DOTTED LINE 15 A SEPARATE UNIT is the chief factor. While the author K XV v has not actually constructed push -pull LS? POWER tst W 1QQ004 00 arrangements, there is little reason to UNIT doubt the success of complete systems. - P"'"1 The absence of bias condensers and the removal of other restricting elements Fig. 4 of the straight systems should result A double -powered amplifier circuit. See the photograph. in beautiful reproduction with tremen EP 180V 1 EG. stE5.5TO4 EP. 250V ED 250V. dous power. The cost, too, is very little TO Eg 13.5V MV 8E 5u15- E9 50V SPEAKER E9 50V more, since the same number of resist- IP a 5 MA. Ir 34 MA Iv 34 MA 45 45 ors would be used and only additional 27 chokes and sockets needed. In a push - pull circuit based on Fig. 4, - the full 180+13.5. wave rectification of the signals would 193.5V. be achieved by the use of twin 55 tubes, each feeding one side of the amplifier, or one 2B7 tube could be used with each diode plate operating into one half of 13.5V. the audio section. In closing, it is appropriate to stress the fact that any amplifier based on this system should be considered more I in the light of a delicate and precise 181.5 V. 48.5V. I z z musical instrument than as a soulless 13.5V. 63 MA 68 MA is 68 MA. I 2881 713 bit of apparatus. It not exacting in 200 OHMS OHMS OHMS its requirements and will perform F8+ miraculously over a wide range of values, but every additional care taken in Fig. 5 its construction is reflected in increased Here is a good circuit for the experimenter, as s,ggested b, the author.

RADIO -CRAFT for SEPTEMBER, 1933 155 THE ANALYSIS OF RADIO RECEIVER SYMPTOMS OPERATING NOTES

R. F. LAMBERT

IN MY prolonged experience with Zenith Model 60 rated in the chassis the white, 250,000 - various types of good, bad, and in- The owner of this model receiver ohm resistor which is generally to be different radio receivers, many complained of abnormal hum in the set. found in the later models. This re- unique and interesting problems This is a common complaint; a great sistor is connected across the grids of have been encountered. While some deal has been written, and numerous the second stage '27 type tubes which of these experiences together with suggestions offered as a cure for this are connected in push -pull. The usual data concerning them may seem ob- objectionable hum. This receiver hap- procedure was followed in installing vious and perhaps even superfluous, pened to be one of the older models, this resistor, but this change did not they contain, however, information and, therefore, did not have incorpo- result in any improvement. The hum which may be applicable to other radio persisted, and was just as loud and receivers afflicted with the same form as annoying as before. On all these of trouble. For that reason, the ex- models it is to be observed that the periences related below may prove to THIS DEPARTMENT wet electrolytic condenser unit is fellow members of housed in a metal can which is made be of interest to There are various ways of presenting the radio fraternity. up of two parts, held together at the service information: first, we could sides outside of print the schematic diagram of a re- with four bolts. The Zenith Model 52 ceiver and give the values of all parts; the can and the part of the chassis An interesting case of intermittent second, we could print, not only the on which the electrolytic condenser operation was encountered in this diagram and values of parts, but a rests are painted; the inside of the can model. Very little, if any information discussion of the circuit itself, and is not painted. Furthermore, this can could be obtained from the owner as leave the trouble hunting to the Serv- is fastened to the chassis with two to the time or duration of these pe- ice Man: third, we could list the symp- bolts; the idea being that by clamping In an toms, troubles, and remedies exactly the sides of the can tightly to the con- riods of intermittent operation. as found by men in the field. effort to determine the exact location denser and by tightening the bolts a No one method is complete in itself; good of the trouble, the chassis, automatic to be complete, service data must con- electrical connection to the chas- tuner, speaker, and the power pack tain a compilation of all three of the sis will be made. were removed from the cabinet. The above methods. The first two methods Too often it will be found -as was usual test and search for intermittent are presented in the Radio Service discovered in this case -that the top bypass Data Sheets, and the third method is portion of the lugs on the can, where short circuited resistors and treated was conducted; but nothing in this department. the heads of the chassis bolts are rest- condensers By splitting the material up into two ing, painted could be found verify our suspicions are thickly and, of course, to sections, it is possible to print much a good electrical connection does not "so- often -found- more than would be pos- directed against these information exist, because of imperfect contact be- guilty" components. sible if everything were bunched together. Then again, sometimes, men tween the bolts and the chassis. By While testing the receiver, it was scraping off this accumulation of paint, discovered by tapping the metal prefer only the schematic; while at that other times they want a discussion. and tightening up the chassis bolts chassis lightly with a hammer or by In any event, this material is avail- while holding the can in place, the ab- shaking the chassis reception could be able for your reference -make the normal hum was entirely eliminated. obtained; but the slightest jar would most of it. See Fig. 2. make the receiver inoperative again. This effect indicated that a loose con- Montgomery Ward 62 -080, 62.090, 62 -100 nection existed somewhere. A system A frequent cause for a blown filter atic search was now instituted in order condenser in these models is generally to locate the guilty member; but the 1st due to loose plate- spring contacts in the rectifying tube socket. This con- results yielded nothing. The set, which ANT L A had been tested with the chassis upside- 6 O O O r dition may be recognized by a loud down in order to get at the wiring, was roar in the speaker, accompanied with now turned right -side up, so that the Ll a mechanical hum; otherwise the set rear of the chassis was visible. In INTERMITTENT RICE/110N WE 10 IMPERFECT CONNECTION NERE is completely dead -as far as broadcast reception is concerned. The me- looking at the rear of the chassis, at- Fig. I A tricky poor connection caused trouble in this chanical hum is due to the fact that tention was attracted to the short pig- Zenith model 52. which goes from the the socket plate- spring contacts do not tail connector grip the plate prongs of the rectifying aerial post to one of the long- or short - tube firmly, thus causing the elements aerial terminal jacks. Upon close ex- in the tube to vibrate violently. This amination, it was discovered that an effect can easily be felt by touching imperfect connection existed inside the the rectifying tube with the fingers. hollow end of the metal pin tip, which The reason for the blown filter con- proved to be the reason for the inter- denser, which is connected across one mittent reception in this receiver. A of the type 80 filament terminals and typical case of plenty of rosin and no ground, is due to the intermittent con- solder. It was now only a matter of tact between the tube plate prongs and HUM DUE TO ACCUMULATION a few minutes to heat up the metal OF PAINT HERE the socket plate- spring contacts, caused pin tip, drop solder into the hollow by vibrations of the tube; it is not due end, and then push in the wire to com- Fig. 2 to a low -voltage rating of the dry elec- Another case where pocr contacts caused trouble; plete this job. See Fig. 1. this time in a Zenith model 60. trolytic condenser, as was first sus-

156 RADIO -CRAFT for SEPTEMBER, 1933 pected. The normal voltage across and first audio stages. Low plate and and aerial connections, and the tubes these points, 80 filament terminal to grid voltages will be indicated for the were carefully inspected and tested and ground, is about 325 volts. Because of type 45 tubes. The shorted condenser found to be normal. This set has a the intermittent contacts between the is one of a bank of six condensers con- "range" control, which is nothing but a plate prongs and the socket- spring contained in the filter -choke cell. The small variable condenser held in place tacts, the current will, at times, be pre- leads are easily discernable by inspec- by a bracket on the chassis. In search- vented from flowing, and a high voltage, tion of the blue leads, after the Bake- ing for the cause of the fading, I exceeding the maximum working volt- lite resistance strip has been removed. caught sight of a short piece of wire age, is built up across the condenser, For replacement, use a 0.5 -mf. con- which was wrapped around the rotor and a break -down generally occurs. As a denser rated at 600 volts. Simply cut shaft of the condenser; the other end precaution against a break -down of the the defective section out of the circuit, was cold -soldered to the chassis. At replacement condenser, an 8 mf. dry connect one lead of the external re- one time this wire evidently was in- electrolytic unit rated as 500 volts, is placement condenser to the blue lead tended as a pigtail connection from inserted. It is first advisable to cor- you have clipped from the shorted unit, ground to the rotor shaft. A very rect the trouble at the socket by bend- and ground the other lead. A con- splendid idea if properly installed. The ing the spring contacts in order to in- venient place to mount this condenser wire which had been cold -soldered to sure a better contact. In some cases is on the side of the large filter con- the shaft was now hanging loose be- it has been found necessary to replace denser, between the metal straps hold- low the shaft and between the stator the socket with a different and better ing this condenser in place. One of plates. Vibrations transmitted to the type in order to remedy this trouble. the straps can be used for holding the set from slamming the refrigerator new condenser securely in its position. door were evidently powerful Atwater Kent 46, 47, 53 enough to cause this wire to move against the These receivers have their filter con- Fading and Noise in Philco SI I stator plates, thus providing a direct densers contained in replaceable cans The complaint on a Philco 511 was path to ground for the incoming sig- in the power pack. This arrangement that the set would perform normally nals, as shown in Fig. 3. makes it a simple matter to replace until the door of a refrigerator in the This wire was removed. A small the condenser unit in case of shorted kitchen was opened and then closed; the hole was drilled and tapped in the end units. However, it seldom happens reception at that moment would drop of the condenser shaft. A lug was that more than one of them is found to to a point where it hardly could be fastened to the shaft by means of a be shorted, and in most cases, it is heard. Opening and closing the door a screw, and a new flexible insulated generally the one connected across the second time would, at times, bring the wire was soldered to the lug on the center tap of the output transformer set back to normal volume; at other end of the rotor shaft; the other end and ground. In this case an externally times it would not. Walking hard on soldered to a lug provided on the chas- connected replacement condenser will the floor and slamming other doors had sis. This procedure eliminated the fad- do very nicely. no effect on the volume. ing signals on this set. After the two terminal strips, the The A.C. plug and cord, the ground Excessive hum in these receivers - condenser unit retaining spring, and provided it is not due to defective the supporting strip have been re- parts-can be greatly reduced, if not moved, you will notice three condenser almost entirely eliminated, by placing leads colored blue, green with yellow a metal shield can over the detector tracer, and white. The end connections tube and grounding the can to the of these wires are embedded in an in- chassis. sulting compound which covers the Majestic 103 condenser unit, the choke, and the output transformer In another case-a Majestic 103 radio unit. Cut the white and phonograph combination-the set lead in the middle and remove part of was noisy and faded suddenly. At the wire insulation Fig. 3 from the other ends. times, the reception would be fine; but Solder a short piece of wire to the stub A cold -soldered ¡oint, a loose connection, and a Philco model SII. suddenly it would die down to a whis- emerging from the condenser unit and per, only to come back again as connect this wire to the black, ground just Sie R. F. strong as ever. From past experiences wire; connect the end of the other with white wire the same type of set having prac- to the positive side of a 2 tically the same trouble, con- mf., 400 volt, it was dry electrolytic condenser, cluded that the trouble must be in the and insulate the joints. The other end DEFECTIVE RESISTOR chassis. After much time wasted in of the condenser connects to the black, ground testing tubes and checking the receiver, lead. There is ample room to only to discover, with keen disappoint- lay the new condenser on top of the OHMS 1110 OHMS SCREW TOPPED INSULATINGt20 INTO ment, that everything seemed to be reassembled PAPER terminal strips in order to normal, it was decided to take a good keep it away from the heat generated look at the ground in the power transformer. and aerial lead -in II RESISTANCE STRIP ¡HIGH wires, and to test them for a possible 2120 OHMS 1110 OHMS RUBBER Ste+art- Warner 950, 960 short circuit; and here is an example CNASSISI 1.14I6H RUDDER DUSHIN6S ¡ BUS HDEING where a simple fault can create a When you find one of these sets com- major pletely disturbance. dead except for a slight speaker The visible parts of these two leads hum, the first thing to suspect is the Fig. 4 consisted of good insulated wires car- bypass The resistance strip in Stewerf- Warner condensers connecting the plate model %0 ried from the binding posts down and the screen grids of the types 24 receivers That "makes noise." and through a hole in the floor to the base- 27 tubes to ground. To determine ment. Close inspection of quickly if is these two this the cause of the set wires disclosed the fact that they were being inoperative, remove the detector spliced, tube, but not taped, directly under- quickly replace it, and note if a neath the floor boards. click is heard in Vibrations the speaker; the same caused the two wires to touch each procedure should be followed in the other momentarily, radio- thus causing tnc frequency stages. If no clicks signals to fade in and out. It may br are heard, it is usually a sure indica- worth while to mention that in future tion that the condenser is shorted. An similar cases the antenna and ground analyzer test will show no plate, no wires are always inspected before any screen grid, and no control -grid volt- Fig. S attempts are made to test the receiver. ages in the radio -frequency, The partially shorted condenser is still another detector cause of noisy reception. (Continued on page 172) RADIO -CRAFT for SEPTEMBER, 1933 157 97 Radio Service Data Sheet

GALVIN MOTOROLA MODEL 77, 7 -TUBE AUTOMOTIVE SUPERHETERODYNE (Self -rectifying Elkonode, separate reproducer, combined oscillator and first-detector, combined A.V.C. and second -detector, push - pull pentode output.)

This superheterodyne has a maximum shank screwdriver or ice -pick in one of the tension coils mounted on the dash or on the sensitivity of .025- microvolt -per- meter; the jacks of this receptacle and adjust up or bulkhead in the driver's compartment are maximum power output, with an input of 1 down for desired indication in window. likely to radiate to the antenna. The most microvolt -per- meter, is 4 W. This excep- (4) Replace the "B" supply. simple and positive remedy for the bulk- tional sensitivity figure permits the A.V.C. The following makes of cars have the head mounted coil is to remove it to the circuit to be designed to maintain the same positive terminal of the car battery con- motor compartment; it can usually be output power level with an input range of nected to ground: Marmon, DeSoto, Cadil- mounted on the opposite side, thus using 1.5 to 125,000 microvolts- per -meter. Refer lac, Pierce- Arrow, Dodge, Packard, Graham, the same mounting holes. Dash -mounted coils to RADIO-CRAFT Data Sheet No. 98, Galvin Plymouth, Studebaker. Auburn, Hupp, Frank- present a problem due to the built -in switch. Motorola model 55, for general aligning pro- lin, Rockne, Ford, Chrysler, Nash twin -ig- It is usually autflcient to shield the high - cedure. The "A" drain is 5.2 A. The plate nition. The following car makes have tension lead from the coil; to prevent leak- potential of V6, V7 is 210 V.; the "B" po- grounded -negative batteries: Reo, Chevro- age, slip loom over the lead before puttng tential of the remaining tubes is 175 V. let, Sluts, Willys- Overland, Cunningham, on the shielding braid. In some instances This receiver must be mounted either in Lincoln, Continental, Buick, Oldsmobile, Pon- it may be necessary to carry the coil shield- an upright or inverted position, but must not tiac, Hudson. Essex, Nash single- ignition. ing still further; a metal shield -can over the be mounted sideways as serious damage can Interference may be classed as chassis front of the coil is sufficient. result. When replacing the Elkonode unit, pick -up or antenna pick -up. The former is Note that merely because a portion of the make sure that it lies with the label either that interference which remains after the car is at ground potential (to D.C.) does down or up, not on its side. antenna connection has been removed from not indicate that it may not be a contribut- An antenna area of 9 sq. ft. is recom- the set. ing factor in noise pick -up. Thus, an in- mended for this set when installed in cars Chassis pick -up via the "A" lead may be terference- radiating unit may be in proxim- which permit the use of a roof antenna. eliminated by connecting a filter condenser, ity to a wire, rod, or other conductor which. The yellow "A" lead of the "77" connects to or, better yet, a Motorola Dome Light Filter, picking up this R.F. radiation, carries the any point on the car's electrical system -am- at the point of the "A" lead attached to interference to a point close to the antenna, meter, starter button or battery. the "A" battery of the car, whether at the where it is re- radiated to the antenna. It is essential that a definite polarity be battery or the starter. If chassis pick -up As the body and frame of the car act as maintained at the Elkonode. For this pur- still occurs, it is due to either of the follow- a return path to the battery for ignition pose a polarity changing switch is provided ing causes: (I) Defective condenser in the current, and as this metal is of a type which at the rear of the set housing. The polarity Elkonode system. Check by replacement. offers considerable R.F. resistance, it is sub- is indicated through a small hole at the (2) Cover of the set not making good ject to very strong eddy currents. The lower right rear corner of the set housing. ground to the set housing. Remove cover, metal corner post up which the lead of the If a red disc appears in the window which and clean lips of cover and set housing with antenna runs, and the metal frame around reads "-i- ground," it means that the "B" fine sandpaper. the top of the car are the most troublesome supply unit is connected for cars having the Antenna pick -up may be reduced or elim- sources of eddy currents. The antenna lead positive aide of the battery grounded; a inated by following the injunctions which should be correctly shielded, and grounded black disc, reading "- ground" indicates have appeared in previous RAD10-CRAFT Data to the metal framework at the top of the connection for negative -grounded batteries. Sheets, and in the book, "Automobile Radio car; the capacity between the shield and the Be sure to determine that the car battery and Servicing." by Louis Martin; additional lead -in sometimes is sufficient to cause eddy is grounded in accordance with the marking data follows. currents to be induced in the antenna -lead on the indicator. To change the polarity, In cars such as the 1982 Pontiac model shield itself by its coming in contact with proceed as follows: (1) Remove "B" supply V -8 car, where the distributor is mounted the dash, which frequently carries violent unit by prying with a screwdriver in the close to the wooden floor -board. it is some- eddy currents that are induced in the wire. slots provided on either side. (2) It will times necessary to tack copper screening Therefore, check to determine whether the then be observed that there are two recep- to the floorboards, grounding the screening noise pick -up is increased when the shield tacles on the rear partition -one on the left to the frame of the car. This prevents the is connected to, or insulated from the dash. and one on the right. The former requires distributor from radiating directly either to The 1931 and 1932 Chevrolets are good no adjustments; the latter may be moved the antenna, or to the antenna via the bodies examples of cars in which the shield should up or down in its slot. 13) Insert a small- of passengers or driver. Cars with high- be insulated from the frame.

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1933 158 RADIO -CRAFT for SEPTEMBER, Radio Service Data Sheet 98

GALVIN MOTOROLA MODEL 55, 5 -TUBE ALL -IN -ONE CAR SUPERHETERODYNE Self- rectifying Elkonode, built -in reproducer, combined oscillator and first- detector, combined A. V. C. and second -detector, single pentode output.) The maximum sensitivity of this receiver that the trimmer must be moved either in (3.) Re -route to primary wire from coil to is 0.75- microvolt -per- meter; the maximum or out to return to resonance, as indicated distributor, keeping it remote from high - power output. with an input of 5 microvolts - on the output meter (a 0 to 10 V., 1000 - tension wire: per- meter, is 2 W. The A.V.C. circuit main- ohms- per -volt voltmeter connected to the (4.) Connect Motorola Dome Lite Filter tains the power level within the input range A.V.C. circuit at X), it is an indication that to dome light wire at entrance of corner of 2.5 to 125,000 microvolts -per- meter. Re- Cl is not at the correct starting position post: fer to RADIO -CRAFT Data Sheet No. 97. for the initial setting of the service oscil- (5.) Shield high tension wire if coil is Galvin Motorola model 77, for interference lator. (If, for example, it is found that the mounted on instrument panel; elimination procedure; also observe the pre- trimmer must be screwed down. it is an in- (6.) Shield antenna lead -in wire from cautions stressed in this Data Sheet. The aication that the R.F. tuning condenser re- radio set to top of front corner post. Ground "A" drain is 4.5 A. The plate potential of quires more capacity at the low -frequency shield at both ends. if advisable; V5 is 210 V.; the "B" potential available end. Therefore, return to the initial high - (7.) Shield primary wire from coil to dis- for the remaining tubes is 175 V. frequency setting of the condenser.) Change tributor: If chassis pick -up occurs, the procedure the service oscillator setting to correspond (8.) Shunt distributor primary breaker is as follows: ( lI Use a Motorola Dome Lite with the changed position of the tuning points with a .002- to .006 -mf. mica con- Filter. Connect one side to the battery cir- condenser. densers. cuit of the car and the other to the end Remember that Cl requires more capacity (9.) Bond upper metal parts of body of the yellow wire. car Connect battery con- at the low- frequency end so it is necessary to one another and return a heavy copper denser wire to the ground. (2) If the high- to move the condenser a few degrees in- bond from these points to car bulk -head. tension coil is located on the instrument ward, which gives more capacity to this (Usually necessary in cars having composite panel, shield the high -tension wire from the condenser, leaving the service oscillator in wood- and -metal body construction) ; coil to the bulkhead, grounding this shield the same position. Adjust the trimmer of at the bulkhead. In some cases (10.) Bond where necessary all control it may be C2 until the signal is brought back, then rods and pipes passing through bulkhead; necessary to cover the head of the ignition check the alignment of both trimmers. coil with a metal shield. Return (11.) Shield head of coil when mounted on Cl and C2 to the 600 kc. position instrument The alignment of cut -plate variable con- and re-check the setting of Cl; if the con- panel; densers differs from the alignment of condenser has been moved sufficiently while (12.) Screen floor boards with copper; densers connected in circuit with a padding making adjustments at the high. frequency (13.) Adjust spark plug points to .028 -in., condenser, in that the cut -plate condenser end the trimmer of Cl will show resonance. approx.; has a fixed mechanical ratio between the If it has been moved too far it will be neces- (14.) Clean and adjust primary distributor capacities of its sections. In the past it sary to loosen the setting of the trimmer in breaker points. has been possible with padders to align the shunt. to Cl, instead of tightening it as (15.) In cars having rubber motor mount- condenser with an accuracy of 10 degrees Previously. ings connect heavy bond from grounded of rotation of the condenser plates -that is, To align the circuits of I.F.T.3, the non- aide of battery directly to frame of car. it could be set at the high -frequency end metallic aligning screwdriver may be inserted (16.) Connect 1 with a .5- to mf. condenser all trimmers in alignment, and then re- in a hole provided in the upper part of the from hot primary aide of ignition coil to alig_.ed at the low -frequency end by rock- chassis located between I.F.T.1 and the "B" ground. ing the condenser while adjusting the pad- power supply housing. (17.) Move ignition der. However, coil to motor compart- this procedure cannot be Spasmodic interference due to an accumu- ment side of bulkhead, if mounted on driv- followed in aligning a cut -plate condenser lative discharge, resembling static interfer- er's side; gang. ence in its irregularity. may be traced to the (18.) Clean ignition system wiring. Clean Use a standard service oscillator and out- distributor. Connect a mica condenser of and brighten all connections. Replace any put meter. Connect a 200 mmf. condenser .002- to .006 -mf. in shunt to the paper con- high tension wiring having imperfect in- in series with the antenna lead of the os- denser which is already across the primary sulation. cillator and connect to the antenna post of breaker points. This mica condenser affords (19.) Ground metal sun visor and rain the radio set. Caution: Before proceeding, power factor control to the paper condenser - trough; be sure that the I.F. transformers have been tends to make it much more effective. in reduc- (20.) Make sure hood of car is well tuned exactly to 456 ke.; otherwise, correct ing interference. grounded. Clean hold -down hasps on both alignment of the R.F. circuits cannot be at- Following is the most complete listing aides. tained. available of steps to be taken. in the numer- (21.) Ground instrument panel and steer- Tune the service oscillator to 1400 kc.. ical sequence, for eliminating interference. ing column to bulkhead. and align the trimmers of Cl, C2. Next, (1.) Apply distributor and spark plug (22.) When under -car aerial is used con- tune the service oscillator to 600 kc. and suppressors; nect a .5 -mf. condenser to tail and spot light check the alignment of Cl. If it is found (2.) Apply generator condenser; wires.

OET 2 50,000 F DYNAMIC Z0 OáC LFt I F 2 jeA VC 0HM5 L A REeRODuCER 77 IFTI 78 I FT 2 7e I F T 3 75 .0005 -r _. s MF

1 e T 11 SI I41# vs Ft' VOICE KV 14 4 X DUNS .OS- OHMS K x COIL OMNS 1 .05.MF O1- (EACH) (EACa) (Ms) MF MEG sso 0MS FI &D 2 COIL oasis .1- 0.1- 0.1-MEG MF X 0.5 OHMS -MEG ME0 .000S. 0 0.5- MEO MF- 50.000 0)1M5/ t-MEG ti MF 2000 .001- VOL UME/ 30 8 i WYVU, CONTROL MEG MF) /MF WNW( I OHMS 2 000 DP ST SWOON ON *OF 10 OOC05-MF-11 0..5 VOL CONTROL X l00 OHMS ) ?5 ONMS 600 ONM e NF YELLOW (EACH) eLACK 4E0 r LLOW 20T NEI2 N ) r' 201 NRIl -_.25MF pp/--- SNIELDT REO c... b SLACK - 1-OMM l 1 fL4 Cie j Ct=D .004-MF BLACK, ,O 460 01-W 5s 0»M MECHANKAL- eONNeCTIONS FOR NEO 1p DNM$ ISODVI RECTIFIER ;) I so sec I I C-) GÑbEO BTT Ç1 I me vIsATOR YELLOW 1HI l r-Ili e" UNIT [ F 456 KC RED , If BLACK eND I I` 1 MF M Lt -MODEL .01 -MF REDy 55- L 'T MACK .002.MF' 4r0CONNECTIONS FOR ooS - (f) SHOED BATT

RADIO -CRAFT for SEPTEMBER, 1933 159 THE BEGINNER'S "1- TUBE" CRYSTAL SUPERHETERODYNE

The beginner usually regards the superheterodyne as a complex "something" which is mastered only by those vested with supernatural powers. This article will do more to bring such notions back to earth than any theoretical "discussions."

FRANCIS R. HARRIS

BEFORE delving too deeply into all excess solder and straightening out namely make certain that the red, or our present -day set we wish to and cleaning all wires -you will find positive, end is attached to the filament call attention to circuits A, B and that you can use most of them again. side of the bias resistor, R5. Also, be C in Fig. 1. Also, for the sake of appearance, sand- sure that the three -circuit tuner, L2, is paper the baseboard and apply a coat wired exactly as shown on the diagram the to THE Technical Editor of RZADIO- of shellac. with connections made the lugs on CRAFT published them, in a contem- Next, mount a pointer on the tun- as marked the coil, being sure that porary publication, in the early part ing condenser C2. Mount the new the lug on the volume control, away of 1925, to answer the "it can't be crystal detector, P2, on a little panel from the end where the switch snaps, done" technicians who claimed, vehe- with soldering lugs, as shown last is connected as shown. mently, that a one -tube superhetero- month for the first one, (this may seem Operation and Theory dyne was an "impossibility." The cir- to be unnecessary trouble, but you will cuit we intend to use, Fig. 2, is sub- find out why later) and mount two Now that we have the set built, the stantially that of A in Fig. 1, with the brackets on the bottom of the interme- next step is to put it into operation; difference that modern practice has diate- frequency transformer, L3. Now and while we are at it, we will learn been applied to the design. To main- you are ready to go ahead and screw why it operates, and thus kill two birds tain the simplicity and low cost that everything to the baseboard in the posi- with one stone. The first test should have characterized all the beginners' tions shown. Then proceed with the be made with the set somewhere in the circuits, (twelve of these are listed on wiring, marking out with a red pencil, general vicinity of your regular broad- pg. 91 of the August, 1933, issue. - as described in the previous articles, cast receiver. Technical Editor) we have used prac- each wire as you put it in place, being First, hook on the "A" battery and tically every part that has been used very careful to make clean, tight sol- place the tubes in their sockets, then previously, and very little else. dered joints -obtained with a clean, turn the combination volume control hot iron, clean surfaces and resin flux. and off-on switch until the battery Construction Never use either paste or liquid flux of switch is "on." The filaments should show a dull red The photograph, Fig. A, shows very any kind on electrical work; no matter glow; if not, find out what the manufacturers say, it will why before going further. Next, plug clearly the position of the parts used. headphones Since the circuit is now totally different eventually corrode and cause noisy or the into the output jack, from any of the previous ones, it is im- inoperative circuits. J2, and attach one wire to the "B" bat- practical to attempt to use the same Not a great deal can be said in the tery, flip the other one across the ter- layout; hence, the first thing to do is way of instruction for this assembly job minal. A sharp click in the phones in- to clear the baseboard entirely and except to repeat what was said regard- dicates probable correct operation; clean up all the apparatus, taking off ing the electrolytic condenser, C9, however, if a large spark recurs do not go any further until you locate the short which is causing it. If everything appears to be O.K., make a per- "B -"AND "A -"AND manent connection at this point. "8 +135 V. "A +2V. Now we are ready to see if our oscil- LEADS LEADS lator "perks." Turn on the broadcast set and tune in a station, preferably w- LI ß TICKLER a weak one which requires that the volume control be turned "way up." If the set is a modern one and fully shielded, it will probably be necessary to run a wire from the antenna post along the dotted line in the diagram of our super. Next, see that the volume control of the super is turned full on (which is the position furthest from the end where the switch snaps), and that the rotor of the oscillator coil, L2, is turned in one of the two directions where its axis is parallel to that of the big coil. Now, slowly rotate the control of oscillator tuning condenser C4 from one end of the dial to the Fig. A other. If the oscillator is working A view of the breadboard crystal superheterodyne. All components are labeled. properly you will hear a squeal from

160 RADIO -CRAFT for SEPTEMBER, 1933 DEAR BEGINNER: do not let the high- falutin' title scare you. It is a contraction of the even longer technical designation, "supersonic heterodyne "; and simply means that the action on which the circuit depends for its operation, and which we will describe, takes place at a frequency which is beyond audibility. Maximum sensitivity and selectivity are obtained through the use of the superheterodyne principle. Only one tube, or oscillator, VI in Fig. 2, is required to obtain this action; V2 is only an A.F. amplifier.

the speaker of the broadcast set as the this, or you are likely to find your sci- would be there nevertheless, and if it frequency at which the oscillator is entific endeavors rudely interrupted.) were fed into a suitable amplifier it operating crosses ( "heterodynes," or Set the broadcast set to a weak station could be built up to any desired level "mixes ") frequencies to which the set with the volume control turned up, and exactly the same as the original is tuned. signal If this squeal does not occur, check the presence of the squeal by roof 300,000 cycles, except that, being a turn the rotor of L2 through a half tating the oscillator dial. Then, very lower turn frequency, it would be much and repeat the tuning. If you do slowly, tune past the point where the easier to handle and could be amplified not get results, check over the circuit squeal occurs. You will hear, first, a far more, or through more stages. carefully as there is something at fault. very high -pitched whistle which will The most likely place for trouble is in decrease in pitch as you turn the dial The Second -Detector or "Demodulator" resistor R2, in the plate circuit of the until the pitch goes below audibility. Now, if this 50,000 -cycle signal were oscillator tube, which may be of in- Continuing to turn the dial will bring fed into correct a second -detector, we would value; try different values, but the whistle back again, but this time have available an audio signal which do not operate is the tube with less than increasing in pitch until it goes above an exact counterpart of that carried by 1,000 ohms here, as it may result in audibility. (The heterodyne action the original 300,000 cycle signal, but at damage to the tube through excessive did not cease when you failed to hear a much higher plate current. level than otherwise. it as the pitch increased; it merely The heterodyned signal carries every After obtaining the squeal which went above audibility, or became single shows modulation which was carried by oscillation at one point, tune the "supersonic. ") either of the two original mixing fre- broadcast set to several others, always A little simple arithmetic here will quencies. choosing Since one of the frequencies a rather weak station, and see emphasize the point clearly. Suppose was a pure, unmodulated note from our that the oscillator is operating over the you had tuned in a station operating local whole range. oscillator, this means that it car- at 300,000 cycles a second (300 "kilo- ries only the modulation present on the Now tune the broadcast set to a posi- cycles," or k.c.), and then set your os- signal tion where from the broadcast station. And there is no reception, turn cillator so that it was operating at 301; that's all there is to a superheterodyne; up the volume control fully and try to 000 cycles a second, the difference fre- not get the squeal. difficult to understand, is it? Don't try too hard, quency would be 1,000 cycles (1 kc.) Having found that the oscillator is though, because you won't get it. The which you would hear as a squeal. squeal If operating, you can now retire with the is due to the heterodyne action you set the oscillator at 299,000 cycles set to your own private and requires corner (much the presence of two fre- you would also hear the same note since to the relief, probably, of the family) quencies. You will hear, if you listen the difference between the two frequen- for carefully, the rest of the adjustments. a "thump" in the broadcast cies is still 1,000 cycles. Now, however, Attach the aerial, and plug the head- set speaker as the oscillator is tuned if the oscillator is set to 350,000 cycles phones into the phone rapidly past the jack, J1; you point to which the the beat note would be 50,000 cycles. may also turn off the filaments as we broadcast receiver is set. You could not hear this note, but it (Continued on page 173) Producing the "Beat" Frequency 2±RYSTAL IQ DlµJ q.t. RR 3-DET ROTOR s0O 1St CRYSTAL CRYSTAL 2+' Let us get back to the heterodyne ac- J WAS P III-OE / T;T OUT tion with LOOP which we are concerned in 1 -DET .00:-W oec ` _ : _ ..- our little set. This action is simply _ _ 10° S00 -I : 1 _i= O the mixing of two different frequencies SWF ` S S ( `)F Sr IAFI', which results in Y. - the production of a $D Mg 1, ! ,EOroR ' third frequency equal to the numerical sao TOR WDII _+ RFC WET difference between the other two. Now LWP NM( P 4. this may sound very complicated, but I w011 M it is really not, and if you keep your i eyes and ears open, you will see many A" - examples of it going on all around you. 7 !hy 1MEG For instance, let two people each _A- )- SOO WO - + S00 whis- M_MF tle a steady tone differing slightly t Á= r II from J 22 6v2v each other. You will hear a "" -13- CRYSTA 2q-DET -C- "chord "; (SUPERMETERODYNE) (TROPADYNE) A-1hV 'IV 22Y2V if you listen closely you will be able to (R[FL[YSLRERM[TERDDYME) distinguish the third Fig. I note which the One- ube superheterodynes published by our Technical Editor musician calls a "beat" note -that "dif- same years back. -7 T7 C5 I J1 PHONE ference" frequency which is the "re- OUTPUT e+ /R2 sultant" of two frequencies. V C11¿! FIRST- T TACKQ JACK This is DET ) ,SECONDSECOND- simply the same heterodyne A.F. J2 C action Ll LS V which took place G o5C. in your radio set when oió 1 MID you produced 30 (ELEC) the squeal; there is a vast C3 difference in the frequencies involved, yct (6 l but the action is identical. _L GND. Now let's try a little more experi- C6 'CSIHI- TOP VIEW OF SW. 23r mentation with the radio and the oscil- VOLUME CONTROL RA V 2 SOCKET 1 + - lator, and fix thoroughly in our minds o just what is this thing called "hetero- MECHANICAL CONNECTION (R5 IS A A- its dyne." (Tip: you'd better pick an eve- .0 BIAS RESISTOR ) \ ning when the family is Fig. 2 out, for all The crystal superheterodyne circuit described in this article. RADIO -CRAFT for SEPTEMBER, 1933 161 READERS' DEPARTMENT

A department in which the reader may convey his thoughts to other readers. Included in this department are letters, kinks, short cuts, and experiments. Send in your ideas.

A 43 -FOOT SOUND CARI The interior hT.s all the appointments All windows are fitted with shades and screens. Exhaust fans keep the in- Well, we might say that he "goes in of a modern home. Dining, kitchen and living rooms, bath and sleeping com- terior ventilated. Electric lights are for sound in a big way" in referring current to the equipment of Mr. P. J. partments. An electric -light plant, available at all vantage points; sound make by 110 V., D.C. Kingsley, of Cohoes, N. Y., whose lav- electric heat, and a water system is furnished a generator ishly sound car, living and traveling a comfort and con- driven by a 4- cylinder gasoline engine. furnished, palatial This will run continuously for said to be the largest privately owned venience. engine This car is divided into three sec- 24 hours on 5 gals. of gasoline and re- in the world, is illustrated in Fig. A. heat Merely to say that the car measures tions. The dining and driving compart- quires very little attention; the 9x9x43 ft. in length does not convey the ment has tables folded into the walls generated is used to heat the interior picture of opulence personified in the to be used for dining ten people at of the car. "bus." Therefore, we have asked Mr. once. The modern kitchen has hot and A ship's ladder takes you to the top J. G. Montross, who designed and in- cold running water, an all- aluminum deck, built for a speaker's platform, stalled the sound equipment, to tell the sink, an electric refrigerator, a 3 -plate which is 7x10 ft. (completely railed in). readers of RADIO-CRAFT some of the electric range with oven, a thrift - Forward of the platform is the sleep- more intimate details of a mobile sound cooker, and a built -in closet holding all ing compartment with four double beds system to which any sound technician dishes, pans, etc. Directly off the accommodating eight adults. For dress- might well aspire. Says Mr. Montross: kitchen is a shower bath, a pullman ing purposes there is provided directly The car illustrated in Fig. A, which toilet and lavatory, with hot water on off the sleeping compartment, a private was built and licensed prior to the re- tap at all times. Under the chassis is space having its own pullman -type strictions as to length, can maintain a stored a 160 -gallon water supply; the wash basin. speed of 60 m.p.h. The motor is a 160 flow is maintained by air pressure. The H.P. Continental; the chassis is a six - rear compartment is fitted as a living The Sound System wheel Safeway, with three forward and reading room; easy chairs, rugs, For sound amplification, two 6 -ft. speeds and one reverse. The car does shaded lamps and a radio receiver with Bud all- aluminum trumpets, with dy- an average of 10 miles on a gallon of remote control make this room very namic units, were placed forward on anybody's gas. home -like. the top deck. Control and field wiring run, in lead- covered conductors, to the driver's compartment. A Capehart ten -record automatic record -changer houses a Sampson PAM -80 amplifier, a microphone amplifier, control panel and output matching transformer. Power is obtained from a 110 V., 300 W., A.C. converter. Microphone plugs are placed on the aTE- speakers' stand and in the forward and EAK rear compartments. The detector tube ADAPTER of the radio set furnishes the driving signal when high -volume broadcast programs are required for the sound system.

PISA Thousands of people paid admission to see the interior of this car, at a (Continued on page 169) Fig. B Photograph of the filter booster described by Mr. Dalpayrat. C3 LAST R F. TUBE IN BALANCING .OUT BROADCAST SET POTENTIOMETER, m TO DET GRID CAP OF BROADCAST SET TUNING D CCZ

CHASSIS OF -TAPPED PR1 C Q CENTER BROADCAST SET

PLATE - BREAK ADAPTER

Fig. A, above LAST R F The $35,000 "sound car" described by its designer. Some toy, eh what' SOCKET IN SET Fig. I, left The schematic circuit of the filter booster pictured in Fig. B.

162 RADIO -CRAFT for SEPTEMBER, 1933 HARRY S. KENYON

Fig. A, left; Fig. B, right The completed decade condenser, left, and one switch, right.

HOW TO CONSTRUCT A DECADE CONDENSER

The one thing that every experimenter wants and needs is a laboratory. In a laboratory, it is necessary that the apparatus be convenient, accurate, and stable. The decade condenser described below fulfills all these requirements.

BECAUSE of financial difficulties, The inductance may then be calculated 00: the average radio .002 1 experimenter from the following formula: .0C3 SECTION must usually be content with 11 004 home -made equipment for his L- F-C .01 laboratory. This article describes ^ 1 a where ^ 1 02 2 no decade condenser which should fill 03 SECTION a = much needed frequency ^ 1 04 place in the test equip- F= in cycles per second; ment of Service Men and experiment- L= inductance in henries; and C=ca- n - 1 pacity in .2 eo ers. It is not only easy to construct, microfarads. .3 SECTION but is quite inexpensive. An A.C. meter may be used as the H .4 resonance indicator. -s- Uses of the Decade Cond The condenser is also very convenient in determining The decade condenser consists the ,1 of a proper value of capacity in hum-bal- oho 0 ionio H small number of fixed condensers and a ancing circuits. Another application is .2 switching arrangement by means oo4o o 4 o o 4 1! of in an audio oscillator to provide a wide which a great number of different ca- range of frequencies. .3 pacities may be obtained; 0004 00444 the actual Figure A shows capacity is readable at a glance. The the appearance of a .4 completed decade condenser uses for a condenser of this type covering 0000 are the range of .001 to .999 mf. in .001 numerous. It may be used in the tem- 0 1 2 3 4 5 6 7 8 9 mf. steps; it is apparent -A- porary setups that the total of filter circuits; it may number of steps is 999. And this sur- be used to pass or suppress certain prising total is obtained from only 12 Fig. audio frequencies; an approximate fixed condensers. This range, Schematic circuit of the decade condenser described value however, by the author. The drawing at A shows connection of the inductance of an audio need not be the same as that specified, for any section. choke may be obtained by using the but may be arranged to satisfy the re- decade condenser to tune the choke to quirements of the constructor. The resonance with a known frequency. box pictured has three units; a two - unit box would have 99 steps; and a four unit box, 9,999 steps. The need for so few condensers is based on the ability of the switching arrangements to connect the four condensers of each unit in the following combinations: Dial Condensers Total Numbers in Parallel Capacity 0 None 0 1 .1 alone .1 2 .2 alone .2 Fig. 3 .3 alone .3 2 Fig. 3 A pictorial view of 4 .4 alone the switch to be made by the Details of the cams, also to be constructed. There .4 experimenter. All dimensions are given. are four cams to a section, three of which are alike. (Continued on page 175) RADIO -CRAFT for SEPTEMBER, 1933 163 A VALUABLE RESISTOR -CONDENSER CHART

The usual bugbear in radio calculations is the long arithmetical work involved. The author presents here a simple "reciprocal chart" which eliminates the necessity of continual division into the numeral I, thus greatly simplifying radio calculations. LOUIS B. SKLAR

or ADIO experimenters and service men are often con - fact, any number of resistors are connected in parallel, fronted with the problem of finding the value of two the final value of C when two or more condensers are con- or more resistances in parallel, or the value of two nected in series, can be easily and accurately obtained. or more condensers in series. The usual procedure From the examples shown below, you will see that these R without the use of any algebraic or results can be obtained is to write down the formula: ¿ =lti +K +R- etc. R= formulas or without any intricate calculations. All that required from anyone who wishes to solve these types RR_R.: R,, is and then substitute the values of R., of problems is a knowledge of plain addition. R.R.- 1- 11,11, --R.R3 1,000,000 units and Ra in the formula and solve for R. One can readily The range of the chart is from .000001 to see that although the method of solving for R is an easy of resistance or capacity. While this range covers almost one, it requires considerable time to go through a large every conceivable value of resistance or capacity that will number of computations in order to arrive at a final result. arise in practical work, care must be taken, however, not Sometimes this method is tiresome, especially during an to use different types of units in the same problem. For experiment when a quick and accurate result (with a fair instance: if you wish to know the value of 1 megohm and tolerance) is required. It is still more bothersome to those 100,000 ohms in parallel, you cannot mix megohms with who lack a good knowledge of algebra or who find it diffi- ohms. What you will have to do, in this particular case, is cult to get the right decimal point in calculations. to change the 100,000 ohm resistor to read .1- megohm, or It was with the view of finding a short cut to the value make the 1 megohm read 1,000,000. The same applies to of R, or C, that the writer designed the chart shown in the farads and microfarads, or microfarads and micro-micro- figure. farads. With this chart, the final value of R when 2, 3, 4 or, in (Continued on page 176)

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000A .001 9 8 7 6 5 4 2 9 B 7 6 5 4 3 2 1

B,r. 1 1!llu1, B 9 1 2 3 4 5 6 7 8 9 5 6 7 8 10,000 1000 2 3 1.00001 .0001 9 8 7 6 5 2 9 8 7 6 5 4 3 2

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I li IJ 11 ! i I 1 ( ll r J B °Iillliiilllli jiili11111i1iiliJl'iiJliJl l rl' rl I rI l III,IIiIII(,IIII(II,Illilll,lllillll+11111 811 I I 6II II5 17 , 7 2 3 4 8 9 1000,000 100000í

for SEPTEMBER, I 9 3 3 164 RADIO -CRAFT REWIRING THE A. K. 70 -Q FROM 6 TO 2 VOLT OPERATION

The A.K. 70 -Q, originally designed for operation from a six -volt storage battery, may now be resu-rected and used with the usual two -volt battery. The author, in this interesting article, gives all essential details.

(500 OHMS, ._.. A. A. JANSZEN DCT, FIL r . BY -PASS

I L _ RED LEAD 2 woBF - LOCAL -DIST SWITCH RADIO Service Men hear frequent FIL. BY-PASS complaints of excessive upkeep from rear of set). This places the costs from owners of the At- Q correct amount of bias on the control - grid of the third water Kent model 70 -Q battery GRID GRID R.F. tube to prevent receiver. This situation may be rem- (.p RETURN RETURN oscillation in the R.F. stages. The LUG R.F.T2 LUG RFT3 center -tap of edied to the advantage and profit of Co the two resistors, which both the set owner and the Service is also bypassed with a .1 -mf. con- Man. The owner, who is usually k- denser, goes to the grid- return lug of cated at a distance from a service sta- the second R.F. transformer, and to tion, will not need to make so many the red lead from the local -distance switch. trips in order to keep his set operat- LEAD TO This red lead was originally ing; -3 V. TERMINAL a connected to chassis. he will have better performance, -C' BATTERY A grid bias of greater economy from the standpoint 1% V. is secured on the control -grids of both "A" and "B" battery consump- of the first and second R.F. tubes when tion and tube replacements, and the the local -distance switch is in the "dis- Service Man will make a profit on the tance" position. The grid- return lugs sale of a set of tubes by modernizing are on the transformer coil forms, Fig. 2 right in the this set. The changes, shown in Fig. 1, A sketch illustrating the placement of the parts chassis opening under the are simple enough, and may be made necessary in rewiring this receiver. transformer shields. The leads from with a minimum amount of these lugs to the condenser rotor equipment springs in a short time. the second R.F. and detector bypass are removed. condensers to remain connected. Connect all filament circuits of the Changing the R. F. end of the Set In order to obtain R.F. tubes in parallel with the detector the correct and A.F. Remove all tubes and tube shields. amount of bias on the control grids of tubes. To your left, toward Turn the set over, with the rear the R.F. tubes, we construct a voltage the front of the chassis, you will find a towards you. This places the filament divider system, consisting of two yellow, spaghetti -encased resistor, con- bypass 500 - nected condenser, H -20, Fig. 2, to your ohm, 1 -W. resistors. These are con- from minus filament on the extreme left. Remove all five flexible, nected in series first audio tube to chassis. This re- and mounted as shown sistor filament resistors; these are thin, in Fig. 2. They are connected between may remain, when an air cell is hunched, white with black tracer. Dis- the -V. tap on the to be used, as the resistor provides the -3 "C" battery and voltage -drop connect the first R.F. filament bypass the chassis. (An extra lead must be required to obtain ex- and the two third R.F. filament bypass brought into the "C" battery compart- actly 2 V. on the filaments of the tubes. condensers from the filament circuits ment for the However, if a two -volt storage cell is -3 V. connection.) to of their respective tubes. These are This 3 V. tap, which be used, this resistor must be re- is bypassed by moved. to be used as bypass units for the two .1 -mf. condensers, is also connect- This completes the changes voltage divider system in the control - ed to underneath the chassis; the bottom the grid- return lug on the No. plate grid circuits of the R.F. tubes. Allow 3 R.F. transformer, (third transformer may now be replaced. Turn the set over and remove the pilot light. If an air cell is to be used it must be left out. With a storage cell it must be replaced with another of the correct voltage rating. The lead from chassis to tube shield for the detector may be removed, as the type 30 is non -microphonic. Type 32 tubes are placed in the three, type 22 sockets, 30's in the detector and first audio sockets, and 31's in the 71A sockets.

The Audio End No changes are required in the A.F. end of the set, except that a potential of only 135 V. is used on the plates Fig. I of the 31's, with only 22% Schematic circuit V. on their of the rewired A.K. 70 -Q receiver. (Continued on page 177) RADIO -CRAFT for SEPTEMBER, 1933 16S RADIO -CRAFT'S INFORMATION BUREAU SPECIAL NOTICE TO CORRESPONDENTS: Ask as many questions as you like, but please observe these rules:

Furnish sufficient information, and draw a careful diagram when and the appearance of its answer here. your meaning; use only one side of the paper. Replies, magazines, etc., cannot be sent C. O. D. needed, to explain by List each question. Inquiries can be answered by mail only when accompanied Those questions which are found to represent the greatest general 25 cents (stamps) for each separate question. interest will be published here, to the extent that space permits. Other inquiries should be marked For Publication." to avoid At least five weeks must elapse between the receipt of a question misunderstanding.

1932 article, adapter No. THE NEW TUBES ceivers incorporating this electron- coupled de- In the October, INTERCHANGING tector- oscillator are shown in Figs. Q.2I2A 944BRR was shown in Fig. 29. A corrected (211) Mr. G. Aliquo, Brooklyn, N. Y. and Q.212B. A photographic illustration of connection for this adapter is given in Fig. (Q.) It seems to me, that judging by the the manner in which the circuit of Fig. Q.213A. Number 9G5DSW, Fig. 9, and 965DW. published characteristics and general descrip- Q.212A "makes up" is illustrated in Fig. Fig. 8, of the same article, are corrected at It. tions, the new tubes need not necessarily be Q212C. The reproducer is in the top of the for the former, and at C, for the latter. used only in new circuits, but may, in many cabinet; the smaller section of the dual knob In the November issue, Fig. 30, adapter instances, be used as replacements of some of controls the off -on switch and volume. No. 944BRA should be connected as shown the older tube types. Please advise regarding The following tube voltage data relate to at D. Figure 37. adapter No. 421X, is cor- the interchangeability of the new tube types. the Philco model 64 receiver. The first tabu- rected at E. Another adapter, the No. 968 (A.) Through the courtesy of the RCA lation refers to a 115 V., A.C. line: the second, unit illustrated in Fig. 38, is corrected at F. Radiotron Co., the following information is 120 V., D.C. At G is a correction of adapter No. 944LS. 44. available. K. to F. 0. -G. S. -G. Plate Fig. Tube In the December article. adapter No. 944F Tube Interchangeable Type Volte Volts Volts Volts Tube Interchangeable been number. ^d 944PT. Type with 0.15 65 84 should have Type with VI 12 The third article. in the January, 1933, issue. 2A5 PZH 50 585,586 V2 12 0.15 52 84 71, 71B showed a No. 944PLC adapter which should 35 51 71A V8 10 0.26 38 36A 80 13 have been the No. 944PL: also, the No. 36 V4 10 0.5 90 84 37 37A 81 16, 16B 944PLS should have been the No. 944PC. V5 ...... 146 38 38A 82 AF (Q.2.) I have built the "Triple- Twin" re- 39 39A, 44 83 AG The filaments in series drop 68 V.: test 98 P-861* ceiver, described in the April, 1932 issue of 44 39. 39A 84 *, with an A.C. voltmeter connected to points X. PZ ( *Mercury vapor type, RADIO CRAFT, in a small cedar chest. Now. 47 Set maximum and station selector at *36 64, 64A *38 68, 68A RI at I would like to add a novelty to the set in *37 67, 67A *39 65, 65A 550 kc. the form of a tuning meter. Please advise ( *Interchangeable only in auto-radio receivers,and in A.C. Tube K. to F. C. -G. S. -G. Plate how this may be accomplished. receivers which do not use serles hinter circuits.) Type Volts Volts Volts Volte ( A.2) The procedure is described in detail. *83 88, 986, 80M 7.6 0.15 70 90 "The Why and Wherefore of ( *Interchangeable only when the set's power transformer will VI in the article. stand additional filament current drain.) V2 7.5 0.16 70 90 Tuning Meters." in the October, 1932 issue of V3 10 0.25 40 RADIO -CRAFT. Merely connect a milliammeter V4 10 0.5 92 90 of suitable range in the plate lead of the type SHORT -WAVE STATIONS- PENTA- V5 27 tube; a 0 -5 ma. instrument is recom- The filaments in series drop 70 V.; test mended. Preferably, it should be of the re- -CONVERTER CIRCUITS service. GRID with a D.C. meter connected to points X. verse- scaled type designed for this (212) Mr. James Brown, Laredo. Texas. Set RI at maximum and station selector at (Q.1.) I wonder if I could get the names of 550 kc. all short -wave stations, the time of day they Power consumption, either connection, 50 W. TYPES AD, AF AND AG "SAFETY" broadcast. the wavelength in meters, and the RECTIFIERS AE TETRODE frequency in kn.? I have received F8ICD, -TYPE Indo- China; CM2MK, Havana, Cuba: and "CONSTRUCTING ADAPTERS " -(A (214) Mr. M. Chernega, New York, N. Y. ZL3CZ, Christchurch. New Zealand, on my 10- VISUAL TUNING (Q.1) What is the difference between the tube Atwater Kent model 480 receiver. Correction)- "safety" rectifiers described in the "Tube (A.1.) Every issue of Snoa. WAvg CRAFT METER Reference Index" in the March. 1933 issue other of a magazine contains one section or the (213) Mr. Woodrow W. Coffin, Treichlers. Pa. of RADIO CRAFT. and any other type of mer- Part 1, two-part station list divided as follows: (Q.1.) The illustration of the adapter for cury vapor rectifier tube? What are the relay broadcasting, and experimental and com- testing Raytheon rectifiers, Fig. 29, in the characteristics of these type AD. AF and mercial radiophone stations; Part II, police, air- article, "Constructing Adapters," in the Oc- AG tubes? port and television stations. tober, 1932, issue of RADIO CRAFT. does not (A.1) The following information concern- Sete (Q.2.) Are there any commercial radio seem to check with the tube connections. ing the "safety" feature in mercury vapor incorporating the new type 6A7 "pentagrid Please advise whether the illustration is cor- rectifier tubes is furnished by courtesy of converter" tube described in the July, 1933 rect. the engineering department of Arcturus Ra- issue Of RADIO- CRAFT? (A.1.) Through the courtesy of the author, dio Tube Co. (A.2.) Two schematic circuits of radio re- the following information concerning the ser- In view of numerous reports from the field ies of articles on adaptera is available. that the newer sets using the types 82 and

.00o25-MF. .000/25.MF 014MF AF OSC.GMT I DET 2 L' 0A0 57 0. 5- 0.5- 2A5 co.a 287 56 l MG MEG / 1. fYELLOW rArE, YELLOW 4PEO

: a MANUAL VOLUME w OM .L 250 CONTROL MF ONMS .1 MF 25,000/ .0l- QIMs r MFG YELLOW = MF

RI RED 0wOM3 CLOCK 4Mfir IT-6,4F 110v, AC 5w o; vo'GE re LOW cou `il1. X /DOOM - 1.900 OMN \FIELD COIL RIO 0.i& SW ARE GANGED r I.F.456 KC.

Fig. Q. 212A, above Schematic circuit of the Velie model KA receiver, using the type 6A7 tube. Fig. Q. 212C, left A view of the Velie model KA receiver. Note the symmetry of design. SEPTEMBER, 1933 166 RADIO -CRAFT for THE 2B6 TUBE (Continued from page 145) Figure 4 shows the relation between power output and load resistance. An inspection of this curve shows that maximum power output occurs at tho same load resistance as minimum total harmonic distortion. In these curves. therefore, an output of 4 watts is secured with tie WEBTON /lieí/wá a load resistance of 5.000 ohms at a total harmonic distortion of 5 %. Figure 5 shows the o relation between distortion and power output also. input signal volts and power. Here again it is seen that at a harmonic content of slightly less than 5% the power output is approximately SELECTIVE 4 watts with an input signal of 25 volts r.m.s. ANALYSIS At this point the question arises as to how the output section, which is a triode, is capable of delivering maximum undistorted output to a Mad impedance which is very nearly equal to its plate impedance, while almost all previous triode class A systems incorporated a load impedance which was twice that of the tube. The explanation for this query may thus be answered by referring to the set of curves shown in Fig. 6. These curves show the relation between plate current and plate voltage. A load line of 5.000 a ohms is shown. It is seen that this load line intersects the 214, volt bias line at right angles and that the extremities of this line intersect the grid voltage curves where the curvatures are opposite; in other words, the load line for example intersects the + 15 -volt grid curve where the curve is concave downward, while it intersects the -15 volt grid curve where it is concave upward. In this manner, distortion approach- ing the extremities of the plate voltage swings cancel, thus permitting maximum undistorted output with the load impedance equal to that of the tube. This tube is also well adapted for push -pull operation, and a typical circuit is shown in flg. 7. A common bias of 270 ohm- is required for the output section, and a bypas, condenser is not required, although it is recommended for high quality. The characteristics of this tube are as follows: ANALYZER OBSOLESCENCE Input Section Plate (max) Pa, 250 -volts (/J á%-!' ;i Lam({ Grid -Gib +2.5 -volts / Plate current, 4.0 -ma. No Amplification factor, 7.0 longer is there the slightest need Next insert the plug Mutual conductance. 600 -micromhos into the tube Plate resistance, 11,650 -ohms for worrying about Analyzer obsoles- socket of the radio set. Load resistance, Then by plug- 8.000 -ohms cence. Weston has found the solution, Output Section ging into the proper jacks, voltage, Plate (max) Pb, 250 -volts providing a design which is always current Grid -Gib -2.5 -volts and resistance may be read up -to -date regardless of Plate current, 40 -ma. tube develop- in any part of the entire network Amplification factor. 18 ments. It's a method Mutual conductance, 8,500- micromhos of Selective leading to the tube socket. Plate resistance, 5,150 -ohms Analysis involving the new Weston Load resistance, 6,000 -ohms The Weston Model 665 Selective Signal volts'. 26 -volts Model 665 Selective Analyzer and Analyzer Power output , 4.0 -watts with Tube Selectors truly is suitable Tube Selectors. universal *Volta r.m.s. for rated power. in its capacity to analyze 5% total harmonic distortion. Weston Model 665 Socket connections of this tube are shown in radio receivers. New Fig. 8. Selective Analyzer tubes merely mean contains all the nec- llodernize Your Analy- zer with Weston a new, inexpensive AN ALL -WAVE essary volt age,current Socket SET Selector Units Tube Selector. That's (Continued from page 145) and resistance ranges. how obsolescence is -watt metallized resistors. 4A, 10; Tube Selectors to ac- Your present Analyzer can be One eliminated. Amperite self -adjusting line voltage con- brought up-to -date and kept Return trol, type 5A -5, 33; commodate 4, 5, 6 and One Acratest power supply transformer, type that way by means of the new, the coupon today for 5502, 31; 7 prong tubes are inexpensive Weston Tube complete One Acratest toggle switch, S. P. D. T. type information provided. You Selectors which can be 4104, 4; mere- used ... Weston Electrical One Acratest switch, double -pole, 5 position, with all models and makes of type 4188, 13; ly attach the proper Analyzers. Return the cou- Instrument Corpora- One Acratest dynamic speaker. 6 in. diem., Tube Selector to output transformer for 7,000 -ohm impedance the pon for descriptive bulletin. tion, 599 Frelinghuy- primary, 2,500 -ohm speaker field, type 490, Selective Analyzer. 27; sen Ave., Newark, N.J. Two Acratest 4 -prong wafer sockets, type 4062, 25, 30; Three Acratest 6 -prong wafer sockets, type Weston Electrical Instrument Corp. 6984, 5, 16, 22; 599 Frelinghuysen Ave., Newark, N. J. One Acratest toggle switch, type 4112, 32; Please send One Acratest full vision dial and escutcheon. bulletin describing Model type 7175; WE S TON 665 Selective Analyzer and Tube One Acratest 4 -prong plug, 26; Selectors. One metal chassis 8 x 5 x 2 ins. high; I1?adû In sf;wmenl-f One piece of No. 18 D.C.C. wire, 1 in. long. Name closely wound over with about 10 turns of No. 18 D.C.C. wire, 2. Address RADIO -CRAFT for SEPTEMBER, 1933 167 pert AOaC DET7AAVE A.F 015 STEPOOWN TRANS r r! AND., p 45 áaeáAwe G M!t + 0:1;W1 _ PRIM 110V !II (N) !06) EVOLTS3AMP5 S Ì 60 CYCLES

PRY-DISC F LTER CONO RECT SPECIAL TYPE FILTER EL 22.5 TUSE CONO

PRIM 110V. e 60 CYCLES q

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FUSE 1 AMP 110.120 V w i aaúeT 5060+ A.0 (nK) I¡y E Mr SW 1 Fig. Q. 215, above 196 aMS' Three types of Yield coil exciters. Fig. Q. 2128, right 0.9 LeG The Philco model 54 receiver. (RESis rAwES OF COLS Au aNOwr, tr. VA4..TNesg) nnwTAn

83 tubes are rendered inoperative by arc - plate to the cathode of one section of the 1,400 V.; maximum D.C. output current (con- over of these rectifiers at the end of their tube and from the cathode to the plate in the tinuous), 250 ma.; maximum peak plate cur- useful life, thus burning out the power trans- section which has "arced over." The filter rent, 800 ma.; tube voltage drop, 15 V. Base former or the fuse, a "safety" feature has been and load are thus effectively short- circuited is type ST -16; base, medium 4 -pin. incorporated in an improved type of mercury and the current through the secondary of (Q.2) What details are there available in vapor rectifier. This tube automatically dis- the plate transformer is limited only by its reference to the type AE tetrode mentioned connects itself from the circuit when arc -over impedance and the drop of approximately 16 in the same listing? occurs. A technical explanation of the tube V. in each section of the tube. (A.2) The following information is given design follows. This circulating current reaches values sev- in connection with the Arcturus type AE out- The functioning of a mercury vapor rec- eral times the normal current and is usually put tetrode. tifier is quite different from that of a high - sufficient to destroy the secondary winding The type AE tetrode is an indirectly- heated vacuum rectifier, such as the type 80. In or the primary winding, in which the current (cathode-type) tube. The plate is so designed the mercury rectifier tube the successful is, of course, increased. This flash -over. or that there is little tendency for secondary operation is accomplished by the combined arc -over, is not indicative of a faulty rectifier. electrons to be attracted to the outer or ac- action of electrons and mercury ions, while It is an inherent limitation of gaseous recti- celerating grid, and the tube therefore oper- in the high- vacuum tube only electrons are fiers, regardless of the skill and care taken ates as a pentode-although no supressor present. in their manufacture and the tube may oper- grid is used. This tube was developed to pro- As the mercury rectifier is used under ate perfectly a moment before it starts to duce as large a power output at low plate and load, a condition gradually develops where posi- flash -over. accelerating grid voltages as possible without tive ion bombardment is very apt to localize Following are the characteristics of specif- consuming more than approximately 10.5 mn. at a spot on the cathode (filament) and raise ic tubes designed to incorporate the "safety" plate and accelerating grid current. The the temperature of this spot far beyond the feature. heater current is 0.3 -A. so the heater may be operating temperature. connected in series with those of other tubes Type AD Mercury -Vapor Rectifier This local heating tends to encourage two of the same rating ; the tube is particularly objectionable and dangerous results: This tube is especially designed for small adapted for use in 110 V., A.C. D.C. receivers. (1) Disintegration of the thermionically ac- radio sets and is especially adapted for use Heater potential, 12.6 V.; heater current, tive material and vaporization of the metal in A.C. -D.C. receivers. 0.3 -A.; plate potential, 100 V.: accelerating filament or cathode at the point where posi- Filament potential, 6.3 V.; filament current, grid potential, 100 V.; control -grid bias, 13.5 tive ion bombardment is concentrated with 300 ma.; maximum plate potential. 350 V.. V. (negative): plate current, 8.5 ma.; acceler- subsequent decrease in emission. resulting in r.m.s.; maximum peak plate potential, 500 V.; ating grid current, 1.76 ma.; amplification con- a greater voltage drop between the plate and maximum D.C. output current (continuous), stant. 20; plate resistance, 12,000 ohms; trans - cathode and a corresponding increase in the 50 ma.; maximum peak plate current, 200 ma.; conductance, 1,650 mhos.; load resistance, velocity of ionic bombardment. tube voltage drop, 15 V. Bulb is type S -12: 13,500 ohms: power output, 400 milliwatts; (2) Heating of the mercury vapor at the base, small 4 -pin (clockwise: heater, plate, maximum grid resistor value, 1 meg. Bulb point where ionization is localized to a tem- cathode, heater). is type ST -12; base, small 6 -pin (clockwise: the vapor emits electrons. control grid, perature at which AF Mercury-Vapor Rectifier heater, plate, accelerating grid, These electrons are drawn to the cathode dur- Type cathode, heater). Full automatic grid bias ing the half -cycle it is positive and consti- Filament potential, 2.5 V.; filament current, is essential when a grid resistor is used. tutes a "back- current" or "arc over." 3 A.; maximum A.C. plate potential, per plate, The electrons comprising the "back -cur- 500 V., r.m.s.; maximum peak inverse poten- rent" mentioned above are drawn from the tial, 1,400 V.; maximum D.C. output current FIELD COIL EXCITERS to both sections (continuous), 125 ma.; maximum peak plate filament, which is common (215) Mr. Charles Davis, Milford, Pa. rectifiers, to the plate of current, 400 ma.; tube voltage drop, 15 V. in most full -wave coil "excitera" and how the other section and back through the Bulb is type S -14; base, medium 4 -pin. (Q.) What are field plate transformer to the are they made? secondary of the Rectifier supplies the D.C. and thence, via beck -emission to Type AG Mercury-Vapor (A.) A field coil exciter first plate a repro- complete circuit is thus Filament potential, 6 V.: filament current, required by the field coil of dynamic the first filament. A coils to 3,000 ohms: secondary of the plate 3 A.; maximum A.C. potential, per plate, 500 ducer. Some field -500 formed comprising the on yep.' 178) transformer and the low resistance from the V., r.m.s.; maximum peak inverse potential, (Continued

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Fig. Q. 213 RADIO -CRAFT. Typographical errors are mentioned in the text. Corrections to the article, "Constructing Adapters," in the Oct. and Nov., 1932, issues of SEPTEMBER, 1933 168 RADIO -CRAFT for READERS' PAGE (Continued from page 162) number of county fairs. A refrigerator manufacturer placed their line of products on display. (A full -size, 20 -sheet bll poster can be place.) on each side for advertising.) The cost of building and equipping this car was nearly for PRECISE $35,000; the car was intended ar a traveling home and office. Measurements HOW TO MAKE A COMBINATION "FILTER-BOOSTER" Editor. RADIO- CIAFT: In Fig. B is illustrated a simple device of USE unique design which may be attached in a few minutes to any rado receiver to improve its operation. This unit has band -pass characteristics which considerably enhance the tone Westinghouse quality; and in many cases the volume is almost doubled without causing circuit oscillation ; finally, the selectivity is increased, resulting in an increase of the signal -noise ratio. The result is shown at Fig. 1. PY -4 Instruments (Although this little instrument has been tested on sets of widely different design, most of the experiments were made in conjunction with a Savil, 110 V., D.C. receiver of the type y[ESTINGHOUSE PY -4 can be readily determined described by Mr. Vilkomerson in the December. vvVV 1932, issue of RADto- CRArT. Consequently, since portable instruments - and practically all receiving - results the will vary somewhat in each individ- moderately priced voltmeters, - ual instance, the description of operating results set alternating current volt- will be confined to this set model.) ammeters and milliammeters ages measured. Resistor R. shown in Fig. 1A, serves the dual -are accurate within á } of purpcee of phase changer and volume control. Mounted in neat, compact When the arm is at the center. the auxiliary 1 per cent of full -scale value circuit receives very little energy and tuning Moldarta cases, these instru- it will not affect the signal strength. However. on alternating current and when ments can easily the contact is moved towards one end. 1% per cent of full -scale value be carried the volume will increase and the tuning effect in your pocket. of C2 will become apparent as the knob is on direct current. adjusted and the selectivity becomes greater. Catalog 43 Moving the arm toward the other end will A wide range of capac- -110 describes usually result in a diminution of volume. By the many refinements of these detuning a little, it is possible to reduce inter- ities are provided. For in- ference without reducing either the strength of instruments, such as non - the signal or the quality of the reproduction. stance, there is a quintuple loseable The filter- booster is designed for T.R.F. sets - terminal nuts, mir- it is not recommended for superhets. Use only range voltmeter with scales ror scales and knife -edge mica condensers for C3 and C4. The band - spread effect that results at the shorter wave- of 0 -4, 0 -8, 0 -16, 0 -150, and pointers, Hypernik iron vanes lengths does not change the selectivity of the 0 -750 volts. With receiver but merely makes the tuning more con- this one in- and heavy shielding. Send venient; this feature i9 of particular merit strument, transformer ratios the coupon for your copy. where the set's tuning gang is controlled by a direct- acting tuning control instead of a vernier. If it is desired to operate the receiver closer to the point of oscillation, reduce the capacity W E S T I N G H O U S E of C4. The plate -break adapter connects into the plate circuit of the receiver's last R.F. tube at X, as shown in Fig. 2A. An off-on switch, Quality workmanship S E N D F O R C A T A L O G ganged with R, may be connected to close the plate circuit, as shown dotted. Resistor R and guarantees every Westinghouse Electric & Manufacturing Company the variable condenser C2 most be completely Westinghouse product Dept. 103, Room 2 -N -East Pittsburgh, Pa. insulated from the shield can. Coil L2 is a Gentlemen: Please send FREE copy of Catalog 43.110, standard broadcast T.R.F. unit; it must not describing the PY -4 line of instruments. approach the shield can closer than % in. at Name the sides, nor closer than y4 in. at the ends. The coil used by the writer was wound on a Ocrepe:ion form one inch in die., with secondary a to Address match the condenser used as C2. The primary I 79613 has 65 turns, center -tapped, wound over one end City State RC 9-33 of the secondary. Four layers of Empire cloth correctly space these two coils. Primary and Be sure to turn to page 136 of this issue and read about the new 1933 OFFICIAL secondary are wound with No. 32 S.C.C. wire. AUTO -RADIO SERVICE MANUAL which is now published. List of Parts One variable condenser (overall, maximum dimensions not to exceed those of the shield - tvn thisRadio can), 350 mmf., C2; One R.F. coil (to match C2), L2; Two mica condensers, C3, C4, 260 mmf.; One plate -break adapter; One potentiometer (with or without switch), straight- line -resistance calibration, 6,000 ohms, R: Y.ai ray only the Fret cost of One 2 in. dial for C2; $9.95 complete with robes One knob STUDY AT HOME oWe fine. guaranteed for R; We guide you step by step- furnish all text din r:. r-leea than One Blan aluminum shield can, 5%x4Vlx3s,(t 3 yenta day. Op.rats atIy- material, including fourteen -volume Law Li- 30 DAY , any current -A. ins. deep ; D.C.._n battery ear. FREE TRIAL - in home. One battery clip brary.Training prepared by leading lawpprofes- S9 camp. shoo. hotel. A bis vali° in (for grid lead), one soldering performance. Mr. Bond. Bloom- lug (for ground lead). 10 ft, flexible rubber - sors and given by members of the bar. Degree ONE YEAR ington Ill- my,: naives e2 covered hook -up wire. of LL.B. conferred. Low cost, easy terms. Get mileis-distant. Send for hn'a en- FREE SERVICE! rol re. how ,a r, n,,. HENRI F. DALPAYRAT. our valuable 64-page "Law Guide" and "Evi- ot Your S1.... ,.r 30 JAY. FH55.. New York, N. Y. dence" books free. Send for them NOW. GOLDENTONE RADIO MFG. CO. Dept. 137, 11704 tivernofs. Detroit. Mich. (Continued on page 174) LaSalle Extension University, Dept L -73 Chicago RADIO -CRAFT for SEPTEMBER, 1933 169 Postal's 1934 Electric A 26 -WATT P. A. SYSTEM (Continued front page 147 , Superheterodyne produce 26 watts, but only require 320 volts at emanating from non -sensitive microphones. poor 100 ma. phono pickups, etc. To provide for maximum Thor,. is available 6 storage volume output, a contained -1111c $I'l'h:lt- a -volt, -battery self- pre -amplifier is 111:TE RU- operated motor generator that was specifically included, and consists of an input stage using DYNE with S wee perfor designed to neat the plate current require- one type 37 tube. itilab . after ments of this amplifier, it is compact and light This first A.F. tube, VI, is resistance coupled lithe of I.. bo- Jevelul thereby facilitating its attachment directly upon into another 37 tube, VT2, which, in turn, is d the amplifier chassis, as resistance coupled to 89 tubes, haut illustrated. (The overall two triode driver actual dimensions of this generator are 5" 1g., 4'4" V3 and V4. Each of these driver tubes is prating comb- wd., 4" hg., and its weight is 7 lbs.) coupled through an individual step -down class B VALUABLE Another factor in favor of the new 53 tube input transformer, Tl and T2 respectively. into FEATURES, is the difference in cost between the D.C. genera- corresponding twin class B 53 output tubes, TRIS RECEIV- ER ACTUAL- tor required for this amplifier, namely approxi- V5 and V6; see Fig. 1. Each of these out- LY IIAS EIt D1r 'JIBE IER- mately $25.00, as compared to approximately put tubes feeds its own channel, equipped with CENUINF.Fl1IIMANCE- $70.00 for an A.C. generator required for the its own universal output transformer, T3 and AUTOMATIC four 50 type tubes. Furthermore, the latter T4, furnished with secondary windings of 500, V O L U M E CONTROL A.C. generator requires two 6 volt storage bat- 200, 15, 8. 4, and 2 ohms, connected to the six INTER. STA-- rION NOISE SUPPRESSOR -10 KILOCYCLE SELEC- teries and consumes approximately 30 amps. binding posts in each channel. It is apparent rIvITY -a GANG CONDENSER- COMPLETE SHIELD - Compare that to the average current drain of 8 there are actually two output channels avail- INO - ABSOI.UTE.LY NOISELESS AND HUM FREE- DAYLIGHT RECEFFION ON ANY TYPE AERIAL -AND amps. consumed by the D.C. motor generator able, which may, or may not, be used together. TITER IMPORTANT FEATURES TOO NUMEROUS TO MENTION. required for the two 53 class B. 26 W. amplifiers Thus, a whole bank of speakers, connected to UNIQUE CONSTRUCTION described here; further, note that this new D.C. one of the output channels, T3, may be in- TMa entire on n mimed cadmium platedd hnnia generator can be operated from only one 6 -volt stantaneously disconnected by means of a switch. nJ e med ha aif utirated l errata! i h >04{{ linrys The, tubes .n nl -0AI. 011. l -tl -. and storage battery; in fact the additional current Sl, without affecting in any way whatsoever the 2-7/1. h e eue of rie enure net u .sly 10 .pe7 " Iù ' $44.50 drain so imposed upon that battery is of small operation of the remaining speakers that may Sold to dealers and servicemen Com- consequence, be connected with accessories including and will not give any cause for to the other output transformer, Tubeswi .nP $24 9S battery troubles. T4 channel. As this switch disconnects the and aerial mDe for only "B" supply voltage to both the 89 driver and Description of Amplifier the corresponding output tubes, maximum eco- NEW ! ! ISO VOLTS AT 50 MILS. It will be observed that the input mixer con- nomy of operation is thereby obtained, which POSTAL I. ,.. trol box can be operated while fastened to the is particularly desirable when operating the hiveIIEI.I: act, r amplifier chassis; or, quickly and conveniently amplifier from either a motor generator or from that .u removed therefrom and operated any distance batte Kies. At maximum output, the average 2ttr3Ó SO mil.. ml . motor- generator battery is T11Rl,1-, from the amplifier, thereby providing for remote consumption only PCRCIAL POW 1.IC 1 placement (out of sight, if desired) of the am- 41-u amps. when only one channel is being used. A PUSrrIYE Atll\,.' Ell, 'Il.lt- ) EM AND A UNIQUE COSH IL plifier proper. Within this control box are con- The secondary windings of each output trans- ):D FULL-wAYE VIBRATOR feature. p,ssihle. tained the input matching transformers. enabl- former, T9 and T4 may be connected either in l:linvaluable,ay be used on the use of a single or double micro-- parallel or in series, thus allowing the or Auto radio having s ing button entire an 9 tulle. and i. lnoe,ushly `nieed. Available phone, high or low impedance phono, pick -ups, audio output of 26 watts produced by this am- n shipment eon,ph.rely ,nred .mÌ te,rM ." nbn$8.s: S radio tuner for programs, etc. plifier to be connected to one single channel con- SL7.S0 The controls on this unit provide for master sisting of either one or several dynamic speak- volume control, fading, and mixing of any two ers, with their voice coils of any usual imped- inputs. A tone control and individual micro- ance value. A further inspection of the schema- phone- button rheostats are also included. Two tic diagram will reveal that each amplifier is POSTAL RADIO CORP. toggle switches permit optional button- current separately filtered- insuring fully atable, hum - 13S LIBERTY ST. N. Y. C. readings on the milliammeter: another switch proof and noiseless operation throughout. As gives phono (or "mike") radio selection. All shown in the top and bottom views, Figs. A connections are easily made on the rear of this and B. all essential components are separately device and a dual conduction cable is run be- mounted within individual shields. tween the control box and the amplifier "input" binding post terminals. shown in Fig. 3. This Changing From 6 Volts D.C. to I IO -volts A.Ce cable can be made up to 20 feet long, without or Vice Verse introducing any appreciable losses or without Without changing any tubes and without LYNCH causing appreciable attenuation of the higher making any alterations or internal or external frequencies. The output impedance of the con- adjustments, you can switch from one type of trol box matches the input impedance of the current source to another! Note how simply RESISTORS grid circuit of the first 37 tube. It is to be this is accomplished: A plug, P1, and cable noted that a master volume control, Rl. is protrude from the amplifier chassis. For opera- Never Fail mounted on the amplifier chassis proper; when tion from the 6 -volt storage- battery -operated the control box is employed. this volume control motor generator, all you need do is insert this is turned completely "off," so as to confine the plug into the socket S9, Fig. 2A, the terminals In Service volume control action entirely within the input of which are, of course, connected to the D.C. control box itself. output of the motor generator. It can thus be One of the main requisites of an amplifier is seen that both the plate and filament voltages gain; the extent of this factor determines the are fed through plug PI from the 6 -volt D.C. possible undistorted output when weak input generator to the amplifier tube filaments and sources are to be amplified, such as those plates.

PT cRFCI C17 1 FUSE HIT. E ABER 521 VT.7

C18 SPEAKER N92 w ITN PNONO EXCITER Hit G 58

UNIVERSAL 110v, SUPERHETERODYNE A.0 TUNER -B-

.NIVERSAL 2 -SPEED -S- PHONO MOTOR. r----- FILTER ONLY NECESSARY AND PICKUP I( 1 R.FC 3 WHEN EMPLOYING TUNER ; 1 i I +370 e1 54 AMPLIFIER ¡ P 6_ o -MOTOR -GEN ^ pKr F Prices of LYNCH Resistors to Jobbers, POWER PACK. AND I I 1 CONTROL BOX ^` _ Dealers and Servicemen no higher than prices of ordinary resistors. 0.FC4 C20 M0T0R- _ L - GENERATOR. Free Dearripeive Folder Upon Request Fig. C. above sÿ -A- The complete system closed for transportation. MANUFACTURING CO., Inc. LYNCH TO STORAGE 7 NOTE - GROUND ONE 51 Vesey S New York, N. Y. Fig. I, right SIDE OF STORAGE BATTERY At A, the Socket S9 into which PI plugs for six -volt . (6 VOCTS) operation; at B, socket S8 for A. C. operation.

170 RADIO -CRAFT for SEPTEMBER, 1933 On the other hand. for operation from the self- contained 110-volt A.C. Power Pack, this same plug n is removed from socket SO and inserted instead into socket S8, Fig. 2B, the UNIVERSALLY -POWERED. terminals of which are connected to the rectified and filtered D.C. output produced in the 110 -volt OPERATES FROM 6 VOLT STORAGE BATTERYMP FROM Mk/MC A.C. power pack ._....._. and to the 6.3 -volt A.C. wind. :::,..,,e:.P.: :a.....,n:mn:a.,.y._, ;.. n^: ::::::::::::...... ing on the power transformer PT. In a like -: :_ ::t _ B,.>s.;.,e.;HAN. manner, for exclusive battery operation. this NEL!: same plug (PI can be inserted into still ::'i an- ...... other socket. not illustrated) may be connected f to a bank of "B" batteries (consisting of seven 45 -volt units) and, of course. to a 6 -volt storage battery. The 53 tubes are of the 2.5 volt type, and to simplify the filament circuit of the entire amplifier so that only one pair of filament leads are required. the two 53 tubes are wired in series along with a .5 -ohm resistor, 1114. which reduces the 6.3 -volt A.C. or D.C. voltage to the required 5 volts for the two tubes. For the same reason, the 37 and E9 types of tubes are employed, their filaments requiring 6.3 volts A.C. or D.C. It was an achievement to build this high powered universal operating amplifier onto so amazingly compact a chassis measuring only 19 ins. long (with the mounting flanges), 10 ins. deep, and 3 ins. high. (The auxiliary components mounted above the chassis add another 5% ins. to the overall height.) Its total weight. including the input control box, 6 -volt D.C. motor generator. and 110 -volt A.C. power pack, is but Designed By 43'4 lbs. GANCHER The 110 -volt LOUIS A.C. power transformer, PT. Reprmess of whether your pr must have 5% voltage regulation, requirements are for an amplifier so that there from will be plenty of reserve power to handle the 110 ob 6 enormous peak Get Into the Profitable Pub - Volt Storage Battery, you should currents drawn by o the two 53 lie Address Field . MAKE purchase this model h.r.n... not. output tubes. A switch S3 turns this A.C. power BIG MONEY BY SELLING l'I.1 OR I, ÌifierlÌ.reta f arrEFFl('IF:.\solely d.. ...I i pack on and off. Two heavy duty 75 ma. R.F. RENTING this completely rina with either e Volt. In Self -contained Portable P. A. Volta RUTeIT ('usTn tall' ` \In chokes R.F.C.1 and R.F.C.2 MORE to hn.r thin UNIVERS :tI. are inserted into System. Thousand., of Audi - POWER each rectifier plate lead; tnrin,. Ball l'arka, FEATURE! Thi Ultra-Com n t. they are used in con- Theatre,. Fen, AssemZ[bled, But and Completely,mpdrtely ,`rY-r'onta,url Stadiums. Beaches, Skating Unwired Amplifier t; r ,lly e Amplifier. n junction with C17 and C18 to eliminate any Rinks, Kit Diagrams. n s ian. Camps, Schools. Carnivals. Race Leen AC Pack. Generator. ` rfa Storage Battery noise p e. M.t t :, when a radio tuner is used. See Fig. 2B. Trarka, Churches, )'arks, Clubs. i Box Case and 50 Örrn lP. Me`'iVlt tolt,i For the "Movies," Conventions. Hotels. Item. Tonna 53150 Power PlntPÌ , ".rinsi. C. I same reason, R.F.C.3 and R.F.C.4. notratione, Boa (Removable, sed the Amplifier nr.r.p et 15 amp. chokes, Halls. etc.. etc., are ideal FACTORY WIRED. which may Ig o together with C19 and C20, are prospects for this complete Interlocking Ready for immediate use. $3 Annals installation (withoutñ the>e' carrying employed with P.A. System which may be Set.ol Matched Tubes t2 -37, 2 -89 a. iln` pi tn t left). Th n.ut "Miter' the D.C. motor generator only if permanent. 2 -53 o ed A a central end Iy or temporarily installed in your ear Storage $5.64 F a radio tuner is to be used in Battery Motor Genet Jr'.Ilfew cónt,, ...Mixes; lip.0-tx, this P.A. instal- for Sound Truck applications, com- at or 519.50 or IW-t,0 uAn ,nepAonee : lation. A toggle switch. S2, controls the on -off pletely operating therein f 6 Volt EY 'p e, $3.00 Additional, zoo, na, on Iliono ',kepi and Sadie 1ÌFilterO Volt AC POWER PACK FACTORY Teen. n "trend Pre.AT mar he action for from s 110 Volt AC Line WIRED, piifd of this motor generator. See Fig. 2A. brought to he c.r a -OR. thin very a including 1-83 Reitfeier $22.50 l le hen to antsystem may he removed frrOn, purpose" Input Miser iiimlrni.e el removed Another valuable feature of Von. ear .v°,i Boxl Control heerom6ÿ this amplifier is es;,.d don. Inc ,ime ben,. ill $1h.ne iiin ñ. Portable Two- . the relatively low plate voltage Volt. AC (or lnr tint -soar, .gain operali., Speed ElectricC Pnono wa i°n :d.úen:1ïs complete control n e requirements, RnI(S from Mover,g Case. For Pickup. amplifier! !proper. 6 -Volt Storage Bol eery Case. which are 320 volts D.C. produced by the motor WHEREVERWIIEILEVEIt 110 VOLT AC IS NOT 6 Volt StorageStore$39B5ú r High Cain Am,Ji a ut lr a AVAILABLEII -a7. - 53. including ` a I - O Vooitr generator, and, 350 i I :C Rectieed Amplifier e 5aa , volts A.C. being produced Specially de.ig ed Oasi Field 12 in. Wright Power S"permitsppiply (Or Amplification above 6 Volt Phono Motor, of even n.kn nt ignei Two outputt by the power transformer. De Cwt.r pyna,nir Spe.Yen together with a The optional use of 6 Volt DC provide for - latter voltage mbinotion 110 Volt AC d 6 Vole or 11 olt thee use UC .0n4e of r oÌ is rectified by the 83 tube Twmiverd Phono Motor Pickup $12.50 Ìhnn,l. 'peak independent r. and, in turn, is ap- Universally d PLC7 12 In. Wright De Coster 25 Watt Peak h... tr desired.: ,t channel.fne,h MR,' Operated fully the ri 7 Dynamic Speaker one. for only plied through two heavy "floating chokes," Tube -Super-Her Toner .vide the midi- Complete with Baffled VE CHI Carrying Case fore Volt DC $21.50 M1 hane mite. Donal ereatiti. u thin unusual and only IÉAl'R r` rlMon,``j ft Aw and CH2, to the remainder of the filter system fully ve le ey.temmpleta Same as above, but for 110 VON AC 'idea fo Áir ,nh one including 280 or channels i thereby economicalnucha d entirely eliminating Phew unit. are housed in identical .ire sturdy Only. 82 Rectifier ari any danger of the self -heal- leatherette-covered carrying canes pad n medium ta ät., sound coy er:` . with hie Duel Meld Speaker Model. Foi Com- ing, 500 -volt electrolytic condensers from hendl.. nose-on aka.' boles bination 6 Volt DC eVoli Volt ever and dedouble ubv locking eatche. fastened a'to each and 110 Volt AC op- T.ÌrnqÌr.iáror IuOpe 110 breaking down. win dentical Thin nion. Complete with Baffled Carry - A;r v en)it e4`liae. `ot . position.. u feure.t make. in` Case. Exciter, the e it 'Á1e to "nest' or "i nter -look one. and 280 or 82 Rec ,.nl any Mier I By employing dual -field Tube.. wioÌr.bth I, located uoihehaauiceout,men dynamic speakers, it is twothree. etc., TiETHER. greatly Portable Loathe $35.50 re mpiifyiug thereby the r rying retteCovered Inter- possible to excite their fields from your optional of the c - locking Carrying Cases. Complete with NO TUBES TO 2 Removable Covers and C'l1ANCE...NO choice of either the 6 -volt storage Both I he uniform 0on cruet ion and interlocking Randle. Inside Snap -on battery or feature Dimensions 19', w AOAPTP.ItA v the she REQUIRED from a suitable 110 volt A.C. exciter. tier and one Speeder only for .. le. 56.75. e r,A TAKES In the same manner. nod rr ll,r rTo, O crtr ner c er-H et a 6 -volt additional Mo here , I storage battery a sy p ur o.d wadi,-a Weds Jn. (aGw Were - operated dire nad ates A NI O dual speed (33', and 78 r.p.m.) phono- NIENT I graph motor (consuming only 2.8 amps.) has been especially designed to be used for this amplifier, operating from either (or both) 6 -volt D.C. (this can vary from 5 to 7 volts) or from ÇVASTT°.CWIST RADIO CURP 110 volts A.C. by virtue of a specially designed power source that converts the 110 volts A.('. R WEST I7 ST. NEW YORK CITY ieto 6 volts D.C. at 3.0 amperes! List of Parts Two Remington class B input transformers, type BACK ISSUES OF RADIO T1E665, TI, T2; Which you -CRAFT might need to complete your files, can Two Remington class B output transformers, still be had at the price of 25c per copy. Send us your requirements, together with type T3E655 with secondary windings of 500, your remittance in check or money order. 200, 15. 8, 4 and 2 ohms, RADIO T3. T4 -CRAFT 98 Park Place Two Remington filter chokes 30 hy., 200 ohms, New York, N. Y. 60 ma., CHI. CH2: One Remington filter choke 30 hy.. 500 ohms. 50 ma., C11-13; I One CRL 500,000 Jobbers- -Mail C H E 0- ohm potentiometer, Rl: Order Houses and Representatives in all Territories M I S T R Y Two Lynch 10.000 ohm, 1 watt, metallized resis- Cnwrr.EE, practical home -study tors. R2, R6: TWO FAST MOVERS sumo courses prepared by of the hest -known chemists in this country. Including Five Lynch 250,000 ohm. 1 watt, metallized ALLEN Ho,:rats, B.S., M.S.. Ph.D. -Head of Industrial of Department resistors. 113, 114, R5, R7. RS; Chemistry, Pratt Institute; L. M. Tot. MAN, 1'11.11.. Vice- president, United Chemical Two Lynch 1.000 ohm, 1 watt, metallized resis- i'nelunts Co.: Bus and Organlo tors, R9, RIO; m. Br STO ,', n,TOS, B.S. -Head of the Lepartuu'nt of Metallurgy. Lehigh University. mid others. Two Lynch 50,000 ohm, 1 watt. metallized resistors. Rll, R12: INTERNATIONAL SCHOOL OF CHEMISTRY One Lynch 1,500 ohm, 3 watt, metallized resistor, R13: Divislon of the International Correspondence Schools One 0.5 -ohm, 3 watt. wire wound Box 6676 -B, Scranton. Penne. resistor, 1114; Free Edat- Com :ind Voice Without cost or obligation, One 60 ohm center Coil And-Field Co Is for all plea o send me tub -tapped resistor. R15: Assemblies Dynamic Speakers details of your hume -stud& c, Two 5 mf., 35 volt, electrolytic condensers, Cl. Wealso Manufacture Various Types ofMagnelicSpeakers Analytical Chemistry O Industrial Chemistry C3; Chemical Engineering Short Chemistry Course Two Aerovox W'n c:m Supply and It my Ynur Speaker Needs, O Pharmacy 0.02 -mt. 400 volt, tubular con- Speaker densers. C2. C4; Mitre. Since 1841 Name LEOTONE (Continued on page 177) RADIO CO., 63 Dey St.,NewYOrh,N.Y. Address

RADIO -CRAFT for SEPTEMBER, 1933 171 even greater OPERATING NOTES A NEW and (Continued from page 157) the Majestic 20 have been litl-Editor.) The cause of hum was explained to our customer; also sug- DIAGNOMETER In this receiver, a Majestic 20, the same gestions were offered as to a better resting trouble of fading of strong local signals was place for the lamp. Our customer, how- the complaint. The customary tests of the ever, insisted that the top of the cabinet The MASTER Series ground, aerial, tubes, and voltages and cur- was the only place for that particular lamp, rent readings disclosed nothing out of the or- and that it was up to me to see to it that r - dinary. Inquiries brought out the fact that the objectionable hum was eliminated. Sim- MOWfrl4. this set had been repaired once before for the ple? Yes, very simple in the customers mind; same trouble. Because of the compactness but, unfortunately, I could not at that moment of this set, and because of the necessity of stare my customers optimistic viewpoint; removing the ends of the chassis to get at and however, it really did later turn out to be a unsolder six leads before the bottom pan can very simple little job. be removed, I hesitated a while before under- By chance, I took hold of the porcelain base taking this operation. with one hand and, touching the chassis with Fading of this nature could possibly be the other, I noticed that the hum ceased en- due to poor socket contacte. The old reliable tirely. If the base had been made of metal, plate- circuit break -in adapter was connected I would have thought it to be natural; but to the milliammeter, and then put into service. this base was made from insulating material! By jiggling the tubes, one at a time, the Here. evidently. was the solution of the prob- trouble was soon discovered to be in the first - lem, namely ground the darn thing. I ob- detector tube socket. Removing the bottom tained from the customer an old, brasa visit- pan -to the accompaniment of a few unkindly ing -card tray which, as chance would have it, thoughts directed to the awkward design of just fitted the bottom of the lamp base. A For those who desire the ultimate in this particular set-something fell out, which wire was connected to the ground post of the later proved to be part of the detector filament set, and the other end of the wire was soldered complete laboratory test equipment. the brass tray. It did the trick. NEWEST socket spring contact. Whether or not this to Tests ALL tubes including defect was due to former attempts to rectify TYPES without adapters -on a meter the same trouble, is difficult to state; how- Radiola 33, D.C. dial which is colored for accurate ever, the repairs in this case necessitated the A Radiola 38. D. C. receiver furnished an- "Bad," "Doubtful," and "Good" trans - installation of a new socket. other interesting problem: the complaint in conductance classifications; and is ad- this case was an intermittent, sputtering justable to varying power supply po- Stewart- Warner Series 950 noise. During inspection, I was informed that the noise was more persistent in the evening Tubes can also be tested 950 emitted an tentials. A Stewart- Warner Series than in the day. The dry -cell "C" battery was from the sockets of operative radios. interrupted buzzing noise which continued with a low resistance voltmeter, and wires had been dis- tested after the ground and aerial found to be practically dead. This condition, The famous patented Supreme MUL- connected. This trouble was quickly remedied of course. would lead one to believe that this TIMETER circuit is calibrated with a by replacing the detector tube with a new 27 battery was the source of the noise; but it to determine whether full -wave crystalline rectifier unit for tube. The easiest way does not account for the increased noise at accurate measurements of: abnormal or excessive hum originates in the night. detector tube or in the first audio tube is to The set was removed from the cabinet and M. ranges /250 disconnect the aerial and ground wires; turn all wires inspected for possible loose can - A. 0/2.5/10/25/100 up; set M. A. and 0/2.5 amperes. on the set and let the tubes warm nections. The four flexible leads connected the volume control on minimum volume posi- to the underside of the detector -tube socket A.C.-D.C. Output ranges 0/2.5/10/ tion; then remove the detector tube. If ab- terminals were suspected. This socket is of tube 25/100/250/1,000 /2,500 volts. normal hum still persists, re- insert the the type known as a "floating socket." and and remove the first audio tube. If the hum here is where the real trouble was found. One Capacity ranges 0 /0.01/1.0/10 mfds. is minimized by this procedure. this tube of the flexible filament leads, which at a first be it is reduced to normal /500,- should replaced. If glance appeared to be a good soldered con- Ohm ranges 0/500/5,000/50,000 by removing the detector tube, then this tube nection, was found to be partly broken off, 000 ohms. should be replaced. Increasing hum with ad- and held only by a few strands of wire to Megohm ranges 0/5/25 megs. vancing volume control is another sign that the spring contacts. Replacing with a slightly the fault is in a defective detector tube. longer piece of flexible wire cured the trouble. All readings made directly on meter In another receiver of the same make and The location of the apartment house and the dials -no charts. model, noisy reception and hum were traced heavy street traffic at night, accounts for the to the two wire -wound resistors, which are increased noise at that time. The exclusive Supreme FREE REF- mounted on a bakelite strip and covered top ERENCE POINT system of analysis and bottom with gray insulating paper. In Clarion A.C. 51 is still further improved in the Mas- taking out these resistors, the strip and the Intermittent reception was the complaint all -to- insulating papers are generally found to be this time. A check with the analyzer dis- ter Diagnometer so that point cannot be handled point analytical measurements are badly burned, and they closed all operating voltages to be practically marked without falling into small pieces. In re- normal; current readings in the radio -fre- made by the use of plainly placing this resistor strip, it is a good idea quency stages seemed to be slightly higher switches. This advance in test instru- to mount the strip on two hard rubber bush- than the recommended values, which pointed so as ment design not only provides maxi- ings, each one about one -inch high, to to a possible short circuit in these stages. mum speed and flexibility but guards bring this strip up and away from the bottom The chassis was pulled out. The green lead against early obsolescence. of the chassis; also, place hard rubber bush- at the volume control. which feeds the screen - ings between the strip and the insulating grid circuit, was unsoldered and the ohm- -stabilized papers in order to give the air a chance to meter was put into service. Placing one of An A.C.-D.C. specially the resistors. It is impor- and completely-shielded 100% modu- circulate around the testleads to the green wire and the other with variable tant at this time to check over the five colored - end to the chassis produced no reading, which lated oscillator circuit carbon -rod resistors which are all mounted eliminated any possible short circuit in these attenuator is employed with tap switch on one strip, as you will find that a few of condensers. The red wire, which feeds the tuning frequencies marked on the panel them possibly have changed considerably from cathode circuit, was next unsoldered, and the so that tuning charts are not required; the recommended values, especially the 20,000. test repeated. The ohmmeter at this test maximum tuning accuracy is assured ohm purple- colored. screen -grid resistor. See indicated a partial reading. The leads at the Fig. 4. radio -frequency grid bypass condensers were at 11 fundamental frequency settings receiver had low 1875 kilocycles, Another Stewart -Warner then removed and tested. The ohm meter read ranging from 130 to volume accompanied by sharp, crackling noises. a partially shorted 80 meter the same, indicating grid and covering the 20, 40, and Visual inspection of the receiver and tubes condenser. A new .1 -mf. condenser was sub- short -wave bands. The most beautiful disclosed the fact that the rectifying tube stituted and the trouble remedied. See Fig. 5. and complete instrument in the world. had a deep blue glow. A new tube was substituted with the same result. This clearly Clarion A.C. 70 trouble lay in the power indicated that the rattle in the speaker is a com- was removed, and the A peculiar Dealers' Net Cash pack. The chassis complaint on Clarion A.C. 70 model re- to a leaky filter condenser mon Wholesale Price $1475° trouble was traced ceivers. A Service Man not familiar with this in the power pack. particular model would ordinarily suspect the speaker, and perhaps spend much time in test- For complete information, write Kolster K28 ing it and other components. The real trouble A Kolster K28 was serviced because of the is generally due to the fact that the screen - complaint of a very abnormal hum. On grid tube is touching the metal shield parti- top of the cabinet rested a very beautiful tion on top of the chassis. Place a few rub. SUPREME electric table lamp with a high porcelain base. ber bands around the tube and the rattle will INSTRUMENTS CORPORATION In lifting off the lamp, prior to an inspection, disappear. of the cabinet, the abnormal Bldg. Greenwood, Moss. from the top 470 Supreme hum ceased immediately. (The lamp must (Continued on page 174) -CRAFT for SEPTEMBER, 1933 172 RADIO THE RADIO BEGINNER (Continued jr "'n pu ye It, I) will not Your Tube Tester is need the tubes for the present. The nary to modify either the coils or the condensers set is now operating as an ordinary crystal job. in order without to tune over the entire broadcast band. tube amplification. Tune in, with Cl, However, some such procedure (and as many stations as possible a tidious, and make a careful complicated one it is) would be required if it record of the exact setting of each one. is OBSOLETE The desired to have the two condenser dials more carefully and painstakingly you do this (Cl. C2) match. part of job, If it does not have Supreme's the and the more stations you "log," While it was stated in the or record, the easier the beginning of this rest of the adjustments article that the super was the most sensitive Free Reference Point System of will be. and selective Next circuit available, do not on this tune in the most powerful station possible account expect too much of Tube Testing and turn on the this little set: it tubes, bringing the volume con- was designed primarily to demonstrate the prim trol to its maximum -volume position. Switch the ciple of operation, not to phone plug to the output be a world beater in jack. Varying the picking up stations. In fact, if you live in a contact between the little wire or catwhisker, and particularly poor radio the crystal- roller location it might be in the second- detector, D2, advisable to add a second stage of audio fre- should now result in scratchy noises in the quency amplification; phones. the circuit following the Adjust this detector so that the wire is second-detector will be exactly just barely making contact, similar to that and then slowly shown in the beginners' article in the July issue. rotate the oscillator condenser. C2, until the same And station if you are real ambitions, you can also add is heard that was previously heard with an R.F. stage as shown the crystal alone. in the August issue. If you have followed the series through carefully Adjust condenser C2 to the position of and intelligently you maximum volume; should be able to do both and the second- detector. D2, of these stunts with little trouble. to its most sensitive position. Then, adjust the Below is given two screws. a complete list of the parts re- through the holes in the top of the quired; those of you that have shield can of the intermediate frequency followed the trans- series, have most of them. Winding data has former. L3. for maximum volume. This opera- been given in previous tion varies the issues for the two R.F. capacity of condensers C3, C4, coils, Ll, L2: it is not recommended and tunes the transformer to the that you intermediate attempt to wind the "intermediates," L3, since frequency of 175.000 cycles, or 175 kc. this is If a job requiring considerable skill and any trouble is had in bringing in the signal, experience. Of course, if you it might be well to adjust happen to have In the new Model 45 Supreme these condensers by in the junk box one of the old-fashion type Tube "feel." turning the screws one way or the other, peaked at 30 k.c. Tester each element in the tube is con- slowly, until or 45 k.c., they will be per- nected to approximately the same pressure fectly satisfactory for this set. the contact arm of an indivi- is required to turn each. But be careful not to dual selector switch so that proper cir- run them so far out that the thread comes loose List of Parts cuit connections can be made to each or you might have difficulty getting the adjust- One two. circuit element REGARDLESS OF ITS TERM- ment tuner, Ll; INAL CONNECTION screw back on again. One three -circuit tuner, L2; AT THE TUBE After you tune in BASE OR METAL your first signal it is simply One 175 kc. intermediate frequency transformer, CAP. a question of varying the adjustments until you L3; All socket holes are numbered in ac- get the maximum results from the circuit. If Two 350 mmf, tuning condensers, cordance with R. M. A. standards. There you do this logically and carefully, Cl, C2: is a always mak- One mica dielectric fixed condenser, 500 mmf., rotary switch for each of these ing it a point to realize exactly what you are C6; socket terminals bearing a correspond- doing each time you turn a knob or screw, you Two Concourse paper ing number. The contact arm of this will soon learn dielectric condensers, a great deal about the most .6 -mf., 200 V., C6, V7: switch is directly connected to the useful and widely -applied circuit known today, socket terminal having One Concourse paper dielectric condenser, 4 the same num- the auperhrterodynr, mf., 200 V., C8; ber. The eleven contacts on each of The reason for making the log of these rotary switches stations with One Concourse dry electrolytic condenser, 20 mf.. are connected to only the crystal will become apparent as you 25 V., C9; various parts of the tube tester circuit work; for you always and know the setting of one One Centralab 25,000 ohm volume control, to a selector of grid and plate volt- tuning dial and have only to find with ages. By the other. switch attached, RI-Sw. ; rotating the contact arm of One 10,000 ohm, the switch, the tube element located at Design Considerations 1/2-watt resistor, R2: the One 5,000 ohm, I watt resistor, R3: particular numbered terminal cor- The reason for mounting the responding to the switch crystal detec- One Amperite filament ballast, type 3H -1, R4; can be con- tors on the panels is to allow of simplified wir- One 750 ohm, %.watt nected to any part of the circuit or ing resistor, R5; to and interchangeability as one may work One type 30 tube, VI; any voltage desired. In this manner if better than the other in a given position. One type 33 tube, a tube has a plate, for example, where Ganging V2; the cathode the two tuning condensers was not One four -prong socket, for V1: is usually located, this plate attempted for the simple reason that the gang- One five -prong socket, element at the cathode location can be ing of an oscillator for V2; connected and R.F. tuning condenser One single -closed- circuit jack, J1; to a suitable plate voltage in- is a rather complicated process, involving the One open -circuit jack, J2: stead of to the -B position in the cir- use of what is called a "padding" circuit in the Two crystal cuit to which the cathode is ordinarily oscillator detectors, DI, D2; section to make the two tuning curves Two dials, for Cl, C2; connected. A COMPLETE CHANGE "line up." You will see what is meant by this One knob, for L2 IN THE LOCATION OF THE TUBE if (tickler) : you plot the curves for the two dials, using Two clips for Ant. and Gnd.; ELEMENTS MAKES NO DIFFER- dial divisions and frequencies along the two One baseboard, ENCE TO THE SUPREME MODEL sides of 10 x 14 x 3; in. thick; 45, Let a piece of ordinary "squared" graph One roll solid push-back hook -up wire; the tube manufacturer locrte paper. Because of the wide capacity -range of Three 45 the plate at the tube cap, the control the V. batteries. "B "; grid in tuning condensers, it was not found neces- One 2 V. storage cell, "A." the plate position and the cathode where the grid is usually placed the Model 45 will test the tube per-- fectly. The group of rotary switches also provides a means of applying al- AN ALL -PURPOSE TESTER ternating potentials of correct value to (Continued front page 149) the tube elements as specified by the tube manufacturers. matically provided. The chief advantage claimed conclude that oscillators %, which are miniature This is important for 100 modulation is that the maximum out- substitutes for broadcast since many times put is obtained from stations should also defects, such as partial shorts, will a radio set at a given be 100% modulated. A special evi- input. An unmodulated R.F. signal stabilized cir- dence themselves, which is not always potential, cuit was developed over a period of several case when applied to a set, will produce no audio months the when a potential is applied to output, although for this oscillator for keeping the a tube element considerably the input signal may be frequency constant with varying lower than strong enough to overload attenuation the operating value. the R.F. or de- and varying power supply potentials. Other tector elements of a receiver. This fact is circuits with various technical FREE REFERENCE POINT SYS- evidenced by connecting names, using TEM an output meter to from one to four tubes, have been developed of tube testing is the greatest a act which is responding to the signals of to accomplish such advance ever made in tube tester de- a broadcast station; desirable stabilization, but sign. End the meter needle will none of these seem to offer any advantages your worries with the Su- respond to the modulation signals of music or over the preme Model 45. Order yours today. voice, but returns present arrangement which has to zero during the intervals proven entirely satisfactory for practical between voice or musical impulses, although servicing radio requirements. DEALERS the carrier energy is just as strong between All of the controls and parts NET CASH signals as it is during modulation. of this tester $2950 With a are symmetrically arranged on a bakelite panel WHOLESALE 100% modulated oscillator, the radioman is which measures PRICE much less likely 11%3(19% inches. The panel to set the attenuation at a is mounted in a beautifully -finished point which will overload the R.F. hardwood or detector carrying case with a slip- hinged cover in which circuits of a get when erroneous adjustments a commodious are likely to result. compartment is provided for the accessories which accompany the tester, Supreme Instruments Corp. Furthermore, most modern broadcasting sta- and for such tions are 100% small tools as the radioman may 468 Supreme modulated, and it is logical to want to use with the tester. Bldg. Greenwood, Miss. RADIO -CRAFT for SEPTEMBER, 1933 173 A 50 -WATT TRANSMITTER AMERICA'S (CuntiouId from paye 131) power amplifier circuits, improved operation has radiated or "broadcast so that they become OUTSTANDING been effected so that the correct phase relation- available to the Radio audience. ship of the various frequencies is maintained. In order that the operators may have proper is essential that It is even more important that the amplification control of this entire process. it the function- MICROPHONE VALUE. be essentially linear so that harmonic frequencies means be made available whereby are not generated to an appreciable extent. ing of the various parts of the transmitting The remote This is accomplished by the use of improved equipment may be readily checked. transformers, balanced push -pull circuit and over control room is equipped with special monitoring conservative use of tubes which are only called loud speakers which may be connected at T h e Lifetime in the circuit for direct quality 88 upon to deliver a fractional part of their max- various points Model No. imum output power. checking by ear. Volume controls are used for Double Button The radio frequency (carrier) for the trans- maintaining the audio currents within pre- of mod- Microphone - mitter is obtained from one of two crystal -con- determined limits. Two different types an actual $35.00 trolled oscillators. The frequency is determined ulation indicating devices are supplied for check- or combining process. One Value offered by a specially ground quartz crystal which is ing the modulating mounted in a compensating holder. This device of these is an oseillograph of special design by at our special or is mounted in a thermally insulated compart- means of which either visual observation introductory combined currents only ment in which the temperature is maintained permanent recording of the price of relatively constant at a predetermined value. may be made. A careful log is kept of the visual Both crystal oscillators are operated continuously indications of this device at regular intervals. $695 day and night so that they are instantly avail- The second device is called a modulation alarm able for use. The highest degree of frequency indicator. This device indicates the degree of stability is thereby attained. This is important modulation by means of a conventional meter. from the listeners' standpoint, since it provides It is also equipped with an automatic alarm the maximum assurance that interference with mechanism so that when a predetermined degree Lifetime 88 is a marvel of other high class stations will not be experienced. of modulation is exceeded it is immediately The radio frequency carrier is further am- called to the operator's attention by an alarm rugged and simple construction plified by screen grid tubes until it is at an buzzer. Such elaborate precautions may seem -3l/8" in diameter -2" thick approximately similar voltage level to the out- superfluous, but recent tests have shown that overall. Accurately machined put of the push -pull audio power amplifier. excessive distortion of signals results if the These currents are then combined or modulated modulation is allowed to exceed 100%. Under audio and beautifully chrome plated. at a comparatively low power level, in a radio such conditions an additional range of Has a gold spot duralumin dia- amplifier unit rated at 250 watts output. Here, frequencies is produced which not only cause a again, design improvements have been made to loss of efficiency but which may cause inter- increased phragm .002" thick -special ad- assure that the carrier will be properly moulded ference in adjacent channels due to the justable stretch ring -gold con- and controlled by the audio signal current so that width of sidebands. the fidelity and phase relationship will not be Frequency monitoring is accomplished at the buttons ohms each a visual indicating tact -200 - changed. transmitter by means of is scientifically dampened and The combined radio and audio currents are meter which is designed to maintain an ac- further amplified by two push -pull radio fre- curacy of plus or minus 10 cycles. Thus fre- has a frequency of between 40 on the operating quency stages rated 5 kw and 50 kw output quent checks may be obtaired to 7500 cycles within 4 DB. respectively. Each of these stages requires the frequency and such checks muy be entered on of tubes whose maximum power output is the operating log sheet. use at the more than four times the rating given above, The antenna current will he measured in order that the combined currents may be transmitter by means of a special rectifying dr- a final check on UNQUESTIONABLY THE amplified with a minimum of distortion. cuit. This gives the operator An automatic signal- From the 50 kw. (maximum rating over 200 the power in the antenna. an alarm GREATEST VALUE EVER kw.) stage the combined currents are sent to the ling device is included which sounds current drops below a pre- IN A CARBON antenna over a new type three wire transmis- in case the antenna OFFERED combined currents are then determined value. MICROPHONE! sion line. The OPERATING NOTES (Continued from page 172) high -51A" ring Desk Stand -8" - was that of an control worked loose, and one little turn of A puzzling phenomenon beautifully chromed -complete with Apex 28A, series 91. The set would play for the volume control knob would be sufficient to $1.95. Transformer to Match about ten or fifteen minutes, and then stop. break off the wires. It is advisable. therefore, springs when confronted with trouble of this nature, 89c. Turning the switch off and on would pro- -shielded $1.45, unshielded duce reception for perhaps another ten or to always inspect these leads, even though Address and Sound Companies fifteen minutes until it stopped again. Visual you may find that the volume control is tight. Public that when leads for our folder of Microphones, inspection of the set disclosed the fact that It is obvious, of course. the -write each time this thing happened, the brightness are found broken, it is only necessary to un- Speakers, and Sound Equipment which of the filaments in all tubes would grow dim- wind a few turns and then resolder them to terminals on the volume controL is offered direct to you at the lowest mer, and then would go out entirely. The the proper A.C. cord, the off and on switch, and the When repair work of this nature happens, it prices in the country. primary of the power transformer were all is desirable to replace the ring nut on the a hexagon nut and given a careful continuity test; but all ap- volume control with thin peared normal. spring washer, so as to preclude the possibil- a non -remunerative call -back in the going over the chassis and pulling ity of After near future. wires for possible shorts or loose connections, The LIFETIME CORP .r ed "óh; nothing was disclosed. The A.C. toggle switch w'as strongly suspected, and it was decided to remove it for closer inspection. When in- READERS' PAGE InPoed specting this switch, it was discovered that ( Continued front. page 183) Audio w RSuPpl YTarenDrnseomlor the brown bakelite housing, which covers the ZENITH 460-(A correction) DUAL-CHANNEL DUAL-OUTPUT lever and spring contacts, was cracked in sev- Class "B 33-76 Watt Amplifier eral This condition evidently partly Editor. RApto- CRAFT: Designed by LOUIS GANCNER places. issue' of released the hold on the spring contacts which, In the June, 1933, "automotive a slight error in t-r.,liei H 14á.. for them to gradually RApto-CRArr there appears á `.üs )I in turn, made it possible ïIrñ"nmn.Tî.. g of the Zenith model 460 2-C1uu "áIt" 'n>a-,Mntai.5n i slip down until they became disengaged from the sensitivity rating 2-41:u, 00. The sensitivity rating is 7 00 the lever. Moving the toggle switch up and automobile receiver. I:,I.t.'.:,, t-!.'_. % I :+l 2 liltr''h..l.,.datlwn,T>n+T3ESrlVl 100 ..Ii.,i...A \I..\ tiI2 1.5 microvolts (A.M.A. standard input required . . them back tempor- .5 T>P. t.Mii...... _.en down evidently brought 1 -rd, Chu,. 011.04. 50 \i. A. CIIJ sess arily, only to drop down again after a short to give an output of 50 milliwatts) or 0.4- micro- SPECIAL OFFER: Complete Nit as Listed above. Srj.sSO this volt -per- meter, instead of 1.5 microvolts -per- cluding Blue Prints. d Dia . interval of time. A new switch solved n 6 Volt Storage 6atery Operated Motor Ganarator meter as you have listed. We will appreciate Neminllt Volts DC problem. Class 8" Regulation Delivers 320 K st this correction. 120 Mils. Consumes only 9.5 amps Low record reproduction in some models. the publication of . - un.b.rod li1v R r 1 r . . i .1{ We feel that the of automobile e ' . wla s radio and publication ^ 1 . r , h:, . l'Iili.r 0 particularly in the General Motors : 1i.,1 ï ï receiver data and schematic diagrams is a real l r ll,'..4. in z P"rt,hl..nP. 11S can often be traced rR' ' t d,i f(..,r I i Ir- ir!"Ir ni1 phonograph combinations, ç'yI n "`-A i .in, I.:.uV.h .4Ái.\, nl Ì ..r corn - boon to the Service Man. We also believe that ó `\\ i the tone . ., . i,... .. N ..t. I. . to broken connections between - wnat '1:., \ e.i ,'I receivers and the volume control. This tone every manufacturer of automobile pensator consider- compensator is hard to get at for testing pur- should give the Service Man special Remington Auto AC Supply Units in the layout and design of his set. The Storage Battery Model, $2/.75 poses, as it is located underneath the motor ation produces AC Watts It is compact construction of modern receivers makes 12 rSS Operated Model. $32.50 board, close to the volume control. dú es 110 Volts AC 150 wound with very fine wire and the ends are this feature doubly important. MAItVIN Hosas, Engineer, Send Today for FREE Valuable Catalogue! soldered directly to the terminals on the Automotive Receiver Section. Remin ton Radio ayd Electric Cor .,125 -R Westl7th St., New York. N.Y volume control. In almost every case the reason for the broken leads is that the volume Zenith Radio Corp. for SEPTEMBER. 1933 174 RADIO -CRAFT NEW ADAPTERS (Continued from page lid) PRPi),/l/j No. 964KS, Fig. 10, VPWO is used to test the 57 and if you were testing a 47. H 58 tubes. The .01- tube tester with which this No. 965AC, Fig. 17, is used to test adapter the 43 or is used must have a common connection 48 tube in the 27 socket of any tube tester. To of the control -grid and screen -grid circuits. test the 43 tube, use a 40 W., 115 V. lamp in The adapter is placed in the 45 socket and the the series socket. Place the 43 tube in the six - NAT AL tube in adapter. Tests are then made in the hole adapter. Then place adapter in the 27 same way that you would test a 45 tube. socket of tester. To test the 48 tube, use a Nolo 60 W., 115 V. lamp in the series ZZ Testing Power Tubes socket and place the 48 tube in the six-hole adapter. Then ITf.Y, No. 965 -79. Fig. 11, is used to test the two place adapter in the 27 socket of tube tester. sections of a 79 tube in the 37 socket of tube If little or no plate current reading is noted, testers. This is an elongated adapter. having then the tube is defective and another one a toggle switch and a control -grid lead Place should be used in its place. OWN METERS, the 79 tube in the adapter and the adapter in the 37 tube socket of tester. Attach the adapter Rectifiers control -grid lead to the control -grid of the tube. No. 964KKH, Fig. 18, is used to test the MANUALS FREE! Then test the 79 tube in the same way that you 25Z5 tube. The tube is placed in the full -wave would test a 37. However, be sure to use the rectifier socket or the one usually used to test Why don't you join the thousands who are toggle switch so that both sections of the tube the 80. 82 or 83 type tube. getting fine equipment for their service business. Tests are then made Free, are tested. in the same way that the full -wave rectifier the easy National Union way? Service No. men who tie up with National Union 964KPPL, Fig. 12, is used to test the 79 tube is tested. This adapter can also be used profit tube in through the sale of tubes whose high quality the 10 or 50 sockets of tube testers. To with any other type of tube tester having stands undisputed and at use the the same time procure adapter, place it in the 10 or 50 socket provisions to measure the plate current of both valuable business assets in meters and service of the tube tester. Then place tube in adapter plates of the rectifier tube, and providing 25 V. manuals at no cost. Let's get together. Send and connect the control -grid lead on adapter to at the filament terminals. coupon. control -grid of tube and test as if you were No. 966PP, Fig. 19, is used to test the 25Z5 testing a 10 50 type or tube. tube in a 43 socket. Place adapter in the 43 Write for special bulletin on new No. 964PP, Fig. 13, is used to test the 19 socket and test as if you were testing a 43 tube. National Union increased profit plan tube. It tests both sections together. Place However, be sure and manipulate the switch adapter in the 30 or 31 socket of any tube on the side of the adapter so as to test both tester. Then place the 19 tube in the adapter plates of the tube. and test the tube as if you were testing a 30 No. 964 -6Z5, Fig. 20, is used to test the 6Z5 or 31 SUPREME MODEL type. tube in the 80 socket of any tube checker. 333 No. 975 -53, Fig. 14, is used to test the 53 Place adapter in 80 socket and then tube in tube in any tube tester. Either section of the adapter and test in the same way that an 80 tube FREE! can be tested by manipulating the switch tube is tested. on the Extra! At Last l Combination Set Analyzer side of the adapter. The adapter is No. 965 -6Z5, Fig. 21, is used to test, separately, and Point placed to Point Tester! in the 27 socket and tests made in the both plates of the 6Z5 tubes. The adapter is New Supreme Model 333 compact and portable, usual way. placed in the socket usually used to test the 37 no larger or heavier than ordinary analyzer. For No. 975CP, Fg. 16, the service man who is used to test both sec- tube. It is then tested in the same way that a wants: 1. A new tions of the 53 tube at the same time. The 37 is tested with the exception that the switch up -to -date analyzer. adapter is in the 2. A Point to Point Tester (Resistarce and placed 27 socket of any tube provided on the side of the adapter must be Voltage). tester. The 63 tube is then inserted in adapter manipulated to test both sections of the tube. 3. A direct reading capacity and tests made in usual meter. the way. No. 955 -84, Fig. 22. is used to test the 84 4. Means of reading the leakage of wet and No. 975KSP, Fig. 16, tests the 59 or other tube. Place the adapter in the 37 socket and dry electrolytic and paper condensers. similar 5. seven -prong tubes in any tube tester test as if you were testing an 80 tube. However, Universal circuit cut -in. which 6. Rectifier type has provision for testing the 47 tube. be sure and manipulate the switch on the output meter. Simply insert side Free with tube purchases. Small deposit. adapter in the regular 47 socket of the adapter so as to test both sections of and then insert 69 tube in adapter and test as the tube. OTHER NATIONAL UNION OFFERS A DECADE CONDENSER You can also get an Oscillator and Output Meter. (Continued from page 16s) Three Service Manuals, Unameter (Tube Tester), Readrite Tube Tester, Bench Kit box, Hickok Ohm -Capacity 6 .4 --.I -Voltmeter. Euuip your shop the aid of a hack saw and file. Notches should be easy National way. 6 Union Small deposit on .4 +.2 .6 cut in the cams as shown in Fig. 3 to provide some items. 7 .4 +.3 .7 locking at each position. 8 .4 +.3 +.1 .8 When completed. the cams may be assembled 9 .4 +.3 +.2 .9 on % -inch rods with % -inch spacers between. NO HIDE 'N' SEEK FOR Care should be taken to have like numbered NATIONAL UNION The above example is for the third section segments in line. of a .1 .9 You haven't time to unit. It is seen that by adding There are two methods to play the game of "Hide of fastening the cams ñ Seek" . when you need units in parallel, each unit having a capacity to tubes you want the shaft. One method is to use a threaded them without . . of .1 of that of delay .it will pay you to ask the next, the range may be rod and clamp the washers (cams) together your National Union jobber extended to that desired. FIRST ... all tube with a nut at each end. This method is shown types kept in stock at all times for your con- There are several possible venience. switching arrange- in the drawing, Fig. 2. The other method . . . ments for the condenser. is to One of these makes clean all parts before assembling, and then, a use of a four -pole, ten point tap switch. The after they are put together on a % -inch rod, switch is rather expensive, however, INTERCHANGEABLE so that the whole assembly is heated with a TUBE for the benefit torch and of those who desire to build solder flowed into all the joints. CHART their own switches, This method a cam switch will be de. was used in the switch pictured in This chart scribed which can Fig. B. gives brief descriptions of all tube be built at quite a low cost. The frame is cut from 1/16 -inch sheet metal types, filament voltages and comparative type Figure IA shows number the connections of one unit and bent into the shape, as shown. It has a of National Union tubes and those of of a decade other manufacturers. condenser using the four pole tap % -inch hole at one end to serve as a bearing It is organized in simple switch. easily readable form. A copy be Any number of consecutive units may for the shaft. The other end has a threaded will sent free be added in parallel. Figure on request Ask for the "National Union Inter- 1B gives the con- bushing which serves the double purpose of a changeable Radio Tube Chart." nections for a complete decade condenser, using bearing for the shaft and a single-hole mounting cam switches, which covers the range from for the unit. .001 mf. to .999 mf. The contact springs are obtained from phone Note: All offers subject to withdrawal The construction and dimensions of a cam fucks or switches; or, in the absence without notice. Send coupon NOW! switch of such are shown in Fig. 2. The cams are cut material, they may be cut from spring brass. from 1/16" sheet metal. A convenient method The condensers of the lower capacities should of construction is, first, to cut out round metal be of the molded mica variety, and may be National washers and then remove the unwanted center stacked and bolted to the under -side of the Union Radio Corp. of N. Y. sections. a 100 Madison Avenue, New York If three unit box is desired, three frame. The higher capacities can be of the City cams Sirs: of a kind will be required for each unit; tubular paper insulated type. and they, also, I am interested in following equipment: Supreme 333 or, a total of four cams for each unit It is should be clamped to the trame. All of the con- Unameter Read - advantageous to clamp three rite Tube Tester Oscillator & Output washers at a time densers should be of non -inductive construction. Meter Service Manuals on a % -inch threaded rod (since, for D Ohm Capa- each unit, A hakelite panel should be provided. The city Bench Kit RC9 three are alike) and cut all three at once. In- numbers 0 to 9 for each switch may be stamped stead of trying to mark the cams directly on on the bakelite; or switch plates, with the num- NAME the metal, it is suggested that round paper bers on them, may be used. A number corre- discs of the same diameter and divided into ten sponding to the lowest capacity setting of that ADDRESS equal sections should be glued to the ends of individual unit should be placed under each CITY.._. the stacks of washers. Then the sections to be switch. Thus. a box such as pictured in Fig. A STATE. removed can be marked and cut out with the would be stamped with .1, .01..001 mf. sections. RADIO -CRAFT for SEPTEMBER, 1933 175 F.1.4s List for .001 to .999 Mf. Condenser Three four -gang 10 point switches (if used); RID Effie BAN D/ One Aerovox fixed condenser, type 1455..001 - mf.; SERVICEMEN One Aerovox fixed condenser, type 1456, .002 - \ WAGrON mf.; RADIO DEALERS One Aerovox fixed condenser. type 1455,.003 - ;.., mf.; SEND FOR THIS One Aerovox fixed condenser, type 1466,.004- mí.; One Acratest tubular condenser, .01 -mf.; FREE I One Acratest tubular condenser, .02 -mf.; .03 -mf.; i One Acratest tubular condenser, CATALOG! B One Acratest tubular condenser, .04 -mf.; One Acratest tubular condenser, .1 -mf.; IT'S CHOCK -FULL One Acratest tubular condenser, .2 -mf.; One Acratest tubular condenser, .3 -mf.; OF BARGAINS FOR YOU One Acratest tubular condenser, .4 -mf.; Three knobs; Radio Dealers and Servicemen Two binding posts; can't afford to be without this One bakelite panel 4x11x 1',; inches; marvelous buys One cabinet 4x11x4 inches; book. It offers Central:1h Miscellaneous sheet metal, machine screws, in Radio Sets, Long and Short and jack springs. Wave Apparatus, Servicemen's MOTOR RADIO Repair and Replacement Parts, AN "R" AND "C" CHART Electrical Goods, Sporting SUPPRESSORS (Continued from page 164) Goods. We will now take a few examples to illustrate the method of using the chart its solving prac- JUST OFF THE PRESS! tical problems of resistors in parallel or con- Be among the first to have the pick of densers in series. great bargains. Mail this coupon now! AUTO radio is playing Example 1.-Three condensers of .0003, .0004 and .0005 mf., respectively, are connected in RADIO CIRCULAR CO., INC. the "center ring" these series; what is their resultant capacity? 225 Varick St. days. Wise manufactur- From the chart we see that the corresponding New York, N. Y. Dept. RC -9 value of .0003 on line A is 3,330 on line B; the Please send me free of charge and with- ers, dealers and service value on line B for .0004 is 2,500; the value on out obligation, your latest catalog. - line B for .0005 is 2,000. Adding together all men are using CENTRA .. -.._ the B values we get 3,330 +2,500+2,000- 7,830. Name-- ..-- ..-- ..-- ..- ..- LAB suppressors because on At 7890 on B we get the answer: .000128 Address they do not (like some line A. take heavy Example 2. -Find the value of the following City_..._. - State suppressors) four resistors in parallel: Rl, 500 ohms; R2, toll of gas consumption. 650 ohms; RS, 800 ohms; R4, 1,000 ohms. The Use Centralab suppressors corresponding volues of Rl, R2, R3, and R4 on scale A are .002, .00155, .00125, and .001, respec- iii for original equipment, tively. The sum of these figures is equal to sfrú eT`>rr!` and for replacements. .0058. The corresponding value for .0058 on scale A gives 172, which is the resultant resist- MICROPHONES ance of the four resistors in parallel. Example 3. -Find the value of the following SHURE BROTHERS COMPANY in 500,000 ohms; R2, Mwrochinw. -ewe., resistors parallel: Rl, sN Bul*E. P.. 200,000 ohms; R3, 20,000 ohms. Following the 177 WEST MADISON ST. CHICAGO. ILLINOIS procedure of the first two examples, we find that the corresponding values on the A scale of the in parallel are. .000002, RADIO LABORATORIES resistors connected (CENTRAL .000005, and .00005. Their sum is .000057. The MILWAUKEE, WISCONSIN on scale B is 17,500, which is RADIO SCHOOL salue for .000057 Courses in Radio Broadcasting. Wireless the answer. Operating, Radio Servicing and Electric The procedure, which is the same for all other Refrigeration. Address POWER problems, is as follows: step No. 1, find the C. VAN HORN known J. corresponding values of the resistors 6 Penmen. Vice -President RCA Inalifufes, Int.) connected in parallel or the corresponding values PHILA. WIRELESS SCHOOL AMPLIFIERS of the known condensers connected in series. 1533 Pine Street Philadelphia, Penna. Using a pencil and paper, write down each cor- FOR EVERY PURPOSE responding number found on the chart for each Direct -coupled circuits, designed resistor or condenser ; step No. 2 add these num- for high output, rich tone and bers to get their total; step No. 3, using this IOSPAGE mod- new number. which is the sum of the reciprocals economical operation. Four of the resistors in parallel or condensers in 1933 RADIO els supplying every public and series, look for its corresponding number on the private need. $32.50 to $195.00, corresponding num- A scale of the chart. The CATAReplete with BARGAINS _ GALORE U Gso, less tubes. ber is the final answer. DEALERS- SERVICEMEN-AMATEURS Write Dept. RC -9 for Catalog Observe that all numbers from 1 to 1,000,000 Send for Your Copt; TODAY f are read from left to right and all numbers less 6gçeoärátpöTr. Rt. New Yor1t. N.IG read from TRY -MO RADIO :° 175 Vartck than one -the decimal numbers -are Dept. C -9 right to left. This may be a little difficult to work with at first, especially to those who are ELECTRAD not acquainted with the use of a slide rule, but after working out a few problems the reader DAUCTO =itT I ) . should have no difficulty in using the chart. Single unit -All electric The chart, as the reader can readily see, is Only one ooh to Iwten -two electrical connection.... and Prr.m' so The DICTATOR ia' talai. A .tube auperh.twod,ne with woe fRafRADIQArAt06 nothing more than a table of reciprocals ar- . automatic voume control. and full electrodynamic speaker.s control tm nu cosily a meeting Recir W ., ranged that it becomes a valuable instrument in andIt y,g 1934 RADIO CATALOG described in this e. oef s wed. Oicia nra Modeel 50. Completa 323,49 solving problems of the type Net. Modelut T It F a1. 515.00 Net. Write for our new catalog now on the press ... most Com- can also be used, however, in other plete line of latest radio sets, service oass supplies, re- article. It AUTOCRAT RADIO COMPANY find the Ave., Chicago, Illinois placenment parti at Invest whoirseln t prices. types of problems where it is required to 3555 N. Mamifton ALLIED RADIO CORP. values of the reciprocals of certain numbers. B35 W. Jatkgen Blvd. CHICAGO (While charts of this type are not suited to uses which require absolute accuracy, they are s satisfactory for most practical purposes. In this SERVICEMEN: The reader THE MOST COMPLETE LINE OF CONDENSERS respect they are great time -savers. 'WAND REBUILT AND RESISTORS FOR EVERY RADIO USE is referred to the following articles in RADIO- e.-rree womb.' our new S.W..," Catalog folder tree of charge CRAFT for additional "chart" information. "Tube mÀdiu.:iiúd at a Glance," August, 1932, page Rf"fOfnadáb.n .pi.e i Characteristics mans ewes. eveni superior than I. 128A. "Tube Data Chart," February, 1933. pg. I mali. mrialuni..d nÌrerfu. 512B. ''Parallel Resistors," March, 1933. PK. rharacrbtk.l Oupect kr..re treinÑ rrtiore- po ndno/writers 552. As additional reference material of this zu,,,, Pennf'ea,Câd will be published. U Nr' nature becomes available it PEMBLETONfLABORATORIFS Brooklyn, N. Y. Technical Editor.) 521 Parkriew Avenue Fort Wayne, Indiana SEPTEMBER, 1933 176 RADIO -CRAFT for A 26 -W. AMPLIFIER Test All the NEW Tubes Continued from page 171) Two 10 mf., 35 volt, electrolytic condensers, with This Improved and C5, C6: Four Aerovox 0.00035 -mf., mica condensers, C7, Modern Instrument C8, C9. C10; pccNYate! One triple 4 mf. 500 -volt electrolytic condenser, The E 34 TUBE TESTER C11, C12, C13; re exibie f Tets all J. 5, 6 & 7 One triple 8 mf. 500 -volt electrolytic condenser, prong tubes in« lud- C14, C15, C16; Ing the new small 7 prong series, the 12- One two foot four -wire cable and five prong f 14 volt, the 25 -30 plug, Pl; o volt, 2A7, 2B7. 6A7, One Remington Power transformer 350 -350 volts, /wore ec 6117, 2A3, 2A5. 5Z3. ore economical! 53. 73 84. 127.3 and 120 ma.. D.C., 5 volts 3 amps.. 6.3 volts, 3.5 2325. Provision made amps., PT; for future type tune.. Gives Short Test: Two Remington heavy duty R.F. chokes, 15 r Grid Change Test, mh., 75 ma., 20 ohms, R.F.C.1, R.F.C.2; Oscillation Test and 'l'ot al Emission Test. Two Remington 15 amps. R.F. chokes, 15 mh., Voltage regulation Po- 1 -1,000 ohms, R.F.C.3, R.F.C.4; 1311 Volts. Top with Two Aerovox .00035 -mf. 600 volt mica con- h:mdle provided. ' TEN DAYS TRIAL densers, C17, C18; -MONEY RE. Two 8 mf. 35 volt non. polarized electrolytic con- FUNDED IF NOT SATISFACTORY densers, C19, C20; E 34 WITH 31/4" One Coast -to -Coast 6 -volt motor generator hav- D'Arsonval METER ing class Net to Dealers & B regulation and delivering 120 ma. Service Men at 320 volts, M.G.; One 2 amp. fuse and mount, F; One Coast -to-Coast amplifier portable leather case. 1941" lg., 151/4" wd., 10" hg.; $215° Two Coast -to-Coast Circular on request dual -field sneakers; Two Coast -to -Coast 110 -volt A.C. exciters for L & L ELECTRIC COMPANY above speakers; 336 Madison Ave Dept. 4 -A Memphis, Tenn. One Coast -to -Coast cadmium -plated base, 18" long, 10" wide, 3" high, drilled, and 2 cans: Two Coast -to -Coast speaker portable leather cases (with celotex baffles) ; One Coast -to -Coast phonograph portable leather Install case; a MILES One Coast -to -Coast 6 -volt D.C. dual -speed phono Complete motor and 12 -in. turntable; Power Amplifier One Coast -to-Coast 110 volt A.C. exciter for above phono motor; Broadcasting System! One dual speed phono pickup; anJ jpvt(.-.1jtinaf_..: One Coast- to-Coast t7 ole batterÿ AC -DC MODEL -110 to 140 7-tube 6 volt D.C. and 110- Co volt A.C. operated Only VOLTS 25 to 60 CYCLES superheterodyne tuner; l t;5t Build a profitable and reputable One Coast -to-Coast portable case for above; e public ddress business this One Coast -to-Coast universal "microphone-phono- ór Dealers llllll et -develop it into a year 'round hs radio meter equipped Input Control mixer The MILES AC -DC Power box. Amplifier Broadcmt ing System employs the latet RCA Tithe,,. It is simple to operate try just slugging into the current line. MODERNIZING Portable ea that it r .a'ay T ried,.. Velrone control perm its (Continued front page 165) el yy r 1 r zr.Tir! AndM dde d n rThì. rumple,' portable grids; this makes possible un', rn.i.f. of rower Amplifier. Stikriret ', - it to use only one . Tain. pula -i Dynnmir Speaker. had.. rower 22 and Gain Control-all within uns ".. V. "C" battery, provided it has a 3 -V. breackabelre sa y o. Equipment oleo eludes sensitive yu extra tap. microphonelb.. and foot flexible subi. Measures 3" r'i O "-- r.itl, Operation Complot kit form Including RCA Tubas, ready to wire The finished Job, after the R.F. compensat- 1 Net ing condensers have been re- adjusted and the TO; EALEIt6 otages hied and aired $21.00 properly aligned, has exceptional dis- ready to armpit, Sl:n it 1:X1E5f tance- getting ability, excellent tone quality, Write for complete circular on Mlles Amplilying and will handle enough volume without t er distortion for ordinary home requirements. The MILES REPRODUCER CO., INC. total drain on the "B" battery is less than 20 244R West 23rd St. New York ma.. at full volume -less than one -half that f the set using 71A's. The "A" battery brain, is, of course, only a fraction of the original -560 ma., well under the maximum allowable for an air cell. In the sets which we have converted we Try this FORMULA have had no trouble with circuit oscillation. Illìs ,;hl , wa to:dc 11 Deend although with the volume control fully ad- Bo itr,,l¢ uln Mien its -iewu , e Voltmeter why out try this FORMULA: vanced a swish is heard as a carrier is ap- Q +A +MD proached. Tuning is very sharp. One of w PwwR before LC these modernized sets which has been in opera- Never have you been able to buy such dependable. thoroughly pear« lesi, quality instruments SO Inn a When Q equals QUALITY and A equals tion for -at ACCURACY eight months is still using the same peke. Thoth-amts of expert se Icemen, dealers and r - MD equals MODERN DESIGN and LCequaL. LOW set of "A" and batteries. When irrimentrrs throughout the world use and endorse Read - (70 )ST and LAST COST then P W W R is always PRECI- "B tested tlte SION WIRE WOUND RESISTORS. last week, the instruments. Your Jobber can supply you. Slake "B" batteries registered 39 V. your tester dollars go further. Send the coupon today. RESISTANCE RANGE« .25 Ohm to 1 Megohm under load, although the owner uses the receiver about five hours per day. READRITE METER WORKS TYPE "F" TYPE 4.11. Dealers. who trade in battery Bets will find 71 College Ave., Bluffton, Ohio Normal Rat. Normal Rat- it profitable to modernize the "70 -Q." Its ins 1 Watt* ing Maximum Maximum5, Watt4 value is increased considerably, and consider- length I. n ing that usually a new set of tubes is in- Si Maxi mu to Mail This CoaponTODeY! Diem ter Diameter stalled when the set is sold second -hand. the cost is negligible. Readrite Meter Worker LengthI of LB gth of 71 College Avenue, Leads 13' Leads 14 Bluffton. Ohio. Furnished Furnished I;ept lenient with No. IS with No. IS i d Tinned y, I me Oapp REMEMBER information about I No SS0; Ohmmeter. r LeapDr - catalog of other servicing Instruments. Free Booklets and Price List Radio Progress Week Precision Custom Built Wire Wound Resistors, Mfg. by October 2 to 7 PRECISION RESISTOR CO. (See page 141) 334 Badger Aye. Newark, N. J. State J RADIO -CRAFT for SEPTEMBER, 1933 177 INFORMATION $1 PAYS FOR $3000 (Continued from page 168) are of high -resistance type; these are quite LIFE PROTECTION suitable as choke coils in the filter circuit anktin of receiver power packs. Other field coils are Even If You Are Past 55 :11v of low -resistance design -5 to 16 ohms (the field coil of the "Motor Majestic" model 110 Quality receiver illustrated by diagram in the August, The National Security Assn., 204 S. Ham- 1932 issue of RAnso- CnArr, pg. 106, for ilton Dr., Dept. 76 -W, Beverly Hills, Calif., TRANSFORMERS example, has a resistance of only 6 ohms); is offering to men, women and children, be- they usually connect directly to a low -voltage tween the ages of 10 and 75, a new Life Pro- for Every Purpose source, such as a storage battery. tection Membership Certificate without medi- Schematic circuits of three differing types cal examination for $1, which pays $1000 REPLACEMENT of exciter units are illustrated at A. B and for death from any cause; $2000 to $3000 C in Fig. Q. 215. for accidental death. SEND NO MONEY. Power At A are shown the connections used in Just your name, age, name of beneficiary, Audio the Amplion model AC 210 exciter; and, at and a Life Certificate, fully made out in Chokes B. the model EL 22 exciter. A better known your name, will be sent to you for 10 Filaments instrument, the Wright- DeCoster model PA- Days' Free Inspection. NO AGENT WILL 20 exciter, is shown at C. CALL. If you decide to keep it, send only SOUND The first two exciters are designed to supply $1 to put your protection in force for power to as many as four, low -resistance field about 45 days -then about 3e a day. If EQUIPMENT coils. The latter is designed to deliver power not, you owe nothing. OFFER LIMITED. to several high -resistance field coils, and will So write today. Power deliver 25 W. to a 2,500 ohm load. Audio Chokes Misers THE AMPERE AND THE E Microphone qn ST. LOUIS OHM THE AMATEUR The following interesting information has recently been published by the Bureau of Stan- AMERICAN TRANSMITTING dards. BOTEL Power Absolute Determination of the Ampere 275 ROOMS Filaments The value of the ampere has been determined WITH BATH Modulators in absolute units at the Bureau, using a cur- $2.00 Up Chokes rent balance, in which the force between coils ...... , The current uso. a. :r- Your Jobber carrying a current is measured. 111: See balance originally used by Rosa, Dorsey, and or Write Direct Miller was employed, but the apparatus has been modified in many important respects. FRANKLIN TRANS- Four sets of coils were used. The important FORMER MFG. CO. constant in the computation of the current from THE between the coils is the ratio of their Dept. RC the force ANNEX radii. Eight experimental determinations of ROOMS -609 22nd Ave. N.E. 226 607 these ratios have been made giving results which WITH BATH Minn. Minneapolis, are self- checking and which show no errors j 1.50 Up larger than f 6 parte in 1,000,000. Four series of determinations of the force give results in which the average deviation from the mean is about f 3 parts in 100.000. The When CONDENSERS results may be expressed as 1 Bureau of Standards International get that Ampere = 0.99994 Absolute Am- pere. "ALL- GONE" feeling A report of this work was made at a meeting of the American Physical Society in Washington, about this time of year, "it's not the and will be published later in the Bureau of heat -it's the humidity." Moisture, Standards Journal of Research. or humidity, combined with high summer temperatures ruins many a Absolute Determination of the Ohm Our Food has made filter and by- A determination of the ohm in terms of the our Reputation COFFEE SHOP OVEN pass condenser units of length and time has been made at the UNTIL MIDNIGHT -and gives Bureau. The method depends on the measure- you plenty of ment of a self -inductance in terms of time and service work. the present unit of resistance, and on the coin But DON'T putation of the inductance from measurements TAKE A of the dimensions of the inductor. were measured. -The Hotel Royal- CHANCE on Three single -layer solenoids of Philadelphia having your They were constructed with such care that the The HOMELIKE Hotel replace- inductance can be computed from the measured at Broad St. & Girard Ave. ments break dimensions with an error of only a few parts in Philadelphia, Pa. down after a a million. The measured inductance can be short time be- measured in terms of resistance and time with Combines every convenience and home cause of this about the same accuracy. The result is expressed comfort and- commends itself to peo- tame humidity. as ple of refinement. MOIST- Install Tobe Surgproof- I 1 Bureau of Standards International S OF CITY HALL URE- PROOF- Service Condensers Ohm = 1.00045., Absolute Ohms. WITHIN MINUTES on and make sure of your profit the This result was presented at a meeting of job. Compact -easily installed -de- the American Physical Society. Rates as low as pendable-unaffected by moisture - $3 $2.60-Single Tobe Service condensers are the 1 2.50 00 & s oule1 choice of discriminating service or- RADIO -DOCTOR, ganizations. We maintain a complete We make it our business to please stock of Tobe condensers at all times. SURGEON In a past issue of Amateur Wireless (Lon- A.k for Mr. Smith, Mgr. Allied Radio Corporation don), we note the following interesting use of 833 West Jackson Boulevard CHICAGO, ILLINOIS telephotography. An Argentinian visitor to Berlin. finding that his eye, which had been troubling him for some time, was rapidly be- ØOLOc,, had his eye photographed and the coming worse, Are you missing any books from the picture was sent by telephotography to the .a mille Aires. It was re- le, ape ,vol .I . ;it`= RADIO -CRAFT LIBRARY SERIES? If family physician in Buenos calIphten :::%s ctntein:'in, oAnne, ceived there in 8 minutes, via the Atlantic pic- Devoted.to a. ace aaHvHealth ity.iene. so, turn to page 132 of this issue, and Contain. 19 important artielee. Questions and A newere, Bonk aerie« ture telegraph service, where it was reproduced -ith at lee saille get complete details about the books doctor, and treat- HearApproach to tba Iileeu.aioon Sexual MaL W,ueta very clearly, examined by the and Mienn ,uidity and lmpnten... Get. copy of SÉxoi."t:r today. a short time by radio sad or send 25e stner.13s For copy «i current you need. Order them ment recommended in SEXOLOGY " 255 West Broadway IHne York. Ñ. Y. telegraphy. RADIO -CRAFT for SEPTEMBER, 1933 178 SERVICE ELECTRIC / ARC THEORY - Re riyerrato,sa WITH PARTICULAR REFERENCE TO Useful Tips In your community there are THE NEW "IGNITRON" TUBE ** dozens of electric refrigerators to be serviced. Many need im- Joseph Slepian and L. R. Ludwig From mediate repairs which can be made quickly, with little expense -and which Other Service Men you can repair with the aid of this au- thoritative Refrigeration Service Man- FOREWORD ual. Make many extra dollars, together Dr. Joseph Slepian and Leon R. Ludwig of with other repair work. Electric refrig- the Westinghouse Research laboratories eration servicing is a well -paying busi- have developed a revolutionary method of ness -start in your spare time-before controlling mercury -arc devices which is long you will devote full time to it. One more positive and many times faster in ac- or two jobs pays the small cost of the tion than methods now in use. The arc can be started 60 times a second at point FREE! OFFICIAL REFRIGERATION SERV- any ICE MANI'AI.. on the voltage wave, and since there is no grid to be protected from heating, but 96 Pages of New Data merely a carborundum- pencil dipping in the mercury pool, large currents can be "Sylvania News" carries a full Have Been Added controlled just as easily as small ones. The to the small laboratory specimen of the new page of practical servicing facts "Ignitron" tube illustrated, will carry 60 OFFICIAL REFRIGERATION amperes at 185 volts D.C. with only 0.15 every month. Mail coupon for SERVICE goo amperes and 30 watts loss In the complimentary subscription. MANUAL control element ( "igniter "). To bring this useful service manual right up -to -date. Mr. L. K. Wright, the editor of the OFFICIAL REFRIGERATION SERV- I I ergs a way to keep up -to- ICE MANUAL, has added a wealth of ma- date on the shortcuts other terial on new electric refrigerators, and HE secret of the Slepian- Ludwig control lies older models as well. As usual every re- in a high - resistance rod, partly immersed in "live" service men are finding frigerator has been accurately described the mercury pool, which from the viewpoint of servicing- diagrams when energized starts valuable in their business. to illustrate the essential parts, so simpli- an arc cathode. For an 'W' resistor rod dip- fied that repairs can easily be made. The ping 'rá" below the surface of the mercury, tests The monthly news and service addition of these new pages will not in- showed the minimum voltage for starting the crease the cost of the book to those who arc was about 130 volts; a sudden application bulletin, "Sylvania News," gives order their copy now. of 250 volts started the arc in less than 5 micro- you this information, as well as seconds. During tests the starter worked Here Are Some of The Important Chapters: equally well in solidified tin, proving that its all the latest news in the radio oit naturt lori t. the Iteai gerat Ion Servicing Itusine -a operation is independent of the degree of im- History of Retrlgerat ion and tube industries. Simply Fundamentals of Refrigeration mersion of the rod and that it does not depend Description of all Known Types of Refrigeration upon an actual breaking of contact with the mail the coupon and the makers Motors Trouble Shoot Ina mercury. Based on careful experiments. the of Sylvania Tubes will put you Unit Parts. Valves and Automatic Equipment extraordinary performance of the "igniter" is on the list for a free subscrip- Makes and Specifications of Units believed to be due to conditions at the rod - Manufacturers of Cabinets mercury Refrigerants and .tutomatlr Equipment and Many junction which is found similar to the tion. No obligations. Other Important Chapter, last contact point of separating contacts. Sidestepping the baffling problems of grid Send in your own servicing tips, control for heavy currents in a single leap, " Ignitrons" give eventual promise of radical im- too. For every one that's printed provements in control methods in industry and in "Sylvania News," you'll get central stations. a free Sylvania Tube (Exactly "how" this new instrument func- (any type tions is a story that involves deep theory, and you select up to $3.00 in one which is presented to those readers of value!). RADIO-CRAFT who want to follow the step-by- step development of technical devices. Technical Editor.) Don't miss this opportunity! Types of Arcs The specific form of electrical discharge in gasses which we know as the electric arc is a most essential and useful element in many types of engineering apparatus and in many applications. Its utility in arc lamps, arc rectifiers. arc welders, lightning arresters and spark gaps THE SET -TESTED RADIO TUBE is generally known. Even in electrical switches, perhaps contrary to popular impression, it plays a useful and desirable role. Sometimes, also, it presents itself in an unwelcome way as in A PRODUCT OF HYGRADE on "sparks" commutators, backfires or arc -backs SYLVANIA CORPORATION in rectifiers, "flash arcs" in radio power tubes, etc. Where the arc is useful, it owes its utility to its ability to carry large currents at a tow Over 1,200 Diagrams voltage to a degree incomparably greater than that of other forms of discharge such as glotcs. 450 Pages Townsend discharges, cathode rays, positive-ion Flexible Looseleaf MAIL COUPON TODAY Binder 'Research Laboratories, Westinghouse Electric .i M,mutart tiring Company. Complete Service Data 'Presented before the winter Convention January 1327, 1933. New York City Hygrade Sylvania Corp. C-2 Mail Coupon Today! Emporium, Pa.

GERNSBACK PUBLICATIONS, Ins. RC -9 96 -98 Park Place, New York, N. Y. Please put my name on the mailing list I erelose herewith my remittance for $5.011 (cheek. fi.r your free radio news bulletin, .i amps or Money Order rr toted) for olden you "Sylvania News." to send i . w ,st age prepaid. 011e copy of the OFFICIAI. REFRIGERATION SERVICE MAN - I -AI together with the extra 96 pages of next ma- teriel at no extra cost. Name

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t :ty State eiU' State An "Ignitron" control tube, left; and right, the pencil of lead dipping into a pool of mercury. si

RADIO -CRAFT for SEPTEMBER, 1933 179 the cathode of several hundred volts, and with a THE NEW current density. at this minimum, of about ten amperes per cm.. at atmospheric pressure and varying as the square of the pressure. Increas- SHALLCROSS ing the current density above this figure raises WHEATSTONE the cathode drop. BRIDGE (No -630) Ionization by collision alone then can account 11íw rugged. and r -l' able only for low current density discharges requiring etatrnutent can be eanily a,. mbled by least hundreds of volts. For an arc cathode lectrical technician. (loud n my 1, at attained by employing a ,et of very s to occur, some new ionizing agent must make Irate SIIALLrItt »H IG,..i. tore and a its appearance. The search for what this new senaitive L & N (lnlvx , ,e'er. ionizing agent may be forms an interesting Range, .01 ohms to III Megohms chapter in electrophysics. Send Ge in atecea fur Halle tin Gan -P OM. was raining fun infurmn+ ion and construction The first theory that thermionic emis- dcmile sion at the cathode is this new ionizing agent. SHALLCROSS MFG. CO. In most types of arcs the cathode is at a high Parker Avenue CollIngdale, Pa. temperature, and for some arcs, certainly at a 700 temperature high enough for glows in times which are too short for the cathode to heat up. Other ionizing agents are necessary for these currents, etc., and where the arc is an undesired f I nonthermionic arcs. Note, however, that for is because of intruder. it unwelcome this same these thermionic arcs a considerable energy in- capacity unique among discharges for carrying put is voltage. example, necessary to bring the cathode up to the large currents at a low For necessary temperature so such an arc Give SERVICE on commutators only existed as that can- if the "sparks" not be formed from a glow in a short time. . would be a very ea, . . . with a Small Inventory glows, commutation prob- Another theory, and one which is widely ac- lem, and if the "back currents" to the anodes as cepted, is that in the arc a very high positive Here is the best Volume Control Proposi- always remained only in the form of glows ion space charge density the cathode reasons on mercury adjacent to tion on the Market. Here are the positive inn currents, backfire limits produces so intense an electric field there that why! arc rectifiers would not exist. capacity to electrons in sufficient number are pulled out 1. Over 400 "exact duplicate" controls The origin or seat of this great from the cathode. To form so intense a space in the "X" series. carry large current at low voltage which is en- definitely at the charge, however, calls for a current density of 2. Yet with SIX controls in the original - joyed by the arc resides quite several thousand amperes per cma so that ac- AD-A- SWITCH- SERIES 0/7 sets can cathode, where with a drop of only ten or twenty cording to this theory such current densities are be serviced. volts, thousands of amperes per cm. are carried. arc necessary before an arc cathode can be formed. 3. By combining controls in both lines In fact it is only at the cathode that the Still another theory is very intense from the glow for which that ther- any requirement can be met with differs essentially mal ionization in the gas layer immediately minimum stock investment. the cathode drop is usually several hundred adjacent to the cathode supplies sufficient posi- 4. Clarostat with its two separate lines volts. and the current density even at atmos- ten amperes per tive ions to carry the current to the cathode. offers the widest range of controls to pheric pressure is only about Here again. because of the large heat loss from cm2. formation of an arc, choose from. The problem of the this hot gas layer to the cold cathode, a con- 5. Clarostat Controls are inseparable as distinguished from a glow or Townsend or to study of siderable current density is necessary. from Quality Service Work. other discharge. then reduces a the We see these cathode of an arc. and the circumstances which that according to all theories Clarostat "X" line has over 400 controls to choose from a considerable energy input density or current as overall residents.. taper. bush bug, cause rather than a glow cathode -exact to electrical rall an arc cathode density at the cathode is a prerequisite shaft length, and x111 lit exact spare in .et. to form. for the Clarostat Ad -A- Switch line comprises the maximum formation of an arc cathode. utility with minimum stock invesunent. Series W (Wire Wound) obtainable from 50 to 50.000 ohms. Series 1t Theories of Cathode of an Are Methods for Initiation of an Are Cathode (new composition element) obtainable front 10.000 to 5.000.000 ohms. 110th lines obtainable in all tapers - Since gases are normally insulating, the main- The problem with which the authors have insulated shaft Ile long. wide use In Indicated an fol- taining of a discharge requires the presence of been concerned, and whose solution forms the lows: w -28 will service 125 sets: C -28 will service 106 by sets; tY -20. 77 sets; t' -59. 66 sets; etc.. etc. ionizing agents. In the gas itself, ionization subject of this paper was the frequent repeated collision with molecules of electrons accelerated initiation of an arc cathode upon a cold elec- NEW CONTROL REPLACEMENT by the electric field, seems to be adequate to trode within a very short and precisely placed GUIDE ON REQUEST account for the observed conductivities, at least time interval, less than a thousandth of a sec- at low gas pressures. At high gas pressures. ond and in gases at low pressures. It is well CLAROSTAT MFG. CO., INC., of the order of atmospheric, thermal ionization to consider the known methods of arc cathode 287 North 6th Street. Brooklyn, N. Y. of the gas seems to play a part, and with gra- initiation to see how closely they come to meet- AD- A- SWITCH was originated by Clarostat. dienta of ten volts per cm. or so. and current ing the requirements of this problem. densities of hundreds of amperes per cm.. as (1) The Thermionic Cathode. The method of are found in arcs, the energy input into the using a cathode with a separate source of en- gas is sufficient to raise it to a temperature ergy to bring it up to a temperature sufficient where thermal ionization plays a part, and ac- for thermionic emission is regularly used in hot -CONCOURSE- tually high enough temperatures are observed. "filament" gas filled tubes. However, If the The current to the anode is carried by elec- "filament" is to be of reasonable size, and the CONDENSERS trons, and since the gas already contains free separate source of energy not excessively large, highest quality for lowest cost electrons sufficient in number to carry the current with a low gradient the anode introduces Every Type of no special problem. The anode drop will gen- 160 erally not exceed the ionizing potential of the Dry Electrolytic gas, since with such a drop ionization by collision in the gas next to the anode will take and Wax Paper place with sufficient intensity to insure a suffi- 140 ciency of electrons to carry the current to the Condenser anode with enough positive ions to neutralize any excessive space charge. All Capacities The cathode, however, does present a problem. á120 The electrons are moved away from the cathode, Z and Voltages and the whole current must be carried either by electrons liberated from the cathode or by To fill every Serviceman's o t00 positive ions from the gas. If the current 0 requirements density is very small, the latter alternative is le Sand in your request for our complete sufficient and is probably the mechanism of the 7 descriptive catalogue Townsend or dark discharge occurring at high gradients. just below the sparking potential for O the electrode configuration in the gas. The t CONCOURSE ionization of the gas near the cathode is pro- 4 duced principally by ionization by collision with gas molecules or positive ions. CONDENSERS in Townsend dis- As the current density the re., 60'. 389 -409 Wales Ave., N. T. City charge is increased, the space charge of positive 40 ions near the cathode causes an increase in the W gradient there, and finally electrons are set free i EASY WAY TORADIO from the cathode by impact of positive ions or excited atoms. The essential character of the 20 MAKE MONEY IN discharge is not changed. however, and the set- I ting free of electrons from the cathode by such Nett training metho -1 r rt:

t i p . 1 . lulu well be included in the general you earning quickb'. t ' .0. ..t o in' n's. impacts may in radio science. preparing you quickly and thoroughly term "ionization by collision." If there is no for good positions or Independent business career. Send source of ionization than ionization by 160 160 170 180 1 0 200 M1a all to other VOLTAO6 ACROSS RISISTOR STARTER SOP. particulars collision as thus generalized, increase in current Radio Training Association of America density will change the Townsend discharge con- Fig. I minimum drop at A voltage -arcing curve. Dept. RCA -9. 4513 Ravenswood Ave., Chicago, III. tinuously into the glow with a

180 RADIO -CRAFT for SEPTEMBER, 1933 the filament cannot be brought up to the necessary temperature in the required small time. Our (2) Separating Contacts. When metallic con- Readers Sag- tacts are separated in circuits carrying an am- -The RADIO -CRAFT INDEX makes it easy to pere or more, an arc is formed at once. Sev- find the exact location of any title or topic ral theories have been advanced as to the way which appeared in RADIO- CRAFT.r Without MAKE EVERY any loss of time you can locate quickly, the ar- in which the arc cathode is formed there. These ticle needed. This hook is a big help to every theories depend radio man-" upon the great concentration of the current and intensification of the electric field at the last contact point of the separating electrodes. Killian observes that the electric gradient will be high enough for electrons to be RADI DaPub/ic drawn from the cathode, and Slepian points out The that the energy input into the last contact point will be great enough to thermally explode AddressSysfem! it into a vapor so highly ionized as to supply RADIO -CRAFT sufficient current density for the maintenance of an arc. Although this method is widely used in Dealers! Service Men! 1 switches, arc lamps, welders, and for starting of mercury arc rectifiera, the mechanical inertia Increase Summer INDEX of the separating contacts makes this method Sales! L It contains a thorough, alphabetical and topical impractical for solving the problem set by the arrangement of EVER Y article and subject authors. which has been published in all the issues of (3) The Blowing Fuse. Closely related to the t' RADIO-CRAFT ¡rom July, 1929 to June. 1922 method of separating contacts is the blowing ' eRadio Modulator! of a fuse wire. The starting of the arc may be It's hero at lent ! Now you con "cash In" on Radio Men hare conclusively proved to us the need and by the intense electric field at the separat- sil the wonderful opportunities for Public Ad- first dnss business. practicability for a book which has included in It, a coming points of the vaporizing fuse following Kil- For. with the RADIO MODU- prehensive and complote listing or errs article which has LATOR you min convert every radio set into u real Mus be, -n lian, but with the rapidly blown fuse the experi- for published In RADIO- CRAFT. A book I'ubllc Address system -ci.si icy- --s uIckly -ut anmz- which has each topic eo sub - divided and cross- indexed ments of Anderson which show the existence of Ilsgly low cost. Jost the Ming for emergency P.A. that a mere gienee at a subject will give you any num- installations; for spot" bromleasting; ber of classifications almost completely thermally ionized vapor make for N'okmgs and uses of ft. For example, if 'xplanhtlons astil sound effects in house tunvie pro- you look at tubes. you 0nd under this tonie, various sub- Slepian's theory more plausible. jection; for addressing meetings of clubs and sis- titles. general, power, transmitting. photo -cell:, testing By using a fuse wire or film, the quick and cI,tles: (tir music stmlruts interested of tubes, ihyratons, etc. Every article or notice In the in gesthsg book has been considered deeply accurate starting of the arc can be accomplished. mierophnae practice at houe; for small audition so important that when studios: show window- you refer to certain classification, listed below the main The requirement of quick and frequent repeti- for attraction. for radio Set demonstrations; and for Tua' sople, you will find perh:q,s a dozen or more articles tion of the starting operation, however, entertainment. treating the subject from different angles. The author in intro- each case is given -the exact Issue In which the article duces difficulties. One possibility is the quick appeared, and on mhat page it is to be found. So ac- formation and re- formation of a conducting film curately cop piled, by C. W. Palmer, one of radio's fore- 6 /. upon an insulating most mriter, that in less than two minutes you can turn surface by condensation from to any rtlele- needless to wade through all the Issues a metal vapor. and the authors have had some of RADIO -CRAFT have which been published during the success in this way, but the method which is wn. > i ,, -7.f..." past three years. described later is believed be The to better. TO ARAL AN S RADIO -CRAFT INDEX Is exactly the same size as GROOMS the monthly magazine has 24 can (4) Spontaneous Transition from Glow to Arc. S OSTa -it pages. It be con- Oa NAD.* veniently kept on file with the copie, of the n agazine- A glow between electrodes may be readily and i set. rsady for quick reference. The Index la printed on good started by the application paper wills self covers. quickly of sufficient voltage. In many circumstances the glow This hook is sold only by the publisher at 25e the A Marvelous Commercial copy. Mail coupon below for your copy of the RADIO - cathode will change spontaneously into an arc Unit, Tested ('RAFT INDEX. cathode. For example, if the energy density at and Approved for all Leading the cathode is large enough, the cathode will Radio Sets Briefly outlined below appears only a partial heat up, contents of the book and may reach a temperature for suf- The RADIO MODULATOR, n new and original de- ficient thermionic emission to permit the change velopment by Shore engineers. is truly u revelation to an arc cathode. to radio men. It makes possible inn new way the AMPLIFIERS PATENTS-. But at low gas pressures. of ANTENNA - since the glow us.' a sensitive, high quality. 2- button protes- SYSTEMS - PHONOGRAPH REPRO- current density is very low, such s'omit type Microphone with the radio set. CABINETS DUCTION Its CIRCUITS - A N D RE- heating cannot occur, and at high gas pressures, quality Is comparable ta that of the best brond- - CORDING - the heating is still too slow to solve the asting stations. Reproduction Is n'nsarkalily ortie CODE- POWER SUPPLY problem COILS AND TUNING AND of the rapid and repeated initiation of the arc MOI virer. l'owrr untput Is the atine is the radio COMPONENTS- - BATTERIES - set itself. All built tu confort,' tu IRE standards COOPERATIVE LABORA- RECEPTION - cathode required by the authors. of engineering. TORY- REMOTE CONTROL- Nevertheless, sudden and rapid SELLING AND transitions to DETECTORS AND MONEY the arc form of cathode do occur in actual A Complete Compact Unit, Easy RECTIFIERS - MAKING SERVICING- to EDUCATION - SET CONSTRUCTION - glows even at low gas pressures. The causes Attach and Operate! INTERFERENCE AND SPEAKERS AND REPRO. of such transitions are not well understood, and Simply- plug ii HUM DUCERS- r lin-connect ELIMINATION L , ,, i,,; ;,.,,nil KINKS- - TELEVISION - the prevention of such occurrences is the funda- the A111011011 II, '.,._ posts of the MANUFACTURING TONE AND VOLUME mental problem of mercury arc rectifiers and radio sot- adjn.t the liming 1i :11-1arn on the - switch-and presto yin him Vs. sa METERS AND TESTING CONTROL - similar devices. Researches of the authors replier P.A. s-vstent. EQUIPMENT- TOOLS and o need to um' ping -in adapters it to re r any MISCELLANEOUS- TRANSFORMERS-- others indicate that these causes are spontaneous tills -s or to tamper with the radio chassis In any MOTION P I C T U R E TRANSMISSION and randomly occurring agents lasting individ- way. Tho Modulator nevi nit he siisamm'ctwl to - use RECORDING AND TRANSMITTERS - ually for only some few millionths of a second, the radio for manier Aronde., st reception. By PROJECTION - TUBES - t n rim l ng off the switch of the Modulator, the radio MUSICAL INSTRU- LIST OF BROADCAST. and which somehow cause a sufficiently high Is really for ose, MENTS- SHORTWAVE AND current density to appear at some point of the NEUTRALIZING- TELEVISION STA - NOVELTIES- TIONS- cathode for maintaining an arc cathode. The SPECIAL INTRODUCTORY OFFER average frequency of occurrence of such causes To introduire the RADIO MODI-LATOIC ABSOLUTELY varies in a direct manner with the current den- to you. we offer it now, for a limited a NOTHING WHICH HAS APPEARED lime, $1970 IN RADIO sity and voltage the low gas at this special reduced Frire. If -CRAFT HAS BEEN OMITTED FROM of glow. At Pres- your jobber dots not have It, use the THIS VALUABLE COMPILATION sures, where the glow current density is very coupon brine. Comes romplrle min) NET three tube, fifty feet of microphone LIST 4 33s raide. sneclal Model 5N taco- button mi- crophonephone and stand. The Radio Modulator is portable Clip and Mail Coupon Today! and m 8"z l',5 e § " Fad -hod In gra hued walnut to ,00 harnuodze with mU r- .ra Publishers of RADIO- CRAFT, RC -933 SHURE BROTHERS COMPANY 08 -98 Park Place, New York, N. Y. i b \ PM SAURE, P.. Enclosed you will find my remittance of Ste (check. 037 WEST MADISON ST. CHICAGO. clamps or n oney order ampted) for which you are ILLINOIS to send me, po -cage prepaid, one Copy of the `b RADIO-CRAFT INDEX. MAIL THIS COUPON TODAY! S Shure Brothers Company Nome m Department BC -9, 337 West Madison St. ; Chicago, Illinois. Enclosed you x111 find my remltance for $10.711 Ide -as for whIch phase send me. prepaid, the RADI., is0 MODULATOR pith complete equipment. a ( ) Check here if you want RADIO MODl'L.t. ó g TOR shipped C.O.D. (20% deposit required,. vt i a a 3 THIS BOOK CANNOT BE C JO CO SO 120 NO ,a0 2 0. 210 BOUGHT ON THE NEWS- 25c ,Mt tag SUCRE aT,aTmO'., ra0'ytrONOy STAND - ONLY DIRECT FROM THE PUBLISHERS THE COPY Fig. 2 City Times distribution at one voltage.

RADIO -CRAFT for SEPTEMBER. 1933 181 small, the average frequency of occurrence of World's Finest these causes is too small for the solution of the Photo -Instrument. authors' problem to be found in this way. Only at high pressures, about atmospheric, is the frequency of occurrence of these causes great enough to give certainty that an arc cathode will Nothing like it! 6 -tube form within a few thousandths of a second. Gotbellltllie gets police (5) The Electric Spark. This method really calls ... has automatic is a form of transition from glow to arc and volume control with might have been discussed in (4), but it de- new duplex diode, tri- serves a special place because it deals with a In all the ode 55 tube; has tre- transient form of glow cathode which is par- mendous power, no ticularly effective in initiating an arc cathode WORLD h u m or distortion, at high gas The is by with 2 Class A pressures. spark initiated Power Pentode high voltage breakdown between spaced elec- No Other 59 tubes; full WO'11rsf 6-tube chassis trodes and since the only ionizing agent at the range tone con- E Dynamic Speaker cathode is ionization by collision, we must de- CAMERA trol; full si'.' acribe the cathode condition as a glow. The speak- TRIAL $4ID5 characterizing feature of is very Like This! er; full vision the spark the spotlight con- rapid growth of the current sent through the trol. Fully selective and sensitive -coast to discharge. Since the glow cathode which The only Quick- Acting. Automatic Winding. Ground mast reception. A full -size radio in every way. "Out- initially covers only a small area spreads rather e;lass performed 12 -tube set in every way " -M. A. Adkins, very high current 1'oeu+ing Camera using Standard (toll Film. W. Va. Complete with beautiful midget cabinet and s slowly, a density may be built Gaol for all purpo.es. No Separate Parts or At- Raytheon tubes $13.s5. GUARANTEED. Send today up momentarily in the glow cathode. It is con- tachments are Nere..ary! for free circular. (Know the newest in auto radio -the ceivable that a sufficiently high current density FORDSON" sensation') may be reached in the glow itself to permit an No Double Exposures with "PAL KO "l FORDSON RADIO MFG. CORP. arc cathode, but it is more probable that in this It THINKS and COUNTS for you. Used by 11700 Li is Ave. Detroit, Mich. high current density the frequency of occurrence U. S. Government, Educational Experts and of spontaneous transition causes becomes suf- Leading Publications, Simple! Positive! De- ficiently great to insure the prompt initiation of pendable! 3 Cameras in One! "PAL KO" takes full postcard 3A, or or % this size an arc cathode. 19 pictures i - epelldable At low gas pressures, even with high applied on a six exposure film! voltages from SAVINGS ON FILMS ALONE WILL SOON sources capable of giving a rapid PAY FOR "PAL KO" ., rate of increase of current, the current density I Ivse`lsottonal SATISFACTORY PERFORMANCE GUARANTEED in the glow cathode remains low and an arc OR MONEY REFUNDED! trHiÚIrce is not struck. Generally. one would say that a SOLD DIRECT FROM MANUFACTURER TO YOU "spark" does not form at low gas pressures. MUTE TODAY FOR FREE CATALOG (6) The High Frequency Discharge. This ...BUD method is closely related to the methods described PAL KO, LOUD SPEAKERS in (4) and (5). A discharge is started between Inc. 817 Wash. Blvd. CHICAGO Dept. R -C NORMAL efficiency 2% to 25 watts spaced electrodes by application of sufficient -Peak capacity 50 watts! BUD'S voltage of high frequency. Again. since the DAYS new diaphragm and voice coil assem- only ionizing agent is ionization by collision, 5 bly assure higher efficiency and far greater dependability! Write for lit- the condition at the momentary cathode must be erature on BUD units, all alumi- described as a glow. However, in the high fre- FREE num, weatherproof NATURAL - CLASSIFIED TONE" trumpets. microphones. ex- quency glow the Current density may be very Trial citers. air column horns. Get de- large compared to that at the cathode of a tails of FIVE -DAY FREE TRIAL! steady or low frequency glow. In the steady ADVERTISEMENTS glow the current density at the cathode is lim- Adyertlsements in this section are inserted at the BUD SPEAKER CO. ited by the space charge of the positive ions. cost of twelve cents per ml for each insertion- But in the high frequency glow such space name. initials and address shs each count as one stord. MU@ DORR 5T. Cash should ccompany all cla:dbed advertisement.. charges do not have time to form. Thus high unless placed by a recognized advertising agency. No TOLL DO. OHIO-U.S.A. density positive ion currents will flow in alter- less than ten kinds are accepted. advertising for the October 1933 Issue should be received not later nate half cycles and with such high current den- than August 9th. sity the frequency of occurrence of spontaneous COMET glow to arc transitions will be very great. The method of the high frequency discharge MISCELLANEOUS appears to be practical according to the ex- PRO perience of the authors, but they believe the new HIGHEST PRICES FOR SCRAP GOLD: method to be described in this paper is better. Rings, watchcases, teeth, etc. Satisfaction The lowest -p rim d COM I'LET E Short - guaranteed or goods returned. C. H. Talley, Wave Superheterodyne. Includes world - 627 E. Kingston Avenue. Charlotte, N. C. famous tuner, built -in power pack, air. tuned transformers and all coils covering 15 to 250 meters, with band -spread tuning POCKET RADIOS at all frequencies. Write Dept. RC-9 for details. GUARANTEED "POCKET RADIO." $2.00. HAMMARLUND MFG. CO., Catalog, 10c. Neil Tasker, Shamokin, Penn- 424 W. 33rd Street, sylvania. New York, N. Y. Sot Bo.XWL Radio' RADIO ELKON DRY DISC RECTIFIER UNITS RE.- ammarlundPRECISION conditioned, $1.75. Send cash with rectifier. Money -back guarantee. Erie Specialty Co.. 4 PRODUCTS 513 West 10th Street, Erie, Pa. RADIO PARTS-WE CARRY EVERYTHING for receiving and transmitting. Wedel Co.. YOU GET THERE! Inc., Wholesale, Seattle. Washington. CRYSTAL SET-SOMETHING NEW. SEPA- With rate. all stations. Operates speaker. Blue- print. 6 others, 25c coin. Modern Radiolabs. RCA Institutes 151 Liberty, San Francisco, Calif. radio training N MATTER what you want to ledin in practical Radio . . whether pal sire elementary or advanced knuu ledge RCA Institutes is fully prepared to give you the training. The Best NEWS RESIDENT SCHOOLS NEW YORK AND CHICAGO illustrated Catalog on Request EXTENTION COURSES FOR HOME STUDY of the Year under convenient no obligation' plan. R.C.A. INSTITUTES, INC. will be found on the Dept RT -9 Fig. 3 75 Variek St. New York 1154 Merchandise Mart. Chieapo Giobar electric gradient demonstrator. Inside Back Cover Turn now and read the "Swap Section" on of this issue. page 184 of this issue.

182 RADIO -CRAFT for SEPTEMBER, 1933 (71 Striking a New Cathode from an Already MMURDO- SILVER Existing Arc. If an electrode is made negative with respect to an already existing discharge, a Build the NEW positive ion current will flow to it, which will generally be limited to a small density by space DO YOU WANT charge. Conditions at such an electrode are PENTAFLEX essentially the same as those at the cathode THE ACTUAL FACTS of a self- maintaining glow, except that the- positive Short -Wave Receiver ion currents may be drawn at a voltage in itself ON ALL CUSTOM BUILT The Pentaflex Short too low for the maintenance of a glow. To in- -Wave Receiver sure the contains a clever, newly- devised re- prompt striking of an arc cathode at RECEIVERS? flex circuit designed by J. A. Wor- such an electrode, the methods already described cester, Jr., formerly of the Bell as effective for the glow may be used. For ex- Telephone Labs. In this ingenious ample. application of a high frequency voltage circuit, one tube does the actual to such an electrode will result in the prompt work of two. formation of an are cathode. Complete Construction Details However, in this case, an additional possibility in exists. The density of ionization of the already the September issue of existing discharge may be raised to so high a SHORT WAVE CRAFT value adjacent to the electrode that even with low applied voltage, the positive ion current 25c A COPY density will be so large that there will be prompt occurrence of a cause for transition to an arc cathode. This is the method used in the Deion circuit breaker for striking new cathodes on the many plates in the deionizing chamber. The MA('ri1ZIIt6 arc which is first drawn at separating contacts is by nt RADIO EXPERIMENTERS r driven a magnetic field up into slots in the There has been so much controversy concerning plates, where the reduction of arc section so the comparative merits of the leading custom - increases the density built receivers, that I have decided to place the BEGINNING: of ionization that arc true cathodes at once facts before you. The Masterpiece and the A NewSe/-/es form on the plates. others have been The authors measured by an independent Wei have also successfully applied this testing laboratory. The findings have been au- /AMATEURS method to the striking of an arc cathode to a thenticated by unbiased authorities. This infor- mercury electrode in an evacuated vessel. An mation , these incontrovertible FACTS . TRANSMITTERS arc from a separately heated thermionic filament together with the complete story of The Master- cathode was started, but it was piece will be sent you upon receipt of 6c in compelled to stamps. Please 9/N BEGINNER take a constricted path close to the mercury, use the coupon, thus causing the density of ionization to be very high there. A small voltage difference between McMurdo Silver, Inc. 1132 W. the mercury and the discharge would cause the Austin Ave., Chicago r prompt formation of an arc cathode on the mercury. McMurdo Silver, Inc., 1132 W. Austin Ave., Chicago The Light Contact Arc Starter fie In stamps closed. Send nie engineering comparison of leading custom -built receivers and 18- A form of arc cathode starter of the separat- page book on Tite Masterpiece. ing contact type devised by the authors deserves Name special mention, because in a considerable degree it was free from inertia difficulty of ordinary Street separating contacts. A small -section, pointed Town_ , State tungsten rod was placed in a mercury arc tube L so that it dipped slightly to a depth of about one millimeter below the mercury surface. On sending sufficient current through the rod, At All the Here's 4 -Color Cover an Easy cathode of an arc was promptly started at Larva 9 "512" In Sis. the Newsstand. Over 200 Illustrations rod mercury junction, and this starting could he regularly repeated sixty times per APIDLY second. MONEY-MAKER Increasing each day are the number of ex- The explanation is believed be ..- in the Short -Wave Held -dev hutment. to as follows: whiel are bringing to this branch of radio thousands of The current through the rod heated the rod - new 'thrill seekers." Experimenters, as In the early mercury junction, but the temperature had only for Alert days of Radlo, gain have the opportunity to bring about stirring new inventions. Read, In SHORT WALE to rise to that at which mercury has a vapor CRAFT, the Experimenter's Magazine, bow you can build pressure of one millimeter. that is, about 125 your own Short- Wave Sets. RADIO DEALERS both transmitters and receiv- degrees Cent. when a film of vapor would ers. SHOAT W.'Y E CRAFT Is exclusively a shortwave form magazine -the kind you have wished for no long. around the rod separating it from the rod and starting an arc cathode and SERVICEMEN Feature Articles in the September Issue on the mercury. In the 31v," Waves Sell this new device Now Practical, by I. E. Mouromtseff, that does away with all 'Research Department, N "estin«hosue Elec. es aerial troubles Mfg. Co. 1100 and installation problems. No more Amateur Transmitters -How to Build, Install, light plug or short -circuit wor- and Operate Them, by Leonard Victor, ries for radio owners. No more er..a' W2DHN. climbing over roofs to install or make repairs on aerials. The MONITOR -flow to Build and Use It. 1gOp DYNA M/C This Hundreds of radio owners will ra-TL NFD 3 -Tube Superhet Has It "- "Foreigns" roll buy on sight + to get rid of ugb AERIAL in Like a Local -And On the Loud Speaker! aerial is Ires. Special exclusive ELIMINATOR By George W. Shuart, W2AMN- W2CBC. tuning feature gets maximum 2 -Tube A.C. Receiver That Works on Your B. C. volum. for different types of Audio, by Henry J. Wagner. 900 sets. Receives up to 1500 in Iles. Attention! All Squads!- Short -Wave Fiction - Improves selectivity. with a wallop! Can be Installed and demonstrated WORLD-WIDE Short -Wave Review -The Best In two minutes. Size only 3 by Inches ; stall Circuits Culled from Foreign Periodicals, by E 9OO r mgh to fit ino back of all except smallut er: midget re- C. W. Palmer. drivers. Send today for your .am de A 5.10 Meter Ultra Short -Wave Converter for > Use with Your B. C. Set. Hats Off to Catherine Martin! Who Built 200 _,00 The New Sets. G Best Short-Ware STATION LIST in Each Issue. á WALCO DYNAMIC x TUNED Il x SPECIAL OFFER COUPON 600 - 1 a Aerial Eliminator O Several can easuy be(tarried in Service SHORT WAVE CRAFT RC -9 kit. Everyone fully tested and guaranteed. RTAILE 99 Park Plate, New York, N. Y. Mall coupon and take advantage of FREE SAMPLE OFFER. Enclose $1 with PRICE GET ACQUAINTED OFFER 500 mon below for sample WAIA'O t EItIAL As Striai 11 $1.00 (Canada ELIMINATOR and special dealer- agent D irn y fur "Ó Offer, enter subscription proposition. Dollar refunded with first order. VI a:11()ltT WAVE xenm aW CRAFT for months. iI understand G that your regular race for a year's tt subscript Ion It $2.5n.i 1 ID Mall me sample ropy of SHORT WAVE ('RAFT for 400 ELECTRICAL LABORATORIES which I enclose 15c (U. S. Stamps G CO.. Dept. 129 or coin accepted). O 141 East 25th St.. New York, N. Y. t enclose Sl. Send sample 1VAIA'() AERIAL Name ELIMINATOR, and special deader -agent prop - sitio. I understand $1 will be refunded will toy first order, making Address 3000 2 a e 12 1c m sample FREE to me. D19TANG( PROM TOP OP OLOeaR - mm Name city State Address Fig. 4 City State Results of gradient tests. RADIO -CRAFT for SEPTEMBER, 1933 ib3 particular tube used, when such an arc cathode started. the current was diverted to another anode and the arc cathode moved on the mercury surface away from the rod junction. With the current diverted from the rod, the film of vapor around the rod point promptly condensed, so that the starter was ready for a repetition OJELAIl of the process within a sixtieth of a second. With an immersion of one millimeter about 200 amperes was necessary for regular striking BUM AT 51 fT ST. of the arc. With less immersion, less current could be used, but with the lesser immersion the mercury would sometimes be thrown mechan- NEW YORK CITY ically out of contact with the rod and would require several sixtieths of a second to return and make contact again. America's Foremost Ballroom and The New Arc Starter Beer Garden In attempting to develop a starter of the type of the preceding section and also of the type mentioned at the end of 3, under "Methods for 2 Nationally Famous Radio Orchestras Initiation of an Arc Cathode." it was discovered that a rod of relatively high resistivity partly Features Every Night immersed in mercury had very extraordinary properties with respect to the initiation of arc cathodes on the mercury surface. The first ob- Continuous Dancing servations were made on a carborundum crystal. It was found that about ten amperes flowing and Dining through the crystal would start an arc cathode, and unlike the tungsen rod of the previous sec- Matinees Wednesdays, Sat- tion, this current magnitude for starting the arc cathode varied very little with the degree of urdays, Sundays immersion of the crystal. The voltage required for starting varied with the length of the crys- 150 Beautiful Hostesses tal above the mercury and was less than 100 volts for moderate lengths. The starting of the arc was extremely regular Exclusive But Not Expensive and reliable. In taking an oscillogram of the operation of a mercury pool cathode vapor tube Comfortably Cool with such a starter, the starter electrode was connected to the anode of the tube through an auxiliary external rectifier, and the whole was placed in an alternating current circuit. As the oscillogram showed, in each half -cycle of polarity correct for sending current through the external rectifier, an arc was started in the tube. flower This extraordinary property for starting an arc cathode was found to be generally enjoyed P.LYMOVTH by materials of considerable resistivity. Thus similar results were obtained with starter rods made of lightning arrester resistor material (clay, lampblack mixtures), glowbar resistors (special carborundum heating elements), galena and ferro- silicon. No wasting away of the starter rods could be observed even after long periods of operation. Some rods on life test have now been operating On the Ocean at Manomet Point sixty times per second, 24 hours per day, for over seven months with no observable deteriora- One of New England's Finest Resort Hotels tion. The mercury pool was not an essential element Surprisingly Inexpensive in the operation of the starter, as regular opera- Special Vacation Tour 9 days 560.00 up including tion was obtained with a starter rod partly transportation, Hotel accommodations, sight seeing, etc. buried in solidified tin, as well as with a molten Smooth Sandy Beach ... Surf Bathing .. . tin cathode. Operation was obtained also in Pool air at atmospheric pressure. Warm Sea Water ... Swimming The time required for the formation of the Tennis Courts ... Golf Course ... On Hotel Grounds arc cathode after the application of the neces- UNDER SAME MANAGEMENT sary voltage was found to be extremely short. MAYFLOWER HOTEL This was investigated with the cathode ray os- HYANNIS .4,r;3t cillograph by W. E. Berkey. The following results are typical. For a resistor rod of M, in. COD'S NEWEST HOTEL 7c CAPE n in mercury dipping 14 in. below the CHARLES A. DOOLEY, MGR. diameter surface and extending }_ in. above the mercury. the minimum voltage for starting the arc before the rod would heat up appreciably was found to COD be approximately 130 volts. A sudden applica- CAPE 250 units would tion of start the arc within less kMASSACHUSETTS

For Sale, Barter and Exchange .ts an alti to our readers, all advertisements to he advertisements for private individuals can be ac- tn.-cried in this department are accepted at 2t a word; c epted. name. address, street number, eta., each counting for one word. No advertisement for less than fifteen RADIO -CRAFT reserves the right to reject anY (15) words accepted. advertisement that conflicts with the polity of this The Publishers are not responsible for difficulties magazine. Send all "Swap" advertisements to arising out of the trades. In this department, only RAD10- CRAFT, 96 -98 Park Platt, New York. N. Y. Stewart-Warner 8-tube broadcast set. table model HERE'S A BARGAIN SWAP! WANTED 1500 No. 80111. original price $59.50. Will sell for $12.00. foreign stamps, not more than 300 duplicates for '- Itembert Short Wave Converter. 3 tubes, with power volume set of "Everybody's Encyclopedia.' Set in supply and automatic switching arrangement. 10 to excellent condition-contains over 1500 pages with 200 meters, brand new, never used, cost $25.00, will hundreds of illustrations. Handy for boy or young sell for $7.50. Zenith. model ZE220 chassis. 36 in. man. First assortment gets books. B. Nussbaum. long. 10 tubes, T.It.F., slightly used, Including 185 Marino Ave.. Brooklyn, N. Y. tubes. equipped with two horns. comes with model ZIH battery eliminator. with Raytheon tube, also Westinghouse Rector trickle charger, original price Will exchange Western Electric 394 Condenser Mi- Unit for 0 to 10 watt antidifier complete. Fig. S $500.00. will sell for $40.00. A. Ilibarsky, 180 Riv- crophone Illinois. erside Drive. New York í'11y. M. Eesmar, 4708 Polk Street, Chicago, Starter -material potential and current lines. for SEPTEMBER. 1933 184 RADIO -CRAFT than flee micro -seconds as indicated by a cathode ray oscillogram of such a starting of an are cathode; as the voltage was reduced longer time ,helles EXTRA Years of Service delays between the application of the voltage and striking of the arc were observed. These times varied considerably in test repetitions. in DEPENDABLE Instruments Figure 1 shows the variation of the mean time Insist on the DEPENDABLZ Model 54e0 with voltage, and Fig. 2 the distribution of the Analyser. It Will Always Be Up.toDatel analyze times obtained at a single voltage. n pr"yides for fnt,re 8- nil 0 -Prone hJfie.e -Irw a ten -wire po,:dysor cable sand employs anp,tuttse selector switches with .1.lditfoaal ints for rowrve capacity. Observations Bearing on the Theory of the AO accurate Voltago-enr ant Analyser plus a complete point-to-point analyser t resistance between any tw,, pint, ¿Inc also betweet New Starter chase's ground andr any point. Momentary itches protect meter against burn.at. Th oh peter completely self-contained. n external The insensitivity of the new starter to the batteries being required. Three sealer, give accurate readings from Sfr ohm degree of its immersion in the mercury indicated to 2,000.000 ohms. Any scale of volt- ohms -milliampere, is automatically that its operation did not depend upon an actual to all circuits. Voltmeter teeth. 0 -5-.50-250-750 volt: milliam- nwadablevoter 0-.5-50 -'2.50 ma. A 3ti inch D'Arsonval moving roil 1000 ohm per breaking of contact with the mercury. This is lt meter insures maximum accuracy. In fact, n ter, shoat and multi. confirmed by the operation of the starter buried ¡,"r deviate less than 2'; from Perfect accuracy. All stales and all range, are availablens for external measurements. Tube testing is provided for by in solidified tin, and it was also confirmed by d grid shift switches.. operation obtained where permanent electrical The Model 5400 An lY'. el at be .aw 1,4ó9 "x5'41 cotmplete ith All o Leer terminals owle rrl.n etched winded i, DEPENDABLE ANALYZER contact below the surface of the mercury was . in' analyse, . 1M be 1 "r a: n eh u ,u lamp lead and romplete - of far mill t n,r a .. mm.Ii.:. insured by means of a tight metal clamp, and , Model 5400 also by a copper sprayed portion of the rod RADIO CITY PRODUCTS CO. 48 West Broadway NEW YORK, N. Y. below the mercury surface. When operated just below the voltage required for regular operation, frequent tiny sparks d_V _ d Xcc would be observed at the mercury-rod junction. (1) This suggested that the seat of the phenomenon dx -2-V x resided at the mercury -rod junction, and also UNIVERSAL suggested that the operation where d is the thickness of the slab, Xa, the Steering Post Remote for might take place gradient along Control in roughly two stages. each stage setting the slab far from the junction, Auto Radio dif- and x, the small distance from ferent requirements. First would be the start- the junction at ing of a tiny arc cathode, the tiny sparks ob- which the gradient exists. According to served above. This would call for a very high dz electric gradient, or very large concentrations this formula, the gradient, and with it the cur- of energy to effect a thermal explosion at the rent density becomes infinite at the junction mercury-rod junction similar to what occurs at where x =0. the last contact point of separating contacts. Of course. the formula (1) may be considered Second would be the building up of the small as applying only so close to the junction as the current flowing from this tiny arc cathode to material may be considered continuous. If we an arc current sufficient to short- circuit the rod assume that we may consider the material con- to the holder or another anode. This would call tinuous down to atomic distances, that is down for the ability of the side of the rod immediately to x =10-5 cm., and if we take the slab thick- adjacent to the tiny "spark" or arc cathode to ness as 0.5 cm., we have for the gradient at the carry considerable current as the anode of an junction, arc. dV .5 Both of these requirements seem call X. 4x c to for Sx1O $500 the existence of an electric gradient down the dx - 2 00-3 rod to the mercury Exclusive -rod junction. The necessity If we adopt as our criterion for the starting p List for such a gradient is beautifully illustrated Features. be of an arc cathode, the appearance of a gradient HET LOCK SWITTC! A_ND VOLUME CONoTRob rrevem some experiments tomperine with - of L. Smede. of 10e volts per cm. at the junction, we have MICROMETER TC \I \Gr-Acr As illustrated in Fig. 3, a hollow cylindrical for gradient, urn elyYe eelihret..l illnrmi,: remote from the junction permits hairline odm.t,mnt through props .uf cam,.. starter. A, made of glowbar was used. Good IdeLLUMINATED DIAL- Indleete, when set is ready Ins .r contact the (3) Mx =200 volts per em. with internal surface of this cylin- DRIVE SHAFT-Ingeniously designed cable prevent. I -k der was made up to a level B by means of Actually, less than 100 volts per cm. were hack lash Theo tuning cable ho. been .erpenthaed under do.. an sufficient Lard. amalgam. The electrical connection to the amal- for starting an arc cathode with the ESCUTCHEON -Coin embossed old bronze finish blending materials tested. seems slob or hardware. gam was brought in under the mercury and It likely that other phe- CONTROL HOUSING-Pre..M steel black ¡spanned embed- of nomena : eichwilve engine.erin. Lattre.. course was insulated from the mercury. A peculiar to the carrying of current across contacts appear also at the junction, TWO TYPE UNITS AVAILABLE barometric connection permitted the mercury such i1 iE 1. as CONTROL.-- Eiagl, TYPE E CONTR transition films high . level to be raised and lowered. of resistivity, or the doser rad ba , pet cabb d v for tuning The voltage re- amramnble T ,e drawing up of small particles forming .. rìnlc,lut o denfa.r e . u Td-Vol. quired by the starter for regular operation was bridges, ne as suggested by Holm. . . 1 l r switch . . Äd to the observed for different levels of the mercury. o.l loom m.Ing on11,1e switch and voeu, The first requirement for the starting o 1. t Ito -k .alleh and ari t «uÌ The results are shown in Fig. 4. of an onto the rets arc cathode at the junction 1' oo- ¡AAA., . Ana The impressed potential existed between the then seems to be o»p'V van .fad ve e-.ferr,lrr ,nto of internal amalgam and the external mercury. the impressing of a gradient of the order of 100 UNITED SCIENTIFIC LABORATORIES, Inc. volts tit West 14th St. When the mercury level was considerably below per cm. along the starter rod. This prac- New York, N. Y. tically sets a lower limit to the resistivity MAKERS OF RADIO PARTSIFOR 12 YEARS B, there would be current flow down the cylin- of the A ten territories open for Jobbers and Dealers. der to the mercury from above, and therefore rod material, since with ordinary metals and Write for complete details a gradient down the starter to the mercury. reasonable rod dimensions, the current required As to maintain the mercury level approached close to B, more such a gradient would be enormous. of the current would flow across the We may perhaps set 10-2 ohms per cm! as the cylinder practical wall to the mercury junction. and less down the lower limit of resistivity of a starter cylinder wall. Hence for a given voltage, the rod of reasonable dimensions. gradient down the rod would The requirements of the second stage of the be lessened. Hence formation if a gradient of a definite magnitude is neces- of the arc, however, set an upper S U C C E E D sary down the starter at the junction, the volt- limit to the resistivity of the rod. The tiny arc age required for starting should rise rapidly which forma at the junction must grow to a as the mercury level approaches B. This the magnitude sufficient to short circuit the rod. IN RADIO Since curve of Fig. 4 shows to have been actually the the tiny arc first flows to the rod side as case. anode, the resistivity of the rod must be low enough to permit the flow A rloNSag in home study, the International Cor e- Theory of the New Starter of sufficient current ependenee Schools haro kept pare with the times and through the rod side without requiring excessive offer courses which give practical instruction in The observations of the previous section sug- voltage. Actually, it was found that the voltage fundamentals and latest developments alike. gest that with respect to voltage and energy required for starting increased with the resistiv- The Complete Radio Course covers the whole field concentration, conditions at the Of radio. The I. C. S. Radio Servicing Course was starter rod -mer- ity of the rod material. We may probably set a prepared specially for men who wish to become ser- cury junction must be similar to those occurring few thousand ohms per cm. as the upper limit vice experts. The L C. 8. Radio Operating Course at the last contact point of separating contacts. for the resistivity of the starter rod. is vital to mastery of operating and transmitting. Electrostatic theory shows that this is the case. MAIL THE COUPON TODAY! Fig. 5 shows the equipotentials and current flow Applications of the New Starter lines slab INTERNATIONAL CORRESPONDENCE SCHOOLS for a of starter material with parallel Applications of the new starter will be obvious plane sides and dipping down a great distance to those familiar with grid controlled gas tubes. Box 6675 -B, Scranton, Penna. into the mercury. (This field distribution is In such tubes, until now, an arc cathode was taken from Maxwell "Electricity and Magnetism" Without cost or obligation, please send ms permanently maintained by a separately heated full :'snit the course 9d edition. particular. I haro checked: Art. 193, p. 297 and assumes that thermionic cathode or a keep -alive arc. The Radio Operating the electrical resistivity of the mercury is starting of an arc to a main anode was Radio Servicing negligible then D compared to that of the starter ma- controlled by a grid. Now the permanent are Navigation Chemistry terial.) The current and voltage concentration Marine Engineering [J1 Drafting cathode and control by the grid may be elimi- at the mercury junction are quite clear. Aviation Engines English nated, and the starting of the arc to the main Electrical Engineering U Accounting From the mathematical formulas of Maxwell anode effected and controlled entirely by " the (in reference we Srtrnr the just given), calculate that new starter. Thus many of the problems asso- ,- e,.,- ...... - ..»...dDe...... the potential gradient along the starter side near ciated with the use of grids, particularly for Address the mercury junction is given by large currents, are completely eliminated. RADIO -CRAFT for SEPTEMBER. 1933 185 TESTING RESISTORS In the early days of radio. fixed resistors New! New!! New!!! were more or less taken for granted. If they showed resistance values of approximately the Two New 250 Short Wave Books desired rating, chances are they would be HERE IS GREAT NEWS used. Little real thought was given to other characteristics which have since been recog- These new hook: alit he welcomed by all short crperimenters. Short Crave fan; and short nave enthusiasts, the a former two nized as all- important. hooks IOW Ti) 111'11.0 AND OPERATE strowr VourAVE RECEIV- Almost every circuit in a modern receiver ERS. anti 110W To BECOME AN AMATEUR RADIO OPERATOR nete rcelcutuem by thousands of our short t friends. now contains a resistor and, from the stand- In conformity with the tines these hanks have been priced at 25e ] oint of the discriminating Service Man, the instead tot :cur. which 1s the price of our other barks. Vet the two mere resistance rating is but one of several tie, adunn's remain a tremendous ant of information. The very important factors about which he wants pe and illu -tr lloo. have been chosen in aurh a s to give you alwoa a tooth for t as you received for',, r ru, heft', to be fully informed. Before risking his repu- of r t hu1 :- Luke t ¡.take i.tg getting either Prr thrill, Ito'. tation for good work on a resistor he wants rID ,, n from o o year, of rape, h n, I r. to know whether it will retain its rated value I _,r you will thank us for having through thick and thin: he wants to know about its voltage coefficient. how much it Ten Most Popular Short Wave Receivers. A Short Wave Beginners Book will deteriorate with age or under conditions - 'he short How to Make and Work Them Brie i- of high heat or humidity and he wants to This new ....loon. i. .. 110 wirli uihl their own eh Ihr `Illrl:'l' WAVE CRAFT hove know about other factors all of which have a nt sow. watt. end t described ...elected andin , r . m s h o r t os rple.t fundsm taw. m the stage of the opt in the n,i,mr ` :F,ve very direct bearing on its ability to deliver ytfin it u known tout It ttlme only ,iced reference hooka shoe s ceiver. Áe. rihed i the t.nvl, rerìronefr theuänere- rl Le. for the begin whether he he w short wave enthusiast. short wove satisfactory reception over a long period of h r ñ . a bet. layout.11w rú,Ì photograph. pit se iru..\tr. t.i` ;. rthwtd enr- F.r avini {{ listener or short wx a f. the simplest urbi n b -rule RF receiver D p nted. time. si The hook is profusely tail lustnw,,I with all sorts of illustrat aria.. e.pletm- Coal l.te Bate f p given t make e h t n. rom tel° a. it Accuracy of rated resistance value can be manly possible tondo. snd everything worthwhile knowing olwut short W.ven in this Contenta and growing Feld. Vet withal, the hook i. not" teehnieal." taken for granted on units which bear the 2 R.F. Pentode SW receiver Soin two of TRF- 2.Tube ùrtIt sh rds with ,or' illustrwtions, plwtoeraphs. simple abort.. hunk stamp of a reliable manufacturer who makes rereiver each 12.500 mile nark Ir Delmar SW r r- uM. eve..orhook All in simple I.nsuwge.r linewe 2- O mile lie r ai - ßn41 Caw" SW rae ver - them not down to a price but who builds a "Stand - The look is rust ehue4 full of information snd you will never regret Iem 2 -t tsh AIWa r -Den d'" -The them up to a standard of quality. For in- It,'Elerrtedt Rl -`h v WrSl adynr -Cunt Y 4 SW r - having sullen this Mumma.,it mman, ve,lume. of pawl eee r i er-A "One- Tuber." RW I todeA -My detavew SW Good in Brief stance, the standard tolerance of stock val- IMPORTANT Getting In Short IV Shor Mod Symbols of Radio- ues of I. R. C. resistors is 10 ^r,. This is de- THERE IS NO DUPLICATION WHATSOEVER BETWEEN THIS Short Wve ,(rsed a l Aeri I. -ledÌ urine Ms,Al de St t -Masi a daily service require- m e cidedly satisfactory for BOOK AND OUR OTHER VOLUME - "HOW TO BUILD ANO shr t Wave set-I . by Adding A she T h' e OPERATE SHORT WAVE THE MATERIAL -ri t W n( Reg n Control-Audiol Amplifiers ments although, if desired for some particular BOOK HAS APPEARED IN Oo t OW sIa-coupling I.. Code-Wave Length ANY BOOK BEFORE. Kilo,,,I . l'hrt -tV hang Chart-Kinky in Short Wove ('on.t n purpose, resistors with a tolerance of only 5% Each book contains 40 pages -over 75 illustrations -25c each can be furnished at a slightly higher price. Not sold on newsstand -Mail Coupon Today! Low Voltage Coefficient SHORT WAVE CRAFT l.s -pat:! Voltage coefficient is another highly impor- 96 -99 Park Place. New York City. tant resistor factor. Good resistors will Gentlemen: measure up to the same resistance values as 1 r lo herewith 25e, for stitch please sod me prepaid, copy of your new book "Tan Most Popular Short Wave ReseReceivers. How to Make and Work Them. long as their voltage ratings are not exceeded. I enclose herew Rh 25e for whlrh please send me prepaid, copy of your new hook "The Short Ways Beginnen However, this point will bear watching in cheap resistors for. obviously, if a unit meas- See for which please qend me. two hooka. Ten Most Popular Short Wave Receivers. Now I enclose prepaid. your ures 1 megohm at 10 volts and 800,000 or Them." and "The Short Wave Beginner's Book." to Make and Work 900,000 ohms at 200 volts it may cause the 1 Send money artier. cheek. or cash or new U. S. stamps. lieu isler letter if it font ains eurrenry ur st aurps.) Service Man no end of trouble when placed Name _..._. Address in a set. Low voltage coefficient simply means that slate ('hy there need be no hesitancy about using the same value of resistor at different voltages. A 500,000 ohm gridleak, for instance, may Here's a book have only a few volts across it whereas a 500,000 ohm coupling resistor may carry as every Radio Man will MAILING LISTS couch as 200 volts and certainly no Service Man will want to be bothered with having refer to dozens of times tut select different types of 500,000 ohm re- Pave way to more sales with actual the to use on these different names and addresses of Live prospect. sistors jobs. every day- Next comes the factor of resistor ageing Get them from the original compilers characteristics. Even wire -wound resistors of basic list information -up to date- show a certain deterioration with age and this accurate--guaranteed. is why, when making resistors for extremely Tell us about your business. We 'll help high precision work. the wire is first aged. you find the prospecta. No ob- Ageing tests over a long period of time on ligation for consultation service. I. R. C. stock resistors have shown a deterioration of less than 2% over a period of years of use. s Humidity characteristics also warrant care- 60 page Reference ful consideration. Humidity tends to increase Book and Mailing the value of resistors. Poorly constructed units under test have shown an increase of LIST CATALOG as much as 50% or 100Só as compared to Gives count. and prices on only 10% for quality resistors. In the I. R. 8,000 lines of business. C. laboratory these tests are made in a "hu- Shows you how to get special lists by ter- midity chamber" which is kept at 40° C. with ritories and line of business. Auto lists of 00% relative humidity, the latter being ob- all kinds. tained by means of a saturated solution of Shows you how to use the rails to sell kept in your and services. Write today. sodium tartrate. Resistors are the products chamber for 100 hours and results clearly show the danger of using inferior resistors R. L. POLK & CO. for it is well known by Service Men that Polk Bldg. -Detroit, Mich. humidity is one of the most potent causes Branches in Principal Cities of resistor failure. World's Largest City Directory Publishers The Heating and Cooling Cycle Mailing List Compiler. Business Statis- It is characteristic of a good resistor that, tics. Producers of Direct Mail Advertising. when its normal rated load is removed and it is allowed to cool, the unit will return to A Valuable RADIO BOOK! is book answers every LOUD HERE one radio that LEARN SPKR on conceivable question interference. It RI contains 76 pages, 86,x11 inches, chock full oDmó .. OtT+ii LR with wiring diagrams, drawings and photo- interference originates Electric graphs showing where -how it is distributed, and how to eliminate it. This is a wealth of information needed by REFRIGERATION L every radio listener, dealer and Service Man. SERVICING Send fifty cents in stamps Rt. CALIBRATED PO,CNTIOMETEO book. Cet a copy of the OFFICIAL REFRIGER- RESISTOR untel TEST or check for this ATION SERVICE MANUAL today. Com- R Quit, REtiSrOt ( Hvl"O ADRRO plete details about this Manual will be found Ira SAME RESISTArdCE RADIO-CRAFT MAGAZINE on page 179 of this los tie. VALUE S a) 96 -98 Park Place New York, N. Y

leo RADIO -CRAFT for SEPTEMBER, 1933 within one or two per cent of the rated value. Some resistors show this permanence of load SURPLUS characteristic under brief tests but fail in longer tests. In the designing of I. R. C.'s, the resistors are given a "life test" of at RADIO least 1,000 hours with a load being applied intermittently, 11/2 hours on and half an hour off. This simulates the heating and cooling cycle encountered in actual set operation and PRODUCTS which has caused many cheap resistors to fail. On good resistors, the change under load averages about 3 t/ %, units returning to with- ORDER DIRECT FROM THIS in 1% of their original value upon cooling. ADVERTISEMENT - WE DO NOT ISSUE ANY CATALOG An overload of from 50% to 100% applied continuously for 100 hours will not cause them to change permanently more than 10 %. All radio resistors emit a certain amount of microphonic noise. When heard over a We bate on hard simple circuit set up made for this purpose, this sounds like a hiss or a rush. The noise is not objectionable when continuous but trouble comes when it changes to an erratic crackle -and it is this cracking that high - 779 grade resistors are designed to eliminate. The accompanying diagram gives a circuit set -up which will give the Service Man an easy UTAH means of testing resistors for noise -a test which will supply convincing evidence in favor of quality units designed and constructed un- DYNAMIC der modern, scientific engineering methods. Thus it becomes evident that the true qual- SPEAKERS ity of a resistor cannot be judged by any sin- (10" Diameter) gle test and further that excellence in a single characteristic is not sufficient to recommend HAVE YOU SEEN IT ?" Field 1,750 a unit for general use. The high -grade re- SPECIFICATIONS: sistor built on quality lines throughout will Filled with valuable data. Character- istic of all RCA -Cunningham. Majestic, ohms; for single '47 tube; meet all of the requirements of the discrimi- and other tubes. Dozens of circuit di- nating Service Man and not just a few of agrams. Finest Public Address circuits equipped with hum-bucking coils them. and parts. Volume control guide - The simple testing circuit illustrated utilizes most complete ever published- volume and bakelite connection strips. an audio controls for every set on the market. amplifier having an overall voltage Resistance Tables -all sizes of wire and amplification of 1,000 or over, with a V. T. Composition resistors. Neu, test equip - PRICE $229 voltmeter reading up to 3 volts on its output. ment -exclusive Radolek design. Na- as long as A battery supplies the rated load to resistor tionally known radio sets. This is a supply lasts Each under test, X, which is in series with a real Profit Guide -a radical departure "quiet," wire -wound resistor of about the from every other publication in Amer- same value, R. Point X is connected to the ica. Your ropy is free. Please enclose input of the amplifier, E, by means of a con- business card or letterhead. Write now- denser. The noise developed can then be heard on the speaker or measured by the V. T. voltmeter. If the needle fluctuates wildly, '300 Sale of 337 the resistor is very noisy. The actual reading is also a measure of the noise developed under load. A high -grade resistor will give a continuous hissing noise when listened to King -Silvertone while a poor one will emit a series of erratic crackles. The potentiometer Rl, switch. etc.. POWER PACKS are used when it is desired to measure the PRICES noise by comparison with a known source of voltage S. A replacement unit for the popular King and Si lontane sets. Con. -Iits of Power Transformer and Choke for Silvertone 1928 nd 1929 E VICE Models, and for King Models H and RADOLER I. Measure 6% x 1% x 2 .r. Wt.. CO., 129 Canal Station, Chicago Oil lbs. Supplies 4 -226. 1 -227. PLANE RADIO VS. FIRES a Dealer Serrlreman D 2 -7IA and 1-280. Speditration :: rate front Shop or Sture O: fron Ilon,. 11 V. at 41/2 amp:.; 214 V. at 1% The radio -phone facilities of Transconti- '. n the fallnaing Test F.eul'went_ amps.: 5 V. at 1A. amp,: 5 V. at 2 nental & Western Air, whose planes fly over training and experience ls: cups.; 600 V. C.T. at 60 mils. Pennsylvania on their coast -to -coast mail and PRICE passenger routes, have been of great value to $173 the state in its efforts to prevent forest fire- Name as long as and preserve the natural forest resources, ac- Address supply lasts I Each cording to George W. Wirt, chief fire warden at Harrisburg, who reports as follows in a recent bulletin: REMIT BY CHECK OR MONEY OR- Pilots of TWA have come to our assistance RADOLEK DER FOR FULL AMOUNT EACH many times by reporting the discovery of forest OF fires by means of their two -way radio -phone ITEM -SHIPPED EXPRESS COL- facilities. The pilot reports the discovery of New! LECT, NO C. O. D. ORDER ACCEPT- the fire to his ground radio stations at Har- MODEL risburg. Pittsburgh, or Philadelphia, and with- UNIVERSAL "E" ED -MONEY REFUNDED IF NOT in a few minutes the fire wardens are in pos- Condenser Type Microphone SATISFIED. session of the information. Often the pilots render particularly valuable service by giving details of location Wellworth Trading Company RC -933 which could not be gained from the warden', III West Lake Street. Chicago. Ill. observation towers. The pilot, of course, Can see the evidences of the fire many miles ahead Enclosed you will lind my remitcmtr of 4 , fur chin, please ,end and is able to get the report to us long before UNIVERSAL MICROPHONE CO., Ltd. our observation posts are aware of the fire. 424 Warren Lane ( ) 10" ,q1 CALIF., S. A. Utah Dynamic Speaker. 62.29 each In one instance a radio report from a plane INGLEWOOD, U. ( ) King-Sibertone Power Peek. S1.73 rash of a fire a short distance outside of Pitts- burgh was in the Harrisburg fire warden', office six minutes after the pilot spotted it. for (Along Name the route of TWA, whose huge tri - SERVICE MEN motor passenger planes and smaller mail 1763 planes operate Brand new EX -STAT replacement manual rives over the shortest route from correct type volume control nstantly. for 1761 coast to coast, there are nineteen radio models. Most completeomplete t listi ng ever m Address ground co- stations. The pilot of each plane is in con- piled. Copy FREE to dealers and qualified stant radio communication with the ground servite men. Send postcard today to through the radio -phone transmitter and re- TILTON MFG. CO. City state ceiver on his plane and on the ground.) 17 E. 26th St., New York, N. Y. RADIO -CRAFT for SEPTEMBER, 1933 187 RADIO FURNITURE BOOR While volumes have been written on radio kadio@ift furniture points out E. C. Ritter, furniture FREE É designer for the Fada Radio & Elec. Corp., the problem that faces the cabinet designer may be stated in a single sentence. It is Readrite insuuments. Worth having. Readrite this: Execute pleasing designs that will fit READERS' BUREAU Meter Works. into average home surroundings. On this page are listed manufacturers' catalogs It all sounds very simple, but as a matter and booklets, chosen because they are of in- 76. Tus COAST-TO -COAST "BROADCAST." The of fact it has not been so easy to design terest to readers of RADIO -CRAFT. You can "Broadcast" is the Spring-Summer 1933 edition cabinets in keeping with the premise of hav- obtain copies FREE by using the coupon below. of a 100 -page mail order catalog that is a veri- ing them fit into the multitude of homes. table encyclopedia. Its listings are very varied, While of course, there have been, and are, and run from soldering lugs to complete 100- watt public address amplifiers. Every article is radio cabinets distinctly following a given has been necessary by 6. CLAROSTAT CONTROL HANDBOOK. A large well illustrated and described for the benefit of furniture "period," it 32 -page book containing detailed specifications radio dealers and Service Men, for whom the and large to keep away from strictly period of volume controls, attenuators, constant -im- volume is specifically intended. Coast -to-Coast design. That means reproducing with ex- pedance controls, phonograph pickup faders, tone Radio Corporation. actitude lines of the great masters of furni- controls, line ballasts, rheostats, potentiometers ture or the periods such as Italian Renais- and fixed resistors of various kinds, together sance, Spanish, Louis XV, Queen Anne and with valuable circuit-design data. Contains many 94. ELECTRAD PRODUCTS. The newest and diagrams and charts, and a guide of replace- latest catalog of Electrad products contains other period pieces. In this respect radio ment volume and tone controls for many com- twelve pages and lists many types of fixed and has been forced to become distinctive to a mercial receivers. Ciarostat Manufacturing Com- variable resistors and five different kinds of degree and strike somewhat of a happy pany. Inc. amplifiers for public address purposes. The medium. popular Truvolt resistors have been improved While one major survey of American by the addition of insulating shields and heat homes showed bed -rooms followed in the or- radiating covers, and a number of new sizes have English, and 6. MEASURING RESISTANCE BY THE DEFLECTION been added to the line. The catalog also con- der named, French, Colonial Meriiop. The conventional method for the meas- tains some valuable data on the application of modernistic style and living rooms in urement of resistance involves the use of the resistors to radio receivers. transmitters, ampli- Colonial, early American, English and French, Wheatstone bridge, a costly piece of apparatus. be seen the bed -room However, there are other methods which provide fiers and sound systems, and suggestions on how it can readily that to compute the value of resistors. A handy and furniture maker for example has quite a small a fair degree of accuracy, enough for all prac- useful catalog. Electrad, tical purposes. The least expensive is the de- Inc. problem compared to the radio cabinet maker. flection method, which makes use of popularly He can manufacture certain accepted stand- priced milliammeters and fixed resistors. This ard pieces, mostly in suites, and the indi- bulletin describes the method completely, and 96. TORE FILTF.RIZER AND CONDENSERS. The vidual purchaser makes a selection in ac- should be very useful to Service Men and ex- Tobe Deutschmann company is now catering to cordance with his taste, type of home, or perimenters with limited meter equipment. the Service Man with an extensive line of filter, Shallcross Manufacturing Company. by -pass and line condensers and radio noise general requirements. But in the case of eliminators. Their latest catalog. describing the radio the problem may be likened to the pur- complete line, has just come off the press. A chase of an odd piece to place in a room full is where the major selection has already been 11. SUPREME INSTRUMENTS. Contains lengthy page given to the new "F9lterizer" noise descriptions of the Supreme service instruments, eliminating antenna system, an item of par- settled. In other words, it is the question including Diagnometer, which is five ticular interest to Service Men because of the of fitting in the radio cabinet to the living the AAA1 money -making opportunities it offers. Tobo instruments in one, the model 90 analyzer, the Deutschmann room, generally speaking. The manufacturer model 40 tube tester and the models 60 and 70 Corporation. of radio sets selling in volume must design oscillators. Interesting to the Service Man be- cabinets as I said at the outset that will fit cause it tells how his work is facilitated by into average home surroundings and that's ingeniously- designed test equipment that indi- 97. ARCO TUBE BULLETIN. A descriptive cates the condition of an entire set in a few folder giving full technical characteristics on the no easy task not only because of individual minutes. New test apparatus to take care of complete line of Arco radio receiving and trans- taste in home furniture but also because of the new tubes is also described. Supreme In- mitting tubes, photo- electric cells, television certain other characteristics of people in a strument Corporation. lamps, hot and cold cathode tubes, cathode ray country as large as ours. tubes, rectifiers and charger bulbs. This can be Leaving out the question of general period posted for easy reference. Arco Tube Company. designs vaguely followed in the making of 19. A BAPTISM of FIRE. Centralab fixed re- home is sistors are made by forcing a carefully calibrated furniture there the question of larger resistance material through a plastic ceramic influences which not only the furniture manu- material, and then baking both under terrific 98. How TO USE NOISE REDUCING ANTENNA facturers must heed but specifically the radio heat. This booklet describes the manufacturing SYSTEM ON BROADCAST WAVES AND SHORT WAVES cabinet designer must be particularly careful the advantages is the title of the latest booklet on this important process in detail, and lists subject. In addition to covering of including in his calculations. I have in claimed for fixed resistors of this type. It is the theory, the mind one section of United interestingly written and illustrated, and makes practical application of the various noise- reduc- the States that good reading. Central Radio Laboratories. Inc. ing systems available for broadcast and short leans heavily toward the more conservative wave use. is described also. Lynch Mfg. Co. designs in furniture and that, of course, includes radio consoles. Then we get into the This six- heart of a great metropolis and find certain 21. READRITE RADIO INSTRUMENTS. 102. AMERICA'S OLDEST RADIO SCHOOL. This sections where elaborate designs with heavy teen -page pamphlet contains some valuable hints attractive 16 -page catalog describes the various on the testing of electrolytic condensers, as well course of instruction carvings are the order of the day. These of priced available at the RCA In- very by as descriptions of the full line popular- titutes, New York. Training is given in the tastes are governed often racial back- following subjects: radio broadcasting. radio op- ground that is stronger than style influences. erating. radio servicing, and sound and public Then we get into another section of the coun- address work. RCA Institutes, Inc. try where old American tradition holds the people to certain well -defined furniture ideas. RADIO -CRAFT 5.106 Then again, in certain cities there will be Readers Bureau 103. MILES PUBLIC ADDRESS SYSTEMS. 96 -98 Park Place, New York, N. Y. A con- several clear -cut major divisions as to types cise R -page catalog listing microphones. loud of stores in regard to will charge the fol - requirements. One Please send me free of speakers, power units, amplifiers, transformers not handle anything ornate sticking to "quiet" h,wing booklets indicated by numbers and incidental accessories. Miles Reproducer Co.. in the published Bet above: Inc. lines while another because of its clientele will have to go in for ornamental design. And so it goes, with varying complications for vary- No, 104. WESTON STANDARDIZED SERVICE UNITS. ing types of trade. And through it all the This folder describes a complete series of stand- radio manufacturer, through his furniture de- ardized service units, consisting of an analyzer, sign, must strike the so tube checker, oscillator, volt-ohmmeter and ca- right average, to pacity meter. The units are of uniform size speak. Radio cabinets, or consoles, must be and may be combined in single cases of various individual and yet not too "different." The- sizes, depending on the requirements of the oretically, it would be ideal to have, say, five Name Service Man. Weston Electrical Instrument cabinet designs to fit each set model and each Corp. pocket book at the same time but this of course, would not be practical since it would Address 105. RAnlo BARGAIN News. This dealers' and mean building a tremendously large selection Service Men's mail order catalog is a veritable for each line of radio receivers. State buyer's guide. Among the hundreds of items Disregarding individual instances of spe- City included are auto radio sets, mobile sound ampli- cially designed period consoles it can be said (Please check the following) fiers, dynamic speakers and replacement parts that whenever radio has tried to bring of every definite I am description. Federated Purchaser, Inc. period models into the fold a flop has re- (1) Service Man (2) Experimenter sulted. The sets that have sold in volume (8) Dealer (4) Jobber have been those that in addition to consider- Radio Engineer (6) 106. EX -STAT SPECIALTIES FOR RADIO SERVICE ations of technical performance, have been (6) Licensed Amateur TECHNICIA NS. A useful catalog of resistors, encased in furniture that struck the eye of the (7) Professional or Amateur Set condensers volume Builder and controls, prepared espe- average as "right" in appearance and fitted cially for the Service Man. Of particular value well into the setting where it was to be This coupon will not be honored unless you is a ten -page section listing the correct replace- check off classification above. ment volume controls for numerous radio replaced. ceivers dating back as far as 1926. Tilton It should be understood that I have not at- Manufacturing Company. tempted to cover this whole subject of radio

188 RADIO -CRAFT for SEPTEMBER, 1933 furniture but merely to touch a few highlights. The next time you see Queen Anne legs on a radio console do not expect the whole cabinet to be Queen Anne. For radio cabinets are, You Servicemen in the main in the minds of the old time furniture people at least -"mongrels," mongrels which perhaps through their trade ac- ceptance by the American public have in turn created a new phase in furniture design and Make Me PROVE That I Can of which time alone can tell whether it is a permanent phase of design or one which will eventually revert to the accepted principles Show You How to Make of design which have characterized the furniture industry for so many years. Cabinet Colors MORE Get My FREE Still another and very important factor is Sample Lesson the color of the cabinet. Where the public MONEY has a choice of colors in the selection of a Mail the coupon bol:,r. I radio cabinet no one color is a general favor- you : 01111) [elf. iniorma - Men! Now is the time to do tlon on my method Of train- ite but there is a surprising degree of uni- some ing. And in addition. III formity in the preference shown for each tall thinking and perhaps send you my latest referee ie color. a bit of stiff work. Review book, 'Modern Automat is your trade and service jour- Volume Controls." This text by new developments. You This is at least the Is tentative conclusion nals for the past few months part of my regular must study the technique of reached by us, based on the initial batches of Course. and In the past servicing so you can go from orders that came upon heels and get a load of the new- only my students could get the of the pro- fangled developments in Ra- it. It rovers such subjects effect to cause -by this I mean duction of the "Super -Fadalette," a miniature as Tuning Indicators; Off that a certain squeal or growl, dio-A. V. C.; Silent A. V. C. Nuters ; D receiver in art -leather of four colors, and in Resonance beer a touch of the grid of a vacuum burl walnut. Muters; Multifunction Tubes; and amplified A.V.C. De- Class B Push -Push Amplifiers; lay: Diaie Detectors ; Serv- tube means something more to Green, red, ivory and brown are the colors icing A.V.C. Systems and you than a noise, involved in this test of public selection. Universal A.C., D.C., and Bat- other Important angles of In tery Receivers; Automatic this interesting subject. Of This Plan Will Make Mora anticipating the public preferential reaction Tone course the book Is right up Money For You in those colors it was decided, after deter- Control; Mercury Vapor to the minute. and gams you mining most likely Rectifiers and the like. Informal inn on the fatten. Here is a fact that you know the shadings to prove Do you N. R.I. .simplified manner. popular, to turn out an equal number of each honestly know how Mall the coupon today anti as well as I do. When you color. Then it was figured that all these complicated circuits take dvantage of this very get stuck on a service job, all production of and tubes Do spetlai offer. the burl walnut should be in the ratio of 40 work? you real- tangled up in the diagnosis ly know what makes the of the trouble, what do you percent as against the total number of art wheels leather cabinets. It was necessary, of course, go around? Can you do? Naturally you start out to grade the quantity as to those colors and honestly say that you are able from the beginning-make a as to what proportion of the burl walnut to keep up with these modern fresh start. Why not apply improvements? the same principle to your cabinets should be made, in advance of any If determination of the public trend. As al- not, let me tell you background of Radio knowl- ready elated it was agreed there should be straight from the shoulder, edge? Let me prove to you that unless you buckle up and that I can give you a fresh no differential in the quantity of any color. get How reasonably correct the prior- to-pro- down to brass tacks, learn start for a lasting association the fundamentals of Radio, a in servicing and one that will duction cabinet orders worked out in rela- new crop tion to the actual sales is revealed in the fol- of Radio servicemen make more money for you, are about to bundle you out of your servic- MAIL THE COUPON lowing approximate ratios: ing job. Out of each 1000 sets sold the division was Get My Sample Lesson and School Catalog as follows: Stop Guessing. Know What You Are Doing My home -study training has helped hundreds of servicemen qualify for better jobs. Red 160 There are three major factors which con- front every modern serviceman. You must Get my school catalog -see the facts for Ivory 142 yourself-what my training covers, what it Green 166 consider the following tacts if you want to has done for others. Read my Money - Brown 171 go on 1. Back Agreement. My catalog and sample You must have a sound fundamental lesson are FREE. See how thorough, how Total Art-Leather 639 practical I've made my training. Send the Burl Walnut knowledge of Radio theory and Radio re- 362 ceiver design practice. If you are not coupon. There's no obligation. Act now. Comparison Unit 1000 grounded in the basic dope you can never J. E. SMITH, Pres., National Radio Institute, keep abreast of new developments. Dept. 3JXA Washington, D.C. While this test is not regarded as abso- 2. lutely conclusive, It is interesting to note the You must have simple but effective test- uniformity with which the public has divided ing and servicing equipment. You can't se- Mail Coupon Today off the four lect them on anyone's say so. You must colors. It is also exceedingly in- I. E. Smith. President. teresting to note that an arbitrary color se- know about everything available and do National Radio Institute. lection by the manufacturers is so closely your own choosing. This requires knowl- Dept. SIRS. Washington. D. C. followed in the field of actual sales. edge. Servicing is two -thirds knowledge Send me your FREE SAMPLE LESSON and your schorol catalog. I'm Interested in learning more about This is probably the first time that actual and one -third testing equipment. It is just my job. but you'll have to prove that you can help color tests as to sales have been made in as necessary to know how your test equip- me before 1 enroll. This request does not obligate radio on a scale of any size. Some man u. ment works as to know how a Radio set me in arty way. (Please print plainly) facturera tried out color sets in the past but works. Name...._...... _...._.. .._..._...... _.._...._....._ Age..._...._ 3. only with the coming of the art leather cab- AJdress inet has it been possible to secure the effect- You must have a carefully selected serv- iveness that color lends to a small radio ice technique which you should follow. It City State.. . cabinet. must be a technique that will stand the Present Job SSBY test of time; that will not be made obsolete

MUZZLING NOISE - The . for adio. °, Live' wire dele r, nd serv- PRODUCERS RADIO PROGRESS icemen AUTO Dey this mummer lin-

better auto-stalling Frank H. Cross WEEK radio seta at prices that RADIOS sensationally low. Physicians, surgeons, osteopaths and others Service Men -get in back of '1 hi. t ttt!NIAN Auto-Radio is alt-eleetcio. employ. 'da using electrical equipment are required to b,. andh es of .audio,. The et ie extremely equip their machines with static eliminators the national publicity which is ap- .:(:l, set and m Ortiz l tin elms. Only three wire. .,.mnovt, , and sot is ready to operate. to reduce radio interference, in an ordinance pearing in support of Radio Prog- wo.. for Iron.. TRUMAN RADIO SHOP recently passed by the City Council of Santa 7443 Stewart Ave. Chicago. Illinois Ana, Calif. The object of the bill is to protect ress Week, October 2 to 7. Every private radio listeners. effort is being made to cause The city electrical inspector will inspect all machines in offices. Mr. John Q. Public to become Build the An elaborate means of tracing radio inter- more "set concious "; to look into ference, which is maintained by AL L- W A V E the Southern the whys and wherefores of new Speeified part, California Radio Interference Association of AEROVO II Fixed C ondem r. rHAMPSRITE Voltav Control. CARDWELL Variable Los Angeles, will assist in making the ordi- radio sets, and the repair of "old ConemrnL RWVnCO DRAlDI TE I ook- nance effective. The measure requires private E ECTDC . n nilF,IN reliable." Keep your eyes and `iw..d Chokr.. I. R. C. Ma'nnrin,lN R,.in. CDoAL..,L . radio listeners to have their sets in approved Complete Air, In Nioek- N "rose for misa. ears open, and prosper with the n.t ac stamp far Free Limm . t S t (:irroi,a. condition for reception, and another section ALLIED ENGINEERING INSTITUTE requires that high -tension power boxes of all other "boys." 9e Park Place New York, N. Y. kinds be equipped with static eliminators.

RADIO -CRAFT for SEPTEMBER. 1933 189 BARGAIN Index to Advertisers

A SALE Aerovox Corporation.._..- ...._._ . 176 Alden Mfg. Company 176 Allied Engineering Institute 189 Allied Radio Corp 176 American Annex Hotels._ 178 of 3000 Autocrat Radio Company_.._ 176 B Bud Speaker Company 182 Westinghouse C Central Radio Laboratories_.._ 176 Clarostat Mfg. Company.._ 178 Power Generator Classified Section 182 Coast -to -Coast Radio Corp 171 Aircraft Transmitters Concourse Electric Company 180 Coyne Electrical School.._.._ 129 D Outside View Hundreds of Uses for View of Aircraft Tobe Deutschmann Corp. 178 of Radio Experimenters Generator with E Aircraft Generator Hood Taken Off Electrad, Inc._.. 176 Electrical Laboratories._ _._.._.._.._.._ 183 The Government Paid Originally $14700 Each Fordson Radio Mfg. Co ._.._.._.._.._ 182 these Westinghouse Generators Franklin Transformer Mfg. Co.- ....__.._.._ 178 for G Goldenton Radio Mfg. Company.._..__..__ 169 OUR PRICE Grenpark Company - _ -._.._ 191 '4 " Hammarlund Mfg: Comppany.._..__..- .._.._ 182 AS LONG AS SUPPLY LASTS Hygrade -Sylvania Corp ..... _.._.._.. 179 I International Corr. Schools_._._. _171, 185 L L & L Electric Company 177 LaSalle Extension University 169 Leotone Radio Company 171 Lifetime Corporation 175 Lynch Mfg. Company--_ ...._ ...... _...... __..__._... 170 M Mayflower Hotel 184 ArKEy `" METAL SWELL Midwest Radio Corporation 184, 135 - Miles Reproducer Company 178 --4' /2V. STARTING SORRY Muter Company, The._...._.._..Inaide front cover N (Technical Specifications) National Radio Institute ...... ___...... _...._..133, 189 National Security Association 178 National Union Radio Corp._ 171 The special generator illustrated is of the end), 2 ins.; diameter, 9 /16 -in.; the end is self -excited inductor type. The rotor serves two threaded for a distance of 1/2-in. At the end entirely distinct purposes: 1. It carries the in- opposite from the drive the shaft extends 11/2a -in. Pal Ko, __ _.. _ 182 ductors which has sta- Case dimensions, exclusive of the shaft, 4'/2x61/4 IncP for the A.C. generator, Pembleton Laboratories 170 tionary field and armature coils. 2. It carries in. in diameter. Philadelphia Wireless School 176 which the D.C. armature, corresponds to the is fed Pierce -Airo, Inc Back covet exciter in other machines. The output of this self- excited generator to a step -up transformer which, in turn, is fed Polk & Company, R. L 186 Popular Book Corp 182, 186 There are two pairs of stator poles -two North to a 12 -point synchronous rotary spark -gap; a and two South. Around these four poles are rocker permits the single stator point to be accu- Postal Radio Corp 170 wound the four field coils which, when energized, rately adjusted to phase the spark and the power Precision Resistor Company--_.._.._ -..__ 178 produce poles of alternate polarity. Each of these supply. The spark gap is included in a second- poles is provided with four slots into which are ary, that comprises a mica fixed condenser, and a fitted the A.C. windings. The rotor is a 12- tapped tuning inductance adjustable in the range Radio Circular Company ._..__.._ 176 tooth inductor that carries the D.C. armature of 250 to 550 meters. This coil consists of 25 Radio City Products Company - 186 coils which supply the D.C. exciter current returns of No. 14 wire wound on a threaded bake- Radio Trading Company 192 k;uired by the alternator; a built -in commutator lite form 3 ins. in diameter and 3 ins. long; the Radio Training Assoc. of America 180 takes off the generated D.C. Three leads extend over -all length is 41/2 ins. One set of taps is Radolek Company 187 through the casing to permit. a 4'/= V. flashlight - brought to a contact plate at one end and pro- RCA Institutes, Inc 182 type battery to be switched into circuit for start- vided with a switch; the other set is brought to Readrite Meter Works 177 ing, and to control the A.C. output of the gen- a contact plate at the opposite end and provided Remington Radio & Elec. Company 174 erator. Rotated at its normal speed of 4,500 with a pair of laboratory- adjusted contacts. A Remington Rand, Inc 176 r.p.m., the output is 200 W., at 115 to 125 V. stream -lined bakelite housing slips over the en- Roseland - ..- .._.._ 184 (on open circuit), 900 cycles. tire transmitter assembly. The over -all length of Hotel Royal.._.._.._ 178 generator (exclusive of shaft) and transmitter is Manufactured by Westinghouse for the U. S. of complete outfit, 20 lbs.; ship- 3 in- 18 ins. Weight Signal Corps, the sturdy construction of this ping weight, 35 lbs. Scott Radio Laboratories, Inc.. E. H 1:31 strument recommends it to the technician. The Sexology 178 in ball bearings. In order to per- rotor turns Shalleross Mfg. Company . 180 fectly withstand the extremes of temperature and TRADING COMPANY Shure Bros. Company 176. 181 in -craft service all the WELLWORTH humidity encountered air Dept. RC -9 McMurdo Silver, Inc 183 coils are thoroughly impregnated with a special Supreme Instruments Corp 172, 173 compound and then baked. Shaft length (driving 711 West Lake Street Chicago, Illinois T Tilton Mfg. Company 187 Clip Coupon and Mail Today! Truman Radio Shop 189 Try Mo Radio Co., Inc 176 U WELLWORTH TRADING CO., Dept. RC -9 United Scientific Laboratories 185 111 W. Lake Street, CHICAGO, Illinois Universal Microphone Company 187 W find for which ship by express collect one Westinghouse Power Generator Aircraft Enclosed $4.95 refund money. 187, 190 Transmitter as per your description. If not satisfied I will return outfit and you will Wellworth Trading Company Westinghouse Electric & Mfg. Co 169 Weston Electrical Instrument Corp 167 NAME

ADDRESS (While every precaution is taken to insure accuracy, we cannot guarantee against the possi- STATE bility of an occasional change or omission in the CITY preparation of this index.) for SEPTEMBER, 1933 190 RADIO -CRAFT Regaining Popularity 6 TUBE CONSOLETTE RADIO The BEAUTY .. . FINE CHARACTERISTICS EXTREMELY LOW PRICE Of this handsome set has regained the pres- tige that the Consolette Radio has main. tained for several years. At last a full sized consolette receiver at the price of an A.C.-D.C. midget. Produces remarkable tone quality with ample sensitivity for all requirements. Employs a highly developed T.R.F. circuit using the latest type tubes, thus producing remarkable performance. Beautiful in appearance, will fit into any surroundings. Supplied in two distinctive cabinet designs. Incorporates the following tubes: 2 -'58, 1 -'57, 1 -'56, 1 -2A5 and 1 -'80 tube. These tubes deliver 6 watts of undistorted output. Only the finest quality parts are used throughout the entire construction. A matched electro dynamic speaker mounted on a special built -in baffle handles the full output with realistic tone. PRESSED WOOD INLAID CABINETS Our Price Handsome walnut two tone finished cabinet created by craftsmen with a background of years of furniture building. Finely blended design with attractive s 129! pressed wood panels. Exquisitely moulded -the contours form a handsome un- Complete Set of Tubes obtrusive $1.95 design. Will harmonize with any home surroundings. Cabinet meas- C abinet Onl y ...... $3.95 ures 351/2 inches high, 21 inches wide, and 103/4 inches deep.

Jensen Model 13.7 R.C.A. 1008-105 Baldwin A.C. and D.C. Dynamic Speaker Chassis A.C. Dynamic Magnetic Chassis The tremendo,.s tower This chas.ais is the identical handling capacity of Chia Is widely used one used in the R.C.A. 100A- speaker makes it suitable as an additional 100B Speakers which list for for use modern conaolo speaker In many as high as Note - receiving seb, or for Moser homes, as well $35.00. built amplifiers. The A. C. as on public ad- in output transformer which model,. are equipped with dress systems. permits use of 450 volts with- a 280 rectifier tale sad an Will handle an out distortion, rattling or blast- 9 mfd.dry electrolytic cone enormous amount ing. Generous oversized mag- denser to reduce A.C. hno.. of volume with- net. The armature D. C. models aailable with n without _ I VtI( nut distorting or thick is ac- output Iran.! urine,. Field resistance of thn rattling. Equipped curately centered, the sturdy D. C. model is 2500 ohms. with a 2110 rec metal frame is lined with a Dimensions: 9Sí inches, high and 7 inches, deep. tiller tube. The special self -baffling fabric, greatly improving (A. C. Model. complete with 280 tube ) speaker a:fires acoustic properties of this sensational speaker. Pries 94.95 7 ^Ç inches bleb. I1'ß, wide, and 7 7 37 the (D. C. Model with output transformer ) aces. Itatae opening required, In In lie-. Note the corrugated surface of cone. an ex- ecomplete clusive enhances perfectional reproduc- Pries 3.25 tupplled tube. feature- (D. C. Model, lass output transform.r ) ir tuehth $8.95 tion qualities considerably; most compactly Price 2.95 made; 9" outside diameter, 41" deep oc ernll. $2.75, Peerless `Our Pries FARRAND A.C. and D.C. FARRAND INDUCTOR Inductor Dynamic Dynamic DYNAMIC 12 Inch Model Speaker Inch Model The 9 inch model has the These models are not b Chassis two magnets parallel to to be confused with L, each with a bracket L1L Poefficient and other the various types powerful repro- placed between them to now on the market ducer. facilitate mounting. Please Ideal for specify tithe and labeled Farrand use with the most powerful public ad- type of power Inductors. dress amplifier. It is equally suited for when ordering. These use with any receiver employing the Price ...50$4. models are all fac- average type of audio amplification sys- tory built and not tem using as low as 90 volts "B" current. just put together The speaker will work with any receiver haphazardly. regardless of output chara7teristics. Replacement D. C. Model ha, a 1.000 ohm field and a The 12 inch models have two magnets push -pull output transformer. A.C. Unit Model standing upright, with a bracket on uses a dry rectifier system with a hum The plae m.n, tint, me,9,. (,r PRd.0 ÁÌ ate ott. nd 100 ..011.,xl r the bottom to ease mounting. Dimen- condenser for ntinimum A.C. hum. eh .s Th'u i I.e y dr- Dimensions: 12 s .iÌ ilea u Ìu el.bM Ì. 6n sions of the 12 inch model: 12 inches inches high and inches

All orders are F. O. B. New York, and subject to prior sale. Terms: A deposit of 20% is required with every order. Balance may be paid on delivery. Or, GRENPARK COMPANY deduct 2% if full amount is sent with order. 245 Greenwich St. Dept. RC New York, N. Y.

RADIO -CRAFT for SEPTEMBER, 933 191 RTC's Big September SPECIALS

Every month we list on this page a few STAR * I STOP Si/OPI)ING -the lowest prices are right on items which are not listed in our this page. No one undersells us. catalog. These are all specials of We meet any price on any new which the quantities on hand are No One in Radio merchandise. Order direct from not sufficient to catalog them. Undersells Us this page and save money. 100% Once sold out, no more can be satisfaction on every transaction. Take hold. ORDER NOW- TODAY. advantage today of these special offers.

*"PEERLESS" T.R FURAD O RECEIVER Bred$ "NEW DEPENDABLE" TESTEER sold Zither Wired or In Lit Form Complete with Full Dynamic Speaker Here Indeed Is roar opportunity to build one of the finest tube checker: eter designed-an instrument Mitch Is MODERN In every sense of the nord. Will lest all the latest type tubes. including those with AND 8 PRONGS- DIRECTLY -without the use of a single adapter! The "NEW DEPENDABLE." despite its high degree of accuracy. is extremely simple to operate. Roth plates of the 80 -82 -83 and other rectifier tubes are readily tested without the use of a "second plate" button. The Instrument employs a high- grade. It'ARSON. Y.U. TYPE. MINING -COIL METER. insuring thereby extreme accuracy. This instrument mill check more than 120 different tubes and even those much have not as yet been played on the market. The tube tester Is amply guarded against tube "shorts." u hirh condition Is indleatetl by the flash- ing of a shall pilot light. All component parts are mounted on a beautifully etched panel and the entire Instrument placed in a sturdily mntructed, leatherette.,overed. carrying case. For operation on 105425 volts, 50/60 eyries, A.C. This Instrument IS available either in kit corn, or completely mired and Irs ted. ready to use. Shipping teelrht lt Ib. NO. 303 "New Dependable' Tube Tenter. NO. 303A "New Dependable" Tube Tester completelyo ly wired and in kit form. tested. Bach View .52 YOUR $13.52 YOUR PRICE 1 PRICE and se i 1 Ity 7 6 The selectivity of this -tube reo ' er due three . tuned stages teen AL IA . eh r p etedthaneha of a expensive I1 -tube Superheterodtyne elver. The )eon I II' t I -standard... Its eireuit ie none other han the " +nod old standby TRF tep which to the nmet reliable. 1 incorporates mower f tuned R.F. emplitication usina Ope-4 Sere grid tube.. the power detector it,t':,. AIRPLANE -TYPE e SinslerSeSege of Mt.., ampliMatum utiliain. the type 27 fuir, Tested. a 247 .uper.pnwer pentode. the hill * U. S. NAVY rectifierfier úis '80. All provision. are vade for .uppl)ins Mld power Ito the v ioeh ennui,,, M "survis. fully dynamicspeaker.ill NUM. reproducer are made Hurles t.. TRANSMITTERS AND RECEIVERS con. of improve the note re. ae t bt)tl a n and í . one ieeelorll.ntnote production. Srz RUBBER TPAH'MITTfp HEAD Tun g b e 1I Impie. the tuned e e Miner rolled by a single r.l knob; , vernir dru m CAR Cep$ illuminated tutting dUÌ' employed. The ,cad knobcontrols the .offe t.1h arltl..thi J. tige du l.. (;i_I.. onde hIte mol. n r hank. , eÌtoke and by -p... condensa Lright.. ka are all eindiviJ ally shieldetd. `Th, imet sell made of taluminum. BREAST r.nlfi The three tuned . uieyi rid be, and highs nK.F. tt. n.l r ether ithcite( 1 y Duse II airing. and . out. huh .sen itivilt. Tine Quality. tconceded e tothat ,rdv for aster. [line.homee met. u c u eo ,elle 47 pentode pplie.sadequate Ipow kh the least distortion.

Why build set when u complete e wired and ready to me and complete with e e:,ter , tie at th' phenomenallyep y ei Here excellent u vlYni.li 'N. Ilence.Efu. um e.fir.t served.O Overall .0 e.1 .. . -.I '. Ship.uwt. ris lbah .EAVY List Price $75.00 INSULATED NO. SP -2000 Peerless 7 -Tube TRF Receiver $ 1 g aLE YOUR PRICE with speaker but less tubes Y a 1 LIMITED SUPPLY -ORDER TODAY -TOMORROW 0 MAY BE TOO LATE TWO CIRCUIT JACK yu Only 300 at This Unheard -of Price Thism sobane'and head set nut fit v 1, i.,t ma Corp for Mane-to -Mane and planets Mond communication.in C, n tr ed The outfit 'ph old eatidedoed metal h tpl t and a t of heavy-duty ne the beckkof he brr p^ t e a 1 mouthed ,e trh .1. hed le he ñhutilt, I , terminating n ÌÁr ohm. turn, Otnn r tl SHORT I ppI t w,th nth o T. TI b tfiel k ...fiai AND of s ofor t u na we tl e, ut RADIO Tlth yo,- t ,1 hl I1 m bai, x00.001 ra.b flu let sell them youy at $1,07. e fou I E:TR. .runt. r in tee its r t in .Ìnt.r..t Thre E hat e, ut Ide u can be found for Mer delicate. .tat ud,y) eon I d i art mente. and y t, . TREATISE traaemttl,e R WAVE entire rT The. l,i.t Price 3400 NO. 5721$ U. n \' Airplane-Type .,. R nPRIer . 11 t ,v 1 FRE Avail 11 t.,II tM,.et.11 NEW READRITE MODEL 710 ANALYZER mari 16 áäï oyur l.1.1inïo. TESTS LATEST TYPE 6 AND 7 PRONG TUBES pages arts Illuslratipns. NINE METER SCALES AVAILABLE ld b..ok in plot NOT CATALOG...timid.- UST eANOTNERtl n m not foumi anywhere

istedhe1o1wl- e , iit,Sst t information .lnoniÌ OF HERE IS A PARTIAL LIST CONTENTS Rad rim yhro ta ot It lo Fundamental soo 10 rwtt, too tvhItte /0 Ill 111, WC yRYt ulna Ohm's awsDis Srly Ica coo WOO `bn¡le-Twln CIUVbNItriT stn lCTOR SWITCH- Amliiie w-AAll a nb-Merde y4DIOTI ICIAM15 dYecrCOnmanaunnF Tao -Tube saort -TrUotfeet" e EtD'.O DEALERS We onRr tern MHOtnRS %InestOeGoe ; etc. macro MULTI -MUS" '57's and '50'. a S Rf tt')RSS f t r 4 (t- TODAY. Enclose o I ...ion, t nel n WRITE Treatise et.t eh -hut .0 l'in . ,sol nal!a cents for postage. me of ale ' mail. t - .rid elk. eñ :.r Ove by return . t.etd nelhot Rothnl cal e ns sent special Adapter 1 1000 e Illustrations. y80 ) rectifier M by ,,1 Etcr f h S NCh sided for resistances and I 11 \ I in h, nl.hifierui.pleter wth ease l.x,l.. , hr. 1 I, _.1,. I c s .,,mater '50 rectifier adapter and rsutance and capacity Clwrt. Model Analyzer. List Mee, $25. YOUR PRICE

ANO CAN NOT You will find special prices from time to WE ARE A WHOLESALE HOUSE THAN $3.00. ORDER FROM THIS PAGE time, in this magazine. Get our big FREE ACCEPT ORDERS FOR LESS remit- C.O.D. shipment e siredipl rem it 20" catalog for the greatest Radio Bargains, tance.It accompanyis all ose Should you wish goods shipped by parcel poet, be sure to include sufficient extra remittance order. discount. Send If accompanies tamps for same. Any excess will be refunded. money a oyder -certifl U. S. Radio Trading Company 102 Park Place New York, N. Y. RADIO -CRAFT for SEPTEMBER, 1933 192 ANNOUNCING THE 1 9 3 4 OFFICIAL RADIO SERVICE MANUAL

This new manual has been in actual preparation for several months. The vast amount of important data, which we have received from manufacturers who are assisting us in the compilation of the book, leads us to believe that the 1934 Manual will be more valuable than any previous editions.

THE necessity of GERNSBACK we then receive will be included before go- As in previous years, the 1934 Man- Manuals in the radio field has been ing to press. ual will also include a FREE QUESTION shown by the fact that the total In preparing this new edition many of AND ANSWER SERVICE. In each book the outstanding problems of the Service will be found 25 coupons, which en- sales of the first three OFFICIAL Men have been RADIO SERVICE MANUALS, considered- methods of title you to free consultation on any radio includ- servicing, the new equipment constantly service topics. These coupons give you a ing the new CONSOLIDATED EDI- needed to cope with new tubes and sets, complete mail service -questions on servic- TION, now exceed 80,000 copies. and the other fields of radio, such as pub- ing and operating on any set or circuit Radio Service Men and are answered promptly and ac- others engaged in various curately by the editors. Re- branches of radio know the member that, at the regular importance of such books, rate of 25c per question which and how they must depend Contents of the 1934 Manual in Brief is usually charged by radio magazines, this service alone upon them for reliable in- Diagrams and service notes, more complete than ever before in is worth $6.00. And for the formation. Whether for any MANUAL. Not merely the schematic hook -ups will be found, but also chassis drawings showing parts layouts, positions of trim- Manual, we charge only $3.50. public- address work, tube mers, neutralizers, elc. information or a circuit It is quite evident that the Voltage readings for practically all sets, as an aid in checking 1934 Edition of the OFFICIAL diagram, the material tubes and wiring. RADIO SERVICE MANUAL needed is certain to be All values of intermediate -frequency transformers used in super - will be a decided improvement found in one of the OF- heterodynes, with the manufacturers' own suggestions as to correct over previous volumes, and FICIAL RADIO SERVICE balancing. will even surpass the high ',Detailed trouble -shooting suggestions and procedure as outlined standard of the former Man- MANUALS. The GERNS- by the manufacturers' own engineers -in other words, authentic BACK Manuals have been "dope" right from headquarters. uals. constantly used in refer- Values of all parts indicated directly on all diagrams. WE WILL ence work by leading radio POSITIVELY NOT INCLUDE DIAGRAMS FOR WHICH PARTS ORDER YOUR COPIES NOW VALUES CANNOT BE OBTAINED. set manufacturers, mail - It is important order houses, jobbers, deal- A special section for reference to A.C.-D.C. cigarbos midgets. to every A special section for reference to automobile radio. Radio Service Man and Dealer ers and, most extensively, that he receive his copy of by Service Men, for whom A special section for reference to public -address amplifiers. the these books are invaluable. A special section for reference to short -wave receivers. 1934 OFFICIAL RADIO A special section for reference to remote- control systems. SERVICE MANUAL as soon In the planning of the as it is published. The new 1934 A complete compilation of radio tube data, covering both the OFFICIAL RADIO old and the many new book prove SERVICE MANUAL many types. will itself to be in- A special section devoted to test equipment, analyzers, etc., with valuable as those volumes of things have been taken into full diagrams and other valuable information. previous years. The book as consideration. First, how we s A complete list of American broadcast stations with their fre- usual comes to you postpaid could reduce our own costs, quencies in kilocycles; extremely useful in calibrating and checking and free and in turn pass these sav- test oscillators and in calibrating receivers. of additional charges. ings on to our readers. Free Question and Answer Service, the same as in our last two No need to delay sending us Second, what information Manuals. your order -the 1934 MAN- not contained in previous No theory; only service information in quickly accessible form. UAL, like its predecessors, is Absolutely no duplication of any diagrams; nothing that appeared a necessity in your business. editions of the Manuals in any of the previous Manuals will appear in the 1934 MANUAL. must be incorporated in This we unconditionally guarantee. We strongly advise you to or- the 1934 edition and would A handy, easily -consulted master Index making it easy for you der your copy today, and then be of utmost importance to to find almost anything pertaining to your service problem in- you will be certain to get one stantly. This index will include all the diagrams published in all from the first printing of the its users. Third, what ad- the previous GERNSBACK Manuals, as well as the 1934 diagrams. vance information we could A big convenience and time saver! book. The 1934 Manual will print that would be useful be ready in about eight weeks. in the future. Mail the coupon After careful analysis we today. found that the total cost of producing lie- address systems, short waves, auto radio r 1934 and others. 111, -s the Manual would be consider- GERNSBACK ably less than in former years, and The illustrations in the 1934 Manual will PUBLICATIONS, Inc. that at this time we could reduce the price be more explicit than before; inasmuch as 96 -98 Park Place, New York, N. Y. the diagrams will not be limited of the book to our readers. The Fourth to the Gentlemen : Enclosed you will find my Edition of the OFFICIAL RADIO SERV- schematic circuit, but other illustrations remittance of $3.50 for which you are ICE MANUAL will sell this year for $3.50. will show the parts layout, positions of to send me One Copy of the 1934 The book will be published like the 1933 trimmers, neutralizers, etc. There will be OFFICIAL RADIO SERVICE MAN- Manual volume will be sent you hundreds of new circuits included, and not UAL as soon as it comes off the press. -the to [Send remittance by check or money complete. As usual, we urge that all our one from any previous edition of the man- order; or register letter if it contains readers place their order early so that uals will be repeated. This we uncondition- cash, currency or unused U. S. Postage they will get a copy of the first printing. ally guarantee. stamps.] Usually, at the last minute a tremendous number of orders come to us and quite The number of pages in the new Manual often orders are held up while the book will exceed 400, with hundreds of illustra- Name is going through a second printing. tions, including diagrams, charts, photos, Anticipating such information as may picture layouts, etc. The size of the Man- Address serve future radio needs, we are holding ual will be the same as that of the former volumes many pages of the Manual open until the -9x12 inches, with a flexible. City very last minute. Any timely "dope" which loose -leaf binder. State

at Your Profits Are Better Than Ever when Vacation Days Arrive DeWald dealers have no summer slump. Their radio profits go up when summer arrives -for here's radio made to order for vacation selling. Portables for campers, boating trips -compacts for country homes, cottages -and a radio for motor car equipment. That's vacation merchandise. And DeWald has built and priced it for volume turnover. Take a look. -Do it soon!

bLWALbTRADE MARK REG.

SIX TUBE $4 950COMPLETE 1 100% Automatic Volume Control- hairline tuning -distortion -proof reception- consol -toned dynamic speaker -positive remote control. Illuminated dial -Lock Switch, and Volume Control. Size 9'W' high x 71/2" w.de x 6S," deep, using new tube. 78, 6A , 55, 37, 41. 84. Three hoses to drill, two MOTORTONE wires to connect. That's all to install. THE VERSATILE NI':\\ Model 552 'l'HE GREAT NEW Model 350 $2650 Five Tube Superhetcrudyne -a t eler that works on 110 -220 volts, AC- $2500 DC-25-60 cycles. Console Tone performance on any circuit. Full Range Identical in chassis with Model 551 Dynamic Speaker -Hair Line Tuning -it has the same astonishing per - Ultra Selectivity -Self Carrying formability as that new "giant Case in mottled brown or black leath- among the midgets." Cabinet uni, erette. A great "vacation" set. is different.

THE SENSATIONAL NEW Model 551 DeLuxe $2 750 Leader of the compactsTsuper- heterodyne-hair line tuning to i 10 kilocycles -110 -220 V.- AC-HC-25-60 cycle a -new type tubes- circuit matched aerial -new tone d y n a m i c 1 speaker -new heatless chassis -beautiful, distinctive cabinet.

llrrdels 5311, 531 and 5.52 corer Police and Broadens' Hand..

Pierce -Airo, Inc., 524 Sixth Ave., New York Cii Y

F O R TWELVE Y E A R S P A C E M A K E R S I N RADIO