r _ ' ,.a RADIO OAD CAST

eoNcf6Ners More About Sound Motion Pictures Whatlrends in Radio Design for 1Q2 Q? Practical Solutions of Radio ServicePrôblems Are theNewBroadcastAllocations Good? Circuits of Manufactured Receivers Buildings Television Receivers

35 ts Doubleday, Doran & Company, cIric. NOV een Garden C3i t y ``New oYl2 www.americanradiohistory.com SIX 'THOUSAND RADIO TRICIANS Are Now Equipped to Custom ituiid

4 NEW HiQ RECEIVE ) S AUTHORIZED Hi -Q Radio -Tricians in every Extreme selectivity - achieved by the new neighborhood are building the 4 new Hi- ly -tuned radio - frequency transfor- Q 29 receivers to special order and to meet mer , . s ich are in reality tuned "band- pass" fi Local conditions -- in every instance finer, more sensitive, more selective and beautifully toned a h degree of selectivity instruments than is possible to secure through -made possi . i e "flat -top" "band - factory-built sets within $50 to $100 of theirprice. pass" filter- tunin acteristic of the radio -frequency amp The new Master Hi -Q 29 typifies the value of the entire group completely stage- shielded Great sensitivity - affordin, ception over ^a t distances by taking + vantage of screen -grid receiver -steel chassis -only the fin- the . .rmous amplification ossibilities est parts available in Radio. Circuit is the re- of the ield -grid tubes us as radio frequency mplifiers. sult of America's leading parts manufacturers. A Band Pass Filter, the latest development in echanical p ection- manifest tures as t flat, rigid, a radio, effects absolute FLAT TOP square cut - off hed met -1 chassis, sn TUNING with 10 kilocycle selectivity. "Cross- and full oating bearing ganged «. ndensers. talk" is impossible. Only one station can be re- ceived at a time even in crowded high -power station areas. A " coast -to- coast" receiver that has wonderful sensitivity; unequalled DX re- ception; and a quality of tone that is totally new in radio. 4 models for battery or A. C.

NEW 80 -PAGE HI -Q 29 CONSTRUCTION MANUAL The biggest and most complete book of its kind ever published! Tells how to build the 4 new Hi- Q Receivers. Photos and diagrams illustrate every detail. Covers power amplifiers, tube and battery combinations, antennae, installation, short -wave adapters, house wiring and a wealth of other data on the Hi -Q custom -built radio. Price 25 cents including postage.

All Hi-Q 29 receivers demand your attention for the same reason as the Master Hi -Q 29 shown above -finest parts, modern stage -shielded cir- cuits, excellent selectivity and sensitivity and wonderful tone -quality at prices unequalled in present day radio. Junior Hi -Q 29 complete without HAMMARLUND - ROBERTS, Inc. cabinet, $59.35; Junior A. C. Hi -Q 29, $103.95; Master Hi -0 29, $99.50; Master A. C. Hi -Q 29, $151.80. 1182 -A BROADWAY, NEW YORK CITY Associate Manufacturers

ARCTURUS- u Als ToÁnRSoR IELECTRADI yrCiR7A

www.americanradiohistory.com RADIO BROADCAST ADVERTISER I \St 'C'

QUALITY is what the radio fan wants -QUALITY in every detail is what he must have, if his receiver is to be worth the effort of building it. Every experienced fan knows that good radio reception depends on the success- ful cooperation of many small parts - any one of which can make or mar the results obtained. Be SAFE -use Hammarlund Parts and you will be following the example of experts throughout the world. Eighteen years of manufacturing pre- cision instruments for radio, telegraph and telephone use are back of every Hammarlund Product. That experience is your protection. Ask your dealer.

HAMMARLUND MANUFACTURING CO. 424 -438 W. 33rd Street New York, N. Y. awn. Radio' WRITE FOR FOLDERS m iaì rul tui ndl -IN PRODUCTS

www.americanradiohistory.com How to be a commercial Radio Operator A practical book that should enable anyone of average intelli- gence to pass the Government's theoretical examination given to applicants for a Commercial Ra- dio Operator's License. INSIDE NEW! Nilson and Hornung's PRACTICAL STUFF RADIO TELEGRAPHY On Reception Where 380 pages, 5 x 8, 223 illustra- tions, $3.00 net, postpaid The hook covers in detail the theory and practical operation of Conditions Are Worst every type of modern, 1628, com- mercial arc, spark, and vacuum tuhe transmitter. It furnishes complete data on commercial F. W. McDonell, a New vacuum tube receivers. It covers York City consulting everything from elementary elec- J° op trici to the practical operation radio engineer, says: 1% of radio compasses. 4epep o,emOtéCOtII+A 3° Some outstanding points Je op 2 Very little mathematics p V/e epO xe 4 épOJgp oo t 2. Assumes no prior knowledge of electricity ot áed e or o mYpOeotopJO ee Jo 3. Covers everything in commer- teo 1 cial radio in detail 1.t G, e e1.p' ee°OpOO b°Tl e°o p 4 or 9 eonib 4. Complete list of self- examina- ,pe J 11 1.ni3 oY4° orK °Lo tion questions ?1 Ne ° e- 4oyper°pe ce4 ei' o0 re ¿ipe. 0 l ot ble ó 5. Simple yet rigidly accurate ç °1 pe1%Y ° 6. Complete op° r. reae pt,oJé wiring diagrams given. orG °aogr°oOpde jOe rY °DP o1.o C,mJ See the hook before p Oreo1. ° AI mf4p 1 you purchase. Fill in and mail just op° 6+ r op° roD. r.í' epl0 o1.op° this coupon. érengd.yoópee oS °éeer°tor ecpeo rOI e Jt6J°e°e e,der ° elmo° o°, liY p° ét.pB ppB 11 ble. IMcGRAW-HILL FREE EXAMINATION COUPON °d 1[s pe[Y °J,, s°mopa e e4tlrS r' per ._repe ,,pe 19 e mO° 1 pcos eoe pe pere e> S,1x e McGraw-Hill 9 or Book Co., Inc. S dem°p 4 1oO _.-.a oo°_ ;7o Seventh Avenue. New York, N. Y. op° ae. o You may send me Nilson and Hornung's epe%rpó oe. r0 PRACTI- ti 1eo° Price of Complete CAL RADIO TELEGRAPHY, $3.co net, postpaid. I will either return the hook, postage prepaid in io t.° Approved Kit,with days, or remit for it at that time. Special Aluminum Cabinet, $130.00. Name...... St. and No.....

City ...... State.. Name of Employer...... t)thcial Position. (Books sent on approval in the l S. and Canada only) R Il 11 -1 -28 L... MD I MIAI MN. .rINI IMO .M.. Meal MIND M.. - MIDGET CODE (..TELEPLEX SENDER ONLY $350 Post- paid Guaranteed

OUR BIG MAIL ORDER DEPARTMENT specializes in quick service on all S -M parts and kits, J and other high quality radio merchandise. Send the Be An Travel coupon below for our new catalog. Liberal discounts to Expert RADIO OPERATOR! p riven ore. amazing instrument teaches you to read code in half the usual time. dealers and setbuilders. Reproduces actual rending of expert operators. Sends you mes- sages, radiograms, etc., anywhere, anytime, any speed. You'll be amazed when you hear it. Just like having an expert operator in your home. Comp/ere instructions recorded on strong, waxed -tape records make everything simple and crear. Send only $3 -50 for Midget Teleplex with lessons; or $5.50 for high- frequenc> key and buzzer. Sati_jveL'n guaranteed. Money hack it not delighted. Send today. Royal Eastern Electrical TELEPLEX CO., Cortlandt St., New York, N, Y.

Supply Company Aerovox Condensers and Re- sistors have been firmly estab- 16 East 22nd Street New York, N. Y. lished as The Specified Products by the more discriminating ra a a a a manufacturers. ROYAL EASTERN ELECTRICAL SUPPLY CO., Dept. RB -11, Write for the Research Worker, 16 East 22nd St., New York, N. Y. a free monthly publication that Please send me free, your latest catalog of radio apparatus, contain- will keep you abreast of Radio's ing full description of the complete S -M line, as well as other leading latest lines of receivers, accessories, kits and parts. developments. Name ERDVOX Lddress 'Suitt Better" m Waehingtan St., Brooklyn, N. Y.

IRAnto Ituo.sii .50T. November, 1!128. l'uhlf.hed monthly. Vol. XIV, No. 1. Published at Garden City, N. Y. Subscription price $9.00 a year. Entered at the post office at (laiden City. N. Y., as second clac, wail matter. Doubleday. Duran & Company, Inn., Garden City, N. Y www.americanradiohistory.com RADIO BROADCAST ADVERTISER THE LINCOLN 8-80 ONE-SPOT-SUPER ASTOUNDS THE RADIO WORLD

4SCREEN GRID TUNABLE TUBES I.F. STAGES f ONE NEW SPOT AUDIO COAST TO COAST RECEPTION Clear Loud Volume in Summertime

HIS is the report from every Lincoln 8-80 receiver CLOUGH AUDIO SYSTEM in Chicago, the worst City in the U. S. for T built Not only In selectivity and quiet operation is the Lincoln long distant reception. Daily reports. by letter 8-80 supreme. Its new audio transformer, utilizing the revo- and.phone, of logs of stations from MAINE to CALI- lutionary Clough System to the -fullest -extent, gives it infinitely better tone, far more volume and less distortion than any other FORNIA, prove that the new principles involved in type of transformer can possibly provide. The effective trans- the LINCOLN 8-80 make every receiver perform alike. formation ratio per stage- exclusive of tuhe gain -averages 4.4 These reports are from set -builders who have built to 1, 50% greater than that of any other and more expensive transformers, and with all this -true reproduction, fidelity of the Lincoln 8-80 for the first time, and many from uncanny realism. a receiver before. tone, and positively men who have never built radio Even in appearance, the 8 -80 is far ahead of any factory Without exception. they all report absolutely no in- built receiver at anywhere near its price. The beautiful Lincoln terference from nearby powerful stations 10 K. C. 112 two -tone metal shielding cabinet ($9.25 additional) houses on low powered sta- the completed receiver and at the same time provides 100% away, and terrific volume distant perfect shielding. It is ALL of these features that make the 8-80 tions, all brought in without oscillation on a ten -foot the sweetest super you've ever tuned. And that is positively antenna. Small stations, heretofore never heard what it is! through the barrage of high powered stations. are re- The price of the complete kit for the 8 -80 is 892.65. And the set you build from it will give these same results, for every set ported with full volume. built tunes easily and positively to peak efficiency, thanks to For the first time in radio history has this sensational per- the new principle of William H. Hollister - -an old -timer in the formance been possible, and the actual performance of the Lin- game who demonstrated "wireless" to college professors before coln 8-80 in the hands of the amateur is proving far more than .Marconi first bridged the Atlantic. And all his experience, we have ever claimed. ranging over a quarter of a century, has gone into the 8-80. The remarkable new Lincoln screen -grid, intermediate-fre- It OUGHT to be some set -AND IT IS! quency amplifier is the secret of the astonishing performance LINCOLN GUARANTEES THAT THE 8 -80 WILL GIVE of the 8 -80. Gone are the well -meant but clumsy methods of the past -complicated shielding "laboratory matched" trans- BETTER RFSULTS THAN ANY OTHER EIGHT-TUBE SUPER formers that are never matched when the set is finished, YOU CAN BUILD. matched sets of tubes, and all of the heretofore "necessary If you want an evening full of straight- from -the -shoulder evils" from which you tried in vain to obtain real reception. super-heterodyne dope written by an engineer who has played 1 can peak the Lincoln Intermediates in 20 seconds when with every super going in the last few years, send 25 cents for your oset is in operation, correcting for all trouble you have had William Il. Ilollister's "Secret of the Super" using the coupon in the past. below. LINCOLN ENGINEERING SERVICE ON STANDARD KITS you can buy the really finer standard kits -those that have conte up to the rigid stand- ards of performance set by the Lincoln Laboratories at standard prices. and at standard discounts if you are a professional setbuilder or dealer? The Lincoln Engineering Ser- KNOW vice means a lot -you are assured not only of same -day shipment, but you have the double assurance of factory inspection, plus Lincoln inspection -and Lincoln offers you DO YOU THAT only complete kits that exhaustive tests bave proved to be right -and then fully guaran- tees each to you. Order to-day for immediate shipment any of the following Lincoln- Guaranteed complete kits:

Sargent -Rayment Seven (S-M 710) kit . . $120.00 Tyrman 80- super -less power pack . . . $131.50 S -M 720 Screen Grid Six 72.50 Tyrman 72 receiver kit . . . '98.50 S -M 720 Screen Grid Six-factory wired . . . 102.00 Tyrman 72AC, with power pack 153.50

1929 Laboratory Superheterodyne. . . 95.70 II. F. L. Isotone 10 -tube super . 195.00

lINCOlN. RAD I COPORATION 329 SOUTH WOOD Sr. - CHICAGO - ILLINOIS. Authorized Distributors for Lincoln 8 -80 Authorized Distributors for Lincoln 8 -80 WESTERN RADIO MFG. CO. CORP. 128 W. Lake St., Chicago LINCOLN RADIO RADIO SUPPLY COMPANY W. C. BRAWN CO. 329 South Wood St., Chicago, Ill. 912 Broadway, Los Angeles 564 W. Randolph St., Chicano Send me your big free catalog. listing a complete line of WHOLESALE RADIO SERVICE WALTER ROWAN CO. 1929 kits for custom building. 6 Church St., New York City 833 Washington St., Chicago Let me have details of your agency plan. F. D. PITTS COMPANY 219 Columbus Ave., Boston ELECTRIC & RADIO SUPPLY Enclose find 25e. for which send me William H. Hollis 22 N. Franklin St.. Chicago ter 's new book.. -The Secret of the Super." HORACE HILLS 533-39 Market St., San Francisco, Calif. Name

Address

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We Think You Ought to Know-

TONE quality is elusive. We can prove, by laboratory measurements and curves, that the new Clough system audio transformers come closer to absolutely faithful reproduction than any others we have ever been able to find, at any price. That may prove nothing to you -but it's true, nevertheless. One by one, we are getting reports of tests - made by impartial engineers for manufacturers and others -agreeing with our own findings that there is nothing on the market to match the tone quality of S -M Clough system audio transformers. That's what the engineers in the world's largest telephone laboratories said. It's what the professors of an old New England engineering school decided. To prove this to the public, here are the two fairest ways we know of-and we're taking both of them: FIRST: We are building, and operating in the most SECOND: We are guaranteeing absolutely that the public places we can find-the big radio shows, hotels, S -M Clough-System transformers large or small cannot dealers' show rooms- comparison amplifiers, with be surpassed by any of the conventional type not utilizing switches to interchange instantly two sets of audio the Clough invention with its practical elimination transformers in the same circuit. We are so well satis- of hysteretic distortion -at any price whatsoever. fied with the sales of S -M audios resulting from this "hard- boiled" method that we printed and distributed If you have the equipment, by all means verify 35,000 copies of an article telling dealers and set - yourself the sweeping claims we make. If you haven't builders how to build such a "comparator ". Do you -then listen to one of the public S -M comparator tests. know of any other transformer manufactl- -er who is If you can't do that -try a pair. Ask your own ears! doing that? If not, why is S -M the only_ who is We think you ought to know. Record of Audio Transformer Tests NOW-Theatre Volume E is the two -stage Any Phonograph curve for the large - ÌrNiÌ from size transformers i1iÌMBÌN 1 !! Iii111i1IN111ii1 (S-M 225, 1st stage; 1111111e1111G111 at Low Cost and 226, 2nd stage, IIÌ11I...... $9.00 each; D is ,« 111i1'III=::.w elesç: !!.s:'Ia. Used with any dynamic speaker u .. M that of the smaller .:rei.r..rr u r .I..u. ì.luFri:Í.\..r,. having a 90 to 110 volt field -or with ones (S -M 255 and íis 13i5i29 -r1. iu.un. 256, $6.00 each). i rr ïüii 1 two dynamic speakers and supplying ínr . mIr Note the marked the field current for one -the new N:!!=s11.1111=! i . . illIu. advantage over A, lN "- S -M 678PD Phonograph Amplifier 13, andC -all " I\"'1 ii irin .iriiiiii will take input from any phono- standard eight and the ten dollar trans ÌiÌfÌÌÌÌIi1nIN.,ÌIÌÌlÌÌÌ graph magnetic pick -up-or from the formers under I set, using adapter equal conditions. ao ISM detector of a radio o w +« i« w+0. M n« ,,. MN plug -and boost it to the tremendous volume output ,.t.MS of a 250 tube with the tone fidelity and freedom from hysteretic distortion provided only by the new S -M Are you receiving "The Radiobuilder" regularly? No. 5 shows Clough- system audio transformers. It operates entirely hotu to build an amplifier for comparing audio transformers. No. 6 from any 105 to 120 volt, 60 cycle light socket and re- tells all about the new S -M Public Address Amplifier. To all Author- ized S -M Service Stations, it comes free of charge; to others a nominal quires: one '81, one '26, and one '50 type tube. Price of charge is made. Use the coupon. complete kit, $66.00, or wired $73.00. If you build professionally, write us about the Service Station franchises. Or if you don't build, yet want your radio to be custom - made, S -M will gladly refer your inquiry to an Authorized Silver - Marshall Service Station near you. SilverMarshall, Inc. 838 W. Jackson Blvd., Chicago, U. S. A. .Please send me, free, the complete S-M CCSEVERAL of our cooperating distributors, Catalog; also sample copy of The Radiobuilder. directly follow, join For enclosed in stamps, send me the whose announcements following: a complete descriptive summary ....(S0c) Next 12 issues of The Radiobuilder us in presenting ($1.00) Next 25 issues of The Radiobuilder of the outstanding values to be found in the S-M DATA SHEETS as follows, at 2c each: ....No. 1. 670B, 670ABC Reservoir Power Units new S -M line. ....No. 2. 685 Public Address Unipac i ....No. 3. 730, 731, 732 "Round- the -World" Short Wave Sets ....No. 4. 223, 225. 226, 255, 256, 251 Audio Trans- formers i ....No. S. 720 Screen Grid Six Receiver SILVER - MARSHALL, Inc. ....No. 6. 740 "Coast-to-Coast" Screen Grid Four ....No. 7. 675ABC High -Voltage Power Supply and 838 West Jackson Blvd., Chicago, U. S. A. 676 Dynamic Speaker Amplifier ....No. 8 Sargent -Rayment Seven ....No. 9 678PD Phonograph Amplifier Name Address

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SM S -M for the Goods SETBLIILDERS for Quick Service

1 720 Screen Grid Six 710 Sargent -Rayment Seven The new S-M 720 embodies in the most Designed by two famous engineers to perfect form the revolution that screen - give the very extreme of results now pos- grid tubes have brought about in long - sible in broadcast reception, irrespective distance reception. Three of these tubes of cost, the S-M 710 Sargent -Rayment in the R.F. stages, with shielded S-M coils, Seven sets an entirely new standard. Ex- bring in distant stations on the next 10 kc. hausting the tremendous distance possi- channel to powerful locals! The new S-M bilities of 4- screen -grid K.F. stages-bring- 255 and 256 transformers set a far nigher ing in a station on every 10- kilocycle standard of tone quality than ever known channel right around its single -control before. Custom -built complete in 700 dial (with five auxiliary vernier knobs) - cabinet, $102.00; complete kit, with equipped with the unequalled S-M Clough pierced metal chassis and antique brass system audio amplifier -yet the 710 is escutcheon but without cabinet, $72.50. only $175 custom -built complete, or $130 for kit including aluminum cabinet. 700 Shielding Cabinet Beautiful two -tone brown moire finish, 730 Round -the -World Four with walnut finish wood base, $9.25. The famous "Thrill Band" set -for long-distance broadcast reception; has S-M Clough -audio-system tone quality- 740 Coast -to -Coast Four splendid also for code. One screen-grid A time- tested and famous circuit -one K.F. stage, regenerative (non- radiating) R.F. stage, regenerative detector (non - detector. Coils in kit tune from 17.4 to radiating) and two A.F. stages -combined 204 meters; S-M 131X Coil ($1.25) ex- with immeasurably finer coils, the high tends range to 350 meters, and 131Y coil efficiency of the screen -grid tube, all the ($1.50) to 650 meters. Aluminum shield- gain of smooth -working regeneration, and ing cabinet included with 730 KIT $51, new S-M Clough -system audios, make the or fully WIRED $66. Also with 731 740 the greatest value in the fifty -dollar Adapter (plugs into any receiver, con- class. WIRED in 700 cabinet: 740 (for verting it to short wave) KIT $36, WIRED D.C. tubes) $75; 740AC (A.C. tubes) $78. $46. 732 Essential Kit, $16.50. Kit less cabinet: 740, $51; 740AC, $53. B and ABC Pr per Supplies 680 Series Unipacs ' The 675ABC with -tdapter allows a Perfect reproduction and hum-free UX210 or UX250 pow 'ube to be used light-socket operation have made S-M in the last stage of any radio receiver -to Unipacs famous. There are four types: which it supplies B power at 425, 135,90, two single -stage, and two two -stage models, and 22 volts; also 22-90 variable. A and using 210 or 250 tubes singly and in C power are supplied to the power tube, push -pull. Each Unipac supplies 45, 90, and 1 t1/2z and 21A volts for A.C. tubes if and 135 volts B to receivers, and two -stage used. Uses one UX281 rectifier. Price models supply in addition 11/2 and 2 t/4 $58 WIRED, or $54 in KIT form. volts for A.C. tube filaments. Available 670ABC Power Supply has max. B as kit or wired. Prices from $81.50 to $117. voltage of 180; otherwise similar to the 675ABC. Price, WIRED, $46; KIT $43. 670B Power Supply for B power only, 685 Public Address Unipac 180 volts max., and lower voltages as in For coverage of crowds of 1,000 to 675ABC: WIRED $43.50; 10,000 people, indoors or outdoors, with KIT $40.50. one to twelve loud -speakers, the 685 Pub- lic Address Unipac furnishes unequalled 676 Dynamic Speaker Amplifier tonal clearness. It uses one UY227, one A single -stage power amplifier, using UX226, one UX250, and two UX281 one 250 type power tube and one 281 rectifiers in three stages for microphone, type rectifier. Used with any receiver, as radio or record pick -up amplification. 685 a third stage before a dynamic speaker, WIRED Unipac is priced at $160.00; or it will give wonderfully improved volume 685 KIT, $125.00. and tone quality, WIRED, $55; KIT $49. We are National Distributors of S -M Products

WE carry for your convenience a complete line of S -M Radio Parts Quick, and Kits, including the 678PD Phonograph Amplifier and all the new Clough audio transformers. Any of these can be shipped at Courteous once, as well as the new Unipacs, power supplies, audio transformers, and other parts. Our new catalog will be a revelation to you-use the coupon and get it now! LIBERAL DISCOUNTS TO THE TRADE, Service

SETBUILDERS SUPPLY CO. 19-3 Romberg Bldg., Chicago, Ill. Send me at once, FREE, complete instructions for building the 1929 "Lab. Super;" also your big Co. new 100 Page Wholesale Catalog listing S-M and SEtbuildErs Supp[j Iother radio parts, cabinets, consoles, and ac- cessories of highest quality. 19 -3 Romberg Building Chicago I Name Address

City St:eee IN13 ®.ZEM

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S -M for Results Graymore $i5o for Service Reception Hear London's Big Ben at a Chime $5O in Your Price Home!

A

FrO the thousands of fans for whom the four tube, R.F. amplifier, regenerative detector and two stage audio ampli- NOT with any ordinary radio receiver, of course -the fier is the time -tested standard of receiver comparison, the Atlantic is too wide for regular broadcast receivers to new Silver -Marshall Coast -to -Coast Four offers the finest per- bring you London programs. But an S -M "Round- the -World" formance yet attained with this remarkable circuit. A screen short -wave set will do just that -quite regularly. Turn yours grid R.F. amplifier stage, immeasurably finer coils than ever on, some night. Don't be surprised if the language you hear before, the new Clough high -gain audio system, and an all - is a foreign one, or if the announcer mentions "Paris" or metal assembly like those of the finest of ready -made sets, "Amsterdam," or "London" instead of the cities you are ac- make the "740" the biggest $51.00 worth of radio set you've customed to hear from. Call your neighbors to listen if you ever listened to. want to-but be cautious about calling anyone who has already explored the mysterious short -wave channels with an S -M The Coast -to -Coast Four, at Chicago, plays on the speaker set -your wonders might sound very tame to him. Perhaps New York, Florida, Texas, and California stations, cutting by this time he is only interested in New Zealand and Japan! through local Chicago interference only 10 or 20 kc. away. For in short -waves almost anything is possible; amazing feats Its tone quality is such as only S -M transformers can provide. of distant reception are becoming a matter of common Housed, like the 720 six, in the new S -M 700 table -model knowledge. metal shielding cabinet, it harmonizes beautifully with any S -M 730 "Round- the -World" complete 4 -tube set, with alum- home furnishings. inum cabinet; factory -wired, $66, or in kit form $51. Despite this demonstrated in respect, S -M 731 "Round- the -World" 2 -tube adapter with same cabinet superiority, every over (converts any broadcast -band set for short -waves) also all other sets in its price class against which we have tested the comes factory -wired, $46, or kit $36. 740, the complete kit of all approved parts costs but $51.00; S -M 732 Essential Kit $16.50. or the 740AC kit, $53.00 complete. The 700 cabinet is $9.25 additional or is included with 740 wired, $75.00; and 740AC S -M 5- Prong MidgetPlug -In Coils wired, $78.00. The new S -M coils for short and We go emphatically on record that no matter what set you broadcast waves. Wound on forms of build or buy, the 740 Coast -to -Coast Four is the best dollar for threaded moulded bakelite. dollar value you can find around fifty dollars. It goes together You can use your Round -the -World easily and simply, performs with a vengeance, and for the pro- Four on broadcast bands with these fessional setbuilder provides a low -priced set that will out - new coils -131X for 190 -350 meters, demonstrate ready -made sets at twice its price. $1.25; 131Y for 360 -650 meters, $1.50. GRAYMORE RADIO CORP. 142 Liberty St. New York, N. Y. S -M Parts Always in Stock We always have a large stock of S -M kits 11=1111 and parts, as well as other high quality GRAYMORE RADIO CORPORATION, 142 Liberty Street, New York, N. Y. apparatus. Send the coupon for our catalog. Please mail your new catalog of quality parts and kits, as advertised Discounts to dealers. Try us for quick service. rI in Radio for November. Broadcast

Name

Address CLARK & TILSON OMMI MI1111= 122 Chambers St. New York, N. Y.

Headquarters for S -M Parts CLARK & TILSON, We are Silver-Marshall's oldest jobbers in 122 Chambers St., New York, N. Y. Please mail your catalog showing SM parts and kits, and other high New York and can fill promptly your mail quality radio apparatus, as advertised in November Radio Broadcast. orders for S -M, as well as for other high quality merchandise. Send coupon for our Name new catalog. Discounts to dealers. I._Address

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www.americanradiohistory.com RÄDIO BROADCAST

WILLIS KINGSLEY WING, Editor NOVEMBER, I9281928 KEITH HENNEY EDGAR H. FELIX Vol. IX. No. Director of the Laboratory Contributing Editor o.

CONTENTS AMONG OTHER THINGS. . AFUNDAMENTAL part of the policy of this magazine Cover Design - - From a Design by Harvey Hopkins Dunn is the careful scrutiny of everything appearing in its Frontispiece pages, from the smallest advertisement to the most intricate of technical articles. We have always felt that our first duty to the Pictures Transmitted in One Minute at Radio World's Fair io reader was to protect him from misleading statements and in- What Prospects of Television Abroad? - Lawrence W. Corbett I1 accuracies of whatever sort. This magazine is not, however, the New Trends in Radio Design for 1929 -3o Keith Heaney 14 expression of one man's opinion, nor even of the group respon- sible for editing and publishing it. We have frequently given The March of Radio - An Editorial Interpretation 16 space to articles on technical subjects in which the authors came New Wavelength Allocation Plan Need for Defining Television Practice variance own opinions. Almost in- What is Public Interest? Newspaper Has Radio Picture Transmitter to conclusions at with our The Race for Television Publicity Commercial Broadcasting Increases variably after the appearance of the magazine we would be del- WRNY Television Broadcasts Here and There uged with letters and telephone calls demanding to know why A Milestone in Television Aircraft Radio this maga- New Nationwide Picture Service Radio in Foreign Countries we "said" this or that. The editorial expressions of zine, whether general or technical are always definitely identi- A Two Tube T.R.F. Short -Wave Receiver fied. Articles from other sources are also indentified, and for William Bostwick and W. T. Thomas 20 the opinions expressed, the author is alone responsible. We wel- "Strays" From the Laboratory Keith Henney 23 come the opportunity of printing controversial articles. Dynamic vs. Magnetic Speakers The "Gyps" Are Still at It Regarding Series -Filament Operation New Precision in Quartz Plates O JUDGE from reports which reach us, the motion -picture Present Designs Do Not Consider Economy Seven New Radio Booklets industry is in nearly as complete a turmoil as that in which How to Stabilize Rice Amplifiers Portable Radio Sets New Radio Tubes Needed Underground Aerials radio found itself some years ago. The cause of the trouble is, of course, the application of synchronized and non -synchronized B. When the Set Stops Working B. Alcorn 25 sound accompaniment to the "feature picture." This develop- "Radio Broadcast's" Home Study Sheets 27 ment is bringing into play practically all of the experience that No. 9. The Effect of an Electric Current No. so. Alternating Current -Part III broadcasters have so laboriously accumulated in the past few A New Audio System for Dynamic Speaker Reproduction years, and is drawing into the movie field many broadcasters Frank C. Jones 29 and other engineers who have developed apparatus and its uses for this work. In this connection, the pages of Carl Dreher's As the Broadcaster Sees It Carl Dreher 32 department, "As the Broadcaster Sees It," are well worth Sound Motion Pictures -Part II Commercial Publications watching, for Mr. Dreher is including much first -hand and A and B Power from the D.C. Lines - - - William B. Dail 34 practical information on sound motion picture work. Much of this work is being done by expert radio service men. Building Receivers for Television Zeh Bouck and James Millen 35 A Modulator for the 1929 Short -Wave Transmitter ANEW ZEALAND radio distributor writes us he is in- Robert S. Kruse 38 terested in communicating with American radio manu- "Radio Broadcast's" Service Data Sheet on IvRnufactured Re- facturers who wish New Zealand distribution for kits or com- plete sets, either a.c. or d.c. operated. Manufacturers who are ceivers 41 interested may communicate with the editor. No. it. Freshman Model "G" Receivers No. is. Freed Eiseman Model NR -8o The Improved Knapp A -Power Unit 43 FOR those to whom the news has not yet traveled, we An Amplifier and Power Supply for the "Vivetone 29" repeat the announcement made in this column last month: BROADCAST Laboratory Information R. F. Goodwin the bound volume of RADIO 45 Sheets Nos. 1 -190 is now available at $1. Order from your "Our Readers Suggest -" 47 newsdealer or directly from the Circulation Department of Short -Wave Plug-in Coils Improving Capacity Feed -Back Circuits Doubleday, Doran. Receiving Without an Aerial Tuning -in With a Distant Loud Speaker Polarity Indicators Home -made L F. Transformers Reducing Hum in the Detector Prolonging the Life of the 171A TO JUDGE from the comments in many letters, the Home Reducing Hum in A.C. Sets Special Soldering Irons for Difficult Jobs Study Sheets are increasing in popularity. It may have The "Chronophase" Screen Grid Receiver Bert E. Smith 49 escaped the attention of many who are following these Sheets The Fellows of the Institute Carl Dreher that we are quite willing to examine the answers to the problems 51 in each Study Sheet. These answers will be promptly examined New Apparatus - - - Useful Information on New Products 52 and returned with our comments. Manufacturers' Booklets 54 article on "Radio Broadcast's" Laboratory Information Sheets 56 THE December issue will contain an interesting No. 233. Balancing Radio Receivers No. 238. Hook -up for Short-Wave and band -pass filters, an interesting and practical article on No. 234. The Audio Transformer Broadcast Receivers television, more good data for the service man and professional No. 235. Television No. 239. Circuit for Short -wave and Broad grind quartz crystals, a No. 236. Moving-Coil Loud Speakers cast Reception set builder, instructions on how to No. 237. Power Output No. 240. Television number of important constructional articles-and our regular departments. The contents of this magazine is indexed in The Readers' Guide -WILLIS KINGSLEY WING. to Periodical Literature. which is on file at all public libraries. ,) DOUBLEDAY, DORAN & COMPANY, INC., Garden City, New York OFFICERS MAGAZINES BOOK SHOPS (Books of all Publishers) OFFICES F. N. DOUBLEDAY, Chairman of the Board COUNTRY LIFE LORD & TAYLOR; JAMES MCCREERY & COMPANY GARDEN CITY, N. Y. PENNSYLVANIA TERMINAL AND 166 WEST 32ND ST. NELSON DOUBLEDAY, President WORLD'S WORK NEW YORK: 244 MADISON AVENUE THE AMERICAN HOME NEW YORK: 848 MADISON AVE. AND 51 EAST 44TH STREET GEORGE H. DORAN, Nice- President 420 AND 526 AND 819 LEXINGTON AVENUE SQUARE BUILDING RADIO BROADCAST BOSTON: PARK S. A. EVERITT, GRAND CENTRAL TERMINAL AND 38 WALL STREET rite-Presideal SHORT STORIES CHICAGO: PEOPLES GAS BUILDING CHICAGO: EAST ADAMS STREET RUSSELL DOUBLEDAY, Secretary LE PETIT JOURNAL 75 ST. Louts: 223 N. 8TH ST. AND 4914 MARYLAND A.VE. SANTA BARBARA. CAL. EL Eco JOHN J. HESSIAN, Treasurer KANSAS CITY: 920 GRAND AVE. AND 2O6 WEST 47TH ST. FRONTIER STORIES LONDON: WM. HEINEMANN, LTD. LILLIAN A. COMSTOCK, Asst't Secretary WEST CLEVELAND: HIGBEE COMPANY THE AMERICAN SKETCH SPRINGFIELD, MASS: MEEKINS, PACKARD & WHEAT TORONTO: DOUBLEDAY, DORAN A GUNDY. LTD. L. J.. McNAUGHTON, Asset Treasurer

Copyright, 1928, in the United States,Newfoundland, Great Britain, Canada, and other countries by Doubleday, Doran er Company. Inc. All rights reserved. TERMS: $4.0o a year; single copies 35 cents. 8 www.americanradiohistory.com RADIO BROADCAST AI)VEkTISEli '+

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www.americanradiohistory.com Pictures Transmitted in One Minute at Radio World's Fair

This radio -photo receiver was demonstrated by the Westinghouse Electric and Manufacturing Company for the first time in the New Madison Square Garden, New York, during the week of the radio show. The apparatus is capable of converting electrical impulses into a complete photograph in less than one minute. Because of the difficulty in securing a wavelength assignment the demonstration was carried on with the use of wires. However, the engineers state that the equipment functions equally well by radio within the limits of fading and static. The chief advantage of this new apparatus is that it reduces the time required for the transmission of a photograph from five minutes to one minute. The size of the repro- duced photograph is five by eight inches 10

www.americanradiohistory.com JEW DEVICE PUTS MOVIES ON THE AIR This apparatus is the heart of the television motion picture transmitter developed by West- inghouse. It is used at RDRA for the broadcasting of radio motion, picture programs What Prospects of Television Abroad? By LAWRENCE W. CORBETT

N DISCUSSING the progress of television the technical press of far back as thirty years ago, and to have recommended the utiliza- the United States and Great Britain appears to take turn in de- tion of cathode rays. As stated in the July article, the proposed equipment I. ploring the lack of initiative of its own countrymen and in originally devised by Mr. Swinton offered possibilities which many of praising that of its rivals across the Atlantic. Yet, if we take the opinion our so-called "advanced" present -day systems do not. of no less an authority than Sir Oliver Lodge, we must admit that the At the time of writing this article (early in August and in London) leading exponents of the art in both countries are equally up against a much is being said about Baird's statement that he will market in stone wall and that the limitation of the apparatus they are using at September a home television receiver which will cost $125.00 The in- present will not permit further ventor has told the writer that improvement. ma" he is already well in production But Sir Oliver Lodge, and other with these receivers and that equally famous scientists whose The British Situation there will be no shortage when opinions incline in his direction, the instruments are released. In are by no means pessimistic of BY NORMAN EDWA RDS fact, the writer has already seen Managing Editor, Popular Wireless and Modern Wireless the ultimate success of television. a finished model in the Baird His criticism applies only to that FOR months past the question of television bas been agitating the minds laboratories. The cabinet houses apparatus now commonly used by of the British public, and day by day the Press in all parts of Great Britain both the television receiver and many of those who claim recog- has been persisting in dinning into the public ear that "television is bere." a electrodynamic loud speaker of nition in the art. Mechanical con- The Baird International Television Development Co., backed by British American pattern. An eight -inch trivances, Sir Oliver believes, are capital, invested for the development of television in England, now definitely diameter circular glass screen is bas promised a television service by the end of the current year, despite the fact by certain physical restric- to the left of the cabinet, and limited that the British Broadcasting Corporation, which bas a monopoly on broad- this screen, but on a tions which it will be inordinately casting in England, bas refused to cooperate with Baird and bis associates be- through impossible to surmount. To use cause, in the opinion of the Chief Engineer of the B. B. C., and bis advisers, smaller -sized square, is seen the his own words: the Baird system is not developed sufficiently to warrant it being utilized as a actual imagine. public service: and the Chief Engineer and bis associates in the British Post When questioned as the avail- Cathode rays or moving elec- Office having investigated the Baird system believe it to be in a state of experi- ability of service to purchasers of trons are the only things likely mental infancy and unfitted for offering a means of service to the public.. these sets (bearing in mind that to be sufficiently docile and con- Furthermore, the Wireless Telegraphy Act, which governs the use of radio in the B. B. C. has refused to trollable to be used as the agents England, legally bas been interpreted to cover television, as the British and cooperate with Baird at the pres- for television. No material things Post Office refused to licence the Baird system as a public utility service, the are likely to be able to move question now arises in the public mind as to what Baird will do. ent time) the inventor informed quickly enough, but electrons re- The Baird people definitely seem to believe that they can find a legal flaw in the writer that he will transmit spond so instantaneously that, if the Act of Parliament which governs the use of radio in Great Britain, and pro- pictures from a 4-kw. (input) devices can be invented for utiliz- pose 'o start a service, without receiving the permission of the British Post Office. transmitter on the roof of his ing them, the theoretical difficul- But it is believed that the Post Office will take steps to prevent Baird gking an laboratories in the heart of Lon- ties with the required rapidity of uruiutbórized service. The position at the moment is complicated. don. These transmissions, it is motion would begin to disappear The reason why the British Post Office and the B. B. C. will not coöperate with planned at the time of writing, will both from the sender and the re- Baird is not due to any prejudice but simply to the technical fact that the experts take place on 200 meters (15oo ceiver, especially as photoelectric concerned do not consider Baird's system likely to be successful in satisfying has response is almost infinitely rapid. the public demand for a television service. Baird still adheres to the mechanical kc.) Mr. Baird no license for system which experts bave pointed out repeatedly-experts which include Sir this transmitter, since, says he, A. Campbell Swinton, whose Oliver Lodge; Dr. Lee de Forest; Captain Eckersley, the Chief Engineer of the one is not required for television early_ apparatus was described in B. B. C., and A. A. Campbell Swinton, F. R. S. shows no likelihood of being transmissions. an article on television which developed in such a way as to provide a commercially possible television service, Here is raised an interesting appeared in RADIO BROADCAST and in fact, not even a service which would warrant the authorities in England point. An English editor of a for July, 1928, by R. P. Clarkson, granting the Baird Company facilities for exploiting it to the public. group of radio publications who I can say in conclusion that Mr. Corbett's article sums up both technically appears to have realized the limita- has studied the and legally, with excellent succinctness, the television situation in Great Britain. British Telegraphy tions that mechanical equipment Act very thoroughly tells the would impose upon television, as 'I ' writer that by no possible inter- 11

www.americanradiohistory.com 12 RADIO BROADCAST NOVEMBER, 1928 pretation of the law may Baird "televise," white) television, however, affords several times CAMPBELL SWINTON'S EXPERIMENTS which in itself constitutes transmission of intelli- as much detail as color television. gence, unless he obtains a license. And he has The following explanation of the principles of THE favorable opinion tendered toward the been refused the necessary license! It has been color television was dictated by Mr. Baird es- suggestion of Oliver Lodge and others who prophesied that Baird will be enjoined by law pecially for RADIO BROADCAST. Except for the suggest the utilization of electrons as a basis from transmitting as soon as he commences to do changes outlined below, the equipment is similar for experiment in the development of television so! Surely this attitude on the part of the to that used by Baird in his monochrome experi- leads one to expect that newer experimenters in authorities can be due to noth- ments and already described in the field will turn their attention to such systems ing more or less than lack of this magazine on several occa- as that avocated by Campbell Swinton. His faith by the British Post sions: experiments have been carried to a much Office engineers (under farther stage than Mr. Clarkson explained in BAIRD'S EXPLANATION whose scrutiny radio is RADIO BROADCAST recently. microscopically preserved) in THE transmitting machine It was only shortly after Braun, in 1897, in- Red_ Baird's present methods . consists of a disc perforated troduced the cathode -ray oscillograph that it oc- Baird, it must be admitted, with three sets of holes ar- curred to Swinton to work on the cathode -ray has made remarkable strides in ranged in spirals and set round principle in an endeavor to make practical some the periphery of the disc. See the advancement of the art system of television. He found in experiments .Green Fig. I. now, is he has come that the cathode-ray beam could be deflected but it felt, One spiral is covered with to the end of his tether, and is both magnetically and electrostatically with re- FIG red filters, the second spiral is being criticized severely for covered with green filters, and markable precision. With two similar cathode - placing on the market appa- the third spiral with blue filters, ray beams simultaneously controlled and de- ratus representing a germ of an idea still in an so that each spiral lets through only light of one flected by electric or magnetic forces due to embryonic stage of undevelopment. color. As the disc revolves, a spot of red light first identical currents Swinton expected to obtain It is argued that Marconi had no more to offer traverses the object being transmitted, this red absolute synchronism in the motions of the light being thrown back from the object and effect- the public in those early days when he first beams with maximum accuracy, irrespective of ing a photo -electric cell. The red light, having about wireless, but speed. to use one Braun's fought to establish his ideas completed this traversal of the object, the green the He planned of os- then, he appealed to a far more critical public spiral next comes into operation and traverses cillographs at the transmitting end and another (and then only to highly- trained engineers) than the object with a spot of green light. This is then one at the receiving end, the beams to be Baird is doing. Moreover, Baird, aided by color- followed by the traversal of the object with a synchronously and simultaneously deflected by ful and exaggerated reports in a general press spot of blue light from the spiral covered with the varying fields of two electromagnets placed that knows nothing more about his invention blue filters. Thus, the object is traversed first at right angles to each other, and energized by than the fans who will be expected to invest in by green, then by red, and then by blue illumina- the same two a. c. currents of widely different tion and three images are sent out to the receiver, his televisors, is meeting with considerably less frequencies. In this manner the moving ex- the first image showing only the red parts of the of the beams would sweep over the opposition than did Marconi. object, the second image showing only the tremities two green parts, and the third image showing only surfaces at the transmitting and receiving ends COLOR TELEVISION the blue parts. with remarkable rapidity and synchronism, so At the receiving station a similar disc to that rapidly, in fact, as to take advantage of the well - COLOR TELEVISION, the latest develop- of the transmitter revolves exactly in step with known phenomenon of persistence of vision. '-J ment of Baird, was described in the London the transmitting disc, and behind this disc in To produce the required picture at the receiving daily papers in glowing terms. The writer was line with the eye of the observer are two glow end it was only necessary that the rapidly scan- given a personal demonstration of this new child discharge lamps -a neon lamp, and a lamp filled ning extremity of the cathode -ray beam be with helium and mercury vapor. The neon lamp of television, by Baird, and was impressed only to impinged on a sensitive fluorescent screen. The supplies the red constituents of the light and that is due to a radical development beam, of course, would be caused to vary in in- the extent the helium and mercury vapor the blue and head, covered yet in its cradle days. A man's green. The eye of the observer sees first a red tensity by the varying signals from the trans- alternately with a blue or red cloth, afforded the image, then a blue image, and then a green mitter, thus producing the necessary graduations subject to be transmitted in the demonstration. image, the images being presented so rapidly of light and shade to produce a picture. Swinton's It was possible to see when the subject opened that persistence of vision causes them to blend real difficulty lay in devising a system which or closed his mouth, put out his tongue, and and the observer to see a composite image made would efficiently accomplish the variations in possibly when he rolled his eyes, and to see the up of these three colors. Now red, green, and blue constitute the three different colors of the head coverings, but to say primary colors from which all other colors are 1000,-71 the features were recognizable would highly that example, is a Per Sec: made up: for purple combination Triode exaggerate the matter. Monochrome (black and is a of red and blue, yellow combination of green Oscillators and red, and in the same way all other colors 10-. are made up of various proportions of these three Per Sec: -1000 - primaries, red, green, and blue. The process Magnets Per Sec used in color television is exactly similar to the Triode -color process used color r Oscillators- -10 three in cinematography. Per Sec The application of color television will natur- Vacuum Magnets-, ally be considerable, but it is not proposed by the Tube Television Company put color machines Baird to c Vapor on the market for some time, as this apparatus u y Chamber Vacuum is still in the experimental stage. The first tele- Tube vision machines to be marketed will be simply o monochrome, showing one color, and these r machines were exhibited at the Radio Exhi- o T bition held at Olympia, on September 22nd 500 Volts i__&11lens Photo- a be at Gauze' Electric last, and will placed on the market Cells price of £25. rfiri The image appears on a glass screen approxi- 500 volts mately eight inches in diameter and the televisor includes a loud speaker of the electrodynamic type. A special receiving device has been de- signed which enables both vision and speech to be received from the same aerial and at the same time. As three separate images must be sent in color television the speed of transmission should be increased three times. In practice, however, it is found that this increase of speed is unnecessary as each of the three images contains in itself quite a large proportion of the visual image received and it is not necessary to transmit at more than twice the speed of normal television to obtain F1G. 2 a satisfactory blend of the images and colors. FIG. 3

www.americanradiohistory.com NOVEMBER, 1928 WHAT PROSPECTS OF TELEVISION ABROAD 13 the transmitted current, which, in turn, de- ww pow «. -...- pended for its variations on variations of the J.r Mir wig rNM MIN SIX NS. ,. the u...,..4u...... J scanning cathode -ray beam at the transmitter. ..ir..e .w a.a sail NMI MN mryl, lr War +w Imp Wow N r woo -RR In these early experiments the use of a selenium .Y + wrrr.l. .a.11f.M. n. cell was depended upon as the link responsible 'NI .lYi for the actual variations in transmitted current. a..N1YOS rll1 In 1911* Swinton first suggested the use of -.xa«aati.=Oa., rf # .. photo -electric cells as the basis for the transmit- iI+.4aY.r . ting screen a single cell, but a fine mosaic -not I...... 1rd , of them -and this idea survives in his latest equipment. Some inventors use the combination of a mechanical arrangement at the transmitting end and the cathode -ray beam at the receiver. Naturally, then, the final result is governed by the speed of the mechanical parts, and the speeding up made possible by the use of electrons throughout is not possible. As a further development, Swinton suggests the use of electrons by means of suitable three - electrode tubes to supply, from batteries or from the mains, the two a. c. currents of largely different frequencies required to actuate the deflecting magnetic or electrostatic systems at the receiving and transmitting ends, used for the purpose of causing the synchronous, com- bined oscillating and traversing movements of the beams. The exact synchronization of these latter could be maintained by special radio signals on a wavelength separate from that used for the transmission. Figs. 2 and 3 show the BAIRD DEMONSTRATES DAYLIGHT TELEVISION latest Swinton transmitter and receiver circuits, In this picture Jack Buchanan, the popular musical comedy star, is shown sitting in front of the new respectively. I n these circuits it will be seen Baird daylight television camera Mr. Baird is standing in the center, and his assistant is adjusting that all mechanical motion has been done away the lense of the television camera with, resulting in circuits hardly more com- plicated than those used at the present time for broadcasting reception. ficent, but having regard to the apparent im- two articles on the subject. In these he entirely possibility of either improving or amplifying to agrees with my view that nothing of this order In describing the operation of his apparatus, any sufficient extent, one doubts whether they can ever be hoped for from material mechanism, Swinton writes as follows: can lead to anything really worth having along and that the only way in which it can ever be their own lines. Surely it would be better policy accomplished is by doing away entirely with At both ends the two cathode -ray beams im- if those who can afford the time and money material moving parts and utilizing the vastly pinge on screens, which they are caused by the would abandon mechanical devices and expend superior agency of electrons, those infinitesimal defecting systems to sweep rhythmically and in their labors on what appear likely to prove the and imponderable unit particles of negative complete synchronization in parallel lines back- ultimately more promising methods in which electricity which are the most mobile things wards and forwards from end to end. In the trans- the only moving parts are imponderable elec- known to science. mitter the screen is composed of a very large trons. A. A. CAMPBELL SWINTON. number of minute photo-electric cells each of which are activated more or less by the amount In a letter which appeared in the London OTHER EUROPEAN INVENTORS of illumination it receives from the image thrown Times Mr. Swinton expressed other views on tele- upon the whole screen by the lens. The end of the vision. Excerpts from the letter follow: NOT a great deal is heard of the effort of transmitting cathode beam explores each of these European inventors on the Continent, al- cells in turn, and as to whether it finds it illumi- To the Editor of the Times: - though from time to time small items of intel- nated and thus activated or not, an electrical The telegram on the progress of television in ligence do come through. In France, M. Bélin, impulse of varying intensity, proportional to the your July 14 issue leads me to think some com- in conjunction with M. Holweck, has succeeded amount of local illumination, is transmitted to ment should be made on the many very absurd the neighboring gauze grid. The varying electric prognostications that have appeared on this im- in transmitting shadows. The apparatus of M. current thus originated after amplification and portant subject. Bélin is unique in that the transmitter makes use conversion into wireless waves is transmitted to It is well known that all methods of television of two mirrors vibrating at right angles to one the receiver, where, after further amplification are based on the same principle as is the repro- another, the combined action of which enables and detection, it varies the strength of the re- duction of pictures in the Press, wherein the pic- the subject transmitted to be explored by a ceiver cathode-ray beam, which, in turn affects ture in each case is composed of a mosaic of potassium photo -electric cell. At the receiving end brightness particular portion of the minute dots so small and so closely packed to- the of that there is a fluorescent screen traversed by a fluorescent screen on which the end of the cath- gether that the individual dots are not recogniz- cathode ray. Thus we get a combination of the ode beam is at that instant impinging. Thus, able as such by the unaided human eye. Let us use on the receiving fluorescent screen a replica of take as an illustration a well -reproduced news- of the mechanical and the electron! the picture thrown by the lens on the transmit- paper half -tone to x 16 inches in size. This con- Another Frenchman, M. Dauvillier, has also ting screen is reproduced. tains more than 250,000 dots. succeeded in transmitting shadows, but admits Very probably with modern knowledge and Now on the same principle that requires that that an increase of one thousandfold in sensi- arrangements the transmitting method in which cinematograph film pictures have to succeed one tivity will be necessary before his apparatus is selenium is used might be got to work, though another at the rate of 16 a second, so as to give perfect. be for showing continuous motion. the perhaps it would too sluggish the illusion of for pur- Other scientists who are bending their efforts rapid movements in the picture transmitted. pose of successful television each of the thousands in an endeavor to be first in the race are Mihàly, of dots has to be registered in its proper place Korn, Nesper, and Muller. The latter has been A CRITICISM OF MODERN METHODS and with its proper strength no fewer than 16 times a second. Thus to transmit the picture experimenting for some time in an endeavor to referred to would require registering the dots at produce metal foils of extreme thinness, and has COMMENTING in a paper on the advances a rate of 4,000,000 a second. produced some of gold a hundred times thinner made in television, whose mechanical Such achievements are obviously entirely than heretofore, so thin, in fact, that printed let- devices formed the nucleus of the apparatus, Mr. beyond the possible capacity of any mechanism ters can be read through six layers. Varying Swinton has said:- with material moving parts and this view, which intensities of light passing through these layers I have personally been inculcating in scientific of foil have been found to alter a current of What has been effected mechanically, more circles for many years, has recently been thor- especially in America, shows what can be done oughly endorsed by no less an authcrity than Sir electricity passing through. The use of this dis- by vast expenditure, labor, and elaboration. As Oliver Lodge, himself a notable pioneer inventor covery may lead to the production of a very experimental shows they were no doubt magni- in wireless telegraphy, who has recently written cheap television equipment, it is hoped.

www.americanradiohistory.com T THE present writing (Sep - below loo cycles. He must put the tember) several distinct speaker in the middle of a rather LLL trends in the progress of large and awkward and solid board radio may be observed by any one not less than three feet square who gets about even a little bit. for best results. His amplifier, to These trends are often first evi- utilize the advantages of this kind denced in home -made receivers and of speaker, must be very good. Be- in the kit sets put out by wide - cause the speaker is more efficient awake manufacturers and are later -at least some of them are-he seen in the sets built by the large can get along with less power, complete -set people. Sometimes, but at present it is not safe to of course, the set manufacturer economize at this point. The con- is in advance of the others, but structor had better plan to use in general the tendency has been 171's or better in his final stage. for this branch of the industry The day of the 199 tube loud to follow the leader. Whether speaker. is not yet here. On the this is due to lack of engineering other hand, we do not believe initiative, or to hesitancy to adopt it necessary for the home listener something new, or to patent arrangements, is diffi- that sound energy will come out, and that to go to 250-type power output tubes, although cult to say. It is true, however, that among the li- there will be no clatter of armature against the reserve power possible with such an ampli- censees of the R.C.A. there have been few major pole pieces. No other type of speaker has been fier as was described in the July RADIO new ideas that have seen the light of the dealers' tested in the Laboratory which reproduced fun- BROADCAST (page 141), is something to strive shelves. These people are still making t.r.f. sets damental tones below too cycles. They emit for as the ultimate. or neutrodynes. Small improvements have been sound, to he sure, but it is not like the original. In the laboratory of Dr. John P. Minton, the made, but they are in the nature of refinements well -known acoustical engineer, we heard a of existing circuits and apparatus. to-inch Peerless dynamic speaker which was What are these new trends, and what do they Will 1929 See These New Develop- mounted in a three -foot baffle of not too solid mean to the future of the radio business -say construction. The speaker was operated from an the 1929 -3o season? ments in Everyday Use? amplifier employing a single 171 -type tube in the output stage, and the results were very 1. THE DYNAMIC SPEAKER satisfac- 1HE DYNAMIC SPEAKER tory. The signals were made louder than could 2. THE BAND SELECTOR WE HAVE already discussed in this maga- be tolerated comfortably in a small apartment, 3. THE ONE -STAGE AUDIO zine the moving -coil or dynamic speaker. and they were considerably "up" from The out- 4. THE FIVE- ELEMENT TUBE After considerable effort to find an unbiased put of a W.E. 56o AW. Persons who invariably source of loud speaker information, we discov- ,u,iu, ,ai,liitru9,moii,imN, ll ammi,mi, ,,inimmi,iriru, talk louder than the radio when the latter is ered Joseph Morgan of the International Resist- turned on would have considerable trouble in ance Company, who wrote the article "All The dynamic speaker, then, is here, and in preventing one enjoying a symphony concert About Loud Speakers" in the August RADIO 1929 will take its place in the best commercial from a local station with such a speaker con - BROADCAST. sets and in the homes of the most critical home nected in the output circuit. There is no doubt that the present season is set builders and engineers. I t entails several At the present time the Laboratory staff is going to be a dynamic speaker season. Nearly hardships on the constructor. The filter in his busy measuring the characteristics of a number every set manufacturer of note will have a model power supply must be better than is necesaary of the newer speakers of this type and when the or two equipped with this newest milestone on with other speakers that do not reproduce tones datum is available in its final form it will be pub- the way toward more perfect re- lished in RADIO BROADCAST. production. There are many such THE BAND-PASS R.F. speakers now on the market; some of them are the Magnavox, Jensen, - Shield ANOTHER very distinct trend Peerless, Rola, Newcombe-Hawley, - - - is the band selector business. Marco, Radiola 105, Farrand, etc. In December, 1927, Dr. F. K. Why is the moving coil speaker Vreeland read a paper before the superior to our present cone and I. R. E. on his ideas of what a good horn types,' Briefly, because it pre- radio-frequency amplifier should be. sents to the final power tube a nearly He had two suggestions. One was pure resistance rather than a com- to stagger the three tuning con- plicated combination of inductance, densers of a t.r.f. set slightly, that capacity, and resistance whose fre- is, tune two of the condensers quency characteristic is anything but slightly above and below the exact a straight line. The dynamic speaker resonance point. This, according has a moving system that can move to Dr. Vreeland, would tend to through large distances, up to a FIG. I broaden the top of the response curve and to steepen its sides. This quarter inch, which means that There are no tubes in the Jones band selector which is shown in schematic plenty of low- frequency power can fora: here. All the selecting is done by one set of apparatus, the amplifying would make it possible to receive be put into it with the certainty by another. The tuned circuits are coupled together by the small inductance, L1 the high audio frequencies that are 14

www.americanradiohistory.com NEW TRENDS IN RADIO DESIGN FOR 1929-30 15 so badly clipped at present, and yet to prevent croFs -talk from adjacent radio channels. Dr. Vreeland's other suggestion has occasioned a lot of discussion. It consists in using in the re- ceiver a band selector composed of -this is oúr interpretation, not Dr. Vreeland's -two tuned circuits coupled closely enough so that the re- sonance curve of such a system has a flat top, a top with a dip in it, or a sharply peaked top de- pending upon the constants of the circuit. According to the discussion, this is not a new idea -we do not know that Dr. Vreeland said it was -but the fact is that in the old spark days, the bane of radio inspectors was the closely coupled antenna -transmitter system which FIG. 2 emitted a broad wave. The circuit diagram of the Vreeland band selector; note the inductance, Xa, which couples together the The effects of staggering are two: (1) to two tuned circuits composed of Xi and X2 and their associated tuning condensers broaden the top of the response curve and there- and (2) to reduce the r.f. by to improve fidelity; plifier. When any good selector is attached to which uses a.c. tubes and has only one audio With deliberate staggering it gain somewhat. any good r.f. and a.f. amplifier units a good re- stage. very selective should be possible to use highly ceiver results. The elimination of the first stage of a.f. reduces loss," if you will. Then the gain circuits -"low In service a similar occurrence takes place. cost, makes a set simpler to construct and should be somewhat greater. The per stage ought to The service man takes with him an extra selector reduce not only tube noises and the tendency to- however, will not be noticeable gain in fidelity, and an r.f. amplifier. If the customer's selector ward severe microphonics, but eliminate con- on the average amplifier and loud speaker. On is out of order, a new unit is slipped into place - siderable a.c. hum, which is a great advantage with a flat audio amplifier, a the other hand, the entire set is not placed out of commission. when the dynamic speaker is used with a good good transmitting station, and a dynamic The Hammarlund- Roberts engineers have amplifier. speaker, the higher frequencies as heard should incorporated the band selector idea in their One well -known physicist -radio engineer states be materially improved. 1929 Master receiver already described in this that in his opinion the proper place for the loud We must now record a visit to the Technidyne magazine (October, page 341). In this receiver speaker is in the detector circuit. Whether the Laboratory, where we again had the pleasure of both the primaries and the secondaries of the set of the future will have no audio amplification chatting with Mr. Joseph Jones who is business r.f. transformers are tuned, the two circuits at all cannot be debated at present. manager of this organization, of which Mr being coupled together by the mutual inductance Lester Jones is the engineer. This was not our existing between the two coils. This is very loose A NEW TUBE IN THE OFFING first meeting or conversation, and only con- mechanical coupling. The Vreeland and the Jones IN ENGLAND there is considerable talk of the vinced us the more that this is an organization system use other types of coupling, it being ` new special -purpose tube with five elements, which will be heard from more and more in the possible, of course, to couple two tuned circuits the Pentode. This is a power valve built along next few years. together with mutual or self- inductance, or with lines similar to our present screen -grid tube. The The Technidyne group has a band selector, idea is to get much greater output power with too, but it differs in several respects. The Jones given input voltages. It is a tube with a large group has in addition a self -shielded coil, a amplification factor and a high plate impedance; loop of similar characteristics. and an untuned with our present low- impedance speakers it may r.f. amplifier of considerable gain. How these require new coupling devices. A number of arti- work into a modern receiver will be indicated cles have appeared in Wireless World (England) below. The coil has two windings, one inside the recently on this tube, which lead us to believe other. The high potential ends of the coil are in- that the Pentode will do much toward making side, so that one can grasp hold of the coil, or unnecessary all the r.f. amplification that elimi- wrap a short -circuited turn of heavy copper FIG 3 nating one audio stage demands at present. wire about it, without destroying signals or The band selector used in the Hammarlund- detuning the set. In our opinion this is an WHAT ARE WE COMING TO? even Roberts "Hi-Q 29" receiver. In this case the tuned resulted extremely useful invention and has in circuits are coupled together by the mutual induc- HERE, then, are the trends in sight. The first. a very valuable patent. So long as coils are tance existing between primary and secondary the dynamic speaker, is here now. It is one used in receivers, there must be means of keep- more step toward better reproduction, greater ing their respective fields from getting out of capacity or resistance or combinations of all of fidelity of voice and music. The second, the band bounds. One method is to encase the coil in a these. selector, is another step toward fidelity, with the metallic can -shielding it -and another is to Here, then, is the second trend toward band possibility of an increase in selectivity. In the use a self- shielded coil. selectors, electrical contrivances which cut out hands of Lester Jones the problem of selectivity The Jones band selector will probably be used of the broadcast spectrum a swath of the desired has been separated from that of amplification - in several receivers, notably the Sparton. I t width. Such circuits have been suggested as a feat we predicted months ago. The super- works out as follows. A band selector is made a relief in the present overcrowded ether heterodyne is such a circuit, although not to up of several coils and condensers and encased conditions. We believe, however, that another the degree the Jones system is. The third trend in a container. This has but one wire coming year will see the band selector the rage is the elimination of the first stage audio. In the from it, the connection to the following unit, in set construction. The Jones system is a pre - Jones system this is done by using greater r.f. the r.f. amplifier, which connects to the detector selector, that is, the signals are first selected and amplification and detectors more heavily biased and the audio system. This amplifier is untuned, then amplified. In the Vreeland and the Master than those of the present. In the super-hetero- has five stages in it, with the gain varying from Hi-Q circuits amplification and selection go on dyne the amplification is at intermediate fre- 3000 to 15,000 from the short to the long waves at the same time. quencies. The Pentode tube may make it possible to offset the lack of coupling on these waves be- to eliminate some of the additional r.f. gain tween set and antenna. When an antenna is THE ABBREVIATED AUDIO now necessary, with an obvious advantage from attached to the amplifier input, the mix -up of THE third noticeable trend is toward the the standpoint of cost and simplicity. signals is worse than anything the Radio Com- elimination of the first stage of audio, and It looks as though it is never safe to predict mission ever imagined. working the power amplifier by the detector. that the time has come when there is nothing This circuit has several obvious advantages. Let us see what this means. First of all it means new under the radio sun. The home constructor, In manufacture there are three belts on which that the detector must supply a much higher however, need not feel it unwise to construct a the selector, the r. f. amplifier, and the a.f. am- output a.f. voltage and therefore must be sup- set at present on the suspicion that next year's plifier are placed for inspection. This is to be plied with a higher input modulated r.f. voltage. circuits will make obsolete his present gear. contrasted to factories in which the completed The Jones system does not use the usual first stage Receivers built to-day according to recognized receiver is placed upon a single belt. If anything of audio. The detector is a C -bias affair with input engineering principles and equipped Witt, good goes wrong with a selector unit, it is removed; r f. voltages of the order of Io to 15 volts. A new amplifiers and speakers will be standards of com- the same thing happens with an r.f. or a.f. am- R. C.A. super has also been put on the market parison for some time to come.

www.americanradiohistory.com N W .S_ AND 1NTERER TMT0 O F- C 1TR PT NIDIUDICTEVENT New Allocation Repairs the Broadcast Structure

THE Federal Radio Commission has, at This, in brief, is the skeleton of the allocation the public with the effect of the provisions of the last, bestirred itself. It has formulated an plan, as it was first announced by the Commis- Amendment in unnecessarily depriving theSouth orderly plan of allocation, based upon con- sion. Undoubtedly, it will be modified. Such and West of broadcasting stations. However, had servative engineering estimates of the capacity dubious features as limiting the maximum power the Commission acted promptly upon the various of the broadcasting band. When the plan is in of permanently licensed stations to 25,000 watts, allocation plans offered it from the very day of smooth operation, it will increase the program on the exclusive channels, is a useless curtail- its organization (of which one, submitted by a service obtainable with any radio receiver cap- ment of the service of these channels. Did it member of the staff of RADIO BROADCAST, pro- able of reaching out beyond neighborhood locals. serve to increase the number of stations which vided almost precisely the structure at last We hesitate to praise any constructive step might be assigned to a channel, it could be justi- agreed upon), the Amendment never would have announced by the Commission because, up to fied on that ground. It amounts only to an order been passed. The year and a half of dilly dallying this time, it has always reversed itself before compelling stations to render less than their best which preceded the adoption of the present plan promised reforms have been put into operation. possible service. Apparently, it is a concession has inflicted a more or less permanent handicap It proposed to eliminate all stations persistently to Judge Robinson, who wanted to put a 5000- upon the broadcast structure in the form of the wandering from their channels, but backwatered watt power limit on broadcasting, thereby re- Davis Amendment. before the echo of its brave statements had died ducing the total area of the United States served To the broadcast listener, the faithful adoption out. It called a host of stations before it to prove by high -grade broadcasting to considerably less of the present plan means clear reception on most they were operating in the public interest, neces- than ten per cent. of the positions of the dial. Forty channels are sity and convenience, with a grand fanfare to the completely cleared, providing for eight stations EFFECT OF THE DAVIS AMENDMENT effect that many would thus be weeded out. but in simultaneous operation per zone. Thirty -four the actual result of the hearings was negligible. THE Davis Amendment requires equal dis- channels are partly cleared for regional service, From past experience, we cannot avoid fearing tribution of channels among the zones, and offering a standard of reception about equal to a complete reversal of form and a repudiation of their distribution within zones according to that heretofore found on the so- called cleared the meritorious broadcast allocation plan. We population. As a consequence of the varying channels. The number of stations reasonably hope that public approval of the announced plans areas of the zones, more than half of the desirable clear of heterodynes, is vastly increased and will be so forcibly expressed that, this time, there regional and national channels necessarily are chain programs will no longer crowd the few will be no turning back. assigned to the Northeastern quarter of the choice dial positions. The plan itself is a normal and sensible classi- country, comprising the first, second and part By taking into consideration the channels fication of channels into local, regional, and na- of the fourth zones. The Western half of the which will be used simultaneously by more than tional groupings. Forty channels, eight per zone, country, the fifth zone, has only one -fifth of the one zone, the total number of stations in the are nationally cleared for exclusive service by total number of cleared channels. The Southern regional class, operating simultaneously at night, stations of 5000 watts or more. Only one station zone, comprising an area of about a fourth of the will be 125, or 25 per zone. These regional sta- is in operation on each channel at a time, al- country, is given only one third the number of tions will give satisfactory service for moderate though time division may be employed in the preferred channels assigned the Northeastern distances beyond the so- called "high -grade case of stations not prepared to operate on a full- quarter of the country. service range" and should be entirely free of time basis, or to permit division of channel The Commission naturally has found these heterodynes within the high-grade service area. facilities among the states according to popula- silly requirements of the pernicious Davis The six channels devoted to local service may tion, as required by the Davis Amendment. Amendment a serious handicap in its work and be duplicated at fairly short distances, but again This exclusive service band lies between I190 has not overlooked any opportunity to impress the Davis Amendment acts to curtail the poten- and 64o kilocycles. tial service of these channels. The Four channels, 146o to 1490 inclus- number of stations per zone upon ive, are devoted to stations of a maxi- these channels must be equalized al- mum power of 5000 watts, to be though, for example, there could shared by two zones, presumably on otherwise be about twenty times as ,opposite coasts of the country, thus many local communities using these providing good regional service. channels in the fifth zone as in the Thirty -five channels, ranging first, without having any greater con- throughout the dials from 1430 to 58o gestion than is found in the first, so kilocycles, are assigned to stations marked are the differences in the having a maximum power of woo areas of these zones. watts. These channels will be used in Another curious consequence of the not less than two nor more than three Davis Amendment is the somewhat zones simultaneously for night broad- diverse effect it has upon the two casting, although in isolated in- centers of broadcast congestion, New stances, the maximum will, for the York and Chicago. Because New York time being, be exceeded when no seri- has such a predominant proportion of ous interference is caused. These are the population of its zone, it suffers a the so- called "regional channels. somewhat smaller curtailment of as- Five additional channels, ranging signments than Chicago. Casual ob- throughout the band, for stations up servation of the Chicago situation to woo watts, will be duplicated in shows a heavy mortality in time on every zone, thus providing medium the air of its all -too-numerous 5000- power, local, and limited regional watt stations, but the actual effect service. will not be nearly as drastic as it Finally, six channels at the lower appears. Many of Chicago's 5000 end of the dials, will be thickly watters have been operating on ex- populated with wo-watt broad- MARCONI'S NEW 6-Kw, 2000-METER TRANSMITTER tensive time division in the past and letters rather casters, accommodating a g re a t This wireless telegraph station at Grytviken, South Georgia, main- others are merely call number of stations providing strictly tains a daily telegraph service with the Falkland Islands which in than actual stations. Practically local service. turn communicate with Montevideo no licenses will be cancelled any- 16

www.americanradiohistory.com NOVEMBER, 1923 WHAT 1S PUBLIC INTEREST? 17 where and, by liberal use of time division and limited application of power cuts, the new struc- ture will work a minimum hardship upon station owners. In spite of the dire predictions of opponents to a plan based upon engineering considerations, the plan supports the contention of engineers that allocation, based upon sound technical eval- uation of the capacity of the broadcast band, does not require heavy mortality of stations.

PLAN BETTER THAN HOPED FOR two years, we have urged in these columns that the nuniber of stations on the air simul- taneously be reduced to 200 or 225; the plan exceeds our fondest hopes because it places only 165 stations in simultaneous operation on 74 channels. The balance of the band is reserved for strictly local services. Receivers in good loca- tions will bring in a parade of unheterodyned stations and good programs will again have al- most nationwide audiences. The wall of local stations, in congested centers, will be partly levelled. Every section will profit by lessened heterodyning. The South and \Vest are seriously restricted by enforced disuse of available chan- THE STAGE OF A TELEVISION DRAMA nels. In the South, this is no immediate hardship, This picture shows how WGY broadcast the first television draiera. " The Queen's Messenger." Three tele- as there are fewer stations in operation but, on vision cameras were used-one for each of the two players and the third for the " props " -and by a twist the Pacific Coast, a great many needless holes in of the knob the director could bring the desired camera into the circuit. Also, a television receiver was in- the ether can be credited to the Davis Amend- stalled in the studio to enable the director to check the image ment. We predict one unexpected result of the new tions; that there is demand for a variety of ser- quencies used to transmit the sixty -line picture broadcasting structure: the restoration of popu- vices, including high -power service, covering lay between 500 and 6o,000 cycles, so that a total larity of long- distance listening. Radio reception large territories, and low -power service for local of 150,000 cycles of ether space would be re- has arrived at a respectable degree of quality of interest; that the broadcasting of phonograph quired to radiate the signal by the conventional, reproduction. Cleared channels will bring back a records as a considerable part of a station's ser- double- side -band method. An extra 5000 -cycle limited amount of dial twisting and, within a vice is not a public service unless special records wave was used for synchronizing purposes. year or two, long distance will again be a desired are developed for broadcasting only; that adver- The usual statement was made that the device quality in a radio receiver. Long distance is the tising should be incidental to a real service ren- would be marketed by the Radio Corporation of magic of radio, just as speed is the zest of motor- dered by a program; that stations of 500 watts America when ready for public consumption. ing. Beauty in appearance and tone will always power or more should not be located in thickly Mr. H. P. Davis, Vice- President of the Westing. predominate as a sales appeal, but the flash of inhabited communities; that very low -power house Company, also stated to the press that the distance will rise again as improved conditions stations should not be permitted in very large device would soon be ready for the home user. make its enjoyment possible. This repeats in cities; such channels being more usefully em- So are steam yachts! radio the cycle of automobile sales appeal: first, ployed in smaller towns; that the character and speed, then an era of emphasis on comfort and financial responsibility of applicants for licenses WRNY Television Transmissions beauty and, finally, these characteristics com- are important considerations; that broadcasting bined, as they are in the products of to -day. time should not be used to air discussions of a STATION WRNY began its transmissions on private nature; that stations, not operating on August 21. Its television signal is now What Is Public Interest? a regular schedule, do not serve the public; that heard from the fifth to the tenth minute of a broadcaster, who is not sufficiently concerned each hour that the station is on the air. A 48 -line OUTS Ct. CALDWELL, as attorney for the with public interest to equip his transmitter with picture is transmitted on the broadcast band, but Commission, on August 25, issued a de- adequate frequency control or check thereon, is its channel width is restricted by sending only tailed interpretation of the so-called public - not entitled to a broadcasting license. These 7.5 pictures a second instead of sixteen. This interest, convenience and necessity provisions considerations were the basis upon which the does not improve the quality of the transmission. of the Radio Act. Inasmuch as the Commission practical application of the broadcast allocation must, sooner or later, prove in the courts that plan were founded when the Commissioners A Milestone in Television the new allocation plan is justified by these con- made their individual station assignments to siderations, that interpretation is virtually the national, regional, and local channels. THE first time that remote-control televi- Commission's plan of defense. The statement sion broadcasting has ever been under- points out particularly that the Davis Amend- The Race for Television Publicity taken was the occasion of Governor Smith's ment, although calling for equalization of powers acceptance speech on August 27. On this occa- and stations in each district, does not set aside THE race for television publicity continues. sion, WGY installed its portable television trans- the public interest, convenience, and necessity The latest to score is the Westinghouse mitter, which makes a 24 -line picture, at the clause and that, therefore, all new stations, Company, which demonstrated a sixty -line State House in Albany. The television signal authorized in under -quota districts, must pass television scanner and reproducer. This is ten was transmitted through eighteen miles of wire qualification standards imposed by these four, lines better than the television elephant which and then radiated by WGY, the General Electric all- important words. It further points out that the Bell Laboratories built some years ago. In- station at Schenectady. renewal of existing licenses is not incumbent stead of scanning a living subject, light was The television pick -up equipment, erected near upon the Federal Radio Commission, unless it passed tothe photo-electriccell through a motion - the microphone, consisted of three units, two finds that public interest, convenience, and neces- picture film. This was proclaimed in the news- tripod -mounted, photo -electric cells in boxes, a sity are served; that the issuance of a license is papers as a radical invention, although the first light source, and a scanning device. The cells not to be regarded as a finding beyond the dura- broadcasting of radio movies, ps we recall it, was were placed at the left of the Governor, within tion of the period covered by said license; re- demonstrated to members of Harding's cabinet three feet of his face, and the light source between licensing in the past, indicating that the station seven years ago. by C. Francis Jenkins. With the cells. A l000-watt lamp was used to play on has met the test of public convenience, does not, amazing ingenuousness, the Westinghouse pub- the Governor's face, the intensity of the light however, bind the Commission to continue past licity stated that Mr.Conrad began his television being broken up by a scanning disc. mistakes, should any have been made inadver- researches only three months ago. The General Electric people did not issue any tently; that public interest, convenience, and The uselessness of the device from a practical applesauce publicity about milestones in history necessity cannot possibly be defined and must viewpoint could be gleaned from a single state- at the time. When they issue a statement that

be judged by individual situations and condi- ment in the publicity to the effect that the fre- home television is practical, we will believe it. .

www.americanradiohistory.com 18 RADIO BROADCAST NOVEMBER, 1928

1927 to 14.5 per cent. in 1928 and the actual number from 41 to 51. Broadcasting is the only one of the eight classifications, into which na- tional advertising falls, that has shown a mar- ked increase in the number of users. The greater the number of national advertisers, seeking to please the public by goodwill programs, the greater the competition for public attention, and consequently the higher the program stand- ards. Better commercial programs also mean fur- ther improvement in standards of non- commer- cial programs and a very happy outlook for the radio listener. Another field which is developing is broadcast advertising by local stations. The peak of direct advertising by the local broad- caster is passing and more intelligent and ser- viceable use of the radio announcement is being made by the smaller stations.

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ANEW chain is again announced on the Pacific Coast, comprising KJR, Seattle; KEX, Portland, KGA, Spokane; KYA, San Francis- co; and KMTR, Los Angeles. Rival chains to the N. B. C. Pacific Coast network which did not materialize have been announced before. Per- hans this new one will.

M R. OSWALD SCHUETTE, professional radio agitator, employed by the Radio Pro- tective Association, offered a petition to the A MODERN RADIO INSTALLATION ABOARD AN ITALIAN LINER Commission that the licenses of WEAF, wlz, WGY, WRC, KOA, KGO, KDKA, KYW, KFKX, WBZ New Nationwide Picture It is too early to propose standards for these and WBLA be revoked on the grounds that the Transmission Service factors because standards imply agreement upon companies operating these stations constitute a practical constants. Television is altogether too radio monopoly. Louis G. Caldwell, counsel for AHEADLINE in the New York Times, an- crude to be standardized. It would have been no the Commission, pointed out that, until the com- nouncing a nationwide television service, more ridiculous, in 1904, to standardized upon panies called are found guilty of monopoly in proved upon analysis to be the announce- 28 x 3 inch automobile tires, than to decide to- the courts, licenses cannot be revoked on that ment of a proposed extension of commercial still- day upon 24 or 48 line scanning discs for tele- ground; that there being no point -to -point com- picture transmission by the R. C. A. A 5000-cycle vision. But it is worth agreeing upon temporary munication, and therefore no competition be- signal, transmitted over a special carrier, is used standards of (1) disc speed, (2) direction of spi- tween cable, wire, telegraph or telephone sys- for synchronization. The image is thrown upon rals, (3) common multiple for number of holes, tems involved, the Commission is powerless, a ground -glass screen and there photographed. and (4) direction of disc rotation. under Sections XIII or XV, to take the silly The device was produced in the laboratories of action proposed by Mr. Schuette and his excited the Westinghouse Company and may be used Newspaper Has Radio Picture associates. This proposal is even more drastic by the R. C. A. in competition with the A. T. & Transmitter than Judge Robinson's suggestion that the power T. system. This is neither television nor broad- of these stations be cut to 5000 watts. It might casting. Otherwise, the headline was correct. THE Edinburgh Scotsman, a leading news - prove a healthy lesson to carry out such a threat, paper, claims the distinction of being the just to witness the storm of listener protest Need for Defining Television first newspaper in the world to own and against the disruption of broadcasting service Practices operate its own photo-telegraphic service for the from favorite stations. regular transmission of news pictures. The time SINCE many broadcasting stations appear of sending pictures from London to Edinburgh AS EVERYONE perforce knows, radio has to be groping toward television, it is desir- has been cut from eight hours to eight minutes. come to its own as a political medium. The able to reduce to a minimum the number The costliness of the several systems in use for Democrats are spending about half a million for of scanning disc apertures and their different commercial picture transmission in the United radio, using six half -hour periods a week, includ- combinations, and to agree upon the direction States have precluded their routine use by news- ing a liberal appeal to the women's audience. of disc spiral and disc speeds to be used. These papers. The A. T. & T. system is well organized, They are also spending $1oo,000 for individual factors are being determined in a very unscientific but newspapers complain that they have to wait programs over independent stations. Entertain- and haphazard fashion. Each individual television so long between the filing of pictures and the time ment is being broadcast in connection with politi- transmitter, being put into operation, seems to they are actually sent that airplane delivery is cal features. The Republicans are using the net- work according to the whim of its builder, with more rapid and desirable. The R. C. A. trans- work three times a week, the entire country being the result that any television receiver now built oceanic service is useful only in the case of pic- covered once a week by the inclusion of the are is capable of receiving from only a single trans- tures of extraordinary interest because trans- Pacific network. Also, 43 half -hour programs mitter, although it may be within range of two atlantic transmission of pictures is difficult. being sent over the Columbia network, thus in- or three signal sources. suring the listener of no rest from political The variables are not confined merely to the Commercial Broadcasting Increases blasting. number of holes in the disc. Some transmitters scan their subjects in such a manner that the AVERY healthy trend in the strengthening Aircraft Radio first sweep of the disc makes the top line of the of the economic foundation of broadcast- picture; others start at the bottom. Some require ing is indicated by the growing percent- CAPTAIN S. C. HOOPER pointed out the the receiving disc to run clockwise; others age of national advertisers using commercial, importance of using the 500- kilocycle counter -clockwise. Still others, intending that goodwill broadcasting, as reported by the Asso- distress frequency on aircraft making universal or direct- current motors be used for ciation of National Advertisers. The figures rep- over -water flights. This enables flyers to establish driving receiving discs, are not operating at resent investigation of the activities of 352 communication with ships at sea and shore sta- closely regulated speeds so that standard syn- leading advertisers. For that number, the per- tions, while utilizing the high frequencies, per- often pre- chronous motors may also be used for reception. centage using radio grew from 11.6 per cent. in mitting long- distance transmission,

www.americanradiohistory.com NOVEMBER, 1928 RADIO IN FOREIGN COUNTRIES 19 dudes nearby reception. For example, the Greater Rockford, which made an amazing land- ing somewhere between Newfoundland and Greenland, was heard successfully in Wisconsin. But none of the shore stations in Canada or Greenland could hear its signals because of skip - distance effect. Had it been possible to take com- pass readings in Greenland or Canada, the . whereabouts of the place would have been much better known and the rescue would have been accomplished very much sooner.

NEW YORK STATE plans an aviation weather service and is establishing twenty weather bureau stations which will make reports to Gustav Lundgren, meteorologist, at Albany. The data will be compiled and telegraphed to every airport in the state, as well as broadcast twice daily through N. B. C. stations.

ADIRECT, high -power service between San Francisco and Tokio, the first occident to orient service to be directly connected by mod- ern, high -speed telegraphy, was announced by the R. C. A. Messages to Japan heretofore have been relayed through Hawaii.

THE Federal Radio Commission authorized the R. C. A. to establish direct communica- tion with Liberia, although a channel for that AN ELECTRODYNAMIC SPEAKER OF DE LUXE DESIGN purpose already has been allocated the Firestone Three dynamic units are used in the loud speaker shown above. The baffle on which the units are mounted Company which, by the way, did not oppose the is of box construction and measures 4 by 51 feet. The designer of the speaker, Mr. Mampe, of Palisade, R. C. A.'s application. If the Commission is N. J., is shown in the picture holding to its promulgated principle, a single radio link is not sufficient to handle all the traffic South- American traffic to European countries is still discouragingly small. Increasing public in- between Liberia and the United States and the where the Mackay Companies have no direct terest promises considerable growth in the future. duplicate services are warranted by the amount communication through their agreement with of message traffic to be handled. Eastern Cables, Ltd. THE British Radio Union, a £3o,000,000 con- cern, will acquire all the ordinary shares of ANOTH ER pair of licenses granted for services THE call letters of the ship and planes of the the Eastern, Eastern Extension, and Western of doubtful value are the permits issued to Byrd Expedition are WFBT, WFA, wFD, WFE, Telegraph Companies and all the ordinary and the Universal Wireless Communication Com- KFK and, for the planes, wFC, WFB and WFF. preference shares and debentures, if any, of the pany for two to,000-watt stations, one for New The wavelengths in meters of the channels to be Marconi Wireless Telegraph Company. This is the practical consummation of the British York and one for Chicago, to operate an overland used will be 91.3, 68.1, 53.1, 45.6, 34.o6. 26.5. radio-telegraph service. Filling channels with 22.8, 17.95. and 13.72. Eavesdropping upon the cable merger plan. unnecessary services means later denials to affairs of the expedition will be possible all over THE British Board of Trade has passed a law, essential services. the United States. The expedition will carry 20 compelling Class 2 ships, freighters with more transmitters and 26 receiving sets and a most than fifty in the crew, to carry automatic dis- THE International Telephone and Telegraph comprehensive line of accessories and parts to tress- signal alarms. Class 3 ships, with less than Company has made an agreement with the keep the installations in operation for two years. fifty in the crew, are unaffected, while Class t Spanish and General Corporation to build a radio- ships, passenger liners and other vessels with telegraph station in the Azores for transatlantic Radio in Foreign Countries than 200 on board are permitted communication. This will distribute North- and more persons to displace one wireless operator with the auto- T THE Berlin Radio Show, there were 35o matic alarm. exhibitors, including the Army and Navy, and the German Lufthansa Postal Ad- DR. McINTYRE of the Ministry of Health ministration. The most interesting television of the British Board of Trade and Drs. H. C. was L device demonstrated the invention of one Case and Philip Morton are experimenting, which gave the shadowy outline of the Mihaly, aboard the S. S. Mauritania, to develop an inter- to on the telephone. person spoken national medical chest, making possible a code, directing medical treatment at sea, which will be TH E Department of Commerce report for understandable in any language. This promises June shows a marked increase in United to be an aid to smaller ships which have no States exports of radio equipment. The greatest physician aboard. growth was in transmitting sets and parts, which, compared with June, 1927, exports of THE National Electrical Manufacturers' As- $5,8o6, rose to just short of $5ó,000. Receiving sociation estimates that, by cutting the total sets rose from $174,433 to $228,983. Radio im- number of its meetings in half and holding the ports were more than $50oo. annual meeting in the fall instead of in the spring, it will save its members, through reduced time, THE Radio Corporation has made an agree- traveling and other expenses, approximately ment for interchange of patent rights and for $300,000. Attendance at some trade association the sale of radio equipment with the State Elec- meetings of the radio industry really makes it trical Trust of Leningrad. doubtful whether such expenses should be charged to personal amusements or as a legiti- APUBLICITY statement from Russia re- mate business expense. The radio industry might ports that there are 67 broadcasting stations employ an accountant to determine the financial now in operation in that country, serving 250,000 loss it suffers by supporting two trade organiza- listeners. Because of the great area involved, tions and then follow the wise example of NEMA Russia will naturally require many broadcasting and reduce the number to one. REAR VIEW OF GIANT SPEAKER stations, although the number of receivers in use -E. H. F.

www.americanradiohistory.com FIG. 5. FRONT VIEW OF RECEIVER TwooTube T.R.F. Shortowave Receiver By WILLIAM BOSTZyICK and W. T. THOMAS

RECEIVER to operate satisfactorily on fication, and also because it is the only tube short waves must fulfill several important FOR the first time we are glad to be able that can supply stability to a short -wave r. f. d ... requirements. and in explaining the design to present a short-wave receiver using amplifier. A 200A detector tube should be used. of the short-wave receiverdescribed in this article, a screen -grid amplifier which is tuned. Up Perhaps a word as to results would not be out it will be well to consider these one by one, so to the present time, designers of such receivers of place at this point. During the short time that the reader may have a clear idea of the va- have been content to use the screen -grid tube that this set has been in operation in our labora- rious phases of the problem at hand. as a sort of blocking tube which prevents tory it has completely and easily covered the In the first place the receiver must be com- oscillations from the detector getting into the world. Phone reception has been effected with pletely free from body capacity, and arranged antenna, and which gives a certain amount of points ranging from Alaska to New Zealand and so that its coils pick up no energy themselves. amplification, it is true, but not an amount from England to Russia and Java, not to men- This means complete housing in good metallic comparable to what is possible when the tion many other foreign stations at lesser shields. amplifier input is tuned. distances, a low gain two-stage audio amplifier The receiver should be equipped with a re- In the Laboratory the receiver worked being used on the output of the set. Quite often generative detector the control of which must be beautifully without any a.f. amplifier, the signals from 5sw, the short -wave broadcasting smooth and easy. Capacity control of regenera- signals from the detector being as loud as station of the British Broadcasting Co., in tion has been selected as best meeting these those from an ordinary short -wave receiver Chelmsford, England, are strong enough to give conditions. using one stage of audio. It is true that loud speaker operation directly off the detector Any receiver placed before the public for such a receiver as this has an additional tun- output. For those interested in amateur c.w. construction, should, in the opinion of the ing control, and that for maximum signal reception it will suffice to say that Australian authors, be a non -radiating device. strength and selectivity, both the amplifier amateurs have been heard in Ithaca, N. Y., at be this The receiver must selective yet must not and the detector circuits must be tuned, but it 3 P.M. with the phones on the table, and cut side bands, and it must cover the required is believed that it is worth it. also right off the detector, using no audio. wavelength range. The writer recommends that ¡So volts be CONSTRUCTION Lastly mentioned but far from last in order of used on the screen -grid plate and 6o volts on importance, the set must have high overall the screening grid of this tube. In the Labora- IT WILL be noticed that in the design of this voltage amplification, yet keep the amplification tory the receiver worked properly with only receiver one of the shield cans called for is of of noise at a minimum. rather large dimensions, necessitated by the t ;5 and 45 volts, respectively, on the plate and both r. and detector tubes in the grid. -THE EDITOR. placing of the f. THE DESIGN OF THE UNIT same compartment, the overall width parallel THE above résumé of what a short -wave set with the panel being 13 ". In some localities should be, is, of course, general, and outlines G9 difficulty may be experienced in obtaining a the things to be expected from the correct re- shield of this size ready made, and for this reason ceiver for this job. The set that we propose to grade audio, or better still, with a power am- it was thought advisable tò include a description develop in this paper is one that fully meets this plifier using a push -pull circuit. The set re- of the shields, for the benefit of those who wish rigid set of requirements, and at a figure that quires the use of a 6-volt storage battery or an to make their own. Let it be said, however, that will not strain the average pocketbook. "A" power unit, and three different B poten- unless one has had some experience in work of The set, as seen in the photographs and tials, namely, the plate voltage for the screen - this nature, he had better take the drawings to diagrams, is composed almost entirely of stand- grid tube, the screen -grid voltage, and the a good tinsmith and have him make them, in ard commercial parts. The tuning range of detector plate voltage. The writers have found which case it will be well to impress upon him the the receiver is from t 5 to 140 meters, effected by that 18o, 6o, and 45 volts, respectively, work out importance of having a close fit around the base; means of three sets of easily interchangeable very well. when the two halves are put together, the gap coils. This range covers to -day's domestic and Impedance coupling is employed in the r.f . should not exceed -2.z" at any point if a really foreign short -wave broadcasting, and the more stage, as this is the only practical method of good job is done. important amateur bands. No audio amplifier is matching the plate impedance of the r. f. tube The material may be either half hard brass or included in the set, which should preferably be at short wavelengths. A screen -grid tube is copper and should be slightly less than -112-". Half used in conjunction with two stages of high- employed on account of its high voltage ampli- hard brass 0.0225" was used by the writers. 20

www.americanradiohistory.com NOVEMBER, 1928 A TWO -TUBE T. R. F. SHORT -WAVE RECEIVER 21

Aluminum may be used equally well but should panel as shown in Fig. 5, holes being drilled two holes exactly 2" apart and on the center line be roughly three times the thickness mentioned. through both the panel and the upright shield of the strips, and of a diameter suitable to take Upon referring to drawings in Fig. 2 it will be fronts; the templates furnished with the conden- the male portion of the General Radio coil mount noted that the developments and bending lines sers giving the exact hole positions and sizes. plugs. The placing of the strips and the method are given, the lettering corresponding with the The holes for the shafts of the two end conden- of holding the coil may be seen from the Fig. 3. assembly sketches. all dimensions being given in This procedure is followed in making the other inches and all bends are at right angles and two coils. should be quite sharp. A wooden block roughly The next thing to be done is to remove the 6 "x 4 "x 7f" was carefully squared up and was primary coil and its supports from the mounting found very usefiil as were also a pair of large base of the Aero coil set. A piece of Bakelite wood clamps and a mallet. 51" x I;" has this primary mounted on it at a It is advisable to commence with piece B point ;" from an end in exactly the same man- in Fig. z being careful to bend exactly on the ner as it was originally mounted on the Aero lines. Next the side pieces, G1 and G2, are cut base. Drill two holes in the new base exactly 2" out and bent along the dotted lines, these form- apart and symmetrically placed with respect ing the sides of the cover can, being soldered to the base. These are io take the female portion along the two diagonal edges and also soldered FIG. 3. DETAIL OF COIL ASSEMBLY of the General Radio plugs. Having completed inside the top piece, B. The rectangular slot this piece, mount it in the first shield as shown in shown in the cover cans are best cut after the the Fig. 4, taking care to raise it enough so that from panel soldering is completed. sers are 3E' the respective edges, and the plugs extending through it do not touch the 3;" down from the top of the panel. The third Next piece A is cut out and bent along the metal shield. To this base is now attached, as and larger condenser, C3, used for regeneration dotted lines, care being taken that the lips on the constructor sees fit, a rigid vertical rod of control, is mounted exactly between the other the portion fitting against the panel are bent so copper or brass extending to a height of 61" two and at the same distance from the top edge as to just allow room to slide the top piece in above,the shield base. This is the "signal artery" of the panel. from above. to the set, and is shown in the photographs and The large can is made in precisely the same THE COILS USED the diagram in Fig. 3. A connection is made at manner except that the two rectangular slots the base between this and the nearest female THE next job is the making of the coils for are provided in the cover can to accommodate the General Radio mount in any convenient manner. various wavelength of two condensers. After the shields are completed, the ranges the r.f. Care must be taken not to permit this upright tuner, together with their mounts. All coils are three small V- shaped notches are cut in both rod to extend through the mounting far enough 3" in diameter and are of the so-called air upper and lower portions in order to allow cer- to come in contact with the shield base. Now wound wire is 16 tain wires to go to the terminal strip and the type. The size of the No. and the placing the small 11-volt biasing battery as winding is spaced the of the wire. jack, as can be seen from the pictures. diameter shown in Fig. 4, and wiring according to Fig. 2, Windings of this type can be purchased by the The next step is the mounting of the shields we are finished with the first can. It might be radio and the panel on the baseboard. The lower por- inch from most stores. There are three of well to mention at this point that both shield these to be 15 tions of the shields are screwed to the base using coils made to cover the -140 bases are connected together by soldering a round -headed screws, being sure to place the meter range, having three, eight, and fifteen short "jumper" wire to each and that the turns respectively. The general form of these small shield at the extreme left of the board, and ground, A minus, B minus leads are common and may be seen in the photographs. The first step in the large one about ',-" from the right -hand ex- connect directly to base shields. construction is to cut three strips of a" bakelite, tremity of the smaller, as shown in the pictures. ì The base for the Aero coils can now be 21" by ". Drill through all three of these The panel mounts directly to the baseboard á strips mounted in the large shield base by means of with four 1" wood screws. The drilling of the wood screws and the feet supplied for the pur- panel is very simple and for that reason no layout pose. Care must again be taken to prevent the is shown. A é" hole is drilled e" from the right - coil plugs from touching the shield base when the hand end of the panel to accommodate the fila- plugs are fully inserted. The location of this ment- control jack. mounting is very important. Its center is placed The three variable condensers, C1 C2 Cs in 61" from the right -hand edge of the large shield Fig. 1, are mounted symmetrically on the base and 3" from the back edge of the same. D The set of Aero coils that are to be used in the detector circuit, with the mount just mentioned, have to undergo a little treatment before they can be put into service. Due to the addition of the r. f. tube to these coils, the wavelength range is raised and we are forced to remove some wire. From the smallest coil one half turn is to be -6' removed from the grid end (end farthest from the tickler coil). To do this unsolder the wire from the lug, slip the wire through the guide GI bars until you reach a point directly above the base, then run the wire directly down diametrically across the coil to the lug where ----- it was at first, cut off the excess and solder. ,I In the same manner one and one half turns must B be removed from the medium coil and three turns G2 from the larger. The detector socket may now be mounted in á---{- -- - ->1 --734-"- -"4-6"- the rear right -hand corner of the large ba ^e shield, so that the tube pin points toward the 13'tl------13"----734- panel. Fig. 4 shows how much clearance should _ be left for the sides of the shield cover. The r. f. -;------socket is also mounted in this base and is located io F1 in the rear left-hand corner, placed so that the pin is parallel to the panel and pointing toward E vI q" k- -} 4" the first shield. This socket is raised up on a .; small wooden block until the control grid cap of F2 the tube is exactly 61" above the shield base. The mounting positions of the two condensers, _V_ _t_ i C5 and Cs, and the two r. f. chokes, 1..2 and Ls, _--g___-_ I I --- -'-13 - - -H are also shown. The 2o-ohm rheostat, R1, on the screen -grid tube should have one lug soldered FIG. 2. DETAIL OF SHIELD COMPARTMENTS directly to the plus filament lug on the r.f. tube

www.americanradiohistory.com 22 RADIO BROADCAST NOVEMBER, 1928 socket, and the 10-ohm rheostat, R3, is likewise fastened to the lug on the detector tube socket. The location of the two fixed condensers, C4 ,Cr, and Ca, is also shown. This places all the apparatus except the grid leak and condenser, whose locations are readily observable. The only point to be noted is the raising of the grid -leak mount from the base shield by the thickness of a Z" wooden block; these parts should be placed as near the detector tube as possible. The terminal strip at the back of the set and the filament -control jack are next mounted as shown. The rheostats are adjusted once, to give the correct tube voltages, and thereafter are left alone. Using a 6 -volt storage A battery, the respective settings were found to be as follows: The r.f. rheostat, RI, was turned on one third from the full off position and the detector rheo- stat, R3. was set one half from the full off posi- tion. FIG. 4. LAYOUT OF PARTS ON BASEBOARD Should the constructor prefer fixed filament resistors may be used for RI and R,, the size required for the screen -grid tube being the same OPERATING DATA maximum energy transfer to the detector), and as for the ux -12o power tube: the detector takes the center dial controls regeneration. It will the usual 'I- ampere (four ohm) type. TO PLACE the set in operation it is but neces- be well to permit the detector to oscillate until In making the wiring to the terminal strip sary to connect it to antenna and ground, as a station carrier-wave is heard, then bring the care should be taken to make sure that the well as the required d.c. potentials, and feed the r.f. stage into resonance with the detector. This notches provided to allow these wires to pass output into a two-stage audio amplifier, to give may de-tune the detector slightly, but a simple through the shields have their sides well rounded the necessary volume for consistent loud- speaker readjustment will care for this. The regenera- with a file so that they will not cut through the operation. It will be found that in all probability tion control may now be backed off and the insulation on the wires. the dials on the tuned stages will not agree detector should slide smoothly out of oscillation; Having finished the preceding operations, particularly well, as it is almost impossible t0 if it does not, a reduction in detector plate there are only two or three things more to be match coils and condensers at the frequencies voltage is advisable. The broadcaster's modula- done before putting the set on the air. When the with which we are dealing. The small coils will be tion should now come through satisfactorily. small shield cover is slipped in place it will be found to cover 14 -38.5 meters; the intermediate, And now a word as to the antennae for use on found that the vertical rod will hit the top of the 35-81 meters; and the large coils 8o-14o meters. short waves. The difference between high or low, cover and accordingly a Z" hole must be drilled These are of necessity approximate values. It is short or long is not very marked. In general a in the cover to accommodate this rod. It will be understood that corresponding pairs of coils are single wire about 6o feet long placed as high as found best to drill a smaller hole first to serve as to be used simultaneously in the coil mounts; possible will answer well. a guide as to the position of the rod. Similarly a the home -built coils in the r f. stage and the '-," hole must be made in the larger shield to commercial coils in the detector stage In chang- LIST OF PARTS allow the cap of the screen -grid tube to protrude. ing coils care must be taken to handle them only Great care must be taken to prevent either of by their bases as the fragile windings and frames THE parts used in the writer's receiver follow. these coming in contact with the shield covers are easily injured. Parts of equal electrical and mechanical and a small wrapping of insulating tape or a After adjusting the filament rheostats and characteristics may be used in place of those small piece of rubber tubing is necessary to applying the necessary voltages, we are ready mentioned in the list, of course. insulate these points. A removable connection to commence operations The set is operated must now be provided to join the top of the rod just like any tuned r f set using detector re- CI, Ce -2 Amsco S.L.F. variable condensers, and the cap of the screen -grid tube when the generation, except that the tuning is extremely Type 1213 shields are in place. This can be made out of sharp. C3 -1 Amsco S.L.F. variable condenser, type 1223 bus wire as shown in the photographs, care being The right -hand dial is the station selector, and Cs, Cr-2 Tobe fixed condensers, o.001 mfd. that a snug connection is made when it is the left tunes the r.f. stage (which must be kept taken Cs, Cs -2 Tobe by-pass condensers, I.o mfd. sprung into place. in resonance with the detector circuit, for C8-1 Tobe fixed condenser, o.000i mfd. LI, La, L4 -1 Set Aero short -wave coils and mount L3, L6 -2 Short-wave r.f. chokes R1 -1 rheostat or fixed resistor, 20 ohms R2-1 Tobe grid leak, and mount, Io meg- Ux-222 Ux 200A ohms R3-1 rheostat, Io ohms, or fixed resistor, ohms

1 14 -volt C battery (flashlight type) 2 Amsco full- floating tube sockets

1 Two -circuit filament -control jack

1 7- contact terminal strip Output 6 General Radio plugs Ct 2 General Radio receptacles +45 1 Bakelite Panel, 7" x 21" 1 Soft wood baseboard, 9" x 20" x z" 2 Shield cans as shown or stock for same O At 3 Marco vernier dials Miscellaenous wood and machine screws, wire, R1 etc., piece of scrapA" bakelite i4" x 54" and 9 OA-B- pieces I" x 2f" x The last two items are for coil mounts and base. To put the receiver into operation the following O Es+ are needed.

1 Screen -grid tube

1 Detector tube (2ooA type) O Ep+ 6-volt storage battery or A supply Source of B power (see text) FIG. I. COMPLETE SCHEMATIC DIAGRAM 2 -stage audio amplifier

www.americanradiohistory.com WE ARE being asked was published in RADIO BROAD( %sr in the Dynamsc vs. our opinion of June, 1927, issue and an article appeared Magnetic the in Speakers "dynamic" speaker at Radio Engineering in the June, 1928, least once a day, and issue. our present ideas are as follows. In the The advantage is as follows: first place, all loud speakers are dynamic, l6 9 9 It is possible to build a quieter receiver in the sense that some of their parts move. for a.c. operation than by the use of a.c. This includes the old horn type, the newer Strays tubes. With excellent amplifiers and dy- cone type, and the newest type in which namic speakers on large baffle boards the coil moves with respect to the field. this is important. With the ordinary So the reader had best look carefully into amplifier and loud speaker it is not im- the claims of speaker advertising, or the portant as the average a.c.- operated set claims of over- the -counter salesmen to from the is quiet enough. make certain that the speaker he is buy- The disadvantage of series -filament ing is the type he wants. operation is that small tubes, such as the Considering the question of fidelity of 199, must be used. his fact makes it response only, not the question of effi- somewhat more tricky to design the cir- ciency, the moving -coil speaker compared Laboratory cuit as when one tube goes bad the others to a good cone will "prove in" only on may follow unless precautions are taken frequencies below ioo cycles. Compared to prevent such difficulty. Also, under to the old stand -by, the W. E. 54o-AW, a some conditions there may be a greater good dynamic speaker unit on a baffle tendency for the receiver to motor- 3' x 5' and one inch thick (a baffle 3' boat. square would be equally effective) repro- Until the ux -2o1B tubes, which re- duced notes below too cycles while the quire only one -eighth ampere for the fila- cone reproduced nothing below that fre- ment and which are now sold in Canada, quency. It is true that tones come out of are released, the 199 -type tubes must the cone when ioo-cycle and lower notes be employed. These tubes have a are put on it, but these are not true tones, rather low gain, and are quite micro- but complicated harmonics of the funda- phonic. Some other tube manufactur- mental tones generated in the speaker ers, Sonatron, for example, make an itself. So when one listens to a good eighth- ampere tube but these have not orchestra with a good amplifier and good been submitted to our Laboratory for cone from a good station, the viola he test and we can therefore neither hears is a synthetic viola made up of recommend nor discourage their use at harmonics generated partially in the the present time. speaker and partially in the ear. Who wants technical data on series - On frequencies above ioo cycles the cone as amplifier, one which is flat from 5o to 5000 filament operation? tested in the Laboratory was about as good as cycles -there are very few of them -and a per- the best of the dynamics. Of course, measure- fectly quiet power -supply unit, and there are ECONOMY in radio receiver Present `Designs ments show that the cone was "down" at fre- very few of them, especially if a c. tubes are operation has been out of the Do Not Consider quencies as low as 20o cycles compared to the used. question for several years. In And there are few stations transmitting Economy moving-coil speaker, but the ear is deceived and programs that will cause one to note the differ- the early days tubes were ex- satisfied easily and reception coming from the ence between an excellent moving -coil speaker pensive, they required high filament currents, 540-AW is, in our opinion, good enough for the and a good cone. Even the few stations that and anyway who would think of investing a average household. The Balsa -wood speaker, transmit down to ioo cycles do not have many hundred dollars in a radio and spending twenty already described in this magazine, is somewhat programs which make one wish for a better dollars a year on upkeep? Nowadays the criterion better than the cones, but suffers from mechanical amplifier and loud speaker. A recent release seems to be how expensive a radio can I build or troubles. from the Freshman Company states there is buy? Multi-tube sets, sets that take power -some The moving -coil speaker, then, is better than little music below 120 cycles. We venture to say of them take lots of it-from the lamp socket, the good cones only on frequencies below loo that the majority of home -made receivers using sets in which tubes don't seem to last as long as cycles. It must be mounted in a rather large good parts is ahead of the majority of broadcast- in the old days are the rule to-day. and solid board, not in a small and beautiful ing stations when one considers fidelity. There is one notable exception to this seeming cabinet. In the latter housing the lower tones will connivance between radio apparatus manufac- be lost, and certain frequencies will be badly re- SEVERAL of the readers turers and the power companies. This is the Regarding inforced due to cabinet resonance; these tones Of RADIO BROADCAST have Eveready set which requires a plate current of Series-Filament will "boom." Operation written for information on the only 8 milliamperes. This receiver is very clearly Because frequencies below too cycles are re- problem of series -filament within the pocketbook requirements of the rural produced -some moving-coil speakers go down operation. Are there other readers who would listener, or the listener who desires not to awe to 5o cycles easily -the filter of one's power- like to have an article on this subject? Some data his neighbors by relating the tales of his ioo-watt supply unit must be such that receiver. This Eveready prod- no 12o-cycle or 6o -cycle hum uct uses high -mu tubes, and, gets through. This means that of course, the output will not . A rcragc nroring Cold Speaker l a. c. tubes are almost out of the 0 ` be called a public nuisance. It question -and our experience is a receiver we are glad to see

has been that when one places (n 5 I ` designed and sold. a socket -operated moving-coil / % \ How many readers of RADIO speaker in the middle of a Z10 / BROADCAST would like to build Cone t large baffle board, the hum is o /.Goorl such a set? u5-15 I pretty bad. If the speaker is a / And while we are asking for d. c. unit, it does not produce N readers' opinions, how many ()-20 / k a hum of its own, but if it has would like to see the contents cc / a small built -in rectifier the ~25 -all ` \-_ of the magazine marked with user may expect some hum - I the Dewey decimal system for if a large baffle is used. -30 article classification? A reader For one who wants the best, brings up the point that it is the in a difficult to index and to file the moving -coil speaker 20 50 100 1000 5000 10,000 baffle contents of the magazine at about three feet square - FREQUENCY IN CYCLES PER SECOND larger if possible -will give it. present, and that each month But with this combination one AVERAGE CHARACTERISTIC CURVES OF DYNAMIC AND he must mark the articles he must have an almost perfect ELECTROMAGNETIC SPEAKERS wants to file according to this 23

www.americanradiohistory.com 24 RADIO BROADCAST NOVEMBER, 1928

well -known system. Such a marking might take but a dollar or two and which was worth nothing be obtained from the Superintendent of Docu- place in the editorial office before the magazine at all. Another example of the way some people ments for five cents, contains in few words a is put on the presses -but it takes work and acquire experience was brought to our attention most readable summary of the entire problem of time, and it is our present opinion that there are recently. the transmission and reception of radio broad-

other things which the readers would sooner see , In a certain store on "Radio Row," New York casting. in these pages than a classification of material. City, a transformer was being sold for $I.00 to which could he added a dry A RECENT copy of the Portable rectifier unit, like the Elkon, Wireless Trader (England) "'Radio and a condenser. This equip- pages Sets devoted sixteen full to ment, it was said, would pro- describing 66 models of porta- vide the purchaser with an ex- ble sets manufactured in that country by no less cellent A -power unit at small than GI manufacturers. Only the most rudi- cost. The idea is perfectly good, mentary arithmetic is necessary to count the the transformer is good, the number of portable sets made in this country; Elkon rectifier units and con- in spite of the fact that there seems to be a densers were good. Where was rather consistent demand for them, to judge by the catch? the letters that come to the Editors. The transformer delivered N.C. only 7 volts, and after passing AVE ARE finding it .difficult through the rectifier and filter Underground to know what stand to take. the potential was reduced to 3.8 cAerials on the underground antenna FIG. I FIG. 2 volts at the output. The com- business. At present the vote Kinks on stabilizing a Rice circuit bination was absolutely worth- among readers of these pages seems about half less unless one were going to and half; some do and others don't like them. THERE are several methods use it on a dry- battery tube set -but nothing A reader in Ontario writes: "have been using How to of keeping a Rice neutralized was said about the voltage obtainable when ground antenna for the past five years with ex- Stabilize Rice out amplifiers amplifier from breaking into the purchaser paid his money. cellent results. It consists of 5o feet of well - oscillations at a very high insulated cable attached to an old galvanized frequency determined by the leakage induc- WE HAVE a letter from water tank three feet in earth. Am able to get New Precision tance of the input coil and the tube capacity in Carl Zeiss, Inc. -whose name British Honduras,'Jamaica, and others on home- in Quartz capacity. One is known to every user of made three -tube regenerative parallel with the neutralizing Plates set." method is to insert a choke coil in the center -tap photographic, microscopic, or Another in Texas writes: "My experience wiih connection of the amplifier input coil as shown telescopic equipment throughout the world - underground antennas is that they are not worth in Fig. 1. This method is used in the R. B. Lab. stating the firm is now building glass discs for planting. and we don't have rocky ground, noth- Circuit. The choke may be replaced by a resis- measuring purposes with an accuracy of l0080ó0 ing but plain silt soil." tance as Mr. Knowles pointed out in his June, of an inch and asking if there is The following letter is from 1928, article. This method is illustrated in need for quartz plates of this a reader in Bangor, Maine: Fig. 2. accuracy. At the present time Another, and less expensive, method is to wind quartz plates for frequency mea- While I can't give you any signal- ratio, measurements. a turn or two of wire about the two ends of a surement and control are sold by static comparing using an underground solenoid coil in such a direction that no loss is but few companies. We should antenna with the usual types. I introduced at broadcast frequencies but a large say that Carl Zeiss, Inc. might have formed my own opinion which the circuit tends sell a number quartz plates loss at the frequency at of along these lines. I installed a to oscillate. The direction of winding is opposite accurately ground. much -advertised device, accord- to the direction in which the tuning inductance FJ ing to directions, and operated it 1 is wound. THE follow- with a Tyrman "7o" screen -grid Seven New 4 If a few ohms of resistance is inserted in this ing booklets super-heterodyne, and I want to radio say that, as an eliminator of winding either by using a concentrated resistor, are more than Booklets static and power -line distur- or by using resistance wire -iron picture wire worthy of bances, it proved to be a dismal will should be read purchased in hardware stores do-the mention -they failure. As an antenna it was parasitic oscillations will not be produced and by "all readers who like to "keep very efficient, but it didn't even everything will be lovely. This system is shown up begin to live up to the claims in Fig. 3. Through Electrical Eyes, by made for it. John Mills. A reprint of an ad- F G. 3 THERE are three Radio- dress given at Atlantic City Extra coil and resis- After reading the letters we New 'Radio Set trons we should like to see re- Nov. 26. 1027, on the physics and tor improves Rice are inclined to believe that the Tubes in the United States. chemistry involved in television. underground antennas are fine Needed leased One is the much heralded Mr. Mills is Director of Publications of the for those who like them and fierce for those eighth-ampere general -purpose tube similar in' its Bell Telephone Laboratories. who don't.

characteristics to our 201N. I t is known as the The Electrad Truvolt Divider Manual, Electrad, The trouble lies, not with the antennas, but

1_0C-201B. I nc. with the advertising. If such advertising states Another is a power tube, called the t;x -121 B. The /Imperil( Blue Book, Radiall Company. that signals will be as loud as signals obtained which is designed for use in the last stage. I t con- The Polymet Manual , [ Engineering Data, with high clear antennas of the conventional sumes a filament current of one -eighth ampere, Polymet Mfg. Corp. sort but devoid of static, the copy should not be uses a C bias of 16.5 volts with a plate potential The Gateway to Better Radio, Clarostat Mfg. trusted too implicitly. On the other hand, if the of 135 volts and can deliver 125 milliwatts of Co. advertisement states that the static will be re- undistorted audio -frequency power, an increase The Boston Post Book on Television by Henry duced and that reception in geneal will be clearer of almost three times the power handling ability M. Lane. it seems a fair gamble. of the 2oI A -type tube. The third tube is the Radio Facts and Principles. The testimony of The underground antenna is not new. It is wx -25 which is a better 11-ampere tube than John V. L. Hogan before Federal Radio Cont- very old. It never gave as strong signals as a the 201A but not as good as our 112 -type tube. mission, July 23, 1928. This booklet, which may free wire high above earth, but under certain The electrical characteristics of conditions it may give reception the three tubes described above will freer of static than the elevated wire. Rp We often disconnect the antenna be found in a table on this page. Designation If vamp. bias In µ Gm P from our own receiver during bad PEOPLE who do ux -2012 .125 amps. 90 4.5 2.5 11000 8 725 15 weather in order to receive local sta- The "gyp?' 135 9 3.0 10000 8 800 55 business with 1000 125 tions with a minimum of static. This are still 121B .125 " 135 16.5 6.0 5000 5 "gyps" must ex- wx -25 .25 90 4.5 3.5 8000 7.9 1000 130 makes it necessary to make the set at it pect to be "gyp- somewhat more sensitive, more Not we an If = Filament current u = Amplification factor sharply tuned, and more critical ped." long ago disclosed Ip = Plate current in mils Gm = Mutual conductance interesting output device which cost Rp = Internal resistance of tube P = Output power in milliwatts of adjustment. -KEITH HENNEY.

www.americanradiohistory.com When the Seit Stops Working A Service Man's Experience By B. B. ALCORN

FROM the standpoint of the radio dealer or troubles are as numerous as the troubles them- of the dials will have very little effect on the service man, the problems arising from the selves; the best method, perhaps, is the use of tuning. Again it may show itself by a zero read- service and repairing of radio sets are a set checking device, of which a large number ing of the voltmeter connected between the plate most complex, as each new advance in radio de- of types are available. While the manufactured terminal of the tube socket and B minus, which of sign creates new.problems in repair, and almost set checkers are all good, their cost in most cases course means an open primary in an r.f. coil. A daily some new radio ailment presents itself for is prohibitive, especially when a dealer or service simple test in such a case is to place the fingers, correction. To cover all the problems of radio shop has a number of service men to provide or a 2- megohm grid leak, across the primary servicing is beyond the scope of this article. but with outfits. The writer has designed a set terminals of the suspected transformer. If the there is room for considerable set is inoperative because of an discussion of the ordinary service open -circuited primary the fingers methods from the point of view or the grid leak will, I have found, of the man in the field who is cause the set to function, though meeting and solving these prob- not at its maximum efficiency.

lems daily. - The fingers may also be used to The troubles encountered in determine whether or not the radio servicing may be divided open is in the audio amplifier by into about ten major divisions, touching the grid lead to the as follows: detector tube. If the audio I. Defective tubes system is o.k. there will generally 2. Defective batteries be produced a low howl from the 3. Open circuits loud speaker. 4. Defective parts Open circuits in the r.f. ampli- 5. Defective antennas fier are among the most difficult 6. Defective grounds of troubles to locate. In the case 7. Use of harmful gadgets of open grid suppressors in mod- 8. Misconnections ern a.c. sets, for example, the 9. Short -circuits writer has found that few if any Io. Defective arresters of the set checks will show this Under each of these major di vi- trouble, which manifests itself by A RADIO SERVICE MAN AT WORK sions are numerous subdivisions. lack of volume -a condition It is the purpose of this article which might be attributed to a to cover the first three of these divisions, particu- checker which is not too costly and which is number of other causes. A quick test for faults larly the third, giving actual cases which have built around the meters which every service man in these resistors, which are usually of the wire - come before the writer. Subsequently articles will who takes his job seriously should already pos- wound type, is to touch the stator plates of the deal with service problems under the remainder sess. This checker will show short circuits, open variable condensers with the point of an ordin- of these divisions. Many of the cases cited are of circuits, and the approximate condition of tubes. ary lead pencil. If the suppressor is open there an unusual nature, such as are not encountered Since, however, this article aims only to tell of will then be a noticeable increase in volume; if in the ordinary day's work, but it is such peculiar some of the cases encountered in radio servicing, not, the volume will decrease. problems which illustrate the repair man's tech- the construction of this tester will be given in a An unusual open was recently encountered by nique better than the rank and file of radio ail- future issue. the writer in a Thermiodyne TF6 which for a time ments. The usual symptom of an open is a loss of was very baffling. The set check showed that all volume or total lack of signal. In most instances the coils and connections were perfect, yet a jar TUBES AND BATTERIES of sets having three dials, the trouble, if it is an would either cause the signals to disappear or THE location and treatment of troubles under r.f. stage, will isolate itself by the fact that one come in more strongly. It certainly looked like major divisions I and 2 require little explana- an open or loose connection, and that was what tion. In the case of batteries a good voltmeter turned out to be, but in a very unusual place Cs.416 Or 140 it - is all that is necessary for locating the trouble; the gang condenser. The condenser was of stand- for testing tubes, a tube tester or a set of tubes ADIO servicing problems, as they ard design. that is, the stator plates were wedged known to be good may be used. Defective tubes present themselves to the man in the into aluminum supports, and it was found that or batteries should, of course, be replaced with field, is the subject dealt with in this article. the plates in the second condenser had become good ones. At this point, however, it is suggested Mr. Alcorn, who has a thriving service busi- loose where they fitted in the stator support. that a very simple and accurate method of deter- ness of his own in Long Island, divides these Some ingenuity was necessary in remedying this mining which tube or tubes are weak is to insert problems into ten major groups, three of trouble, as it was impossible to get a new gang a o-5o milliammeter in series with the minus B which he discusses in detail; the remainder condenser for some time, and difficulties in sol- lead. First take the total reading, then remove will be treated in subsequent articles. If the dering aluminum made it impractical to solder the tubes one at a time and note the current drop great number of service men and professional the plates in place. As a solution a magneto file, heed at each removal. The tube (not counting the set builders any one thing, it is to ex- such as is used to clean breaker points, was detector) whose removal gives the smallest drop change information with one another, and ground to a chisel edge, and a wedge driven under we In current is the weak tube -assuming, of course, hope, in these articles and a special page the condenser to break the force of pounding we that all the tubes are supplied with the same B for service men which shall soon inaugur- upon it. Then with the improvised chisel, which be and C voltages. A recheck on this method can be ate, to help in that direction. We will de- fitted easily between the stator plates, a burr was made by replacing the tubes one by one and lighted to hear from service men about the struck on each side of the loose plates, causing noting the gain per tube. subjects they would like to have Mr. Alcorn the metal of the plate supporter to grip them discuss. Short illustrated contributions, not tightly. The job was reassembled, and the con- OPEN CIRCUITS longer than 500 words, dealing with "kinks" tact formed between the plates and the supporter work, invited accepted, UN DER the heading of open circuits the serv- in service are and if was found to be sufficient to make the set operate be ice problems are very numerous, and may will paid for at our regular rates. without fading regardless of the amount of jog- apply to any part of the receiver or accessory -THE EDITOR. ging. apparatus. The methods of locating these 079 IN`) At the shop we recently ran into another very 25

www.americanradiohistory.com 26 RADIO BROADCAST NOVEMBER, 1928 peculiar open in the r.f. amplifier of a Radi- near-by and powerful stations would come stated that the trouble did not always show up ola 18. This particular open had all the symp- through, and their signals came in accompanied at first, but nothing happened. I t seemed to be toms of a short -circuit. When the call for service by a hissing, frying sound. It was necesary in a case of local disturbance. The service man came in over the phone the owner stated that the this case to resort to a voltmeter and low- voltage returned. He had hardly reached the shop, how- set had been performing satisfactorily when battery to locate the open in an r.f. coil. The coil ever, when the owner called by telephone to say suddenly it had died down, come in strong again, had to be rewound. that the receiver was "acting up" again. He was and then stopped entirely. It looked as though Another case occurred recently in which an requested to leave the set going until the service the trouble came from a defective UT-227, and open that appeared to be in the set turned out man arrived. Upon arrival the service man found the only equipment taken on the call was a good to be in a vacuum tube. The tube in question was the loud speaker giving out a continuous buzz tube. Upon arrival at the owner's home all the used in the audio, and the first diagnosis was a that the removal of the antenna, ground and tubes were found to be lighting properly, but burnt -out audio transformer. However, test of three r.f. tubes did not diminish to any apprecia- no signals came through. It was then noted that the transformers showed them to be in good con- ble extent. The trouble turned out to be in the the power-pack was beginning to smoke; the set dition. When a new tube was used in place of relay, the spring of which had somehow increased was therefore brought back to the shop, as it was one of the audio tubes the receiver functioned its tension to such an extent that it caused arcing thought that the power supply was at fault. Up- perfectly. The defective tube was tested in the at the contacts; this caused a noise that fed on removal from the cabinet, one section of the shop and showed no plate current, although it through to the set. It was necessary for the set voltage -divider resistance was found to be so appeared to be in good condition. A section of the to remain in operation from thirty to fifty min- hot that it could not be touched. Nevertheless, base was then cut off and showed an open circuit utes before this happehed, the cause being the when the power unit was given the manufac- in the plate lead. This is the first case of this sort heating of the relay. turer's test it proved to be in good condition, that we have encountered. Before concluding it is well to call the atten- and when connected to another receiver of the A curious case of coincidence once occurred tion of all service men to the importance of con- same type it worked without heating. when two sets in different parts of the town, sulting the owner of a defective set as to any Next the receiver was given a continuity test identical in installation, came to us at the same unusual effects he has noticed in its operation - and strange to say, came through with flying time with exactly the same defect. The first diag- just as a doctor inquires as to the symptoms of a colors. There seemed nothing to which to attri- nosis was an open circuit, but both sets were patient. Many times the hints dropped by the bute the heating of the voltage divider except a found to be in good condition, as were the an- set owner are invaluable in localizing the trouble short -circuit. However, as a final test a set tennas. Still neither of the receivers gave any and making an exhaustive test unnecessary. checker was used on the receiver, and when signals, or at best very weak signals. The owner Another thing that all service men should ask is plugged into the third r.f. socket showed an open of one of the receivers was asked whether he had whether any attempt has been made to remedy in the plate circuit. This was located in the noticed anything unusual about his receiver pre- the set before he arrived. In many cases an in- primary of the third ri. coil, and when remedied vious to its breakdown, and recalled that about expert attempt to remedy a minor trouble has the set performed better than ever, according a week previous to the breakdown the set had resulted in serious breakdown. A recent case to its owner. In my opinion the heating of the stopped altogether and had started up again occurred where the only trouble was the removal voltage divider was caused by the feeding back when he had opened a window. The window was of the attachment plug of a light- socket operated to the power unit of the current that was sup- the one through which the lead -in wire entered receiver. The owner, who knew nothing of radio, posed to flow through the defective primary. the house. An inspection of the lead -in wire attempted to remedy the receiver by changing The symptoms were certainly those of a short - showed that it was broken inside the insulation six connections on the power unit. He said noth- circuit and not an open. The reason that the about a foot from the lead -in strip, and that when ing of what he had done, and a service fee of open did not show up in the continuity test was the window was raised it released the tension ten dollars was charged against him for the tests that the break was so minute that the high volt- on the wire and allowed the two broken ends to which were necessary. If he had been asked or age used in the test -we used 40o volts d.c. from meet and form a contact. However, after a week had told of his own attempt, the repair could a B -power unit that we happened to have in the of constant tension the insulation stretched so have been made in a few minutes. shop-jumped the break and thus gave a reading much that it kept the two ends permanently The foregoing are among the most unusual on the meter. Fig. i shows the Radiola t8 circuit. separated. cases of open circuits encountered by the writer, An easy method of localizing opens in the r.f. A unique case of an open in an accessory oc- and it is quite certain that equally peculiar cases side of almost any receiver is the well -known one curred in a Zenith six-tube receiver equipped with will turn up in the future. It is hoped that space of disconnecting the antenna and connecting it a B -power unit, trickle charger, battery and re- will permit to pass these on to the readers of successively to the grids of each of the r.f. tubes lay. The combination had been giving good RADIO BROADCAST. The next article in this series up to and including the detector. This method service for a long while when the service man was will be devoted to troubles arising from defective was tried without success in a recent case of an called in on the complaint that the set was very parts-a category that includes a wide variety Atwater Kent Model 35 which had an open of noisy. The set was turned on when the service of radio "griefs." The article will also include a such microscopic size that the circuit continuity man arrived. and a test showed it to be o.k. The description of the construction and use of the set seemed to be o.k. when tested. Still only two man waited about half an hour, as the owner tester referred to in this article.

12 Ht H2 I1-I1- -1-. H3

O F O O O O O J O O O O -UX- B- B+ C Bi- -UX -- B+ 226 227 45 9 135 171 Power

THIS SCHEMATIC DIAGRAM SHOWS THE R. F., DETECTOR AND A. F. CIRCUITS OF THE RADIOLA 18.

www.americanradiohistory.com NOVEMBER, 1928 RADIO BROADCAST 27

O N®.9 RADIO BROADCAST'S HOME -STUDY SHEETS November, 1928

The Effects of an Electric Current

SUPPOSE we have a source of electricity, a battery for example. How can we be made aware of its presence? To demonstrate the effects of the electric current, which are (A) chemical, (B) heating, and (C) magnetic, we shall need the following apparatus: LIST OF APPARATUS 1. Six -volt storage battery or three dry- cells; 2. Mariner's compass costing about $1.00; 3. One -half pound of bell wire; 4. Copper- sulphate crystals. about 25 cents worth; 5. Glass tumbler; 6. Rheostat, 30 ohms; 7. Two Morse Eureka spring clips; 8. Two Fahnestock clips; 9. Brass angles, screws, bakelite strip, etc.. for mounting compass; 10. Metals, such as brass screws, zinc battery case, iron, etc., for chemical experiment. PROCEDURE

A. To demonstrate the magnetic effect of the electric current: 1. Wind about 30 turns of bell wire into a coil about! six inches in diameter. The exact size of wire, number of turns, and size or form of coil are not important. At about the 10th and 20th turns make a twist in the wire and scrape the insulation from it so that the Eureka clip may be attached to these points. FIG. 3. DEMONSTRATING ELECTROLYSIS 2. Mount the compass on a supporting stand in the center of the coil as shown in Fig. 2. 3. Connect the rheostat, coil, battery, and clip as shown in Fig. 1. it with water and throw it away. If some of the acid gets on the hands or 4. Place this home -made assembly, known as a galvanometer. with clothing, cover acid at once with ammonia or borax solution. respect to the earth's North and South poles so that when looking down on the device the compass needle is parallel with the coil. C. To demonstrate the heating effect of the electric current: 5. Note the effect on compass needle when: (a) the clip is placed on 1. If you have not already accidentally demonstrated the heating various turns of wire and the circuit is closed by moving rheostat arm, effect of the electric current in experiment A by turning the rheostat too (b) the battery connections are reversed, and (c) the voltage is varied near the "all out" position, do so now, taking care not to let the current by using only one, two or three cells of the flow through the last few turns of the rheo- battery with rheostat in same position. stat long enough to burn them off. 6. Remove compass from its support and place it over, and then under, one of the wires DISCUSSION connecting the battery and coil. Close circuit to coil. Note effect on needle when (a) position A. The fact that the compass needle moves of compass is changed, (b) battery connections when it is near a wire, or a coil, carrying an are reversed. (c) strength of current through electric current indicates that a magnetic field wire is changed with rheostat arm and (d) dis- surrounds such conductors. When the current tance of compass from wire is increased. is turned off this field no longer exists and the 7. Note what is said about electro-magnetism needle is then influenced only by the earth's on pages 100 -105 of the Signal Corps book, magnetism. The stronger the current, or the "Principles Underlying Radio Communica- greater the number of turns of wire, the tion." ($1.00 Government Printing Office). greater is this electric field, and for this reason it will exert an influence on a compass at a B. To demonstrate chemical effect of the electric greater distance, or at a given distance the current: needle will be caused to swing a greater num- 1. Place a few crystals of copper sulphate ber of degrees. When the direction of the cur- in a glass container, such as a tumbler, and rent flow through the wire or the coil changes, cover with water. Attach a large copper lug, a the needle changes its direction too. The gal- washer or a penny with a hole in it to a wire vanometer. therefore, is a sensitive detector and connect it to one terminal of the battery. not only of the existence of current but of its To the other terminal of the battery attach a FIG. I strength and direction too. Measuring instru- wire to which may be connected. by means of ments. such as voltmeters and ammeters, util- an Eureka clip. with the various metals such as ize the principle demonstrated here although a steel screw driver, iron screws. brass strip. nickel -plated binding posts in a much more exact and precise manner. or washers, part of the zinc case of a dry cell, etc. B. When two dissimilar metals are placed in a solution- copper and 2. Note effect upon these metals when they are submerged in the zinc in a copper -sulphate solution, for example-and a current is passed copper -sulphate solution and current is passing through the circuit. through the circuit, various things happen. The solution may change 3. Reverse battery connections in each case and note result. color. bubbles may be seen coming from one of the metals, or one piece 4. If a voltmeter, reading not over 5 volts, is handy. connect its term- of metal, known as the electrode, may have a deposit on it. This is the inals to the two wires from the copper -sulphate container. Note the principle which underlies the electroplating of metals. Storage and dry voltage developed by the cell and its polarity when various metals are cells are commercial applications of the fact demonstrated in paragraph used. Use galvanometer already descnbed if voltmeter is not available. B4, that two dissimilar metals in a proper solution develop a voltage. 5. Replace copper -sulphate solution with a small amount of the elec- C. The fact that a wire ets hot when sufficient current flows through trolyte from the storage battery. Remove electrolyte from battery with it demonstrates another of the effects of the electric current. The amount a hydrometer or medicine dropper, taking care that no acid touches of heat generated per unit of time depends upon the strength of the cur- anything but the glass container. Repeat experiment above. Do not rent and the resistance of the wire. This effect is made use of in electric return electrolyte to the battery, since it is now quite impure.Dilute irons, water boilers, toasters, etc. Some wires when heated change in length appreciably. If such a wire is stretched between two fixed points, the extent to which it sags may be used to determine the amount of current flowing. A device using such a principle is known as a " hot - wire ammeter" and such meters are used to measure antenna current, or for measuring current in circuits where an electromagnetic type of meter cannot be used.

QUESTIONS 1. Suppose current flows out of a battery from the positive terminal through the circuit and into the battery at the negative terminal. Can you determine a law relating the direction of current flow and the move- ment of the compass needle? 2. Do you know the "right -hand rule" for determining direction of current flow and needle- swing? 3. Can you explain what happens in the process of electroplating? 4. Why is a voltage developed in the copper -sulphate experiment? 5. What determines the polarity and magnitude of the voltage? o 6. What are the bubbles appearing at one of the metals in the acid solution? 7. What generates the heat in a wire when current passes through it? 8. Do you know the law applying to resistance, heat, and current? 9. Why is manganin or nichrome wire used instead of copper where considerable heat is to be developed? NOTE. The answers to these questions will be found in the Signal Corps FIG. 2. DEMONSTRATING MAGNETIC FORCE book.

www.americanradiohistory.com ')8 RADIO BROADCAST NOVEMBER, 1928

N®. 10 RADIO BROADCAST'S HOME STUDY SHEETS November, 1928

Alternating Current

Part III

HOME -STUDY Sheets 7 and 8 Note: The sin of angles greater gave some of the properties of than 90° may be found from the a.c. circuits. and of the effects of essionn, )sin (90° + A °) = sin an inductance upon such circuits. (180e Since radio circuits are made up Fig. 3 is a vector diagram of the largely of inductances and capaci- above example. It is drawn to scale ties, it remains to study the effect so that the various lengths of lines of a condenser upon an a.c. circuit. represent the various values of cur- In many ways the effect of a coil 90 180` 2 360° rent and voltage. and a condenser are opposite, for example, the larger the inductance CURRENT IN CAPACITIVE CIRCUIT the more it opposes the flow of a.c. current. but the larger the Con- The current in a resistance circuit denser the less it opposes the flow is given by Ohm's Law; the current of a.c. current. The higher the fre- is equal to the voltage divided by quency of the a.c. voltage, the less current will flow through a given FIG the resistance, i.e., I = inductance and the more current will The current in an inductive circuit flow through a condenser. When a is equal to the voltage divided by combination of coil. condenser. and frequency is chosen so that a condition called resonance o. curs, the the inductive reactance, i.e. I = effects of the inductance and condensr are exactly equal and opposite. Kl so that their opposition to the flow of a.c. currents cancel each other. Similarly, the current in a capacitive circuit is equal to the voltage divided by the capacitive reactance. i.e., I = CAPACITY REACTANCE }Cc The opposition to the flow of a.c. currents offered by a condenser is I =E' 6.28'.fvC inversely proportional to its capacity, the property of a condenser which tends to prevent any change in the voltage of a circuit and if the voltage is effective, maximum or instantaneous, the current When current flows into a condenser, from a battery. for example, has corresponding values. a voltage is built up across the plates. When this voltage equals the IMPEDANCE voltage of the battery no more electricity flows into the condenser. and we say it is charged. If the battery is removed. and a wire connected Suppose a circuit has resistance and capacity, resistance and induc- across the plates of a condenser. a spark jumps and the quantity of tance, or a combina- electricity stored there rushes through the wire. The condenser is now tion of all three said to be discharged. When an a.c voltage is impressed on a condenser. factors. each of the quantity or charge flows into it until the condenser is at the same which is tending to voltage as the charging voltage. At this point, the voltage of the a.c. oppose the flow of circuit changes polarity; that is, it is now in the opposite direction. The a.c. current. What condenser, however, is still at its original polarity. and tends to dis- is the resultant op- charge into the line and to maintain the voltage of the line. A condenser. position or imped- then, helps to maintain the voltage of a circuit constant, and by so doing ance? In a resistance it resembles a reservoir which is filled up when the voltage is high. and or reactive circuit is allowed to discharge when the voltage is low. we can add the When the condenser is charged, it is surrounded by an electrostatic several values to get field just as a coil carrying a current is surrounded by an electromag- the final resultant netic field. -- remembering that The opposition which a condenser offers to the flow of current is the effect of a capa- known as its Reactance, and is measured in ohms just as resistance city is opposite to or inductive reactance is. This capacity reactance is inversely propor- that of an induct- tional to the capacity and the frequency of the circuit. The abbreviation ance so their react- and formula for capacity reactance are, ances must be sub- tracted -but when x= 4 resistance and react- Xc= - 1 ance are combined FIG. 3 6.28 x C v f we cannot add them the reactance. algebraically. They Thus, doubling the capacity or the frequency, halves must be added vectorially, that is according to the formula Since the voltage across a condenser does not rise to its maximum value as soon as current flows into it. there is a lag between the times Z2 =R2 +X2 of maximum cur- rent and maximum Z = y/ R2 + X2 voltage. However, = 1V R2 + (XL - Xc)2 as we express the current phase with This can be done by arithmetic, or by graphical means. respect to the volt- Example. What is the impedance when R = 3 ohms, X = 4 ohms? age phase, we say the current into a Z2 =324.42 condenser leads the Z =V9 +16 E =10 voltage across it. =5 I = l0 As a matter of fact, 90° the maximum volt- This expression may remind the experimenter of one of the first age is not reached laws in geometry he learned. namely, the 'square on the hypotenuse of a right -angled triangle is equal to the sum of the squares on the two `-S 150 until the current has gone through sides." If. therefore, in Fig. 3. we lay off a line equal in length to three 90 degrees. or one units and label it R, and make another line perpendicular to it equal to 4 and call it X, the length of the line that closes the triangle will be v fourth of its cycle. In other words, the equal to Z. current in a capa- The reactance, X. in this problem can be pure a inductive reactance FIG. 2 city circuit is said of 4 ohms or a capacity reactance of 4 ohms, or a combination of in- to lead the volt- ductive and capacitive reactance such that the resultant obtained by age by 90 degrees. subtracting them equals 4 ohms. For example, if Xi. = 8 ohms, 4 ohms This is illustrated in Fig. 1 in which the maximum value of voltage is Xc = then reached 90 degrees after the maximum current. It is also illustrated in X = (XL Xc) = (8 4) = 4 Fig. 2 in which are two arms rotating at the same speed but 90 degrees - - apart. In the case of an inductive circuit the maximum value of the or if Xi. = 4 ohms. and Xc = 8 ohms. then voltage is ahead of the maximum value of the current; in the capacity X = (XL - Xc) = (4 -8) = -4 case the voltage is behind the current. Since the maximum values of current and voltage are 90 degrees When, however, this value of minus 4 ohms is squared it becomes a apart, we must take this fact into account when we desire to know the positive quantity equal to 16 and may be fitted directly into the equa- instantaneous voltage or value of the current. If the voltage is at the tion to determine the impedance. 60- degree phase. the current is at the 150 -degree phase. This angle of PROBLEMS 90° is called the angle of lead, or the phase angle between the voltage and current. The instantaneous value of the current is given by 1. Plot the reactance of a 1 -mfd. condenser as the frequency is varied from 100 cycles to 10,000 cycles. What is the reactance of a 0.001 -mfd. i I sin (Q) 90°) - + condenser at 10 kc.? At 1000 kc.? EXAMPLE. What is the instantaneous current in a capacitive circuit 2. Make a vector diagram for the following condition and solve by when the voltage is at the 60- dcgree phase if the maximum current is means of the formulas above. In a capacitive circuit the instantaneous 10 amperes? The answer may be calculated as follows: voltage at the 30 -degree phase is 5 volts; what is the instantaneous i = 10 sin (60 + 90 °) current if the effective current is 10 amperes? = 10 sin 150 3. What is the reactance at 1000 cycles in a circuit which has a = 10 x .5 025 -henry inductance and a 0.01 -mfd. condenser? If the condenser = 5 amperes has a capacity of 0.001 mfd.?

www.americanradiohistory.com PLOTTING TRANSFORMER CURVES IN A RADIO LABORATORY A New Audio System for Dynamic Speaker Reproduction By FRANK C. JONES Consulting Engineer, Gray ô Danielson Mfg. Co.

IN ORDER to reproduce radio programs in value of effective tube input capacity. This effect since the impedance at the lowest frequency sufficient volume to fill a room from a loud- is generally overlooked, although it is actually desired must be several times greater than the speaker, some type of audio amplifying sys- very important, as can be seen from the follow- tube impedance. The principle of resonance may tem following the detector tube is necessary. ing. The input capacity of a tube is obtained be used to overcome this loss at low frequencies Immediately difficulties are inevitable from from the formula, but not the loss at the upper audio frequencies. this necessity, since to obtain good reproduction Another factor for either of the above systems it is necessary to amplify equally all tones or is the relatively low gain, so that with 20IA or C = Cgf + Cgp [ I + prp frequencies up to at least 5000 cycles and down rp + rI ] 226 tubes about three stages would have to pre-. to less than loo cycles per second. There cede a type 250 power tube. This are several types of audio amplifiers in means a four-stage amplifier, which is IPA widespread use which must first be con- uneconomical besides having wonderful briefly before going on to a de- of singing or -boating. sidered Cr HE question as to whether each piece of apparatus possibilities motor scription of a new audio system designed The next amplifier to be considered 1 in a radio receiver should be perfected, or whether overcome many of the defects of is the transformer -coupled type. This type to better results would be obtained if the entire system were present of amplifier has been developed about systems. designed to have a "fiat characteristic," has been the cause as as it can within of considerable discussion.. The advantage of the latter far practical limits RESISTANCE AND TRANSFORMER COUPLING using special alloy cores and special method is that a higher over -all amplification may be FIRST let us consider the usual re- secured. The Remler amplifying system employs two windings. By keeping the turn ratio sistance-coupled amplifier where the fairly low, 2 or 3 to I, the response curve audio -frequency stages, each of which produces some is tube be a plate connected to the next distortion, but the defects of one compensate those of the can made to cover frequency range of through a coupling condenser and the from 70 or 8o cycles up to 5000 or 6000 other. -THE EDITOR plate and grid potentials are fed in cycles without much droop at either end. through resistances. If the plate re- The advantage of transformer coupling sistor, RI, in Fig. I, is equal to or lies in the fact that low -mu tubes may greater than the plate impedance of be used and good gain per stage may the tube, the tube will operate over a straight Where Cgf = grid -filament capacity of tube. still be obtained. Herein also lies a disadvantage. part of its characteristic curve, so that Cgp = grid -plate capacity of tube. since with the new dynamic loud speakers and the voltage impressed on the first grid circuit may rp =plate resistance of tube. type 25o power tubes, a greater amount of gain is be amplified without distortion. Now if the coup- r, = coupling resistance. required. Let us consider the requirements set ling condenser, C, is made so large that its re- A typical example is up by the use of a good dynamic loud speaker. actance is small in comparison to the grid re- sistor value, the loss in amplification will not be 3o x 250,000 LOUD SPEAKERS AND POWER TUBES C = 6 + 12 27o mmtd. great. However, a large condenser takes a longer 1 + loo,000] - AN YON E who has listened to a good dynamic period to discharge, so that if a large a.c. voltage loud speaker will admit that this type is should be impressed across it- enough to swing This value is enough to practically short -circuit very much better than the magnetic drive types. the grid of the next tube positive -the tube will the higher audio frequencies. The higher the The improvement is so great that this coming block and become inoperative. Using a small amplification constant of the tube, the greater year will see a rise in popularity probably as great salue of grid resistor, R2, or a small coupling this capacity will be. as the magnetic -cone speakers had over the old condenser, the low frequencies will be discrimin- The latter effect is present in impedance cou- horn -type speakers of a few years ago. The older ated against enough to cause the response curve pled amplifiers to even a greater extent than in type of cone speakers using a magnetic drive to fall off rapidly. Another drawback to resist- other systems because the distributed capacity unit, are incapable of reproducting low notes or ance- coupled amplifiers is the low gain obtained of the coupling choke coils adds to this capacity. very high notes either. The magnetic type of when using ordinary 201 A or 226 tubes. The use of The actual tube input capacity may be less speaker that will actually reproduce tones below high -mu tubes will overcome this, but then the but the other capacities generally more than 200 or Soo cycles per second is very rare and none high frequencies may be lost due to the larger make up for it. The low frequencies may be lost will give a true response below loo cycles. The 29

www.americanradiohistory.com 30 RADIO BROADCAST NOVEMBER, 1928

author has had the opportunity of running re- nearly negligible. Now consider the case where a 61 to 1 ratio could be designed with a frequency sponse curves on about three dozen different pair of transformers having an effective turn ratio response as shown by the curve of Fig. 2. types of loud speakers and it was found that the of 3 to I are used. The voltage available to swing There is a drop on the low frequencies even when response below the limits mentioned is only ap- the grid of the power tube can be figured from using a I I2A tube having a plate impedance of parent; that is, the response is not actually the E =; x 3 x 8 x 3= 24 volts, which is not suffi- about 5000 ohms. Using a 201A tube having a real low tones but consists of higher harmonics. cient. This figure of 24 volts shows that the detec- plate impedance of about io,000 ohms, there is a For example, one very excellent magnetic-type tor would have to put out nearly I volt across the very bad drop at both the high and low frequen- speaker at 6o cycles gave a good apparent re- primary of the first audio transformer to obtain cies, giving the effect of a peaked amplifier. Using sponse but when the wave was a 70 -volt power tube grid swing, a 112A tube, such a transformer would be fine for analyzed it was found to con- and this would be an enormous the second stage but would be hopeless for con- sist of less than 5 per cent overload on the detector. The necting to a detector having a high plate imped- fundamental tones of 6o cycles. above values of voltage are all ance. That problem and also the one of compen- All of the "noise" consisted of in terms of maximum a.c. volt- sating for the low frequency droop of the second higher harmonics which would age, not average values, and stage were solved as in the manner described be- mean very serious distortion of the first amplifier tube was low. the low frequencies in music assumed to have an effective A RESONATED PRIMARY reproduction. On the other gain of 8, since the mu of a hand, a good dynamic loud 201A tube is about 8.5 or more. FOR several years the different telephone re- speaker in a large baffle -board FIG. I This means that the trans- peaters and many broadcast station ampli- or large cabinet is capable of formers will have to have a fiers have used the principle of resonance in the true response down to 3o or much larger turn ratio than 3 transformer primaries to bring up the low -fre-

4o cycles and up to between 5000 and 7500 to 1 unless more than two stages are to be used. quency response. There is no reason why this cycles per second. Below the cut-off of the More than two stages are rather undesirable from arrangement should not be used in radio receiving baffleboard or cabinet the response is similar to a cost and space required basis as well as because set amplifiers, so a first -stage transformer was a magnetic -type speaker in that it consists nearly of more tube noise and motor-boating possibilities. designed with primary resonated at about 3o entirely of harmonics. A dynamic speaker re- Increasing the turn ratio means that the prim- cycles per second. Fig. 3 shows a complete audio quires an amplifier of large power rating if low ary windings will have to be diminished in size amplifier with the first transformer primary wind- frequencies are to be reproduced without over- or the secondaries increased. Decreasing the ing resonated by means of condenser C1. Re- loading. A good loud speaker mounted in a large primary turn lowers the primary impedance to sonance has the effect of lowering the total plate cabinet, or in a large baffleboard, or better yet, low notes so that the response to these notes will circuit impedance to that of the a.c. resistance in a wall, will take nearly the full output of a be poor. Increasing the secondary turn increases of the circuit only. The action is as follows: At type 25o power tube for even good room volume. the secondary capacity to ground or distributed resonance the current is increased through the A good deal of power is necessary for the low capacity to such an extent that the higher fre- detector plate circuit load, since the impedance notes, and the better the frequency response quencies are lost. This is very important because at resonance is equal to the resistance component range of a loud speaker, the greater must be the brilliant reproduction depends on the presence only. This means that the voltage drop across the power output of the audio amplifier for the of frequencies up to 5000 or 6000 cycles per condenser and across the inductance of the same apparent volume. A type 25o power tube second. primary winding will be increased due to the or its equivalent must be used to prevent over- The only way seems to be to cut down on the increased current flow. The increased voltage loading on the very low notes such as may be primary number of turns, since even resonating drop across the primary, causes a larger voltage transmitted from an organ, a bass viol or tuba, the distributed and shunt capacities with the to be generated across the secondary, with or even a bass voice. To hear the bass notes in transformer leakage reactance does not make a a rise in the response curve. The amount of their proper relation to the higher notes from a good high -frequency response when a large rise at resonancedepends on the circuit constants, radio receiver is to have real enjoyment from secondary winding is used. By using a large that is, the plate impedance of the detector tube, good radio programs. core of very high -grade material, a nickel -steel the value of the resistance, RI, and the relative To project equal volumes of sound into the alloy. the impedance presented to the tube can sizes of the condenser, C1, and the primary in- air at woo and Poo cycles it requires a much be increased so that it is still several times that ductance of the transformer. The resistance, RI, greater movement of the sound- producing dia- of the tube even at the low frequencies. The im- may be made part of the resonant circuit by phragm at the lower frequency. The dynamic pedance increases with frequency, so that most making it relatively small, or it may be made speaker has the ability to reproduce these low of the voltage generated by the tube appears high, on the order 6f loo,000 ohms, so that it notes partly because the movement of its dia- across the transformer primary for higher notes. tends to isolate the resonant part of the audio phragm may be much greater without mechan- Since the primary impedance is less for lower circuit from the plate supply unit. In this case it ical rattling than is possible in the magnetic frequencies, the proportion of voltage drop across confines the audio frequencies to the path type. These large movements, in turn, imply the tube impedance is greater, causing a droop through condenser C1 and the primary winding that considerable electrical power is available to in the response curve. It was found by laboratory to the filament. By keeping R1 high in value, drive the moving parts of the speaker, and tests that a very good transformer of as high as the loss due to it at higher frequencies is re- this in turn means that a power duced. Since the audio- frequency tube with considerable output path in this circuit is isolated from must be used. The 250-type tube the plate -supply unit, the chances has sufficient output for this 1 1 Over all charaeteristujamptiier.... -. _. _._...... - 60 of audio regeneration or motor- purpose. ------..._.. boating are practically eliminated. removes a bugbear which is 3 I \ 50 This THE IMPORTANCE OF THE TURN generally very troublesome in high - RATIO \ gain amplifier systems. 1 I 40 TO WORK a type 25o power An auto -transformer connection tube to its full capacity the is used in the first stage, since the 18 audio transformers preceding it effective turn ratio is much greater i6y:1 16 z should have a rather large turn Second-stage transformer-To z for the same total number of turns. ratio in order to prevent overload ..- _ - The response characteristic of such of the detector tube. A detector 12 a resonated transformer is shown First-stage curve Fig. 2. tube produces higher harmonics transformer-ratio 4 s'1 10 by the lower of any audio tone, and these are a The resultant characteristic for of 8 source of distortion, since they the two transformers is shown on 6 change the character of the re- I the same curve sheet and it is flat . q produced tone. The greater the down to 5o cycles per second. Cer- output required of the detector 2 tainly no ordinary transformer - tube, the more apparent this effect ______r, .. c coupled amplifier could be de- - 0 0 LO 0 CO ó O O0 O becomes, so it is desirable to limit Ñ r.) C tf) CC) O N D signed which would amplify so the detector tube output to less FREQUENCY,CYCLES PER SECOND evenly all frequencies as will this than ; of a volt. With outputs of special combination. The total less than 1 of a volt the ordinary FIG. 2. RESPONSE CURVES OBTAINED gain using a I12A tube and a 201A detector tube distortion is WITH HIGH -RATIO TRANSFORMERS type 25o power tube is about

www.americanradiohistory.com A NEW AUDIO SYSTEM FOR DYNAMIC SPEAKER REPRODUCTION 31

57 TU. This does not include the detector audio Rat o Ratio 6i:1 gain. r---- c, 112A The use of the same resonating idea in the second transformer is unnecessary, since we' are interested only in obtaining a perfectly flat characteristic with a very large voltage gain. One difficulty is that the d.c. voltage drop through a shunt resistance would be enormous unless small values were used. For example, 3 through ol milliamperes ioo,000 ohms would cause 11H 61 J F a 30o volt drop. The heating effect would be troublesome also since nearly one watt would have to be dissipated in the form of heat. If low values-less than 30,000 ohms used, -were . 450 the audio-frequency loss through the shunt 135 resistance would be a large percentage of the FIG. 3. SCHEMATIC DIAGRAM OF COMPLETE REMLER AMPLIFIER gain of the transformer. In that case an ordinary low- ratio, high -quality transformer might as well have been used. audio stage, since the amplification is so tubes, since the low notes are well reproduced THE OUTPUT TRANSFORMER high at Go cycles. However, experiments with when a good dynamic speaker is used. Nearly I N CONNECTION with the complete amplifier special amplifiers cutting off very sharply 95 per cent. of the very low notes such as those I system, the last, and perhaps the most im- just above 6o cycles per second, have shown from an organ, as played over the radio, are portant link in the chain, is the output device. that the hum when using a.c. tubes may between 8o and zoo cycles per second. Very few It was found that the best output transformers be made nearly negligible. The reason for cutting people realize this and most people will quite on the market were quite unsatisfactory below off above 6o cycles is apparent when it is re- willingly swear that they hear 30- to 50-cycle 200 cycles per second when the full plate current membered that ordinary loud speakers are excel- notes in their radio sets when in nearly all of a type 25o power tube was flowing through lent harmonic producers on low frequencies. cases their loud speakers and amplifiers will the primary. Core saturation takes place and The use of raw a.c. on the filaments of the tubes not reproduce anything below ioo cycles per even with a good -sized air -gap in the core few causes a 6o-cycle component to be impressed second. notes below 200 cycles reach the loud speaker. in the grid circuits with the result that if the am- Another advantage of cutting off sharply a However, an output transformer is quite neces- plifier system is good as low as Go cycles, this little below ioo cycles is that a smaller power sary with a dynamic loud speaker in order to frequency will be amplified and reproduced by tube may be used, such as a 171 tube. The ap- match properly the load to the power tube. By the speaker. The speaker, in case it is a cone or parent room volume of sound with the a.c. keeping the d.c. current out of the output trans- small horn will reproduce it as 120 cycle and system will be about the same as with the first former by means of a choke coil, Lam, and conden- higher tones. The point is that by not amplifying d.c. amplifier system developed, since in this ser, Q, as shown in Fig. 3, the transformer may the Go cycle component, practically all of the case the lowest note reproduced will be about 7o be made very excellent for even the very low composite a.c. hum in the loud speaker is cycles as against 25 or 3o cycles in the d.c. sys- frequencies. The condenser, C2, may be made to eliminated. tem. This makes more power available for the resonate with the transformer primary to com- Immediately the idea of resonating the prim- tones which are reproduced. Incidentally, the pensate for the loss due to the shunt choke coil, ary of one of the transformers at about 8o cycles, cost of manufacturing such transformers is less. 14, and series condenser reactance on the low was used to make the complete amplifier cut off Most a.c. set manufacturers use audio trans- frequencies. Another advantage is that the audio- sharply just above Go cycles per second. The cut- formers which will not pass 6o -cycle signals, in frequency path is through the condenser and off is a great many times sharper below resonance order to minimize a.c. hum and in so doing gen- transformer primary back to filament instead of than when the transformer itself is made to have erally lose in efficiency up to 300 or 400 cycles. through the power- supply unit. This prevents a fairly good audio response. The audio voltage This is bound to happen because it is not possible audio feedback to preceding stages. drop across the resonating condenser increases to obtain a really sharp low- frequency cut-off The result is a very stable high -gain amplifying as the frequency becomes less, giving a very using ordinary transformers. The resonant prim- system which has more gain than even an audio sharp cut-off belcfw resonance. By designing the ary principle should go far towards solving the amplifier using a screen -grid tube in the first circuit constants properly. one transformer may a.c. hum problem in a.c. receivers. stage. The use of a screen-grid tube, even as a be made to compensate for the other as shown in l t will be noticed that only the transformers space -charge amplifier, means that impedance Fig. 4 from about 5000 or 6000 cycles down working out of the detector tube in both the d.c. coupling should be used between that tube and to at least 8o cycles per second. This makes an and a.c. systems have resonated primaries. This the power tube, which gives, roughly figuring, ideal arrangement for receiving sets using a.c. arrangement keeps the d.c. plate current out of X3 X 5oX IX4X; =loo volts the primaries and so prevents across the output device. This as- core saturation and generation sumes a i -volt detector output. a 3 of harmonics due to this effect. to 1 a gain 5o in use transformer, of 30 50 By the of very large cores the screen -grid tube, a gain of IOverall charact Iristic for amplifier of nickel -steel alloy, the chances 4 in the power tube and that I of of core saturation from d.c. are this voltage appears across the out- 100 f 40 practically eliminated. If small put device and ; across the power cores are used and large primaries, tube plate resistance. For the 30 -TRANSFORMERS WITH SHARP CUT -OFF ABOVE 60 CYCLES-- 30 that is, a large number of turns, amplifier described, using 4 and core saturation may take place Detector: Rp 2000 ohms 6Z to 1 ratio transformers and with bad distortion effects. First audio tube Rp- 5000 ohmsjp 6ma The tubes giving a gain of 8 and 4. Power tube CX -371 A transformers described are built the total voltage appearing across ~ along ample lines to overcome 14 the output would be If X41X8X °> the possibility of trouble from First -s age trans or er 'a io3 1 61 X 4 X ; = 156. The ordinary 4 12 core satuation. aTrarufo erRatie3Ary js:t amplifier using 3 to 1 transformers - Seeond-sta 10 The possibilities of audio ampli- and tubes giving the same gains 8 fier systems using the low -fre- of 8 and 4 would give an output 6 quency resonated primary prin- of;X3X8X3X4Xá ciple are many and it is =48. 4 quite likely that this scheme will be A MODIFICATION FOR A.C. OPERA- 2 widely used to make better audio TION amplifier systems. It is the en- ó ó 8 e THIS amplifier having such an ñ °o $ 8 8 § 3 g $e gineer's problem to forever strive I excellent frequency character- FREOUENCY,CYCLES PER SECOND towards perfection, never reaching istic should be used preferably it but always advancing: and this with d.c. filament tubes in the FIG. 4. RESPONSE CURVES OBTAINED design, it is hoped, is a step in r.f. stages, detector and first WITH 31 TO I RATIO TRANSFORMERS that direction.

www.americanradiohistory.com Sound Motion Pictures Part II

IN OUR October issue the processes of syn- The exciting lamps used are on this account of volume, so the whole system must be properly chronous sound and movie -picture record- the high- intensity type, so that the amount of lined up. If the filament of the exciting lamp sags, ing and reproduction were described in a light passing through the film during low volume the image cannot be accurately centered on the general way. In successive articles some of the portions will still meet marginal requirements. slit, and a loss of volume results. In this case, points which were only briefly touched on in In some other respects the photo -electric cell as well as when the glass of the high intensity the first paper will receive further discussion. is superior to the best grades of microphones. lamp begins to darken, the lamp must be re- I do not expect to present any original material It has no natural period of its own and any lag placed. However, a loss in volume may also re- in this series nor to assume a professional tone. which it may introduce would have to he mea- sult from a photo-cell losing its emitting quali- The object is merely to bring together data sured in billionths of a second; the response, to ties. A microammeter is useful in checking from widely scattered sources which are not all intents and purposes, is instantaneous. Sel- this. readily accessible to the many radio broadcast enium, the substance which was used as the The method of fading from one projector to operators, motion -picture projectionists, and original intermediary between light and elec- another, insofar as it affects the photo-cells, is others who are interested in sound -movie tech- tricity, did not change its resistance immediately another point of interest. This is shown in Fig. nique. under the influence of light. 5. A potentiometer with a neutral midpoint is One portion of the reproducing equipment As the energy output of the photo -electric cell, the essential part of the diagram. As the trans- which was merely mentioned in the October although accurately proportional to the light formers pass only the alternating component of article is the photo -electric cell used in film entering it, is so small, it must be used, even the photo -cell current, the operation of the po- systems. This variety of electron tube has been for measurement purposes, with vacuum -tube tentiometer will be noiseless. It will be noticed likened to an electric eye; its function is to trans- amplifiers. This combination was described in that there is considerable similarity between form optical variations into proportionate elec- the Physical Review as long ago as 19í7, and this circuit and microphone mixers in broadcast- tric currents. In the art of sound reproduction there may be earlier citations. Figs. 3 and 4 ing. from films, as well as in television, the photo- show two methods of coupling a photo -cell to electric cell plays a part analogous to that of the inpu t of a vacuum tube. The transformer Commercial Publications the microphone in telephony. The microphone, method seems to be preferred in commercial however, takes speech or music directly from sound motion -picture systems. NATIONAL RADIO TUBE COMPANY. This concern, the air, whereas in motion picture work the Inasmuch as our interest in photo -electric whose address is 3420 Eighteenth Street, San photocell receives light which has been modu- cells is in connection with motion -picture pro- Francisco. is circulating an offer to rebuild lated by a film record. In this application, there- jection, two special points may be taken up burned out, or otherwise defective transmitting fore, the rôle of the photo-cell is more strictly here. One is the method of getting the light tubes, for broadcast stations. They claim means parallel to that of a phonograph pick -up, which through the film to the cell, as shown in Fig. 2. of re- processing tubes so that they will be as takes mechanical vibration from a rotating The lamp in this case has a straight filament at good as new at about half the cost of a disc and transforms it into corresponding elec- right angles to the paper, so that it is shown replacement. tric pulsations. in the diagram as a dot. This source is brought GENERAL RADIO COMPANY. The General Radio Fig. i shows a schematic view of a photo- approximately to focus on a parallel horizontal Experimenter continues to present material of electric cell. The bulb is made of quartz or glass, slit about 1.5 mils high, and the image of the interest to broadcasters. The May issue contains coated on the inside with silver, except for a slit projected onto the film, giving a light rec- an article on "An Artificial Cable Box." Such a window a half inch or so in diameter which re- tangle a little narrower than the sound track device makes it possible to simulate the behavior mains clear for the passage of the light which (about 8o mils) and about a mil high. The gates of actual telephone lines and cables in the is to act on the cell. Opposite the window a layer and aperture plates about the film are not shown. laboratory. The circuit used is shown in Fig. 6. of the active material of the cell is deposited on The light which gets through the film then Here the loop resistance of the section, 4R, and the silver. This substance is usually a com- spreads out and goes through the window of the the shunt capacitance C, are made the same as pound of the so-called alkali metals, potas- photo -electric cell. Of course if the cell is dis- the equivalent quantities in the type of line sium, rubidium, or caesium, which have similar placed, so that only part of the light gets whose behavior is to be studied. chemical and physical properties. They re- through, there will be a corresponding loss in Inasmuch as an actual cable has its constants semble silver in appearance and are quite soft. distributed along its length, an artificial cable Some of their compounds, such as potassium simulates the behavior of a real one more closely hydride, have marked photo-electric qualities; when it is built up of a considerable number of Light that is, light causes them to emit electrons much -Window uniform sections. as heat makes the filament of a vacuum tube A type of cable box with the designation 321 - do the same thing. The next step, referring to C, marketed by the General Radio Company, is Fig. i again, is to place an anode in the tube to the electrical equivalent of 32 miles of standard pick up the electrons as they are released. If paper telephone cable in the usual wire gauges. this anode is placed in the path of the light corn- Within a cabinet 15 by 8 by 51 inches there are ing in through the window it is made in the --Silver seven units of the following electrical lengths. : 0.5 form of a wire loop but it may also be a .-Photoetectric Cathode respectively 19- 8-4-2-I- -0.5 miles. These small metal plate displaced a little to let the are controlled by telephone key switches so that light pass. The final step is to connect between any combination may be secured, making it the photo-electric cathode and the anode a possible to get any length up to 32 miles in half - circuit for coupling the cell to the input of mile steps. an amplifier and for keeping a positive poten- The 16-, 8-, and 4 -mile sections are not tial on the anode so that it collects the emit- lumped, but built up of 2 -mile units, and the ted electrons more effectively. Frequently a gas, smaller lengths are similarly split up. The re- Filament- such as argon, is used to increase ionization and Photo sistance elements, wound non -inductively, are Cell thus to make the cell more sensitive. Even so calibrated to 0.25 per cent., while the rolled paper the space current in such devices amounts to Optical : condensers have a precision of o.5 per cent. The System only a few microamperes. maximum potential which may be safely applied The photo-electric cell is liable to the sanie to the box is 300 volts. difficulty as a carbon telephone transmitter -it Boxes of this type are supplied to represent has its inherent noises arising from internal FIGS. I AND 2 16, 19, and 22 gauge non -loaded paper cable. turbulences and the input must be high enough. These drawings show how photo -electric cells The constants at the mean speech frequency, even at its lowest levels, to override the noise. are used in sound motion- picture apparatus 796 cycles, are given as follows: 32

www.americanradiohistory.com CIRCUITS FOR PHOTO- ELECTRIC CELLS 33

Resistance Transformer Gauge per Capacity per Cell No.1 Loop Mile Mile t6 B & S 42.2 ohms 0.062 mfd 19 83.2 .062 22 171. .073 _- In cables of this type the inductance may be neglected, but General Radio also designs + special artificial circuits to simulate loaded lines, I1I0I ¡- in which case an appropriate amount of in- ductance is included in each loop mile, or open wire lines. The same issue of the Experimenter describes a 600,000 -ohm potentiometer suitable for use in the grid circuit of an amplifier tube as a gain con- trol. The circuit, which is familiar to most broad- \ L cast engineers, is shown in Fig. 7. Such a poten- tiometer requires a high resistance in order that it may not draw appreciable current from the preceding element. This particular design, Transformer known as the Type 452. covers 3o TU in 15 steps of 2 TU each. Fig. 5 The August issue of the General Radio Com- pany's bulletin contains a discussion of electrical PHOTO -ELECTRIC CELL CIRCUITS USED IN SOUND MOTION PICTURES filters, which are divided into four groups: (1) Low-pass filters which cut off all frequencies above a certain value; (2) High -pass filters which types of filters regularly marketed by General should be interesting as a general treatment for cut off all frequencies below a certain value: (3) Radio are of these classes, designed for im- broadcast operators who have not devoted atten- Band -elimination filters which block all fre- pedances of Goo and 6000 ohms, and with cut-off tion to' the subject. A schematic diagram is quencies between certain limits; and (4) Band - frequencies of 500, 1000, and a000 cycles. That included. pass filters which block all frequencies on either is, one may order from stock a G000 -ohm filter This issue also contains a description of the side of a section which is permitted to get of the high -pass type, for example, to cut off Type. 426-A thermionic voltmeter, including a through. everything below low cycles. diagram of the bridge circuit employed with the Classes I, 2, and 4 have been discussed pre- It may be shown that, given the iterative im- vacuum tube. The range is o-3 volts, and under viously in this department. Type 3 is new in this pedance Z and the cut-off frequency F for which the usual conditions of use the calibration is respect, and as it is not described in the General a filter is to be designed, the value of the ele- maintained to within o.5 per cent. for about Radio article I might point out that an audio ments is given for a high -pass filter section by í00o hours, and is good over the whole audio- rejector of the sort shown in Fig. 8 is an ele- frequency range. Even at 20 kilocycles there is 0.07958 mentary form of band elimination filter. In farads only a 2 per cent. error, and less than 3 per cent. parallel with the speech coil of a loud speaker, C1= FZ at 300 kilocycles. At broadcast and higher fre- for example, it may be used to smooth out a peak 0.07958Z quencies the calibration is no longer valid. The L2= henries in the response. The effect of the resistance in F entire instrument, including the battery, is self - series with the capacitive and inductive elements contained. is to broaden the resonance curve and to limit the while for a low -pass filter we have similarly Another item in the September issue concerns effect of the device. If the resistance is very low the Type S32 Station Frequency Meter, the en- 0.3183 practically no current of the resonant frequency C:- farads tire scale of which covers only 0.3 per cent. of the will get past the shunt circuit, but by adjusting frequency of the designated station, the variable the resistance one may balance the by- passing 0.3183Z condenser being connected across a larger fixed Lt- henries effect of the shunt circuit against the undesired F capacity. This gives ten scale divisions per peak in the instrument under treatment and get kilocycle. The resonant frequency is read by an a flat over -all characteristic. Compare this use In each case F is in cycles per second, while Z ingenious method, which consists in connecting of the resistance element with its similar function is in ohms. across the main condenser a small auxiliary in a line equalizer (Fig. 9) which is also a form of The September issue of the Experimenter capacity to shift the peak of the meter from filter. carries as the leading article, "Notes on Group one side of the station peak to the other. The Coming back from this digression to the Gen- Address Systems," by C. T. Burke. Since papers frequency meter is adjusted until the indicating eral Radio discussion, we note there sketches of on public address technique have appeared in galvanometer does not change its reading when sections of high-pass and low -pass filters, here this department of RADIO BROADCAST Mr. Burke's the button connecting this condenser is pressed. reproduced as Figs. io and 1 1, respectively. The discussion will not be abstracted here, but it This gives a more accurate setting than an at- tempt to find the exact peak by the maximum galvanometer reading. The accuracy of this meter is certified as within Soo cycles with a

R R temperature variation of not over 5 degrees Fahrenheit from the temperature specified in Fig. 6 Input Output Imam C the calibration. The guarantee is six Fig. 9 for months, R after which the instrument must be recali- brated. The General Radio Experimenter is a very commendable publication, to my mind, and p broadcast technicians should get their names upon its mailing list. It is sent free on application Fig. 7 Input Fig. 10 to the company's offices at Cambridge, Mass. It is a commercial publication, but the discussions are severely free from advertising blather and generally contain as much general theory on the subject as specific description of the General

LI Radio Company product. A commercial publica- tion which is scientifically and informatively Fig. 8 Speaker input + i Cz Output Fig. 11 C2 written is better than a sensational medium whose ultimate commercial aims are less frankly T revealed, and if you fail to extract a few dollars' L. P. Filler r worth of data from the Experimenter it is your A GROUP OF INTERESTING FILTER CIRCUITS fault.

www.americanradiohistory.com A and Power from the D. Co ]Lines By WILLIAM B. FALL

WHERE i io volts d.c. is the house-light- This little battery has another important to cut the 41 volts across the A- battery sub- ing current supplied by the local power function if used as indicated, which cannot stitute to 3 volts for the set of five 199's. company, there is opportunity for sup- be performed by high -capacity condensers. It If the reading lamp used in connection with planting storage or dry batteries for both fila- will absorb what otherwise might be a consider- this A- battery substitute is to be lighted at times ment and plate circuits in a radio set by means able voltage rise and so protect the tubes in the when the set's operation is not desired, a snap of comparatively simple and inexpensive devices. set against burn -out. switch, indicated in dotted lines in Fig. 2, may These have been described in the columns of The danger in the use of the d.c. A battery be connected across the A plus and A minus just radio periodicals and are fairly well understood substitute described, lies in the fact that if a back of the relay. When that switch is open, the by those who "roll their own" in d.c. dis- tube be removed from the set while the current lamp will light and the set operate; when that tricts. is on, or if a tube filament should fail or a fila- switch is closed, the lamp will light but the set There are a few pitfalls in this sort of appara- ment prong become open -circuited, the voltage will be off. I t is understood, of course, that the tus which have been touched on in the form of at the A plus and A minus posts will at once switch on the set itself is always left in the "on" warnings, but practicable solutions do not seem increase considerably. Excess current will con- position, the whole apparatus being controlled sequently be forced on the remaining tubes in from the light socket at which the current origi- the set. If that shock blows a second tube, an- nates. other rise occurs and the remaining tubes are 3amp fuse -, s- 110 Volt D.C. 3amp fuse sure to go. With the handy little 4z -volt battery A B -POWER UNIT FOR D.C. OPERATION 111111 iI ii Ii across the set, one tube may be taken out of 'THE B -power unit side of a 1 io d.c. outfit is 2 ampchoke 30 henry choke 4 Mfd a 4 -tube set and the voltage on the remaining I simple. One 3o- to 6o -henry choke, of d.c. -Soc2 Mf.. ket where three will rise only about ,30- of a volt (varying resistance not exceeding 600 ohms (preferably connection to a bit with the internal resistance of the battery), lower), and two 4- microfarad condensers (good light bulbs is 2 Mfd plugged in instead of jumping about IZ volts as would be by -pass condensers will do, as the voltage does I Mfd. the case without the dry battery shunt. Conse- not exceed an adequate R, -r" 1io) comprise filter. quently a tube filament may fail and the other Allowing for a voltage drop through the filter, 30 Ohms 20.000 Ohms 500,000 Ohms tubes in the set will be perfectly safe. On the an output of 90 to loo volts is obtained. One same principle this battery also absorbs voltage variable high resistance gives the 45 -volt tap +100 A+ A- B- B+45 f3 surges. for detector. Fig. 1 shows the hook -up. Were the dry battery to be left in this circuit With a push -pull last stage audio for four FIG. I after the house current was turned off it would power tubes, as described in RADIO BROADCAST drain itself in a few moments in a vain endeavor for May, 1928 (page 18 -19), the B plus is taken to be generally known. The purpose of this article to supply current to the set. To make disconnec- directly from the light- socket connection around is to indicate means for polishing off some of these tion of the battery automatic, a relay comes in the filter, since thereby the full 1 io to 115 volts rough edges. handy wired as indicated in Fig. 2. Any of the is obtained for the power tube plates and any First let us state briefly the sort of A battery types used for cutting out chargers and cutting hum is balanced out by the push -pull arrange- substitute used. In simplest form it is a bank of in B power units will serve. In such a relay the ment. electric light bulbs, wired in parallel, in series two contacts on the plug by which connection is It is customary to equip these power devices with the filament circuit of the radio set and the usually made to the light socket may be con- with 3- ampere fuses. This is of course protection light socket. The total wattage of the bulbs is nected to A plus and to A minus, and the leads to the house fuses, but not to the radio apparatus. adjusted to the current consumptionof the set, from the B power unit socket on the relay con- At 3 amperes, a short -circuit could play consid- the basis being about 3o watts per quarter -am- nected to the C battery. The actuating coil of the erable havoc with good radio equipment. To ob- pere tube. This is a little in excess of actual relay goes in series with the A plus lead. It is viate this danger, the writer has inserted an old needs, but the excess may be bypassed around essential that this coil lie between the point at 199 tube in series with the B plus I io-volt plate the set through a 3o- or 50-ohm rheostat, R, in which + C is connected and the line, and not supply lead. This limits the current through this Fig. 1, the varying of which offers a form of fila- between the C battery connection and the set. lead to 6o milliamperes. The drop across the tube ment control to compensate line voltage varia- In the latter position the relay will not function at a drain of 4o mils is only 2 volts, and all tubes tions. This resistance is across the current source, properly and there would be a considerable drain and associated apparatus are well protected. The and consequently the current into the set in- on the C battery as the latter would still be feed- 199 tube used may be an old one, whose de- creases as the resistance is increased. The bank ing the set through the relay. In the correct creased filament emission renders it unfit for of bulbs may be one or several reading lamps position, the relay action is instantaneous. One radio set use. which in the evening would be lighted anyway, C battery lead may be broken, or two, as many The tapped choke output for push -pull stage and, as a result, the set current costs the user commercial relays are equipped with a double is a satisfactory substitute in the use of two nothing additional except for daytime opera- set of contacts. 3o-henry chokes, the two outside connections tion. going to the plates and speaker, and the inside WAYS FOR ECONOMIZING ON CURRENT common connection to both chokes going to the HOW TO REDUCE COMMUTATOR HUM OPERATING multi -tube sets on 1o-volt B plus. This kink permits the use of chokes ACHOKE coil. capable of carrying about 2 lJ d.c: for filament supply is not economical which the builder may have on hand. amperes, and capacities across the line, al- unless the current -limiting resistances (in the are case electric bulbs) are used at though not always necessary, frequently described, light Switch used as a filter to curtail commutator hum which the same time for lighting the room. A six - is present in the d.c. supply voltage. See Fig. 1. tube set using quarter -ampere tubes would The writer has found that various types of require the use of the equivalent of 180 watts of 5 -volt tubes operate with complete satisfaction such bulbs, which, on an average use of four at 41 volts. His ear at least can detect no differ- hours per day, would add 22 kilowatt -hours to ence between a set operating at 4Z and one the electric light bill each month. To cut this operating at 5 volts. An inexpensive and compact current consumption the kink is to use the 199- dry battery of 41 volts is everywhere available type tubes up to, but not including, the last in the form of a C battery. If the voltage at the audio stage. set is adjusted to 41, and a 41-volt C battery is If five tubes be so changed, we have .o6 x 5 placed across the A substitute, the plus to plus = 0.3 ampere, instead of .25 x 5 = 1.25 ampere and the minus to minus, the hum, if there be for 201A -type tubes, a saving of nearly one any in the speaker, will decrease to a negligible ampere of filament current. The saving is nearly amount. In normal operation there will be no 120 watts, or two thirds of the original con- current drawn from the battery and its life will sumption. A 15-ohm rheostat in series with the consequently be long. A plus lead to the 199 -type tubes is sufficient FIG. 2 34

www.americanradiohistory.com Complete Equipment Fig. 1. For Television' Zeh Bouck's Reception Televisor

uilding Receivers For Television By ZEH OUCK By JAMES MILLEN

TELEVISION signals are transmitted to-day to a rapidly increasing INSTALLI NG and operating an experimental television receiver number of experimenters throughout the world. The interest and is not difficult for the average radio set builder or amateur experi- pleasure associated with their reception is found in the novelty menter. In this connection a description of the equipment used by and fascination of the achievement with home -made apparatus the writer should be of considerable interest, especially as the same rather than in esthetic considerations associated with the reproduction. apparatus may be employed by experimenters in other parts of the country Television signals when properly for receiving any television station by transmitted and received portray the merely selecting a scanning disc of the instantaneous characteristics of the proper type for the particular signal object being scanned at the transmit- being received. For instance, when ter. This is accomplished by inter- using a 24 -hole disc the wcv 21- preting at the transmitter the visual meter television signal may be received aspects of the televised object as elec- all along the West coast. Then, there trical variations which, at the receiver, are the KDKA experimental signals are reconverted into properly distri- which require a 6o-hole receiving disc. buted shades and high -lights. The majority of stations, however, are The quality of the received picture transmitting a 48 -line picture. depends upon how good a signal is Any good receiver capable of being transmitted in the first place, and tuned to the wavelength of the desired upon how well it is reproduced at the television transmitting station may be receiving end. Here the amplifier used used. The short -wave receiver employed following the detector plays the import- by the writer is the standard kit sold ant part. Theoretically the signal to by the National Company, all of the be received should contain important parts of which are available in the open frequencies from as low as the number market. It was described in detail on of pictures per second to those lying far page 286 in the August, 1928 issue of above the highest audio frequency used RADIO BROADCAST. The 222 -type r.f. in music. tube is followed by a regenerative However, television programs in detector. This system prevents radia- the broadcast band cannot contain FIG. 2. ZEH BOUCK'S AMPLIFIER tion-a problem which would soon be- frequencies above 5000 cycles since come quite serious if all the short -wave this is the highest frequency at which receivers were of the radiating variety. a broadcasting station is permitted to modulate, In building any type receiver, especially for and everi when the transmissions are on short short -wave reception, and particularly one for are given waves, the improvement in reception obtained IN THIS article descriptions of the television work where a motor and scanning disc through the use of a special amplifier going up to work of two experimenters well known to are located in the same room, considerable at- readers of RADIO BROADCAST -Zeb Bouck 15 or 20 kilocycles isn't worth the expense of tention must be given to rigidity of construction. constructing it least it doesn't appear to be and James Millen-both of whom have set This applies to the coils and their mountings as -at received worth doing until the quality of the transmissions up apparatus and successfully tele- well as the wiring and other parts of the set. are much improved over what they are to -day. vision programs. The differences in the We find from experience that the ordinary especially the amplifier A start can be made with any good amplifier and, apparatus- equip- audio amplifier, such as you use at present for give the reader a good idea after the best possible results have been obtained ment -will of the speech and music, is good enough to provide from it, there will be time to construct an am- circuits which may be adapted to present day picture reproduction sufficiently clear to dis- reception. the develops plifier designed especially for television reception. television As art more tinguish forms, such as the outline of a hand or requirements be It is the purpose of these notes to describe the stringent will set up as to head, and to follow motion. This is perfectly amplifier and scanning combination used by the the characteristic of the audio amplifier but it O. K. for a starter, and your present audio writer. This apparatus will reproduce television is evident from the data given here that for the amplifier can be used, provided it has at least good images when attached to any receiver capable of present at least almost any amplifier may the gain of a good two -stage transformer - delivering a signal of requisite strength from the be used. coupled unit. EDITOR. desired transmitting station. -THE For receiving 3XK in Boston it was found ad- (Continued on page 36) (Continued on page 37) 35

www.americanradiohistory.com 4 36 RADIO BROADCAST NOVEMBER, 1928

0 06 mfd. 0.06 mfd. 0.06 mfd. the panel, and these provide a very accurate motor control. The rheostats are in series with some additional resistors in accordance with the Output direction's accompanying the motor. O By means of the rheostats, in conjunction with a simple mechanical brake described in the paragraph on operating directions, it is possible to maintain the speed of the motor sufficiently close to synchronism with the transmitting disc.

IhI MI THE CIRCUIT ARRANGEMENT ¡ Y Speaker HE detector tube has been incorporated in T the amplifier constructed by the writer. When used with the average receiver, posts one and three in Fig. 3 will be bridged, and post I two will be plugged into the grid prong on the detector socket of the receiver. In the case of a O O F. regenerative receiver, the plate of the exterior - 6V.+ +C -9V. -45V. +450 IT +220 C C 200 to 450 detector tube will be wired to the plate terminal on the detector socket while post three will be

FIG. 3. SCHEMATIC DIAGRAM OF TELEVISION AMPLIFIER led to the plus detector terminal on the set. I n other words, the tickler or regenerative coil is connected in between the plate of the detector (Continued from page 35) practically the same with either the loud speaker tube and the coupling resistor. If it is desired to -I he essential parts of a television reproducer or neon tube, thus prolonging the life of the í71A use the detector socket in the receiver (and this are a tuner (any kind will do that is capable of tube and making unnecessary any variation in may be the more simple procedure in many providing a good loud- speaker signal in ordinary the C-bias potentiometer, R6. When the amplifier cases) post three is led to the plate terminal of reception), an audio amplifier, a neon tube and a is operating the loud speaker about 200 volts the detector tube. scanning disc turned by a motor mechanically are employed, while with the neon tube the full The neon tube is connected in place of the arranged so that the holes in the disc scan the 45o volts is applied. These voltages can be sup- loud speaker or output device. This is a simple surface of the glowing plate. series connection and is quite effective. While The amplifier used by the writer is shown dia- there are other systems of inputting to the neon grammatically in Fig. 3, while constructional tube, concomitant complications hardly rec- points are suggested in the pictures, Figs. I and ílllllll 11 \\ 0 ommend them for an initial attempt. 2. The amplifier can be built from any standard Cross Bar 1 The apparatus described was designed pri- apparatus; it employs the usual three -stage marily for the reception of the television signals resistance -capacity -coupled circuit. broadcast from WRNY, New York City, em- Brass Strip-- ár ploying a 48 -hole disc at a speed of 45o revolu- APPARATUS REQUIRED tions per minute. A National Company disc is THE following is a complete list of the parts Disk>1 used in the illustrated apparatus. required for the construction of the writer's television amplifier: Motor Shaft, OPERATING DIRECTIONS R1 Wire -wound resistors, too,000- -3 signal is first tuned in on the loud speaker ohm ; THEin the usual way, a loud clear signal being the R_, R4 Grid -leak resistors, i-meg., 0.5- R3, -3 desired result. The motor should be started and meg., and 50,000 -ohm, respectively; Looking down or up the disc brought up rapidly to approximately Rs Rheostat, io-ohm; -I FIG. 4. MECHANICAL SPEED CONTROL the speed desired. This can be accomplished by R6 -1 Potentiometer, 200,00o -ohm; means of a switch short -circuiting the speed - C1 Mica fixed condenser, o.00i -mfd.; -I governing resistors. C2-4 Filter condensers, 400 -volt, 2 -mfd.; plied either by a B battery or a power -supply The output of the amplifier is now switched C3, C4. C5-6 Mica condensers, o.ol mfd.; unit. A Receptrad Powerizer was used in the over to the neon tube, which, when the television L -1 Pilot light; author's laboratory as shown in the picture of the signal is received, should show a definite pattern SI Toggle switch; entire set -up, Fig. I. -I when viewed through the disc. As the disc ap- -4 Vacuum -tube sockets. ux -type; SCANNING DISC ASSEMBLY proaches synchronism with the transmitting 6 Resistor mountings; disc, the pattern will resolve itself into more to Binding posts; THE televising apparatus consists of the scanning disc driven by an adequate motor, definite lines slanting away from the perpendic- I Front panel, 7 x to x c -inch; some form of motor speed control, and the neon ular. The lines become more and more perpen- i Sub -panel, 7 x lox 6 -inch; (Continued on page 37) 2 Sub -panel brackets. tube, combined in a convenient and efficient mechanical arrangement. A box frame, such as is The pilot light and toggle switch are, of course, illustrated in the pictures, Figs. I and 5, provides unessential, but were incorporated in the am- a simple and satisfactory unit. The motor shelf is plifier for convenience. The amplifier eventually so positioned that the driving shaft can be will be mounted in the cabinet, and the pilot centered exactly. The shelf is clamped between light will give some indication of current condi- cushions of soft rubber which reduce the tions behind the panel. The switch (S1) controls vibration. the filaments of the detector and amplifier tubes, The neon tube is mounted with its plates while the other switch, visible in the pictures, parallel to the scanning disc, so that the holes was used to start the motor turning the scan- in the latter pass over its entire surface. The neon SUPPLIED WITH ning disc. tube is a Raytheon Kino -Lamp and it should be MOTOR The four filter condensers (G) are connected placed in a horizontal position on the upper shelf in parallel to bypass the amplifier plate voltage. as close to the scanning disc as possible. The and reduce the tendency to motorboat. In the Baldor type -MV2 variable -speed motor may be amplifier pictured the coupling condensers are used for turning the disc. For observing the built up in stack form, and consist of six o.oi- picture square hole, I z x it inches, is cut in the mfd. mica condensers. face of the front panel exactly in front of the In operation it will be convenient to be able to plate of the neon tube. switch easily from the loud speaker to the neon The inside dimensions of the entire box, as tube, an operation that is facilitated by the pictured, measure 25 x 25 inches. It is built of double -pole, double-throw switching arrange- half-inch wood (heavier material is desirable) and ment suggested in Fig. 3. By means of the two the front panel is 7 x 26 inches. Two ten -ohm battery taps the voltage applied to the tube is rheostats, connected in series, are mounted on FIG. 5. REAR VIEW OF TELEVISOR

www.americanradiohistory.com NOVEMBER, 1928 JAMES MILLEN'S TELEVISION RECEIVER 37

(Continued from page 35) quietly. The swish of the NEON MSC C.;1% VO_ 4:7 IUIrATOR visable to use a three -stage amplifier using disc through the air con- National transformers -see Fig. 3. Then stitutes the major por- being at of noise, and this again, the pictures transmitted by 3xK tion the NECEIVrR present are merely silhouettes, which do not is quite insignificant. require an amplifier with as wide a frequency Special rubber vibration range as if half-tones were being transmitted. absorbers are supplie d

As a rule, with a three -stage a.f. unit, the with the motor for mount- AUDIO amplifier noise will not be very great. Vibration ing purposes. AMPLIFIER from the receiving disc or its motor, which are transmitted to the amplifier or especially the MOTOR SPEED CONTROL detector tube, however, will introduce a periodic THE diagram (Fig. 3) noise that will cause a black streak across the shows the method for field of the picture. Any periodic interference, speed control. For the such as a 6o -cycle hum, that may get into the variable resistor RI. a 75- signal will also cause streaks across the picture, watt, 4- to loo -ohm wire- but these will not remain stationary, but will wound resistor with a move upward or downward across the field of the sliding contact is used. FIG. 1. GENERAL VIEW OF TELEVISION LAYOUT picture. The other resistor may be a to-ohm to-watt re- CIRCUIT THE OUTPUT sistance. This is labeled " R1" in the diagram inside the tube are placed in a plane at right THE output circuit of the amplifier is ar- and is shunted by the push- button speed- 'angles to the axis of the "Pin" of the base. If ranged so that the neon or Kino-Lamp is control leads. the pin, therefore, is pointed toward the disc always illuminated, and, when a station is re- The resistance R4 is so adjusted that with the when inserted in the socket, the plates inside ceived, the brilliancy of illumination merely push button released, the motor runs at slightly the tube will then be parallel to the disc. The varies in accordance with the signal. A good below the proper synchronous speed. Then, when tube should be mounted at the proper height to background will be obtained if the d_c. current the push button is depressed, the disc tends to cover the il-inch square scanned by the revolv- through the neon tube is limited to to or 20 speed up. ing disc. The plates are connected to the "plate "' milliamperes. More current will cause the lamp Do not mount the television receiver in the and "filament" prongs of the tube base. to glow brighter and brighter but there is no same cabinet with the disc. Vibrations of the advantage in this so far as the picture is con- motor will introduce a synchronous noise that cerned and it only serves to shorten the life of the will result in a series of horizontal lines being Zeh B®uek9s Televisor lamp. Accordingly, care should be taken to ad- drawn across the picture. Therefore. it is im- just the current to the minimum satisfactory value. (Continued front page 36) A Clarostat has been found excellent for such dicular as the correct motor speed is approached, use, and it may be mounted conveniently on the finally forming the image of the televised object. front of the frame supporting the scanning Final tuning should now be effected on the re- apparatus, as shown in Figs. i and 2. For ceiver. Also, the bias to the last tube should be a MR varied, by means of the high -range potentiometer illuminating the Kino-Lamp either standard 6 CCONTOr LASERS high -grade B socket -power unit or heavy -duty R6, for best results. B batteries may be used. MECHANICAL BRAKE NEEDED Several different concerns are manufacturing scanning discs suitable for use in receiving the IT IS desirable to use some simple form of signals now on the air. The better grade discs mechanical brake in conjunction with the are well made mechanically, so as to run true rheostats to control the motor. The device and require little power. The holes in such discs shown in Fig. 4 was designed by the writer for are also punched to the degree of accuracy this purpose. necessary if the received image is to be free from An iron cross piece was fastened to the box black lines and streaks. The National disc uses housing the revolving apparatus so that it crossed radially -shaped holes, rather than round holes, in front of the motor shaft. A hole was drilled to for with this design the "lines" across the image the exact center of the shaft, and the nut from a are much less obvious. i-inch iron bolt was soldered to the cross arm. A FIG. 2. REAR VIEW OF SCANNING DISC In driving the scanning disc successful results brass strip was bent as shown in the illustration, have been obtained with a number of different and bolted to the cross piece. The head of the types of small motors. However, the motos portant to keep the receiver and amplifier on a i-inch bolt was sawed off and a knob mounted which the writer is using at present is the 1-horse- support separate from that for the disc. on the end. By screwing in the bolt, the brass power type-Y IV variable -speed condenser -type The experimenter will find that the following strip is pressed against the end of the shaft, Baldor which is intended for operation on t to- convention has been adopted by the Raytheon giving a very delicate braking action. The brass volt, single -phase, 6o -cycle a.c. line. This is a ball - Company in regard to neon tube mountings. The strip should be taped where it touches the bearing motor that operates very smoothly and tube is fitted with a standard ux base. The plates shaft.

112 - A 112 -A 210 National Disc Neon

I Tube': 4 mfd.

2 mfd.

411, t - Short Volts Circuiting 9 750 ohms Switch I

Volts¡ 30-henry from Separate 25 mA / R2 &Power Unit Choke Coit 210 or Batterie's

I +45 4-135 4-45 A-B-A+ I +67 +135 +450 I------L------1------JI 110V.A.C. RECEIVER AMPLIFIER TELEVISOR FIG. 3. COMPLETE SCHEMATIC DIAGRAM OF JAMES MILLEN'S TELEVISION RECEIVER

www.americanradiohistory.com A Modulator for the 1929 Shorto Wave Transmitter

By ROBERT S. KRUSE

AWRITER on the Hartford Times tells resistence R2 we find (by watching the meter I) Wandering into L and the tube "Mod" where it me that all radio men write stories that the current through R1 changes for only a would be wasted. The vacuum tube labeled badly; that is, they always leave the moment when this is done. The explanation is " Mod," which is used as a voice -operated re- thrill until the last, instead of putting it into the this; the choke L is (after the fashion of induc- sistance, is substituted in the circuit in place of headline. In this three-part tale of improved tances) an electrical "stand- patter," i.e., always the resistor R2. A microphone and amplifier feed short -wave transmission, I seem to be guilty of opposing a sudden change. Thus, if we suddenly voice -currents to the grid of this tube, and, as this offense, for I am waiting they cause the voltage of this until the third installment to grid to change, the current to the speak of the uses of such trans- amplifier tube varies, causing cor- mitters, and, of course. that is responding changes in the r.f. where the thrill comes in. For the current in the L. C2 circuit from present we shall give additional which the antenna power is data on the constant -frequency taken. It is only fair to say that transmitter described last month. this method of operation does and explain those devices which not permit the highest amplifica- make it useful, which is to say tion to take place in the ampli- the key or microphone. fier and that .a "straight" r.f. A transmitter without modula- amplifier should be added if the tion is useless, since it can send full power- rating of that size of out only a "carrier wave." To tube is desired. However, this place variations on that carrier added complexity does not seem which a radio receiving set can warranted in a small set since the "unscramble" into code or voice range increase is not large. is the business of the apparatus The circuit arrangement in described in this article. It was complete form is shown in Fig. 3. explained in the October issue The picture in Fig. I shows how that voice, or radio-phone trans- simply the whole works goes to- mission, has the advantage of gether. In listing the particular speed while, with the same makes of apparatus which are power, radio-telegraph transmis- given below, the writer has no sion has the advantage of greater particular desire to favor any range. Very evidently these two FIG. I. TOP VIEW OF MODULATOR UNIT manufacturer but rather his mo- systems may be used with the tive is to remove uncertainty by same transmitter to excellent advantage, and reduce R2 we do not change the total current listing those parts which have been used with it is my suggestion that provision be made through the choke immediately but simply satisfaction in short -wave transmitters. In for both. change its division between the two paths, several cases it was found that other equipment, therefore, the current through A drops sharply which seemingly had every right to be as good, CONCERNING INTERFERENCE until L'finally agrees to allow more current to was thoroughly unfitted for this somewhat 'T'O MANY amateurs a recommendation of pass. On the other hand, if we suddenly raise the special purpose. If changes in the assembly are radiophone is as a rag to a bull; it causes resistance of R2 we force additional current considered necessary they should, therefore, be them to paw up dirt and bellow about the awful made one at a time and the effect noted. The interference caused by the microphone -operated parts used in my set -up are as follows: sets. This opinion is a bit out of date. Two years ago amateur oscillators were so unstable that LIST OF APPARATUS the addition of equipment did have a TRANSMITTER, according to Mr. modulating Mike -Western Electric type 348BW or Federal distressing way of causing the signal to smear Kruse, without a means of modulation type 260W. over a wider band than one cares to think of. is as bad as a ship without a sail. Inasmuch R1 -Used to reduce microphone current to prop- Also, the did the same thing transmitters exactly as the transmitter itself was described in er value. Not necessary in most cases. when keyed, but, in that case, the interference October, a transmitter that is designed to stay R2 -Gain control. Frost Ioo,000- or 200,000 -ohm consisted of mumbles, thumps, and "yips" on its assigned frequency, the modulation type. which were identify. Since that time harder to equipment necessarily had to follow. Here it R, -Shunt resistance, exchangeable in clip to our preaching for better tuned circuits.has had a is. -THE EDITOR suit tube and transformer used. I megohm is good effect, and the coming of crystal -control usually satisfactory. a of good has set examples. As result the number R4- Filament rheostat, 6 -ohm. amateur radiophones has increased so that we L- General Radio choke, type 485 -S. accusation against the phone. must withdraw the TRI -General Radio type 485 -M (for single bat- through RI L permits the total current to To sum up -with an oscillator- controlled until button mike) with or voice as die down. Thus, the effect of any sudden changes tery set we may modulate key TR- General Radio type 485 -D being in R2 causes corresponding sudden changes in we please with no fear of "wobbulation" SW- Switch to cut off d.c. filaments and micro- The the the current passing through RI. added to "modulation." circuit of phone. No a.c. circuits should go through or shown in Fig. 3. In Fig. 213 we show how this principle is used oscillator-amplifier set -up is near this switch. in our set. The oscillator tube feeds radio-fre- THE CIRCUIT ARRANGEMENT quency power to the grid of the r.f. amplifier CONCERNING TUBE EQUIPMENT THE circuit is the almost standard Heising tube where it is amplified and passed to the cir- constant -current arrangement. In Fig. 2A cuit 1.4 Q. The current is then transferred to the FOR the sake of simplicity, and to minimize we review the general principle. Current from the antenna, but this does not concern us just now. A.C. hum, it is recommended strongly that battery flows through the high- inductance choke, The plate power for the amplifier tube is supplied for voice operation 20IA -type tubes be used in L, to the point B, then divides and returns in two through a choke coil L, of at least 6 henries, just the oscillator (see p. 344 of October RADIO parts through the two resistances R1 and R2. as the current in Fig. 2A was supplied. The radio- BROADCAST) and in the first socket of the modu- If we suddenly change the setting of the variable frequency choke (r.f.c.) is to prevent the r.f. lator, and that their filaments be operated from 38

www.americanradiohistory.com NOVEMBER, 1928 A MODULATOR FOR THE 1929 SHORT -WAVE TRANSMITTER 39

a 6 -volt storage battery, which is necessary for the microphone in any case. The r.f. amplifier Ant. tube in the October article and the modulator A tube in the present set -up may be a 112 -, 171 -, 210-type tube, a or or corresponding a.c. tube. et The ux25o may be used but is not recom- 0 C3 C6 C mended. It is possible to use a.c. tubes in place & Gna of the 210 tubes recommended, but make sure that they are of the "heater" type, such as the Arcturus tubes or the uY227, and not of the RFC4 -C5 ^Q9Q9/-0 +Amplifier type represented "thick- filament" by the ux226. high Care must be taken to keep the filament leads voltage clear of the grid circuits and even with these precautions the hum problem is apt to be bother- some. With batteries on the tubes mentioned above this difficulty is removed. Still another combination is possible, namely to operate 20IA- FIG. 3. THE SCHEMATIC DIAGRAM OF OSCILLATOR -AMPLIFIER type tubes in the first sockets and 2lo-type tubes in the Amp. and Mod. sockets with a.c. on all denser C must of course be readjusted when (C6) used to load the amplifier plate circuit will the filaments. This is done by connecting the such a change is made. not survive with the 21o, therefore one of two 201A filaments in parallel and running them Since the 210-type tube is used with the things may be done. Either the coil inductance through two equal fixed resistors to posts D and thought of obtaining an increased output it is must be increased or else the 250-mmfd. tuning F of the October set -up. If the October set alone operated at high voltage and with a plate current condenser C3 should be replaced by a 500-mmfd. is used for c.w. these resistors must produce a of about 4o milliamperes per tube -making 8o Equitune. The dial degrees of the two tuned drop of 1.25 volts each at a current of amp.. for the modulator and amplifier. This current circuits, i.e., the oscillator and the amplifier, will therefore, they must have a resistance of 2.5 to would destroy the windings of the National type then not run together as nicely as was the case 3 ohms. If the complete set -up, i.e., oscillator. 90 choke in the plate circuit of these two tubes. before. Of course, if one is really fussy about and, therefore, it must be replaced this point it is possible to use two Equitunes, of by a more substantial choke which the 25o size, set end to end and connected in will operate over all the wavebands parallel, one being fixed at maximum and the we are interested in. I can find other variable as usual. Personally, I prefer in- none of the transmitting -type creasing the inductance. chokes which will do this, and. Finally -if someone wishes to use a 210-type therefore. suggest a combination tube as oscillator, that too can be done by con- consisting of a single-layer choke necting posts ABC in Fig. 3 to DEF in Fig. 5. in series with a General Radio The plate potential of the oscillator should not type 379 T, Aero Products type be increased above 18o volts. This combination 248 (transmitter type) or a Na- isn't bad at the upper wavebands but offers tional Type 90 re -wound with some slight difficulty at to meters. At present No. 32 or 34 d.c.c. wire. The single - I cannot give the exact dimensions of the some- B FIG. 2 layer choke, which is substituted what smaller coil that will be required. The Diagram A (left): schematic in the clip for the former choke. diameter will be ?bout 1" smaller than shown in showing constant -current consists of a e" rod of insulating the October article. The other wavelengths will modulation principle. Dia- material wound for ii" with a shift somewhat but not badly, because of the gram B (above): circuit used single layer of No. 34 or 36 d.s.c. large condenser which is used. in set. A by -pass condenser or s.c.c. wire. The other choke between B- and the plate side of KEYING AND OPERATING WITH VOICE R. F.C. would improve results. may be mounted on the back of the panel near the amplifier tube NO MATTER which sort of operating is to be amplifier. and modulator is being used the cur- and antenna ammeter. Its business begins at 20 taken up the first job is to secure a steady rent will be ; amp. and the resistors may have a meters where the little choke stops. output. Some suggestions were given in the resistance 1.25 to 1.5 ohms each. A pair of I- or In Fig. 8A other changes are suggested that may October article. To these can be added the fact i-ohm filament- ballasts resistors will do very be necessary if the 210-type tubes are operated that it is of comparatively little importance what nicely. It is advisable to twist all a.c. leads into at voltages above 250-as they usually are since plate voltage is used as long as the plates remain pairs and to inspect the various center-tapped their rating is 35o. The condenser Cs should be at a sane temperature. For the oscillator this resistors to make sure they are in good condition. replaced by a i000-volt Sangamo unit of the larg- means no visible color, for the amplifier it means An open resistor will cause considerable noise; est capacity available. If this cannot be done a red that is not too violent. The type of tube an off -rating one will produce less noise that is conveniently a change to the shunt method of used and the recommendations of the maker still quite noticeable. feeding (shown in Fig..8B) is advised. This may should be considered. It is helpful to listen to the be necessary in any case if voltages above 400 un- modulated output with a little "breadboard" THE UX -210 TUBE are used. Here CS replaces Cs. receiver using the circuit of Fig. 6. With a 199 I F ONE uses 112- or 171 -type tubes in the r.f. The 250-micro-microfarad plug -in condenser tube and a 22 -volt battery the whole thing can amplifier and modulator sockets it is be put on a 7" x lo" base, including a possible to cut down the plate voltage 41-volt C battery for the filament of the oscillator, thus reducing the supply. Shielding is neither necessary batteries. This should nor desirable for such a device; it is a drain from the FILAMENT RHEOSTAT not be carried to the point where un- GAIN nuisance in fact. When the note seems R4 steadiness results. In my particular CONTROL O.K.. and free from 6o-cycle ripple, set 90 volts at the oscillator handles a one may key slowly and then proceed t a s 171 -type amplifier running at 300 with voice -modulation. For this the volts with very fine steadiness. pick -up receiver is stopped from oscil- When using the UX-210 tube or MI NE lating. SWITCH INPUT equivalent in the amplifier and modu- ll "PERFECT MODULATION" lator sockets the oscillator tube should have a plate potential of approxi- HE voice -input system shown will mately 18o volts. It must, of course. T do good work if given a chance. never show plate- heating to a visible O O There are several ways of making the degree. If desired, the feed condenser H O O adjustments. One is to have an assis- Cr may be changed in size. provided tant speak into the mike -preferably it is not made large enough to cause reading steadily from a book -while difficulty in reaching down to the various things are changed and the io-meter band. The neutralizing con- FIG. 4. FRONT VIEW OF MODULATOR UNIT results noted as the signal is heard

www.americanradiohistory.com 40 RADIO BROADCAST NOVEMBER, 1 92b

sloppy handling of the tamed. Warning -the antenna meter is easily "mike." One must keep burned out if kept off -scale long. If it runs off - at a fixed distance detune or pull the switch instantly. Then shunt and speak in an even the meter with a length of wire-6 inches at a tone of voice. Looking guess -and try again. If it still runs off shorten around the room does the shunt until it does not. The process takes not help, nor does a some practice and should be done for all the cigarette or cigar be- bands after which we will be ready to-but that's tween the lips. Con- next months story. sider the good care 10 b11 012 13 14 taken in broadcast an- AMATEUR WAVELENGTHS +B - C + - B + C "--r-' TTo+Bo1 nouncements as com- -4 S lo-9 ToA&Col 90 To DEFoI C+sc:Amp. OscAmp. AsvAmp. pared to the ignorant THAT there be no confusion regarding who use of the same equip- I may transmit, and what frequencies are avail- FIG. 5. SCHEMATIC DIAGRAM OF MODULATOR ment by a new speaker able for amateur operations, the following quota- on his first broadcast tion from " Revised Amateur Regulations" in the phones of the pick -up receiver. The from a not -too-good station. dated March 6, 1928, and signed by W. D. Ter- assistant must enunciate decently as other- rell, Chief, Radio Division of the Department wise he is worse than useless. He also must AND AS FOR THE KEY- of Commerce, gives all the necessary infor- hold the mike in the proper position and at mation. the correct distance. With these conditions as a WITH the key one may do many things in- "An amateur station is a station operated by good start one may now adjust the gain control, correctly. The best rule is to send little a person interested in radio technique solely with microphone voltage and bias of the modulator and listen much until one learns the manner in a personal aim and without a pecuniary interest. tube. The bias may be set at 10 per cent. of the which not to do things. This is easily done for Amateur licenses will not be issued to stations modulator plate voltage at the beginning, and of other classes. varied from this point. In general a large bias "Amateur radio stations are authorized for has an advantage in keeping the tube cool. If communication only with similarly licensed one has meters available it will be found good stations, except as indicated below, and on wave- practice to adjust the currents to modulator and lengths or frequencies within the following bands: amplifier tubes so that they are of nearly equal value. Having once found a good setting one Kilocycles Meters may watch the antenna meter thereafter, judging 401,000 to 400,000 0.7477 to 0.7496 from its movements the degree to which things 64,000 to 56,000 4.69 to 5.35 remain the same. A better way of doing this is 30,000 to 28,000 9.99 to 10.71 to 18.7 to 21.4 to put a d.c. milliammeter in the modulator 16,000 14,000 8,000 to 7,000 37.5 to 42.8 plate lead -and leave it there. FIG. 6. PICK -UI' RECEIVER USING A 4,000 to 3,500 75.0 to 85.7 If an assistant is not available one may place 199 TUBE 2,000 to 1,500 150.0 to 200.0 the " mike" before a good loud speaker running at a moderate level on some decent input -not and at all times unless interference is caused with a jazz band. The listening is then done as before. the average performance is not perfect and the other radio services, in which event a silent pe- It is scarcely necessary to say that all adjust- air is still cluttered up with tireless "CQ" callers riod must be observed between the hours of 8:oo ments of this sort should be made with the an- who make the most imperfect phone seem holy p. m. and Io:3o p. m., local time, and on Sundays tenna cut off. and pure. When one does call -let it be at a during local church services. The beginner will find himself confused when speed where the send- trying to determine the difference between good ing will be readable for and bad speech from his own set. He is able to " I t isn't the words per find some help from the fact that a bad phone minute but the messages makes no difference between the letters F and S, per hour that count" - B T. In addi- and very little between P, B, D and and again -" What prof- Sw tion to this it very probably will "blast" on some iteth speed when but used notes and on some of the vowel letters, especially to repeat what was sent O. the groups of letters Repeating alphabet and badly?" A,KEYS-B 13.-KEYS R.F.cct. C: KEYS BOTH -B & R.F just mentioned, together with reading and Of the set itself little FIG. 7. CONTROL CIRCUITS counting are all good tests. One entirely useless need be said when oper- test is to get on the air and work someone. The ating for radio-telegraph truth does not lie in that quarter -or perhaps transmission only. The connections are ex- Amateur radio telephone operation will be I lack faith through being neither a " brass - plained in the diagrams; the standard prac- permitted only in the following bands: pounder" nor very much of a "ragchewer," but tices are too lengthy to be put down here. Meters mainly an occasional transmitting experimenter. The Radio Manual by Sterling at this mo- Kilocycles One very important point to remember is that ment seems alone to contain the new regula- 64,000 to 56.000 4.69 to 5.35 the best of phones will not compensate for tions. 3,550 to 3,500 84.5 to 85.7 2,000 to 1,715 150.0 to 175.0 One comment with regard to the set can be made. If for any reason it is desired to use C bias on the r.f. amplifier tube in place of the un-

orthodox resistance bias shown in the October R F C. R.F C the C battery C6 (PN guy paper this may be done by feeding V to the clips of the cartridge- resistance-mounting. Cy The oscillator -amplifier set -up has been so laid out that the C battery can be placed behind it and leads run in without difficulty. If, as case, the is to use the set- in my intention O+B up portably the clips themsevles should not 2 be disturbed. + Amplifier o-B Perhaps I have been wrong in the assumption G High Voltage that tuning the oscillator -amplifier is self- evident. The procedure is to set the oscillator with the z aid of the wavemeter, then to place the little FIG. ó A. lamp -loop near the amplifier plate-coil (Aero B Imo) for greatest bright- FIG. 8 This circuit is utilized when a 210 -type r.f. tube Coil and,tune that circuit if the conden- with a plate potential in the order of ness, finally to revolve the antenna condenser This arrangement must be employed is used plate voltages 400 volts until the greatest antenna meter reading is ob- sers will not stand the high amplifier

www.americanradiohistory.com NOVEMBER, 1928 RADIO BROADCAST 41

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N®. 11. November, 1928. RADIO BROADCAST'S Service Data Sheets on Manufactured Receivers

Freshman Model "G99 Radi® Receivers

The Model "G " Freshman receiver is six - and supplied with current from a 1.5-volt tube tuned radio -frequency set having three transformer winding (Si) in the power sup- stages of tuned radio -frequency amplifica- ply. The midpoint of this circuit is obtained tion, a detector and two stages of audio- from the center -tapped resistor (Ri) con- frequency amplification. The receiver is nected across the filament circuit. The operated directly from 110- to 120 -volt heater leads from the 227 -type detector 60 -cycle alternating -current house -lighting tube are fed from the secondary (S2) mains and employs the G-60 -S power -supply which delivers 2.5 volts. The winding is unit to convert the current into the form arranged with a center tap which is grounded necessary for the operation of the receiver. to prevent hum. The secondary Si supplies In normal operation the receiver has all its 5 volts for the 171A-type power tube, and this grid returns grounded to the frame and winding is also used to light the dial lamp. its filaments floating at postive potentials above the frame to furnish the necessary 5. Plate Circuits. grid -bias voltages. The power- supply unit The plates of 226-type tubes in the r.f. contains a transformer for heating the vari- and first a.f. stages are supplied with a ous filaments and a rectifier -filter system plate potential of about 130 volts from tIle for furnishing the plate current. power unit. The plate of the detector re- ceives about 50 volts. The plate of the 1. The Tuning System. power tube receives about 180 volts. which This receiver has four tuned circuits. is the maximum permissible voltage for a including a tuned antenna stage. The pri- 171A -type tube. mary of the antenna r.f. transformer con- nects to A and A2, the first terminal to he 6. Grid Circuits. used with a long antenna and A2 to be used At a plate potential of 130 volts, 226 - with a short antenna. Across the first tuning type tubes require a grid bias of about 9 condenser. CI is connected a midget con- volts which is supplied. in this receiver, by denser Cs to permit adjusting the first tuned the resistor Rs connected between the ground circuit to exact resonance. and the center -tapped resistor, R. This The method of preventing oscillations in resistor is bypassed by condenser Ce. The the r.f- amplifier is unusual. "Equaphase" grid leak of the detector is returned directly is the name which has been given to this part to the cathode of the 227 -type tube, A grid of the circuit, as indicated in the circuit dia- bias of about 40 volts for the 171A -type gram. The circuit, consisting of RI, Cs and the be used unless the loud speaker is equipped with a tube is obtained by connecting a 2000ohm resis- effective primary inductance, of the r.f. transformer, coupling transformer that can carry safely about 20 tor (R6) as shown. when properly adjusted acts like a pure resistance milliamperes, the plate current of a 171A -type tube. at all frequencies and the tube cannot oscillate. 7. Power Supply. 3. Volume Control. The B -power unit employs the power transformer 2. Detector and Audio System. The volume control consists of a high -resistance IT) with two secondary windings. Si and Ss. The A leak-condenser system is used in the grid - potentiometer, R2, connected across the second- 280 -type rectifier tube is supplied with filament circuit of the detector in this receiver. This is ary of the first -stage audio -frequency trans- current from Si and plate voltage from Ss. The filter followed by a two -stage transformer -coupled a.f. former. The low -potential end of the secondary of system consists of Li. L2 and Cio. Cu. and Cie, and amplifier. A small fixed condenser in the plate this transformer is grounded as is the movable the voltage- dividing resistor R6 with the necessary circuit of the detector bypasses the r.`. current arm of the potentiometer. by -pass condensers Cu and Cu connected across the to ground and provides the low- impedance path output terminals of the filter. Transformer T2 sup - for the r.f. current, essential if the detector is 4. Filament Circuits. plies filament energy for the various tubes in the set. to operate efficiently. No output device is included The filaments of the three radio -frequency and The receiver is designed for operation on a 110- to in the set but it generally is advisable that one first audio-frequency tubes are connected in parallel 120 -volt 60- cycles a.c. supply.

Cl C5 226 226 a6 227 226 171 -A

ì

Dial Lamp

R SET CIRCJIT 0O RECEIVING Ai Gnd Rá = Cat Renal

2

13

110.120 V 60 ~ Supply

POWER SUPPLY CIRCUIT

THE RECEIVER CIRCUIT

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www.americanradiohistory.com 42 RADIO BROADCAST NOVEMBER, 1928

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10T®. 12. November, 1928. RADIO BROADCAST'S Service Data Sheets on Manufactured Receivers 1Freed . Eisemanmi N11.80 Receivers

THE NR -80 is one of the latest re- ceives about 45 volts. and 157 volts ceivers developed by the Freed - is delivered to the plate of the Eisemann Co m pa n y . The set is power tube. Individual 0.5 -mfd. by- mounted in a reinforced steel cabinet pass condensers Ca Cr and Cs bypass and is designed for use on 110- to 120 - the plate circuits of the various r.f. v o I t. 60- c ye le alternating-current tubes so that there will be no r.f. supply. current flowing through the power unit where they might cause coup- TECHNICAL DISCUSSION ling which would make the r.f. ampli- 1. The Tuning System. fier oscillate. These condensers also There are four tuning condensers, serve to bypass the audio- frequency CI, Cr. C3 and CI. In the antenna cir- currents in the plate circuit of the first cuit is employed a special choke which a.f. stage. is designed to give somewhat greater gain at the low -frequency end of the 6. Grid Circuits. broadcast band, thereby off-setting, The grid circuits of the r.f. tubes to some extent, the opposite charac- obtain a bias from the power unit and teristic of a tuned r.f. amplifier. The somewhat greater bias is supplied antenna circuit does not require any from the power unit to the first audio tuning condenser. To compensate for tube. To obtain bias on the power the slight variations in the tuning coils tube a separate resistor is used. Rz in of the individual stages small **vanes" the diagram, with a value of 1650 are used. These may be moved nearer THE NR-.80 RECEIVER ohms. These various resistors which to, or away from, the main inductance supply bias are bypassed by var- of the tuning coils, and are adjusted ious condensers in the condenser at the factory to the correct position. Each r. f. the arm of the unit is rotated in the direction which block. If these resistors were not bypassed, an audio- transformer is shielded as indicated by the dotted reduces its resistance, it gradually shunts the prim- frequency voltage would be impressed back on the lines. The various tubes are neutralized by connect- ary winding and decreases the amount of signal grid circuits of the various tubes and either an in- ing neutralizing condensers. marked N.C. in the voltage which is fed into the detector tube. crease or decrease of amplification at certain fre- diagram, from the grid of the tube to the secondary quencies would result. of the following r.f. transformer. 4. Filament Circuits. Four filament windings which supply current to 7. The Power Supply. 2. Detector and Audio Systems. the tubes in the receiver are placed on the power The power supply is a conventional one using a The grid leak and condenser type detector used transformer. A 1.5 -volt winding (Ss) supplies all the 280 -type tube as the rectifier in a full -wave cir- in this receiver utilizes a 0.00025 -mfd. grid con- 226 -type r.f. tubes, a 2.5 -volt winding (Si) supplies cuit. The filament of the rectifier is supplied with denser and a 2- megohm grid leak. The detector the 227 -type detector tube, another 1.5 -volt winding current by a secondary winding (Si) on the power tube is a type 227. The plate circuit feeds into a (Ss) supplies the first audio tube. and a 5 -volt wind- transformer T. Plate voltage for the rectifier is two -stage transformer -coupled amplifier using 3:1- ing (Ss) supplies the power tube. Two 1.5 -volt wind - supplied by secondary Sr. The output of the rectifier ratio transformers. The 171A-type power tube feeds ings. one for the r.f. tubes and one for the first audio feeds into a filter system consisting of Cs. Cis and into an output transformer with a turns -ratio of 1:1; tube are used so that a better hum balance may Cii located in the condenser block and Li and Li. the purpose of this transformer is to keep the d.c. be obtained. These windings are shunted by poten- which are filter choke coils. plate current of the power tube out of the loud- tiometers R2 and Rs, each of twenty ohms. which The output of this filter system in turn feeds into speaker circuit. The plate circuit of the detector are adjusted at the factory to the point of min- the potential divider, Rs consisting of a number of tube contains a condenser Cs. with a value of 0.001 imum hum in the loud speaker. fixed resistors connected in series and having the mfd. to bypass the r.f. currents to the ground. values indicated on the diagram. At the junctions 5. Plate Circuits. between these resistors wires are connected for ob- 3. Volume Control. Three different values of plate voltage ere supplied taining the various voltages required for the correct The volume control of the receiver is located in to the receiver by the power unit. The same value operation of the different tubes in the receiver. the r.f. amplifier. It consists of a variable resistor, of voltage is supplied to the plates of the r.f. tubes Power to the receiver is controlled entirely by the Ri. with a value of 2000 ohms. It is connected directly and also to the plate of the first a.f. tube; this poten- switch connected in series with the primary winding across the primary of the last r.f. transformer. As tial is approximately 100 volts. The detector re- of the power transformer.

226 171 -A

Pilot Light

Condenser [3lock .z i .1. .L .t ett

R3

0. AAA- 2000 350 25,000 15,000 4000 Ohms Ohms Ohms Ohms Ohms SS -CXXxJ t1 111111111

DIAGRAM OF RECEIVER AND POWER SUPPLY

1Un91m1111R,1,11-

www.americanradiohistory.com The Improved Knapp Ao Power Unit

OBTA I N I NG a satisfactory source in the choke construction and through of power for heating the filaments the use of an extra high -capacity, dry- of tubes in a radio receiver has electrolytic condenser. Another improve- been one of the chief problems confront- ment is found in the rotary switch which ing engineers since the early days of replaces the old- style, plug -type voltage broadcasting. Of course, from the electri- adjustment. The result of these changes cal viewpoint the storage battery is ideal is that the unit is not only more efficient for the purpose, but broadcast listeners electrically but it requires less space in and radio experimenters demand a device the cabinet. which is capable of providing equally sat- POWER UNIT VS. A. C. TUBES isfactory results and which does not re- quire constant attention. When a receiver BEFORE continuing further with this is operated with a storage battery it is article it might be wise to clear up necessary to recharge the battery and one point which probably has entered the add distilled water at quite frequent minds of many readers; namely, why intervals. should a power unit be employed for Filament -supply units consisting of a supplying filament current for d.c. tubes power transformer, rectifier and filter when it is possible to electrify a receiver system have proved to be one of the best with a power transformer, wiring harness, solutions to the A -power problem, and and set of a.c. tubes? Of course, both this article describes one of the most re- systems possess merit, but it is safe to cently developed devices of this type. It is say that the A -power unit provides the known as the Knapp A power, and was simpler and more "sure- fire" method of developed in the engineering laboratories the two, as in order to employ a.c. tubes of Knapp Electric, Inc., of Port Chester, it usually is necessary to make a number THE WITH IN N. Y. The unit is available as a kit, i.e., POWER UNIT METAL CASE PLACE of changes in the circuit as well as several in knocked -down form, and the infor- adjustments to reduce the hum. Also, the mation contained in this article relative to March, 1928, issue of RADIO BROADCAST an arti- arrangement of apparatus in a set may be such the electrical characteristics, assembly and cle entitled, "A New A -Power Unit" by Ralph that the constructor will not be able to eliminate operation of the device was supplied by the Barclay described an early model of the device the hum without considerable difficulty. manufacturer. now under consideration. This power unit has When comparing the cost of equipping and The Knapp A Power converts current sup- provided many readers with excellen t results, operating receivers with these two systems of plied by a standard u uo-volt a.c. line into a but the new model is improved considerably electrification several points must be taken into filtered 6 -volt d.c. supply, which is satisfactory and is capable of giving better performance, consideration. With the power-unit method the for the operation of standard radio tubes. The especially with modern receivers which employ cost of electrifying the set is limited to the cost rectifier and filter condensers of the unit are of amplifiers with better bass -note reproduction of the power unit, but when a c. tubes are the dry -electrolytic type, thus avoiding entirely characteristics. Also, in the July, t928, issue of installed it is necessary to buy a power trans- the usual maintenance operation of adding dis- RADIO BROADCAST the early model of this power former, wiring harness, volume control, voltage water tilled to the cells. Also, because of the unit was the basis of the power unit described in regulator, complete set of tubes, etc. With both enormous capacities which it is possible to ob- an article entitled, "An Interesting A -B -C- systems the current consumed from the 1 Io-volt tain with dry- electrolytic condensers, the a.c. Power and One by J. Unit -Stage Amplifier" line is about the same, but the cost of replacing hum is eliminated almost entirely in the filter George Uzmann. This article served to illus- tubes is two or three times as great when a.c. circuit and cannot be detected with the usual trate how any home-made or factory-constructed tubes are used. In both cost and simplicity it receiver. set could be electrified easily and inex- would seem, therefore, that the method of ob- From a practical viewpoint this A -power unit pensively. taining light- socket operation by the use of a has other advantages. When operated from a A glance at the pictures and diagram on these B -power unit in conjunction with an A -power I io-volt a.c. supply it may be employed to sup- pages shows how the new Knapp A power differs unit, is to be preferred to rewiring the receiver ply filament current to any standard home -made from last year's model. In the first place, it is for the use of a.c. tubes. A set will operate from or factory- constructed receiver using up to 8 completely enclosed within a metal case, more an A -power unit just as satisfactorily as from a tubes of the 2oIA type, or a combination of tubes pleasing in appearance and of more sturdy de- storage battery -and the power unit requires which requires a filament current of not greater sign. The electrical circuit has been improved no attention. than 2 amperes. The unit may be connected but is fundamentally the same as before. It was In an directly with the A binding posts of the receiver found that the general use of high -quality selecting A -power unit the amount of voltage without making any changes in wiring, and it is amplifier systems in 1929 receivers demanded current and which it will deliver at the connected with the house current by inserting a that the background of a.c. hum be reduced output binding posts is another important factor; is, plug in a wall receptacle. The efficiency of the still further than it was in last year's model, that it is necessary to makesure that an ample device is comparatively high; that is, it should and this improvement was effected by a change supply is available for heating the tubes of the not increase, the electric bill more than 25 or 5o receiver, notwithstanding normal line voltage cents per month. fluctuations. In this connection two graphs showing the voltage -regulation characteristics SIMPLE ELECTRIFICATION SYSTEM of the Knapp A -Power are given in Figs. 2 and 3. ANOTHER thing which should be pointed Fig. 2 shows the output voltages obtainable with out in connection with this power unit is the switch, SW2, set at each of the eight contacts that it provides the nucleus for converting any when the input potential is 116 volts. Fig. 3 d.c. receiver into a completely -electrified set. indicates the output of Marty excellent devices are available which pro- the power unit with the vide B and C potentials for the operation of all switch, SW2, on the types of receivers, thus the use of batteries may fifth contact when input be avoided entirely. Provision is also made in the potentials of 95, loo, unit for controlling the power to the B- supply los and IIo volts are unit with the switch employed for turning the A applied. power on and off; for this purpose a standard 110- The graphs described volt receptacle is included in the unit. above show that the Power units of the type described in this article power unit is capable of are not a new development; in fact, they have VIEW OF POWER UNIT supplying about two been in use generally for almost a year. In the WITH METAL CASE REMOVED amperes of rectified cur- 43

www.americanradiohistory.com 44 RADIO BROADCAST NOVEMBER, 1928

rent at a potential of six volts, or in other words brackets, front panel and steel box body. First, This precaution is necessary to insure the elimi- it will deliver ample power for heating the fila- the two choke coils, L1 and L2, are mounted in nation of all moisture which may have collected ments of eight tubes of the 2oIA, 112A or 171A place in the positions indicated in the picture. in the condensers. types. Secondly, it is shown that by means of Next, the transformer is fastened on the right Through experience it has been found that best the rotary switch, SW2, the voltage may be ad- side of the base opposite the choke L2 so that the results are obtained from the power unit when it justed to the proper value for receiver whether taps are on the front edge. However, before is used every day. On the other hand, if the the line voltage is above or below normal. mounting the transformer the primary leads receiver is not used for a week or two the power should be arranged so that they pass through unit should be disconnected from the set and CONSTRUCTION OF UNIT the top and they should be scraped free from operated for an hour without load. Also, the insulation. To complete the assembly of parts operation of the power unit may be improved THIS article has now reached the point where on the base the condensers are fastened in materially by operating it without the receiver I the construction of the A power unit may be place with their brackets, as indicated in the connected two or three hours each month. considered. The reader interested in building the picture. After long service it will be found that the out- power unit will find a complete list of the ap- The front panel of the power unit is supplied put voltage of the power unit will begin to de- paratus used in this new model at crease and it will be necessary to the end of this article. Also, there correct the control, Sw2, to a tap are two pictures which show the giving greater voltage. The rectifier appearance of the unit, and a com- unit will finally require replacement. plete schematic wiring diagram is It is a very simple task to put in a given in Fig. 1. new rectifier and these units are The picture of the completed 2 available at all radio stores. power unit shows clearly the out- In operating the power unit there Tot 0Vo s ward appearance of the device. All 60 Cycles is only one knob, Sw2, which may of the apparatus is housed within be adjusted and this controls the the metal case and the voltage - s output voltage of the unit. In control switch is regulated by the adjusting this control the proper knob on the right of the panel. The FIG. I. SCHEMATIC DIAGRAM OF THE POWER UNIT setting may be determined by plac- output binding posts are located in ing the switch at the lowest tap the center of the panel near the top, and with all necessary holes drilled and tapped, and which provides satisfactory performance, but a at the left of the panel is a receptacle for the mounting of parts requires only a few mo- much more satisfactory arrangement would be plugging-in the B socket -power unit. The metal ments' time. The receptacle for the B socket - to connect a o-lo volt d.c. voltmeter across the. box mounted on the front panel conceals power unit is first mounted in the large hole output binding posts of the power unit. The the rectifier unit, the cord on the left is for provided for it in the upper left corner, meter is particularly valuable in districts connection with the light socket and the cord the eight- contact switch is mounted in a where there are frequent variations in the on the right is equipped with a switch for turn- similar position on the right side of the panel, line voltage. . ing the unit on and off. and the output binding posts are located in the LIST OF PARTS Fig. I shows the complete wiring of the unit. two holes in the center of the panel near is having a secondary with the upper edge. T a power transformer THE following is a complete list of the ap- voltage R is a -wave The assembly of the rectifier mounting con- eight taps for control, and full paratus included in the Knapp A Power Kit' dry- electrolytic rectifier. The two heavy -duty tacts is very simple. Five holes are drilled in the choke coils, which are of identical construction, front panel for the contacts which are fastened T-One Power Transformer . are located at LI and Li, and the three dry - in place with nuts and washers. L1. L2 -2 heavy-duty a.f. choke coils electrolytic condenser units. also of similar de- The wiring of the unit is shown clearly in the CI, C2, Ca-3 Dry-electrolytic condensers sign, are connected at Cl, C2 and Ca. P is the diagram and an explanation of the connections R-One Elkon dry -electrolytic rectifier unit receptacle for the power lead from B -power unit, is hardly necessary. In wiring the complete SWI-One Pendant switch and cord SW1 is the off and on switch, and SW2 is the unit only eight feet of rubber -covered hook -up SW2-One Special 8 -point switch, knob and plate voltage control. wire is needed and, of course, the connec- P -I Receptacle for B unit 1 The actual construction of the power unit is tions should be soldered if best results are I Attachment cord and plug very simple. The assembly divides itself into desired. I Celeron front panel three major steps; viz, mounting parts on base I Base plate plate, mounting parts on front panel and as- OPERATION I Set of condenser brackets and clamp angles sembly of mounting contacts for the rectifier 1 Metal box and cover unit. After the parts have been mounted the AFTER the construction of the Knapp A I Rectifier cover wiring may be accomplished quickly and Power has been completed the wiring I Celeron connector strip easily. should be checked carefully, and then the unit I Rubber bushing The base plate for the power unit is die cast may be placed in operation. However, before 2 Output binding posts and has been drilled with all holes necessary for the unit is connected to a radio receiver it should I Roll of hook -up wire mounting the chokes, transformer, condenser be operated for at least an hour without load. Mounting screws, nuts, bushings, etc.

14 14 KNAPP A POWER KNAPP -A- POWER D.C.Output Power vs Regulation Curves A C. Line Voltage Curves A C. Line Volt'g =11C 12 Switch Tap E

10 \.\` - - 1 `-`. . T.+P % "arch -`... :... `=_ L`` f^.-. ft. « '\\. ....oft,. 110 ` 95 V. .t 2

o 15 5 15 25 LOAD IN AMPEFES 0 C LOAD IN AMPERES-0.0 4 b 8 10 2 4 6 8 ID NO OFkAMPTU8ES1201 A,112 A.171 A) NO OF 14 AMP TU8CS(201 A,112 A,171 A) FIG. 2. FIG.3. THESE GRAPHS SHOW THE OPERATING CHARACTERISTICS OF THE KNAPP A -POWER UNDER VARIOUS CONDITIONS

www.americanradiohistory.com An Amplifier and Power Supply for the "Vivetoney 29" By R. F. GL3ODWIIN

IN THE October number of this magazine the This method of voltage control is not auto- The audio portion incorporates two stages of writer introduced the "Vivetone 29" re- matic; it need not be, because line voltage varia- transformer-coupled audio amplification utilizing ceiver. Readers of the article will recall that tions seldom occur more than once or twice in the new Thordarson R -300 transformers. For the in the design of the tuner quality and efficiency 24 hours, with the exception of dark stormy days output a choke and condenser device is used to were the main objectives. These same qualities when the power station is heavily taxed. Under prevent the high voltage from damaging the are outstanding in the power supply and ampli- such conditions the voltage control, PR -o5o, is speaker windings. For the first audio stage a fier unit which has been designed to work type cx -327 tube is used, and in the last in conjunction with the tuner, which stage a Cx -310 power tube is required. and kilro is described in this article. The power supply portion utilizes a Power amplification is. of course, an Cr HE amplifier and power -supply unit described in this half -wave rectifier system using a cx -381 admitted necessity in the modern receiver. 1 article was designed especially for use in connection tube. The voltage required to operate this Radio entertainment is no longer a nov- with the "Vivetone 29" receiver which was presented in the tube is procured from a Thordarson R -210 elty or plaything, and radio builders and October issue of RADIO BROADCAST. However, equally suc- power pack. It supplies the high voltage owners now demand the quality of repro- cessful results may be obtained when the unit is connected for the plate of the rectifier and has two duction that comes only with power am- with other standard a.c. receivers. The amplifier of the unit filament windings, one for the rectifier plification and the use of an up-to-date employs two transformer-colpled stages with a 310-type tube and one for the 310 power tube. loud speaker, such as the dynamic cone. tube in the output circuit. t be power- supply circuit pro - There are also the two necessary filter This quality is assured in the Vivetone vides normal values of B potential for the receiver and am- chokes incorporated in the unit. amplifier by the use of a 310 tube in the plifier, as well as the necessary a.c. potentials for beating The low- voltage transformer, T -2445, output and a scientifically designed the filaments of the tubes. -THE EDITOR. which supplies the voltage for the 326 coupling device. .lt has enough reserve and 327 tubes and the pilot lamp, is also power to eliminate the danger of overload ee/ rather compact in design. It will be distortion, and it will be found that full noticed that this unit is mounted along- volume is seldom necessary for satisfactory decreased until the meter on the receiver panel side of the power pack, R -210. Next to it is reproduction in the home. reads one or two tenths be'ow the proper specified the filter condenser block, PL -575, a I2 -mfd. The power supply incorporated in the unit reading. unit properly divided with terminals placed so furnishes all the operating voltages for the am- Although it was designed especially for the as to simplify wiring. plifier and the tuner, and serves to make the en- "Vivetone 29" receiver, the amplifier power unit Since the entire layout of the parts is so clearly semble completely light- socket operated. One of can be used with other a c. tuners as an audio shown in the top view and the picture wiring the most important features of the power supply channel and power supply. It will operate ex- diagram, Figs. 2 and 3, it will be unnecessary is the incorporation in it of an adequate means cellently as a phonograph amplifier by connect- to give further details concerning their positions. of voltage control. This feature appears to have ing a good electrical pick -up unit across P and B OPERATION been neglected in most of the designs of our plus of the first -stage transformer. present all-electric receivers. ASTUDY of Fig. 1 and the figures in the CONSTRUCTION Practical control of voltage is accomplished in article in the October number of RADIO the Vivetone power unit with two low- resistance THE entire amplifier and power unit is con- BROADCAST (page 367 -368) illustrating the con- power rheostats, one being a 50-ohm voltage - structed on a baseboard measuring 8" in struction of the Vivetone 29 receiver, will show control rheostat, PR -o5o, which is connected in width and Io" in length. being Z" thick. The audio the constructor exactly how to connect the two series with the primaries of both the power trans- portion, as shown in Fig. 2 and 3, is mounted units for operation. The only operating adjust- formers, while the other is a o.2 -ohm rheostat, at the left -hand end of the baseboard and the ment that is necessary on the power unit is the PR -21o, which is connected in series with the supply portion on the right. A Micarta 8" by 20" adjustment of the voltage -regulating rheostats. I+ -volt secondary winding of the low -voltage panel is used to mount the necessary resistances, which is a very simple matter. transformer, T -2445 Fig. I shows the location and binding posts, a.c. outlet and speaker jack. To obtain smooth voltage regulation from the wiring of these parts. power unit is a simple Many may wonder matter. With all the why a rheostat was not specified tubes in their also connected in series respective sockets, all with the 2Z -volt wind- the leads of the re- ing. The reason is, first, ceiver correctly con- that the 21-volt wind- nected to their proper \ngs of these trans- posts on the power formers generally have unit, and an a.c. volt- the correct voltage, meter temporarily whereas the IZ -volt connected across the winding will be found heater terminals of the to deliver slightly detector tube socket more than its rating: (type 27 tube) the and second, the volt- house power is turned age- control rheostat on, the secondary will take care of any rheostat, PR -21o, change in line voltage turned entirely to the that would increase or left (full resistance), decrease the voltage of and the voltage con- the 2f -volt secondary trol rheostat, PR -o5o, or any of the other turned entirely to the voltages after they right. Allow the detec- have been once ad- tor tube about one justed. Therefore, only minute to heat up and one secondary rheostat then adjust the setting is required, which is FIG. 2 of the voltage control in the 11-volt circuit. Rear view showing layout of parts on baseboard rheostat, PR -o5o, until 45

www.americanradiohistory.com 46 RADIO BROADCAST NOVEMBER, 1928

O Input tally and electrically equivalent parts can be rR21o? 50711 OB+ made by the experienced set builder. -THE 90V. EDITOR.] 11 G`--'1,11,. B+ 2 -- 2 4s Cost of Parts -Not over $95.00 HP-010 ... OB T81 75 FP.6000 1 Thordarson filament -supply transformer type T-2245 1r5v. , I Thordarson power pack, type R -2 to O 1 A.c. I Thordarson choke coil, type R -196 2 Thordarson audio transformers, type R -3oo O 2.5V. Dubilier condenser block, type PL -575 0 }A.C. 1 Dubilier condenser, t mfd., No. 907 PR 210 I Dubilier condenser, 2.0 mfd., No. 9o3 11.5 V. I Centralab heavy -duty potentiometer to,000 A.C. ohms, type HP-oto I Centralab fourth -terminal potentiometer, 6000 ohms, type PF -6000 701 4T2445 I Centralab power rheostat, 5o ohms, type J PR-050 I Centralab power rheostat, o 2 ohm, type PR -210 t Ward Leonard resistor, to,000 ohms, No. I 40 4111 4111. 41W ler, 410-01. 4/10 411. Or 41111. 41* 40 411I 411111. 41111, 507-I 41 PR 05v Ward Leonard resistor, loco ohms, No. 507-14 1 Ward Leonard resistor, 225 ohms, No. FIG. I 507 -20 Schematic diagram of Viretone Power Unit I Benjamin five- prong, green top socket, No. 9036 t Benjamin four -prong, black top socket, the meter registers approximately 2 I-46 volts Vivetone receiver and power unit number one. No. 9040 (but not over 22 volts). Blueprints describing another power unit have t Benjamin four-prong, red top socket, No. The meter is then disconnected from the de- also been prepared. This unit consists of a push - 9040 I Yaxley junior jack, No. 701 tector socket and temporarily connected to the pull 3 to power amplifier utilizing a 327 in the I roll flexible "Braidite" wire filament terminals of one of the r.f. sockets. first stage, as in power unit number one, and a I roll Solid "Braidite" wire Then the position of the secondary rheostat, full -wave rectifying system using two 381 recti- Io Eby Binding posts PR -21o, is corrected until a reading of approx- fier tubes. This unit is suggested for those who I Westinghouse Micarta panel, II" x I I" imately 11 volts is obtained. With this done the require tremendous volume and wish to use I Westinghouse Micarta panel, 1" x 2" meter is connected permanently to the heater more than one speaker. I Westinghouse Micarta panel, 20" x 8" terminals of the detector socket. The setting of Nuts, screws, etc. LIST the secondary rheostat is then permanent and is OF PARTS For operating the unit in conjunction with an r. f. tuner, the following accessories are not to be disturbed. required: [The list below gives the parts used in the unit t Cunningham cx -381 rectifier tube To complete the regulation process, the proper described by the writer. Since all the parts are Cunningham cx -310 power tube B voltages be are to determined. To accomplish of standard design, the substitution of mechani- 1 Cunningham cx -327 tube this a high- resistance voltmeter would greatly simplify matters but for the benefit of those who have no meters the position of the arm of HP-oto . r69' on the power unit should be approximately half- way between both end terminals, whereas the arm of HP -6000 should be approximately three quarters of the way to theright(farthest from the negative end). The fourth terminal of PP-6000 should be approximately ; of an inch from the negative end terminal. This completes the regu- lation of voltages. Now if a line variation occurs it will be indi- cated by the a.c. voltmeter, and only the voltage control rheostat, PR -050, need be manipulated to compensate for the line variation. In other words, by increasing or decreasing the resistance of this control all the voltages, a.c. and d.c., will increase or decrease respectively. By keeping the a.c. meter at approximately 21 volts all these voltages will be permanently correct. In tuning the receiver there is really nothing difficult. After the current has been turned on, the tubes should be given at least a minute to heat up; then signals should come in with great volume and without hum. Should there be any noticeable hum it can be eliminated by correcting the arm position of the potentiometer, PP -o15, on the receiver chassis. It should be remembered that the arm of the resistor, PP-200o, on the set chassis should be approximately one third of the way from front end terminal when the condenser plates are completely meshed. Should the reader desire complete construc- PR210 tional blueprints or detail information concern- 110 V A.C. ing the function of the receiver they may be 507- I I obtained by addressing the writer in care of this INPUT B+ B+ B- magazine. The blueprints are priced at $1.o0 and 90v. 4V are sold at their actual cost, including postage. They consist of complete full -size wired layout FIG. 3 drawings, schematics, panel layouts, etc. of both Complete picture wiring diagrau:

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OUR Readers Suggest" is a clearing house base apart, when the solder is melted from the test is also simple and definite. Place two leads for short radio articles. There are many prongs. from the doubtful d.c_. source into a glass of interesting ideas germane to the science of radio C. S. TAYLOR, Ft. William, Canada. salt water. Bubbles will rise to the surface about transmission and reception that can be made clear both leads, but more bubbles will surround the in a concise exposition, and it is to these abbrevi- positive wire. ated notes that this. department is dedicated. While Receiving Without an Aerial some of these contributions are from the pens of THE writer has discovered that his particular professional writers and engineers, we particularly . Reducing Hum in the Detector solicit short manuscripts from the average reader Atwater -Kent receiver functions quite satis- describing the various "kinks," radio short cuts, factorily when operated without an aerial, the WHEN a combination of A and B and economies that he necessarily runs across from ground wire being connected to the antenna socket -power units is used with d.c. tubes, time to time. A glance over this "Our Readers Sug- post, and the ground post left unconnected. a slight amount of a.c. hum generally is present the that is acceptable. gest" will indicate material Operation is more selective and good volume is in the loud speaker output. This hum can be Photographs are especially desirable and will be had on fairly distant stations. Occasionally a reduced materially, if not eliminated, by con- paid for. Material accepted will be paid for on pub - lication at our usual rates with extra consideration variable condenser, in series with the ground necting a 3o-ohm potentiometer across the fila- for particularly meritorious ideas. lead, is effective. ment terminals of the detector tube. The grid -THE EDITOR. GEORGE N. CooK, Allenwood, Pa. return is then connected to the slider contact of the potentiometer, instead of to one side of the Bakelite Tube filament. When the potentiometer is adjusted Short -Wave Plug -in Coils to its mid -position, or approximately so, practi- Plate Coil cally all trace of a.c. hum should disappear. A 1.5- HE idea of using "dud" tube bases as a volt flashlight cell, connected as in the diagram, Grid Coil mounting for short -wave coils is certainly Fig. 2, will provide the positive or negative grid T a good one, but some fans seem to have bias required for the operation of 201A- or 2ooA- difficulty in making a really rigid job. The -Tube Base type tubes respectively. been use method illustrated in Fig. i has in in Supporting CHARLES D. SAVAGE, Portland, Ore. the writer's set for some time, and although the Collars coils are subject to a lot of rough usage, thby are just as strong and rigid as when first made. FIG. I. COIL KINK The solution to the difficulties associated with Tube-base plug -in coils of very rugged construction Reducing Hum in A.C. Sets may be made by mounting a bakelite tube on an old these coils is found in winding the coils them- the tube base. AGREAT deal of hum in an a.c. home - selves on separate forms rather than on the tube constructed set 'comes from parallel leads base. This also provides greater latitude in wind- and leads placed too close to the power trans- ing specifications. Polarity Indicators former. A simple way to overcome this difficulty The coils are wound on a piece of thin bakelite is to use the conventional automobile " BX" IS often necessary to find the polarity of a tubing somewhat larger in diameter than a tube cable for all filament wiring and then ground the ITline or pair of wires from a battery. In the base. Holes ;g inch in diameter are drilled 120° metal casing on these leads as well as the trans- absence of a meter the following methods may be apart around the bottom edge of the tubing to former shell. This trick has cured more than one used to determine the polarity of a source of admit a A machine screw. Holes are also drilled baulky set. direct current. and tapped 12o° apart about ; inch from top J. B. BAYLEY, Jersey City, N. J. edge of the tube base. The tubing is supported A small section of blueprint paper, such as from the base by small collars made of brass is used in reproducing mechanical drawings, STAFF COMMENT tubing, and cut just long enough to fill the space. should be moistened and the two leads brought The remedy suggested by Mr. Bayley will be The whole is held together with A round -head into contact with the surface. For voltages up effective in many cases. Shielding of the type he machine screws, as illustrated in Fig. 1. to one hundred, the leads should be separated suggests should always be used, as a precaution, After the coils are wound, they are given a about one -half inch; for higher potentials this in wiring a.c. amplifiers for television reception. coat of cement made of celluloid dissolved in distance should be increased correspondingly. size be obtained amyl acetate which insures the wire remaining When the two leads are removed there will be a Small BX cable can at any auto- mobile-supply store or large garage. tight. The number of turns to use is not specified, small bleached section where the negative lead as this information has appeared several times touched the paper. in RADIO BROADCAST and of course varies Another simple test for polarity can be made Improving Capacity Feed -Back with the tuning condenser with a potato. The potato is Regenerative Circuits and also with the diameter cut in half. Stick the two wires of the coil. The reader is re- to be tested into the freshly HAVE just built the adapter described in your ferred particularly to the de- cut surface, about one inch l July issue and, while 1 think it provides the scription of the Cornet receiver apart. In a short time you will last word in satisfactory performance, I observe of Lieutenant Wenstrom, which find that the potato has turned the presence of the familiar trouble of jumping appeared in September RADIO green around the negative suddenly into oscillation. The setting of the plate BROADCAST. wire. condenser is too critical for voice. It follows the Some readers may find diffi- J. B. BAYLEY, Jersey City, N.J. tuning condenser too closely, to say nothing culty in removing the vacuum of the fact that the dial setting of the tuning STAFF COMMENT tubes from their bases. The condenser is affected by changes in the coupling easiest method seems to be to The blueprint paper should condenser. This is an objection I have noted in poura little wood alcohol To -A" Un t be partially exposed before all receivers employing this system of oscillation through a small hole drilled in FIG. 2 being used for the test. The control. the base. After standing awhile When a.c. tubes are used this potato idea is an old one but However, as soon as a universal -range Claro- the cement will be softened simple circuit will often effect worth reprinting for the benefit stat was connected across the tickler, these ob- enough to pull the tube and a marked reduction in hum. of the new fan. 'The salt -water jections disappeared. The variable resistor be 47

www.americanradiohistory.com 48 RADIO BROADCAST NOVEMBER, 1928

1st.Audio to a comfortable degree, by means of the resistor, As these newer tubes draw only one -quarter Stage and the set always is tuned to approximately ampere filament current, naturally the filament - the same volume. supply winding on the transformer, which has been designed for a one -half ampere load, will Home -Made I.F. Transformers provide an increase in voltage, and soon ruin a quarter-ampere filament. This same effect has IN THESE days of cheap retail radio prices, also been found in battery sets where the audio l there are few pieces of apparatus that the fan tubes are controlled by a fixed resistor. will find it worth while to make. However, the The remedy is extremely simple. Shunt a 20- 1 intermediate r.f. transformers for a super- ohm resistor across the filament terminals of the heterodyne are an exception. Efficient trans- tube sockets, thereby adding another quarter- Insert Phones here when tuning formers may be made easily at a considerable ampere load to the circuit, and the tube will saving by the super-heterodyne enthusiast. then have a normal life. The following notes describe an intermediate Another trouble which I have run across is B+ transformer. designed for 201 or similar tubes, due to a low value of grid voltage on the tube. FIG. 3. SIMPLE OUTPUT CIRCUIT having a natural wavelength in the circuit of This is sometimes caused by a variation in the H ith this arrangement it is possible to change front about 2000 meters -giving a wide separation resistor which provides the voltage drop for the phones to loud speaker without disturbing the tun- between repeat tuning points on the oscillator negative bias. When this grid voltage is low, ing adtustnients. dial. the tube draws an excessive plate current, which Two discs of wood ; inch thick by 14 inches in soon lowers its electron- emitting characteristic. diameter and a wooden core ; inch thick by This can be prevented by adding sufficient re- comes the main control and should be mounted inch in diameter are required for each transform- sistance to the C-bias resistor, to bring the on the panel and the midget condenser, now an er. These pieces are assembled as in Fig. 4. grid voltage up to the proper value to balance auxiliary, is relegated to the sub -panel. The Small wire brads may be used to fasten the the plate voltage, which figure may be deter- over -all flexibility, ease of tuning, and reduction discs to the core. Before winding, two holes mined from the tube chart, supplied by the man- of body- capacity effects show a marked im- should be drilled in each disc, near the outside ufacturer of the tube. Probably an additional provement. for connecting terminals. loo -ohm unit would be good as a trial resistance. E. W. MATTHEWS, Augusta, Ga. The windings consist of aoo turns for the pri- I cannot recall a single instance of power tube STAFF COMMENT mary and 800for the secondary of number 32 s.c.c. failure, where the tube itself has been at fault. or enameled wire. The wire should be wound A. H. GOUD, S. Portland, Me. The control of regeneration by means of a haphazard fashion. First wind the primary over variable resistor connected across the feed -back STAFF COMMENT which place a layer of thin paper and then wind coil is not new, but it seldom is employed in on the secondary in the same direction as the If it is possible to locate conveniently the capacity -controlled circuits. However, as a resistor through which the filament current to matter of general principle, the use of a con- 7F- the power tube is fed (in the case of d.c. sets tinuously variable resistor, so connected in any I designed for the 171 tube), this can be.replaced regenerative circuit, will provide the smoothest i by a 4-ohm resistor, or any quarter- ampere possible regeneration. The resistor, as suggested, ,r-- y ballast resistor, with the same result. is connected directly across the terminals of the ti IN tickler coil. i__. Special Soldering Irons for Tuning -in With a Distant Difficult Jobs Loud Speaker SET- BUILDERS and repairmen are running continually into odd soldering jobs which REGENERATIVE detectors, followed by require a great deal of valuable time and are very two audio stages, are found in many mod- trying on the patience. A set of irons similar to ern and ancient receivers. When the speaker is F G. 4. DETAIL OF SPINDLE those illustrated in Fig. 5 will make soldering moved to some remote point, the operator is The coils of an intermediate frequency transformer less troublesome. confronted with the problem of tuning the set may be wound on this simple spindle. Heavy card - The general type, shown in diagram A, is may be used the end by the phones. This is easy enough to accom- board for pieces if desired. followed by the manufacturers of both electri- plish in itself, simply by plugging into the detector cally and externally- heated irons. jack, but it will be found, as a rule, that when primary. Boil the completed unit in paraffine Mounting the heads at right angles to the the phones are removed, the constants of the (make sure that the paraffine is not hot enough to shafts as shown in drawings B and C greatly plate circuit are so changed that the point of smoke) for about a half hour. Terminal posts facilitates working in out -of- the -way places. optimum regeneration is passed. and the set may now be inserted in the four holes drilled Drawing D shows a third modification with the may even break into oscillation. If we plug in the discs and marked PRIMARY, Plate and B head at a forty -five -degree angle to the shaft into the loud- speaker jack, we get unbearably plus, and SECONDARY, Grid and Filament. The making an arrangement that should do the trick loud signals which may injure the phones, to say start of the primary is connected to the B plus when all others fail. nothing of the ears! and the finish to the plate. The start of the A copper bar, one -inch square, was used for There are many what might be called "ortho- secondary goes to the filament and the finish to all the irons mentioned and found to be quite dox" ways of overcoming this difficulty, probably the grid. satisfactory. the simplest of which is shown in Fig. 3. The No matching of the transformers is necessary GEORGE W. LINN, New York City. value of the resistance R depends upon local as they were found to tune close enough. conditions. Between 5000 and Io,000 ohms will No filter circuit is required as the combination r--- 1e---1 fit most cases, but the best way, if you have a of two or three of these transformers provides -1f- Clarostat or Royalty or other make of variable a band -pass of about the correct width. ' high resistance handy, is to connect it at R, set R. W. TANNER, Springfield, Ohio. it to a comfortable volume of an average signal, % iI measure the resistance and buy a cheap power- Prolonging the Life of the 17iA i' J unit resistor near the value found, which is wired tAl (Bfr into place permanently. THE Laboratory Information sheet number W. BRUCE Ross, Westmount, P. O. 204, appearing in July issue of RADIO BROAD - CAST contained information concerning the STAFF COMMENT short life of the 171 -type tube, used in a.c. sets. A perhaps more universal and equally simple As a radio service man with considerable ex- arrangement for tuning with the telephone re- perience in servicing electric sets, I can name -Ig (D/ ceiver, is to shunt a Centralab modulator plug two causes for the trouble, other than fluctuating (C/ (or any variable resistor having a range between line voltage. one hundred and two thousand ohms) across the I believe that the greatest source of difficulty FIG. 5. SPECIAL SOLDERING IRONS telephone receivers and plug the phones into the arises from using 171A -and 371A- type tubes in Difficult soldering jobs are greatly facilitated loud speaker jack. The volume can be adjusted, sets w hich were designed for the 171 or 371 types. by using home -made irons of special design.

www.americanradiohistory.com THIS PICTURE- SHQWS THE ARRANGEMENT OF APPARATUS ON THE CHASSÏS OF THE RECEIVER The "Chronophase" ScreenoGrid Receiver

ElIT E. SMITH Aero Products, Inc.

WH the course of research, which was with a voltage amplification of about eleven per the "Chronophase" system that too great a undertaken for the purpose of deter- stage, which is provided by the "Chronophase" phase -angle difference in the dielectric would mining the best type of circuit arrange- stages. seriously affect the operation of the circuit. ment, as well as coil construction for the screen - An inspection of the picture will show that arid tube, left no doubt that the final method MECHANICAL DESIGN there are practically no connections on the top of evolved gave the optimum results not only with HAVING both the audio-frequency and the subpanel other than those running from the this tube but also with standard a.c. and d.c. radio-frequency amplifiers determined, it stators of the variable condensers to the No. 6 tubes, it was decided to proceed with the con- was now only necessary to design the receiver in terminals on the coils. The coils are mounted struction of a receiver utilizing this arrangement such a way that no serious losses would result in with three machine screws, and the o.001 -mfd. which, from its characteristics of adjusted phase the layout and construction. condensers between the plates of the tubes and relations, was called the "Chronophase." Always presuming that the coils and con- the taps on coils are connected to the mounting inasmuch as the "Chronophase" receiver was densers of a radio-frequency amplifier are of the screw between terminals 3 and 4 on the under- being planned to secure "DX" reception, through best quality obtainable, one of the most prolific side of the panel. A piece of flexible wire is at- strong local interference, it was decided that a sources of difficulty has been found to be in long tached to the top of this screw, the other end of signal strength of one per cent., fifty kilocycles leads, particularly in the grid circuits which are which can then be connected to whichever ter- on each side of the resonant frequency, was the prone to pick up unwanted signals. The plate minal of the coil gives the desired results as will maximum allowable. With an experimental set- leads come next in sensitivity to external in- be explained later. up entirely unshielded and with the coils fluences. In order to keep both of these as short separated by eight inches, it was found that such as possible, the arrangement of parts indicated in WIRING THE RECEIVER selectivity was secured by the use of two stages the picture was employed. Stators of the conden- AFTER making these connections, wire up of radio frequency utilizing a 20o-foot antenna sers, which perforce must be in the grid circuit the filament circuit, twisting the leads into approximately 5o feet high. anyway, are used as grid leads, allowing the a cable which more or less follows the outside Next came the question of audio-frequency placing of each tube very close to the subsequent lines of the sides and back of the panel. All fila- amplification. The most powerful audio equip- radio-frequency transformer, and permitting ment, B -plus, and C -minus wires can be twisted ment which can be built into a receiver, in most extremely short leads. A triple condenser with into the cable wherever convenient, but the plate instances, will employ a 171 -type tube which trimmers for compensating any slight differences and grid leads should always be kept free, with has an amplification factor of about three. With in capacity is used to tune the amplifier. It was the exception of the audio output lead which this tube in the last stage 65o milliwatts of un- deemed advisable because of antenna variations can be cabled with everything else. distorted output is obtained under proper load to put the midget condenser, used as a vernier for When the wiring job is completed the set can conditions when an alternating potential having the first stage, on the panel. A variation of this be tested out before being put into the cabinet a value of 281 volts r.m.s is impressed on the was required on both sides of the normal ca- by placing an old dial on the condenser shaft grid. A transformer recently has been made pacity of the condenser. and attaching the oscillation control and midget available of a type with a much flatter curve The illustration shows the complete layout condenser with flexible leads. The circuits should over the audible range than is ordinarily obtain- finally adopted for the receiver. The Central be balanced, as will be explained in another able and continuing the flat portion of this curve Radio Laboratories manufacture a special step - paragraph, after it is mounted in the cabinet by out beyond the audible range so that there will less variable resistance for the stabilizing control attaching the mounting pillars to the screws in be no loss of overtones and harmonics. These which can be adjusted to hair -line accuracy. the subpanel in such position that they will be transformers give a voltage amplification of 3, so The Allen -Bradley grid leaks used are built from exactly over the bottom holes in the cabinet. if we use a 2o1A -type tube in the first stage of the a solid block of non-hygroscopic carbon this unit Lower the set into the cabinet with the front end audio amplifier, we have an amplification factor is unaffected by weather changes, making it down and start the condenser shaft into the dial, between the detector output and the input to the possible to solder the grid leak permanently into and then dropping it back in until it fits into grid of the last audio tube of 3 x 8 x 3 or 72. place without using the ordinary grid -leak clips place. Now connect the flexible leads which were Since our tube required a maximum voltage of which are a fertile source of trouble, due to left for the midget condenser and resistance, 28.5 r.m.s. to secure its greatest possible output, oxidized and poor connections and consequent tighten up the screws in the holes in the bottom the corresponding detector output would have to noisy operation. of the cabinet and the set screw binding the dial be about 40o millivolts which is readily obtain- The fixed condensers were also selected with to the shaft, and the set will be ready for able following two stages of r.f. amplification great care, since they are in such a position in operation. 49

www.americanradiohistory.com 50 RADIO BROADCAST NOVEMBER, 1928

The matter of balancing up the set is not at all Using the particular receiver described in the In the Laboratory the difference between difficult but will require quite a bit of time. In article, on a 200-foot antenna, sufficient selec- operating the receiver at normal voltages and most cases, regardless of the type of tube used, tivity was obtained to bring in woc while WE BH those recommended by the Aero Products the set will be found to operate to the best ad- and wBBM were both in full operation, although Company was hardly noticeable, although this vantage with the antenna on tap No. 2, the first WEBH is located within a mile of the point where is evidently not true in all cases, since the Aero radio-frequency coil connected to tap No. 3, the set was tested. With the same adjustments Company advises that they obtained much and the second radio-frequency coil at tap No. I exactly, and during the same evening, the set better results with higher voltages. The disad- or tap No. 2. For a comparatively short antenna, brought in stations over a thousand miles distant vantage of using higher than the rated voltage on it may be desirable to put the tap the antenna with full loud- speaker volume. Over a short is that shorter tube life results. -THE EDITOR.] coil on No. 3 or No. 4, and for maximum selec- period of testing, stations on both coasts were tivity with a long antenna, tap No. 1 should be received. LIST OF APPARATUS used. The need for careful adjustment of both taps and trimmers on the multiple BALANCING PROCEDURE condenser cannot T H E following is the list of parts recommended be too strongly emphasized. If either adjustment I by the author of this article. Other parts of ASUGGESTED method of procedure for is not correct, there will be a pronounced lack of similar characteristics may be used if the con- balancing is as follows: selectivity and the receiver will probably bring structor desires. The coils are 2" in diameter, After connecting the taps as suggested, tune- in nothing but local stations. wound with 90 turns of No. 22 B & S d.c.c. wire in a station which will give a fairly weak signal air spaced .005 inches and tapped as shown on the when the set is not oscillating. Turn up the stabi- OUTPUT DEVICE NEEDED circuit diagram. The list price of the parts in lizer until the set oscillates. Then, with the set in kit form is $74.50. -THE EDITOR. oscillation, adjust the trimmer units on the two IT PROBABLY will be noticed that no provi- rear sections of the multiple condenser until sion has been made on this receiver for an C1, C2, C3 -I Aero gang condenser, .00035 -mfd., maximum volume is obtained, retuning to a output device. Many of the modern types of Type AE -2155 weaker station if necessary, so that while adjust- dynamic speakers contain a transformer and, C5 -1 Aero midget condenser, No. 940 ing, the volume is always kept at a comparatively accordingly, it is unnecessary or desirable to C6, C7, C10 -3 Aerovox mica condensers, .00l- low value. When perfectly balanced, the set have an additional transformer built into the infd. should go into oscillation with the stabilizer receiver. Furthermore, some builders prefer a C8 -I Aerovox mica condenser, .003 -mfd. about one third of the distance from minimum choke and condenser output coupling, while C9 -1 Aerovox mica condenser, .00025 -mfd, resistance, and should go in and out of oscilla- others are strongly in favor of an output trans- LI, L2, L3 -1 Aero coil kit, No. U -203 tion at the same point; that is, it should be un- former. So with the idea of leaving the receiver L3, L5-2 Aero NoSkip chokes, No. C-6o necessary after the set breaks into oscillation to as versatile as possible, the matter of output R1 -1 Aero variable resistor, Type AE250 retard the control beyond the point where it device was left to the builder. R2--1 Bradley Grid leak, 3- megohms went into oscillation to clear it up again. If Under no circumstances, however, should the set R3 -1 Daven ballast, No. 5 the set does not oscillate easily enough, raise the be used without some kind of satisfactory device R4 -1 Yaxley resistance, No. 810 tap on the detector input coil. If it oscillates too to keep the direct current from the loud speaker T1, T2 -2 Aero audio-frequency transformers, easily, reduce this to tap No. I. If insufficient windings. Type AE77o selectivity is obtainable even with the antenna [NOTE: The voltages suggested by the author Y -1 Yaxley cable connecter, No. 669 coil at tap No. 1, reduce the tapped portion of for use on the screen -grid tubes are higher than A -Aero split -brass bushings, S-1 the middle coil. With everything properly ad- those recommended by the manufacturers of Type justed, the removal of the cap from either of the these tubes. Normal screen -grid, control -grid, I National dial, Type E screen grid tubes should practically stop the set and plate potentials are 45, 1.5 and 135 volts, 3 Kurz -Kasch walnut knobs, No. 98 from operating, although if it is tuned to a respectively. The simplest way to get such volt- 2 Carter screen -grid connecters, No. 342 strong local station, the removal of the cap from ages to the proper places within the set is to con- 1 Eby Junior binding post the second tube may leave a trace of signal. nect the screen -grid leads to the blue 45 -volt 1 Aero cabinet, Type 400 Touching the first section of the tuning condenser lead which at present is connected only to 1 No. 20 drilled Formica base -panel with alt should completely stop operation. Touching the primary of the first audio transformer. To sockets, grid -leak clips, etc. mounted 135 on of it the second section should almost stop operation get volts the plates these tubes will 9 Kellogg solder connecters, No. 2 and touching the third stage, should reduce the be necessary to run a separatc lead to a 135 -volt 5o ft. Rubber -covered stranded hook -up wire volume considerably. source, or to operate the power tube at this 4 ft. Rosin -core solder If the set is lacking in volume, or if a continu- voltage when no change in the wiring will be 5 Aero S4 ous high -pitched whistle or growling note is necessary. The io -ohm resistor R4 should be mounting posts heard, a 1.0- or 2.o-mfd. condenser should be connected in the plus filament lead to the two 3 Aero S3 bakelite bushings connected across the B minus and B plus 180- screen -grid tubes instead of in the negative 1 Aero No. 3 screw assortment 7// 6 11 volt taps. lead. Brass machine screws R. H., N. P., 5á xßä Ant. ,_------7 0.000257 0.001 mfd 0.001 mfd VT mfd. / VT3 TI VT4 T2 VT5 i/ /VTi d / 2 IC' n 6 - 0 ó R 1 2 2 10 3 3 0.001 4 4 ., -+ mfd. B 5 5 mg. 1.1 10 ohms 4. R4 3 790 Gray - Green C -40 g 0.003 mfd. Blue +45...r , Brown B -C +Yellow -,I h turns No.22 D.C.C. -'7180 1.1 ° L 2 =L 3 =90 f Y Ground A -Black on 2mform.Taps at 5.10.18.30 turns \ ; Ai-Red-4

Speaker

FIG. I. COMPLETE SCHEMATIC DIAGRAM OF THE "CHRONOPHASE" RECEIVER

www.americanradiohistory.com Who Are the Fellows of the Institute? BY CARL DREHER

AFEW years ago, before industry deprived cently read through the list of members of all he has since come up for the grade of Fellow, me altogether of leisure, I was returning grades published in the 1928 Year Book to see however. More than one of the luminaries skip by train from a walking trip in the what the'74 indigenous Fellows did during their the Member grade, apparently. Stuart Ballan- country which had lasted several days and left business hours. Thirteen, I found, are engineers tine became a Fellow in 1928, also, rising from me with a coat of tan and a considerable growth employed by Radio Corporation, General Elec- Associate; he must be one of the youngest among of beard. The train boy, happening to speak to tric, and Westinghouse, and two are non -engi- the Fellows, but his recondite and brilliant re- me when I purchased some of his wares, began a searches deserve the honor. Harold H. Beverage sentence with the words, "All right, sir," but, remains a Member in the 1928 Year Book. Mr. glancing up at me as his lips formed the sibilant H. O. Boehme is also down as a Member ('15). of the respectful title, and beholding my sweater If you don't remember him, you don't remem- and beard, he changed it hurriedly to " Feller." ber the Atlantic Communication Company He was a class -conscious train boy. I reflected either, and if you don't remember the A. C. C. that the word Fellow has numerous meanings, you are no radio man. But where is the name and I could not tell whether he intended the of George H. Clark? He doesn't seem to be a one numbered in Webster 2. A companion; member of the Institute at all, these days. comrade; associate; contemporary or 3, An John M. Clayton, the Secretary of the Institute, equal in power, rank, character, etc.; or perhaps is a Member. Powell Crosley, Jr. is a Member. even 6, A man of low breeding or of little worth; H. P. Davis, the Vice -President of the West- but I bought the lemon drops anyway. inghouse Company, who is probably responsible Little did that snobbish youth know that the in greater measure for the existence of broadcast- term which he used disparagingly also has ing than any other man and who is an engineer learned associations, and, in scientific circles, to boot, is not listed. Dr. J. H. Dellinger was entitles one to all the honors of a bishop among elected a Fellow in 1923 and became President the men of God. Nevertheless, it is so, as he of the Institute in 1925. Carl R. Englund of the would see were he to consult the 1928 Year Book Bell Telephone Laboratories, one of the most of the Institute of Radio Engineers. Of a total brilliant controversialists in the Institute, was of 4200 members on December 1, 1927 (it is only an Associate in 1927; he has since been probably thirty or fifty per cent. greater by this elevated to the Fellow grade. C. L. Farrand seem- time), 3543 were resident in the continental ingly has no desire to rise above the Member United States, the Canal Zone, Philippine degree. A. H. Grebe, although a Manager for Islands, and Alaska, and of all these radio en- three years, remains an Associate. Similarly gineers and aspirants under the flag of the David Grimes. And ditto Charles A. Hoxie. So United States only 74, I ascertained by a statis- does Edward J. Nally, the first President of tical investigation, are Fellows. It is easy, if the Radio Corporation of America, modestly one is of normally good character, to become remain an Associate. Hudson R. Searing, an an Associate Member. Full Members, although electrical engineer who was one of the pioneers not born, may be made. But a Fellow! He is one among the New York amateurs, and Harry W. OF of the 2 per cent., and a rare zoological speci- CHIEF THE INSTITUTE Secor, who was writing radio articles during the men even at a meeting of the Institute. Contrary Dr. Alfred N. Goldsmith, president, years of radio antiquity, are both associates, to the advertisements celebrating the prevalence the Institute of Radio Engineers Mr. Secor since 1912, when the Institute was of a certain affliction, four out of five cannot even founded. Hendrik J. Van DerBijl, the author of hope to get it, and most of the remainder are neering employees of this group of companies. the well -known text on vacuum tubes, is a turned down by the Committee on Admissions, Ten are engineers for the American Telephone Member in South Africa. Irving Vermilya is a of which Dr. Frank Conrad was Chairman in and Telegraph Company. Seven are engineers Member also; ten years before there were broad- 1927, while Mr. R. A. Heising holds the helm for miscellaneous radio concerns. Six are con- cast listeners to be annoyed, he was a master of this year. In 1927 10 Members had the temerity sulting engineers. Eleven are executives. One is spark sets from one end of Long Island Sound to seek admission to the Fellow grade; six were in the sound-movie business. Two are definitely to the other. admitted, while four applications were denied. outside of radio in their business connections. On the same page of the Year Book one's eye One Fellow was elected directly. Professors of engineering or allied subjects at strikes the name of Manfred" von Ardenne, the The Constitution of the Institute provides universities number 6. There are 3 army or navy German baron who, as a radio engineer and that a Fellow shall not be less than thirty years officers, and 5 in civilian government positions. mathematician, was able to hold his own with of age. He may be elected under one of several In 6 cases no vocational information is given. some of the Fellows of the Institute during his provisions. If he is a radio engineer by profes- My object in printing this is to render some visit a year ago, but who is so young that he can sion, "he shall be qualified to design and take of the impassioned opponents of the big cor- only qualify as a Junior. Finally, among the responsible charge of important radio work; he porations privy to the hitherto unrevealed fact Z's, just before the name of Prof. Jonathan shall have been in the active practice of his pro- that over a third of the leading radio engineers Zenneck, the Fellow who came from Germany fession for at least seven years, and shall have of the country are already in the hands of these this year to receive the Institute's Medal of had responsible charge of important radio work octopi, and all of them may be swallowed unless Honor, there is Harold R. Zeamans, who ranks for at least three years." Asa professor of physical Congress does something about it. among the Associates, for he is a lawyer and not science or of electrical engineering he is subject Other interesting facts may be gleaned from an engineer, but for all that he is one of the old- to equally severe requirements, if he seeks the the Year Book. As they are published for all to est members of the organization and has been honor in that section. By "notable original work see, I may be permitted to comment on them presenting it with legal counsel since 1912. in radio science," inventions, or contributions without scandal. Note, that Major E. H. Arm- Thus there are great and prominent men to literature giving an applicant "a recognized strong, indubitably one of the genuinely great on the lower ranks of the hierarchy, as well as standing at least equivalent" to the above he men of radio, did not become a Fellow until among the Fellows. Prominent or not, they can may also hope to become a Fellow. Under these 1927. He could have been one any time after vote, speak their minds at the meetings, and provisions noted radio executives, like Mr. he wrote his classical paper on the vacuum preserve the Proceedings in their libraries. There Sarnoff and Mr. Young, are admitted to the tube, in 1915, or as soon thereafter as he became are, however, privileges which they do not en- august company of their own chief engineers, 3o years old. Why didn't he bid for the honor joy. Only the Fellows have the right to wear and,Ilike them, pay annual dues of $15, but they sooner? Maybe he just didn't give a damn; badges with blue lettering on a gold background, don't have to read the Proceedings unless they that would be like Armstrong. W. R. G. Baker, only Fellows may aspire to election to the offices want to. Managing Engineer of the Radio Department of President and Vice -President, and only Moved by a perhaps unseemly curiosity, I re- of General Electric, is still down as an Associate; Fellows are ipso facto famous.

51

www.americanradiohistory.com New Apparatus

fact, with a 15 -inch disc the motor may run up PRODUCTS of radio manufacturers whether to within 5o to 75 revolutions of synchronous new or old are always interesting to our speed which is 1800 RPM. In order to reduce readers. These pages, a feature of RADIO BROAD- this speed to what is required it is only necessary CAST, explain and illustrate products which have to place a series resistance in the circuit with a been selected for publication because of their special means of short circuiting about 15% of the total interest to our readers. This information is pre- resistance in the form of a key. For example, for pared by the Technical Staff and is in a form which a disc 15 inches in diameter, inch thick with a we believe will be most useful. We have, wherever e required of 1080 possible, suggested special uses for the device nnen- speed RPM there is required a tioned. It is of course not possible to include all fixed resistance of 16o ohms with a key shunting the information about each device which is avail- around 25 to 3o ohms. able. Each description bears a serial number "There is a means of obtaining somewhat and if you desire additional information direct more stable operation, which is to load the motor from the manufacturer concerned, please address a THE NATIONAL TWO -STAGE in some way (a flat disc is practically a friction- letter to the Service Department, RADIO BROAD- POWER AMPLIFIER less load), as for example, by a fan. If we place CAST, Garden City, New York, referring to the six small blades, 1 by 2 inches on the side of the serial numbers of the devices which interest you, scanning disc, we will have and we shall see that your request is promptly accomplished the single -phase, 1800-RPM motor for receiving handled. -THE EDITOR. result we are looking for; namely, a slight load sets employing 9- to 18 -inch aluminum scanning on the motor, enabling the operator to hold the Cala discs. The motor revolves 1750 RPM at full speed of the disc more nearly constant. The mo- load and a variable speed range of 750 to 1700 tor now requires only a 3o-ohm fixed resistance Two -Stage Power Amplifier for RPM is obtained with a 6o-ohm rheostat. Price. with approximately 5 ohms short circuited with A.C. or D.C. Operation $23 .00. a key, assuming a 15 -inch diameter disc is used Machined flange for scanning disc for all mo- and a speed of io8o RPM is desired." X71 tors. Price: $3.00. Device: NATIONAL PUSH -PULL AMPLIFIER. This Rubber -cushioned base. Price: $2.50. High Grade A.C. Meters is a complete two -stage transformer -coupled Manufacturer: Interstate Electric Company. power amplifier. It does not contain any power Application: This motor is of the induction type, X73 supply, but it may he light- socket operated by not relying upon a commutator, either for start- Device: PORTABLE NLTERNAT1NG-CURRENT IN- the use of a 227 -type tube in the first audio stage ing or running. Because of the fact that the motor STRUMENTS FOR LABORATORY USE. The Westing- and two 210- or 25o -type tubes in the output is placed in close proximity to the television house Company have recently developed a new stage, which is push -pull. An extra socket is amplifier, tiny sparks, such as are produced by line of portable alternating -current instruments provided so that those who desire may use a brushes sliding over the surface of a commutator for laboratory use. These instruments are oper- while the motor is running, would ated on the electric- dynamometer principle, con- create disturbing electrical To line waves, taining two stationary coils and a moving coil. which if picked up by the amplifier The unit shown on this page is a single -phase may cause distortion or fogging to (1 Slow Fast wattmeter. The unit illustrated has a case 1C such a degree that the sought for made of wood. However, they are now being Conden- Continuously variable Black Black ser resistance picture would be a failure. This manufactured with cases of built -up sheet mi- Box motor is silent in operation and carta. This construction of case is novel and free from hum, either of which 17-77- gives the units a great many advantages which Connect Color to Color affects the amplifier because of dis- wooden cases do not possess. The finish on the tortion lack of FIG. I. and clearness. The micarta case is that of burl walnut and is very circuit is given in Fig.i. hard, not easily scratched or marred like the Diagram shows method of connecting Baldor The following excerpt from one finish on the wooden case instruments. The dials motor with condenser block and a.c. line of the engineering Test Depart- of the instruments are metal under which is a ment Reports of the Interstate mirror so as to prevent parallax reading of the i 12A -type tube in the first stage and operate Electric Co. is of interest: "The scanning discs as knife -edge pointer. The scale is 51" long with the amplifier from a storage battery. Resistances used to-day for television reception are anywhere quite uniform markings throughout. Although are contained within the device so that the proper from 9 to 24 inches in diameter, and ore inch the design of these instruments is primarily for C -bias potential is supplied automatically to thick, usually of aluminum. These discs, may be alternating current use they can be used on di- the tubes. The unit is wired completely. driven by an M2V, 'SHP; Baldor motor, which rect current and are just as accurate as on alter- Manufacturer: National Company, Inc. Price: has ample power for this purpose. As a matter of nating current when the average of the direct $40.00 completely wired but without tubes. and reverse readings are taken. The instrument Application: The amplifier may be used readily element has an iron shield around it so as to in conjunction with radio tuners or it may be make it immune from external stray magnetic used with a phonograph pick -up for the electrical fields. The accuracy of the instrument is 4 of i reproduction of phonograph records. It may also per cent., of full scale deflection. The terminals be used to replace poor audio systems in old supplied on the instruments are non -removable, sets, thereby improving the quality of the engraved with the scale value and have large reproduction. contact surface. Ammeters are made in double -scale ranges Improved Motor for Television from z to 30 amperes in capacities multiple of 2. The voltmeters are also made in double ranges of 72 multiples of 2 capacities, from 3 volts to Goo Device: BALDOR BALL -BEARING MOTOR. These volts. The double range o-3 and o-6 volts or o -71 motors are intended for use in television receivers and 0 -15 volts are particularly desirable for mea- for driving the scanning disc. Two types are suring the filament voltages of the radio tubes in available. laboratory testing. The instruments are also pro- Type Y I V is a ö -H P, r i o-Volt, 6o-cycle, vided in single -phase wattmeters with voltages single -phase, 1800-RPM motor designed for as low as 3o volts up to Goo volts and currents receiving sets using a 24 -inch scanning disc. It is from z ampere up to 3o amperes. designed to maintain a constant speed between Manufacturer: Westinghouse Electric and Manu- 750 and 1700 RPM with a 5- to 45-ohm variable facturing Company. resistance. Price: $30.00. NEW PORTABLE METER MADE Application: The usefulness of such instruments Type M2V is a ls -HP, I to -Volt, 6o- cycle, BY WESTINGHOUSE in any electrical laboratory is obvious. The 52

www.americanradiohistory.com ' NOVEMBER, 1928 NEW APPARATUS 53

ranges being manufactured cover all values of volts. Tap B4 is the 45 -volt tap current, voltage, and wattage ordinarily dealt capable of supplying a range of with in radio work. voltages from 20 to 55. Tap B5 is the negative B. Tap C6 is the low An Adjustable Resistor Network for voltage C terminal and it will B -Power Units supply a grid bias from minus 1 to minus 20 volts. For higher C X74 biases tap C7 is used. It supplies Device: TRUVOLT DIVIDER. A compact unit con- voltages from minus 20 to minus sisting of a network of resistances mounted in a 4o. The connection of this device small nicely finished container and designed to a typical B power unit is in- for use in conjunction with all types of B -power dicated in Fig. 2. units delivering voltages not in excess of 220. It Because the resistances used in permits one to obtain readily output voltages of this divider are of a type which various values between o and 18o and to also can be accurately calibrated it is obtain two values of C voltage. It can be used possible by the use of either tables with any type of rectifier or filter circuit. or curves to adjust the various Manufacturer: Electrad, Inc. Price: $12.50. controls to give the proper volt- Application: The problem of obtaining from the ages without the use of a volt- output of a B -power unit the correct voltage for meter. If a voltmeter is available, application to any given receiver is a serious one. it of course affords a simple, rapid, Fixed resistances across the output of a B -power and certain method of adjusting unit have the disadvantage that the voltage the unit. The voltmeter is shunted which will be delivered from the various taps between that particular tap which varies considerably according to the amount of is being adjusted and the negative current drawn from these taps. The use of varia- B and the control varied until the ble resistances for each tap has the disadvantage correct voltage is supplied. This that the range of voltage which can be delivered test is, of course, made with the RADIO TEST SET MADE BY SUPREME from each resistance is very wide and therefore receiver connected to the unit. INSTRUMENT CORP. rather difficult to adjust accurately. A compro- Many experimenters desiring mise between these two is probably the best. to use this device will prob- We therefore make use in the Truvolt Divider of ably not have available a high-resistance and high- resistance joints in any parts of the the combination of fixed and variable resistances voltmeter; for them it would be helpful to circuit. so that the voltage from each tap is approxi- have the booklet supplied with the divider, The instrument contains a complete set of mately fixed but can be varied over a range suffi- which describes in detail how to adjust the re- tools with space for spare tubes. The supplies ciently wide to adapt the unit to practically any sistors for any given receiver. This booklet, include a rachet screw driver, soldering iron, receiver. This might be called a universal divider which is called the Truvolt Divider Manual, is hook-up wire, various adapters, test leads, etc. since it can be used interchangeably with any not only very helpful in adjusting this device, The instruments in the tester are: a double - receiver and any power unit and can be adjusted but also contains a great deal of excellent in- range milliammeter, o-5o and o-loo; a triple - to supply the correct voltages to the set. The formation in connection with the output circuits range voltmeter, o -to, o-5o, and o-250, and a unit will find application not only in the con- of a B -power unit. triple -range a.c. voltmeter, o-3, o -18 and o-15o. struction of new power units but in conjunction The photograph illustrates the Model 10OA with old power units which perhaps deliver in- Useful Tester for Radio Sets instrument priced at $108.5o. correct voltages or have not sufficient voltage Manufacturer: Supreme Instrument Corporation. taps. Also by using the Truvolt Divider we can X 75 Application: Indicated above. It should prove obtain from a power unit that ordinarily de- Device: SET TESTER. This tester is designed to invaluable to service men. livers only B voltages two values of C voltages as aid in servicing all types of a.c.- and d.c.- operated well as the B voltages. receivers. The following paragraphs indicate Hook -up Wire for Various Uses The Truvolt Divider is designed to supply four some of the tests which may be made. B voltages and two C voltages. The voltage ob- In balancing the various tuning condensers in x76 tained from the Bt tap is the maximum voltage a single -control receiver the tester is very useful. Device: CELATSITE HOOK -UP WIRE. The follow- from the B -power unit. Tap B2 supplies an This test is made by placing a tube in one of the ing kinds can be obtained average voltage of 135 but this voltage can be sockets of the tester and inserting a plug into 1. Celatsite Flexible Wire. A flexible hook -up adjusted to any value between 1 to and t6o volts. the power-tube socket of the receiver, thus con- wire consisting of tinned stranded copper wire Tap B3 supplies an average of 90 volts which can verting the tester into an oscillator. When these covered with a non -inflammable insulation. be adjusted between the limits of 65 and i to connections are made, and the set is turned on, Available in the following colors and wire sizes. it will be found that the milliammeter in the No. 22 -$ .7o per 25 -ft. > > ,n ó tester will jump as the No. 20- .75 " " 11oV. v o+ set is tuned to resonance No. 18- .8o " No. Loo A with the oscillations 16- " No 14- 1.00 " " produced by the tester. Colors: Black, Yellow, Red, Green, Brown, Each individual tuning Slate, Blue, White, Maroon. 0 condenser is then ad- MM justed to resonance, as 2. Celatsite twisted wire for a.c. filament indicated by the move- circuits. One strand of Red and one strand of .1 ment of the meter. Black No. 18 Flexible Celatsite twisted together. B5 B4 B3 B2 B1 The tester will mea- The two colors are used so that, if desired, the N 8 Mfd. sure the normal emis- same sides of all filaments can be maintained at BH mi. !. +OM sion, and the emission the same relative potential. Packed in 25 ft. > 0.1 2 Mfd when oscillating, of all coils. List price: $1.75 per carton. Mfd 3. Solid Celatsite wire. Bus -bar made of Ñ _ types of tubes. In addi- 2 Mfd. tion it will indicate the tinned No. 14 copper wire and covered with a - C7 C6 - plate voltage, grid volt- non -inflammable insulation. Strips easily for age, and filament volt- soldering. Available in same colors as the flexible age of each tube of a wire. Price; $.o9 per 3o -inch length. set, both under load con- Manufacturer: Acme Wire Company. r and no load. The above material has been used -40V. -9V. dition with Application: Another important in the Laboratory for some time in constructing FIG. 2. application is the detec- receivers and power units and has been quite Method of connecting Truvolt divider in a B -power unit tion of open, short, satisfactory.

www.americanradiohistory.com 108. VACUUM TUBES -Operating characteristics of an a.c. tube with curves and circuit diagram for connection in converting various receivers to a.c. operation with a Manufacturers' ooklets four-prong a.c. tube. ARCTURUS RADIO COMPANY. 112. HEAVY-DUTY RESISTORS -Circuit calculations and data on receiving and transmitting resistances for a variety to Radio and Allied of uses, diagrams for popular power supply circuits, d.c. re- A Varied List of Books Pertaining sistors for battery charging use. WARD LEONARD ELECTRIC the Accompanying Coupon COMPANY. Subjects Obtainable Free With 113. CONE LOUD SPEAKERS -Technical and practical in- formation on electro- dynamic and permanent magnet type cone loud speakers. THE MAGNAVOX COMPANY. lbe booklets listed below by us- 89. SHORT -WAVE TRANSMITTING EQUIPMENT. Data and may obtain anyof all popular short-wave 114. TUBE ADAPTERS -Concise information concerning READERScoupon printed on Ibis page. Order by number only. wiring diagrams on construction of ing the transmitters, operating instructions, keying, antennas; in- simplified methods of including various power tubes in formation and wiring diagrams on receiving apparatus; data existing receivers. ALDEN MANUFACTURING COMPANY. high- work. I. FILAMENT CONTROL -Problems of filament supply, on variety of apparatus used in frequency 115. WHAT SET SHALL I Bu1LD ?- Descriptive matter, voltage regulation, and effect on various circuits. 1928 re- RADIO ENGINEERING LABORATORIES. with illustrations, of fourteen popular receivers for the home vised booklet, with circuit diagrams of popular kits. RADIALL 90. IMPEDANCE AMPLIFICATION -The theory and prac- constructor. HERBERT H. FROST, INCORPORATED. COMPANY. tice of a special type of dual- impedance audio amplification 118. RADIO INSTRUMENTS. CIRCULAR "J"-A descrip- COMPANY. 5. CARBORUNDUM IN RADIO -A book giving pertinent are given. ALDEN MANUFACTURING tive manual on the use of measuring instruments for every data on the crystal as used for detection, with hook -ups, and 92. RESISTORS FOR A. C. OPERATED RECEIVERS -A radio circuit requirement. A complete listing of models for a section giving information on the use of resistors. THE booklet giving circuit suggestions for building a.c. operated transmitters, receivers, set servicing, and power unit con- CARBORUNDUM COMPANY. receivers, together with a diagram of the circuit used with trol. WESTON ELECTRICAL INSTRUMENT CORPORATION. rectifier tube. CARTER RADIO COM- 12. DISTORTION AND WHAT CAUSES IT -Hook-ups of the new 400-milliampere 120. THE RESEARCH WORKER -A monthly bulletin of resistance -coupled amplifiers with standard circuits. ALLEN - PANY, interest to the engineer and home builder. Each issue con- BRADLEY COMPANY. tains special articles on radio design and construction with 15. B- ELIMINATOR AND POWER AMPLIFIER-Instruc- nnmumnr7 ,I, 111, 1 innminn .nn,nnnnnrnnnnnnm7nnnn,m, 1171111 111111711117117171111111111111M11111111.01111 special emphasis on resistors and condensers. AEROVOX tions for assembly and operation using Raytheon tube. WIRELESS CORPORATION. I GENERAL RADIO COMPANY. I21. FILTER CONDENSERS-Some practical points on the 15a. B- ELIMINATOR AND POWER AMPLIFIER- Instruc- Radio Broadcast manufacture and use of filter condensers. The difference be- tions for assembly and operation using an R. C. A. rectifier. tween inductive and non -inductive condensers. POLYMET GENERAL RADIO COMPANY. Laboratory Information Sheets MFG. CORP. 17. BAKELITE -A description of various uses of bakelite 123. B SUPPLY DEvICES- Circuit diagrams, characteris- in radio. its manufacture, and its properties. BAKELITE (Nos. 1 -190) tics, and list of parts for nationally known power supply CORPORATION units. ELECTRAD, INC. 22. A PRIMER OF ELECTRICITY-Fundamentals of in of 124. POWER AMPLIFIER AND B SUPPLY -A booklet electricity with special reference to the application dry giving several circuit arrangements and constructional and uses. Constructional data on buzzers, cells to radio other information and a combined B supply and push -pull audio NATIONAL CARBON COM- BOUND VOLUMES automatic switches, alarms, etc. amplifier, the latter using 210 type tubes. THORDARSON PANY. ELECTRIC MFG. CO. 23. AUTOMATIC RELAY CONNECTIONS-A data sheet Ask any news dealer for "Radio Broadcast Data 125. A. C. TUBE OPERATION small but complete showing how a relay may be used to control A and B cir- or to the -A Sheets" write direct Circulation Depart- booklet describing a method of supply a.c. CUits. YAXLEY MANUFACTURING COMPANY. filament for tubes. ment, Doubleday, Doran & Co., Inc. See page 56 THORDARSON ELECTRIC MFG. CO. 30. TUBE CHARACTERISTICS -A data sheet giving con- for further details. Price $1.00 stants of tubes. C. E. MANUFACTURING COMPANY. 126. MICROMETRIC RESISTANCE-HOW tO use resistances for: Sensitivity control; oscillation control; volume control; 132. METERS FOR RADIO-A catalogue of meters used in Wmn,n,nmm11,mnminnnnun17mmnn"mwmm11717a,nwnnini11nnn,innnnimm11minnnmmiunnn111anueinm. regeneration control; tone radio, with diagrams. BURTON -ROGERS COMPANY. control; detector plate voltage control; resistance and impedance coupling: loud speaker PORTABLE METERS booklet 33. SWITCHBOARD AND -A control. etc. CLARGSTAT MFG. CO. giving dimensions, specifications, and shunts used with 95. Resistance Data -Successive bulletins regarding various meters. BURTON -ROGERS COMPANY. the use of resistors in various parts of the radio circuit. 129. TONE -Some model audio hook -ups, with an ex- the pro r use of transformers and chokes. 37. WHY RADIO IS BETTER WITH BATTERY POWER-Ad- INTERNATIONAL RESISTANCE COMPANY. of ANGAMO ELECTRIC vice on what dry cell battery to use: their application to 98. COPPER SHIELDING-A booklet giving information Splanation radio, with wiring diagrams. NATIONAL CARBON COMPANY. on the use of shielding in radio receivers. with notes and 130. SCREEN -GRID AUDIO AMPLIFICATION -Diagrams 46. AUDIO- FREQUENCY CHOKES -A pamphlet showing diagrams showing how it may be applied practically. Of and constructional details for remodeling old audio ampli- positions in the circuit where audio -frequency chokes may special interest to the home constructor. THE COPPER AND fiers for operation with screen -grid tubes. THORDARSON be used. SAMSON ELECTRIC COMPANY. BRASS RESEARCH ASSOCIATION. ELECTRIC MFG. CO. 47. RADIO-FREQUENCY CHOKES -Circuit diagrams il- 99. RADIO CONVENIENCE OUTLETS-A folder giving 131. THE MERSHON CONDENSER-An illustrated book- lustrating the use of chokes to keep out radio-frequency diagrams and specifications for installing loud speakers in let giving the theory and uses of the electrolytic condenser. currents from definite points. SAMSON ELECTRIC COMPANY. various locations at some distance from the receiving set, AMRAD CORPORATION. also antenna ground and battery connections. YAXLEY 48. TRANSFORMER AND IMPEDANCE DATA -Tables giv- 132. THE NATIONAL SCREEN -GRID SHORT-WAVE RE- ing the mechanical and electrical characteristics of trans- MANUFACTURING COMPANY. CEIVER- Constructional and operating data, with diagrams formers and impedances. together with a short description of loi. USING CHOKES -A folder with circuit diagrams of and photographs. JAMES MILLEN. their use in the circuit. SAMSON ELECTRIC COMPANY. the more popular circuits showing where choke coils may 133. THE NATIONAL SHIELD -GRID FIVE-A circuit dia- 53. TUBE REACTIVATOR- Information on the care of be placed to produce better results. SAMSON ELECTRIC COMPANY. gram with constructional and operating notes on this re- vacuum tubes, with notes on how and when they should be ceiver. JAMES MILLEN. reactivated. THE STERLING MANUFACTURING COMPANY. 102. RADIO POWER BULLETINS- CirCUit diagrams, 134. REMLER SERVICE BULLETINS regular service for VARIABLE CONDENSERS bulletin theory constants, and trouble-shooting hints for units em- -A 56. -A giving an the professional set builder, giving constructional data, various condensers together with their character - ploying the BH or B rectifier tubes. RAYTHEON MANU- analysis of and hints on marketing. GRAY & DANIELSON MFG. Co. istiCS. GENERAL RADIO COMPANY. FACTURING COMPANY. 104. CONTROL RADIOBUILDER periodic 57. FILTER DATA -Facts about the filtering of direct OSCILLATION WITH THE " PHASATROL"- 135. THE -A bulletin giving ad- and current supplied by means of motor -generator outfits used Circuit diagrams, details for connection in circuit, and vance information,i constructional operating data on with transmitters. ELECTRIC SPECIALTY COMPANY. specific operating suggestions for using the "Phasatrol" S -M products. SILVER -MARSHALL, INC. as a balancing device to control oscillation. ELECTRAD, 58. How TO SELECT A RECEIVER common -sense 136. SILVER MARSHALL DATA SHEETS-These data -A INCORPORATED. booklet describing what a radio set is. and what you should sheets cover all problems of construction and operation on expect from it. in language that anyone can understand. 105. RECEIVING AND TRANSMITTING CIRCUITS. Con- Silver- Marshall products. SILVER -MARSHALL, Inc. struction booklet with data on 25 receivers and transmitters DAY -FAN ELECTRIC COMPANY. 139. POWER UNIT DESIGN -Periodical data sheets together with discussion of low losses in receiv r tuning cir- on 67. WEATHER FOR RADIO --A very interesting booklet power unit problems, design, and construction. RAYTHEON cuits. AERO PRODUCTS COMPANY. on the relationship between weather and radio reception, MFG. CO. with maps and data on forecasting the probable results. 140. POWER UNIT PROBLEMS -Resistance problems in TAYLOR INSTRUMENT COMPANIES. power units. with informative tables and circuit diagrams. 69. VACUUM TUBES -A booklet giving the characteris- ELECTRAD, INC. tube types a short tics of the various with description of In sending the coupon below, make sure that your name AUDIO POWER UNITS be the list 141. AND -Illustrated descriptions where they may used in circuit; of American and and address are included and are plainly written. Also of power amplifiers and power supplies, with circuit dia- Canadian broadcast stations. RADIO CORPORATION OF make sure that the listing of booklets from which you grams. THORDARSON ELECTRIC MFG. CO. AMERICA. choose is that of the latest issue of the magazine, as Radio OF VOLUME AND VOLTAGE 72. PLATE SUPPLY SYSTEMS. Technical information on delivery not 142. USE CONTROLS. A com- Broadcast cannot guarantee the of booklets data on useful audio and power systems. Bulletins dealing with two-stage listed in its current issue. plete booklet with apparatus and circuits for transformer amplifier systems, two-stage push -pull, three - application in receiving, power, amateur transmitter, and phonograph pick -up CIrcUIts.CENTRAL RADIO LABORATORIES. stage push -pull, arallel push -pull, and other audio ampli- ,11n111n11.n7,n,n1,n7,1,7,m7nn1,nnnm,n71177,:1,n1,1nm7,7"11m,17,m,,a1,,,111,11,m,717,7 1,n,.,,7.L,7n-n,nn, fier, plate, and filament supply systems. AMERICAN TRANS- 143. RADIO THEORY. Simplified explanation of radio FORMER COMPANY. USE THIS BOOKLET COUPON phenomena with especial reference to the vacuum tube, 73. RADIO SIMPLIFIED -A non- technical booklet giving with data on various tubes. DE FOREST RADIO COMPANY. pertinent data on various radio subjects. Of especial in- RADIO BROADCAST SERVICE DEPARTMENT 144. A.C. DETECTOR TUBE. Data on characteristics and Garden N. Y. terest to the beginner and set owner. CROSLEY RADIO COR- RADIO BROADCAST, City, ; O eration of 2.5 -volt a.c. detector tubes. ARCTURUS RADIO book- PORATION. Please send me (at no expense) the following COMPANY. lets indicated by numbers in the published list above: 76. RADIO INSTRUMENTS -A description of various 145. AUDIO UNITS. Circuits and data on transformers meters used in radio and electrical circuits together with a and impedances for use in audio -amplifier circuits. plate and short discussion of their uses. JEWELL ELECTRICAL INSTRU- output impedances and special apparatus for use with dy- MENT COMPANY. namic speakers. SANGAMO ELECTRIC COMPANY. 78. ELECTRICAL TROUBLES -A pamphlet describing the 146. RECEIVER CIRCUIT DATA. Circuits for using re- use of electrical testing instruments in automotive work sistances in receivers, and in power units with descriptions of combined with a description of the cadmium test for stor- other apparatus. I I. I I. FROST, INC. storage age batteries. Of interest to the owner of batteries. 147. SUPER- HETERODYNE CONSTRUCTION. Construction BURTON ROGERS COMPANY. and operation of a nine-tube screen -grid super-heterodyne. BETTER TUNING booklet 81. -A giving much general in- IName SET BUILDERS' SUPPLY COMPANY. formation on the subject of radio reception with specific (Number) (Street) illustrations. Primarily for the non-technical home con- i 148. SHORT-WAVE RECEIVER. Constructional and opera- on a short -wave receiver. structor. BREMER -TULLY MANUFACTURING COMPANY. Address tion data four -tube KARAS ELEC- 84. FIVE -TUBE EQUAMATIc-Panel layout, circuit dia- (City) (State) TRIC COMPANY. grams. and instructions for building a five-tube receiver. to- LLL 149. FIVE -TUBE SCREEN -GRID RECEIVER. Blueprint gether with data on theoperationoftuned radio-frequency with full constructional details for building a broadcast re- transformers of special design. KARAS ELECTRIC COMPANY. ceiver using two screen -grid tubes. KARAS ELECTRIC COM- 88. SUPER -HETERODYNE CONSTRUCTION -A booklet giv- ORDER BY NUMBER ONLY PANY. ing full instructions, together with a blue print and necessary This coupon must accompany every request. R B 11 -28 150. FIVE -TUBE A.C. RECEIVER. Blueprint for con- data, for building an eight -tube receiver. THE GEORGE W. structing a five -tube a.c. receiver employing the "equamatic WALKER COMPANY. nmm11inuninnnma.innnm.nnnnnlmnninnmm111munmmmm71inmm11,nnxmimmm111i7num1ninim system:" KARAS ELECTRIC COMPANY. 54

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www.americanradiohistory.com 56 RADIO BROADCAST ADVERTBER The Radi® roadcast Here's the Answer LA ORATORY INFORMATION to every question about the SHEETS principles, methods, or apparatus of radio trans- `rHE aim of the Radio Broadcast Laboratory Information Sheets is to present, in a mitting and receiving. f convenient form, concise and accurate information in the field of radio and closely allied sciences. It is not the purpose of the Sheets to include only new information, but to present practical data, whether new or old, that may be of value to the experimenter, set THE builder or service man. In order to make the Sheets easier to refer to, they are arranged so that they may be cut from the magazine and preserved, either in a blank book or on 4" x 6" filing cards. The cards should be arranged in numerical order. RADIO Since they began, in June, 1926, the popularity of the Information Sheets has increased so greatly that it has been decided to reprint the first one hundred and ninety of them (June, 1926 May, 1928) in a single substantially bound volume. This volume, "Radio MANUAL Broadcast's Data Sheets" may now be bought on the newsstands, or from the Circulation A Complete Course in Department, Doubleday, Doran & Company, Inc., Garden City, New York, for $I.00. Inside each volume is a credit coupon which is worth $1.00 toward the subscription price Radio Operation of this magazine. In other words, a year's subscription to RADIO BROADCAST, accompanied In a Single Volume by this $1 .00 credit coupon, gives you RADIO BROADCAST for one year for $3.00, instead of the usual subscription price of $4.00. A Handbook for Students -THE EDITOR. Amateurs Operators Inspectors For the first time an No. 233 RADIO BROADCAST Laboratory Information Sheet November, entire course cf train- 1928 ing in one book-the most complete and Balancing Radio Receivers up- to-date work on radio. Developed simply and clearly AN EASY METHOD rent of the detector tube will decrease if the former from the elementary arrangement is used and increase with a C- battery stage right through THE change in the plate current of the detector detector circuit, the amount of the increase or de- all phases of princi- tube, when a signal is being received, may be crease being proportional to the strength of the sig- ples, practise, and ap- utilized to balance the various tuned circuits in a nal -the stronger the signal the greater the change paratus so that a be- single -control receiver. If the several tuned circuits in current. Therefore, when the set is accurately ginner with noknowl- in a multi -stage r.f. amplifier are not properly tuned and all of the_condensers are perfectly aligned edge of electricity ganged, the set will be in- the deflection of the meter - may get all he needs either for sensitive and the selectivity and therefore the output of amateur operation or to qualify will be poor. It is essential, the set -will be greatest. for a government license as opera- therefore, that the various Balancing therefore be- tor inspector. stages be accurately aligned. comes a matter of tuning in or How this can be done is some station, preferably one the subject of this Lab- operating on a short wave- Prepared by Official oratory Sheet. The method length, and then adjusting used is simple and is based the various condensers, by Examining Officer on the action of a detect whatever means are pro- tor when a signal is being vided by the manufacturer, The author, G. E. Sterling, is Radio Inspector and Examining Officer, Radio Division, U. S. Dept. received. so that the greatest change of edited in detail by If a milliammeter with a is indicated on the meter in Commerce. The book has been range about 2 milliam- circuit of the de- Robert S. Kruse for five years Technical Editor of the plate of QST., the Magazine of the Radio Relay League. peres is connected in series tector. When circuits have experts assisted with the B -plus lead to the been adjusted so that the Many other them. detector, as indicated in the greatest current change is Elementary Electricity diagram, it will be found to obtained, the set is balanced. 16 Chapters Cover: and Magnetism; Mo- read about I. mA. if the de- It is best to make this ad- tors and Generators; Storage Batteries and Charging tector is of the grid leak and justment with the set tuned Circuits; The Vacuum Tube; Circuits Employed in condenser type and about to a short wavelength, for it Vacuum Tube Transmitters; Modulating Systems; 0.2 mA. if a C-battery type is in this part of a receiver Wavemeters; Piezo-Electric Oscillators; Wave Traps; detector is used. If a station range that the greatest lack Marine Vacuum Tube Transmitters; Radio Broadcast- is tuned -in, the plate cur- of balance is liable to occur. ing Equipment; Arc Transmitters; Spark Transmitters; Commercial Radio Receivers; Radio Beacons and Di- rection Finders; Radio Laws and Regulations; Hand- ling and Abstracting Traffic. never before available such New Information as a complete description of the Western Electric 5 Kilowatt Broadcasting Trans- RADIO BROADCAST Laboratory Information Sheet 1928 mitter; description and circuit diagram of Western No. 234 November, Electric Superheterodyne Radio Receiving Outfit type 6004 -C; Navy Standard 2-Kilowatt Spark Transmitter; etc., etc. Every detail up to the minute. Last Chance for The Audio Transformer OPERATION AT HIGH AUDIO FREQUENCIES tend to lower the voltage across it at high fre- Special Low Price quencies. In some transformers, however, there is "The Radio Manual" will be ready in a few days. IN LABORATORY Sheet No. 227, in the October a marked peak at about 6000 cycles, corresponding Over goo pages. Profusely illustrated. Bound in number, we studied the characteristics of audio to the resonant frequency of La and C in series, the Flexible Fabrikoid. Regular price after publication transformers and pointed out that the lowest output falling off rapidly beyond the point. be $6.00. Orders received now will be accepted frequency response depends upon the ratio of the If this upper resonant peak is very pronounced will reactance of the transformer to the plate resistance the gain of the entire amplifier will increase greatly at the special advance price of $4.95 -an amazingly amplifiers oscil- low price for the ilaest Radio book available. Send for of the tube. Here we will consider the high fre- at this point, tending to make the examination. Pay or return in ten days. quencies. For convenience we have reprinted here late. Good design requires that the peak be kept as free the diagram from Sheet No. 227. small as possible. At high frequencies the reactance of L is very At frequencies higher than that at which La and Order on This Coupon large in comparison with C, and it may therefore be C resonate, the reactance of La continues to in- neglected. Essentially, we then have a circuit con- crease, and the reactance of C to decrease; there- sisting of Rp, La and C in fore, the voltage across D. Van'Nostrand Co., Inc., series. As La and C come C rapidly falls. If some 8 Warren St., New York into resonance, the impe- transformer curves are dance of the circuit will examined, it will fre- Send me THE RADIO MANUAL for exam- found ination. Within ten days after receipt I will decrease and more current quently be that will flow, thereby tending the curve drops rapidly either return the volume or send you $4.95 -the the upper reso. special advance price.. to increase the voltage beyond (Radio Broadcast sr -28) across C, which is the nant point. voltage applied to the grid The problem of design of the next tube. How- o is to adjust the leakage Name ever, the voltage across C, inductance, La, and the for a given current, is in- effective capacity, C, so St. & No. versly proportional to the as to give satisfactory ( B) high -frequency response. City and State frequency, and this will (A)

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THE FINEST No. 235 RADIO BROADCAST Laboratory Information Sheet November, 1928

BROWNING - DRAKE Television

ASSEMBLY FREQUENCY BAND REQUIRED be 50 times 50, or 2500. If we transmit 20 pictures per second, the total number of elements trans- TELEVISION transmission a problem which mitted per second will be 50,000. The highest EVER DESIGNED INmust be given careful consideration is the width frequency which must be transmitted, to get good of the band of frequencies which must be transmit- quality, can be taken as equal to half this figure, ted to reproduce at the receiver end, with good or p5,000 cycles. The table given herewith shows quality, the scene being scanned by the television how the value of the highest frequency which should transmitter. be transmitted varies with the number of scanning Theoretically. a television signal contains com- lines and the number of pictures per second. For ponents of all frequencies from zero to infinity. In example, a 50 -line picture sent 15 times per second practice the frequency band is much more re- requires up to 19,000 cycles. stricted and depends upon various factors. A station transmitting within a broadcast band The width of the band of frequencies which must is limited to 5000-cycle modulation. Therefore, any be transmitted is a func- broadcast station trans- tion of the number of ele- mitting television pro- ments scanned per second No. of pictures per second grams and using a number at the transmitter. For No. of of lines and number of example, if the number of lines pictures per second such lines into which the pic- 10 15 20 that requires a frequency ture is broken -which is band greater than 5000 equal to the number of 25 3,100 4,700 6,000 cycles must either modu- new A. C. Shield Grid holes in the scanning disc 50 12,000 19,000 late above the legal limit The -is 50, then the number 75 28,000 42,000 56,000 or suppress in the ampli- of elements into which the 100 50.000 75,000 100,000 fiers the frequencies above Browning -Drake assembly picture will be broken will 5000 cycles. is a combination of all the most modern and advanced ideas of receiver construc- tion. The famous Kit has No. 236 RADIO BROADCAST Laboratory Information Sheet November, 1928 been designed this summer Moving-Coil Loud Speakers THEIR OPERATION tisements of "dynamic" loud speakers which con- by Professor Browning for sisted mainly of an ordinary electromagnetic unit important characteristic of the dynamic or, coupled to a cone. This term used to describe such assembly with shield grid THEmore properly named, moving -coil type loud loud speakers is probably misleading to some al- speaker is the fact that it has a coil fastened directly though technically it is not incorrect. tubes, both A. C. and D. C. to the cone, which is caused to move back and forth in an air gap in a magnetic circuit, the movements being in accordance with the frequencies flowing For the first time this well - through the coil. The moving coil is mounted at the apex of the known circuit has been re- cone, as indicated in the diagram, and connects to the secondary of the transformer, T, the primary of duced to single control, which connects to the plate of the power tube. The moving coil of a well- designed unit has a fairly constant impedance over the entire range of audio while the tickler feedback frequencies and the transformer, T, is designed to "match" the coil's impedance to the output im- control is retained for the pedance of the tube. So long as the power tube works into an impedance about equal to or some- exceptional sensitivity for what greater than twice the tube's plate impedance, satisfactory power transfer from the tube to the moving coil will be obtained. The instructions which it is noted. covering the use of one of these loud speakers should indicate what tubes or combination of tubes are Leads from L recommended for use with the unit. movingCoil' .. The term "dynamic loud speaker" is not a very Leads from Complete parts list at only accurate description of a type of loud speaker whose field winding distinguishing feature is that it has a moving coil. $59.50, the lowest list price The word "dynamic" is defined as "mechanics Power treating of the motion of bodies and of the action Tube yet reached by a kit assem- of forces in producing or changing their motion." Since all loud speakers move they can all be called bly of the highest quality. "dynamic." We have seen descriptions and adver- Full constructional details including full scale picture wiring diagram may be ob- No. 237 RADIO BROADCAST Laboratory Information Sheet November, 1928 tained free on request. Power Output HOW IT DEPENDS UPON IMPEDANCE RATIOS under such conditions the tube's characteristic is curved (see Laboratory Sheet No. 124) and this We have some territory open HAS been proved mathematically and experi- curved characteristic introduces distortion. ITmentally that a tube delivers the maximum In cases where the element of the loud speaker for exclusive distributors amount of undistorted power when it works into a has a low impedance, for example, it is necessary load resistance equal to twice the plate resistance to use a transformer between the tube and the loud and authorized dealers hand- of the tube; maximum power output, however, speaker to compensate the differences in impedance. is obtained when the load resistance equals the A moving -coil type, i.e., dynamic loud speaker, ling factory -built Browning - tube's plate resistance. The curve on this sheet in- might have an impedance of, say, 20 ohms at some dicates relatively in TU how the power in the load frequencies, and if it is to be used with a 2000 -ohm Drake receivers. Write for varies with the ratio of the load resistance to the tube (171A) which requires a load impedance of tube's plate resistance (sometimes called plate im- 4000 ohms to get maximum undistorted power, our proposition on this line pedance). The X on the curve indicates where a then the coupling transformer would have an im- tube is normally operated, the load resistance at the pedance ratio of 4000 divided by 20, or 200, cor- which brings both profit point being twice the tube resistance. responding to a turns ratio of the square root cf We frequently see statements to the effect that 200, or 14. and prestige. the loud speaker we use must be matched to the tube to get the largest amount of undis- torted power into the loud BROWNING - DRAKE CORP. speaker. Such is the case, but the +5 curve indicates that there can be 0 considerable mismatching with- Cambridge, Mass. out serious loss of power. For ex- ample, even when the load resis- 1 tance is about five times greater than the tube's resistance, there is only a 2 TU loss -a loss which BROWNING-DRAKE would hardly be noticeable to the ear. 1 2 3 4 5 6 It is unwise. however, to work RADIO a tube into a load resistance less LOAD RESISTANCE than its own resistance, because PLATE RESISTANCE OF TUBE

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i BROADCAST The Choice No. 238 RADIO Laboratory Information Sheet November, 1928 A Hook -up for Short -Wave and of the Broadcast Receivers

A METHOD FOR SWITCHING OVER The two plates are permanently wired together. Leaders and for this reason the arrangement we have in- IS general practice in constructing short -wave dicated should only be used when the two sets are ITadapters to arrange them with extension leads so located close to each other (which is usually the that they may be plugged into the broadcast set in case) so that the plate lead running from one set the detector socket in place of the regular detector to the other is not more than 1 or 2 feet long. tube. This practice is all right when one is building Most of us have available only one antenna to an adapter that perhaps will not be used continually, use with both sets. To use it with both receivers a but when both the broadcast and the short -wave single -pole double -throw switch, S , can be placed tuners are going to be used frequently, it is better to in the antenna circuit; thrown to one side it con- arrange the circuit as indicated in the diagram on nects the antenna to the broadcast set, and thrown Sheet No. 239, which permits one to change from the other way it connects the short-wave receiver. broadcast to short waves by a simpler means than An easier arrangement, which works well in taking out a tube and plugging in an adapter. practically all cases ¡how well it works depends upon The diagram shows the detector of the broadcast the characteristics of the two receivers) is indicated receiver and the detector of the short -wave re- by dotted lines. The antenna is connected directly ceiver. They are both wired to the same A and B to the broadcast set and through a 50 -mmfd. con- voltages, and either set is thrown in or out of oper- denser, C, to the short -wave set. This small con- ation by simply turning the proper filament switch, Si denser will block the broadcast signals from the or Sr; Si turns on and off the broadcast receiver and short -wave set but permit these latter currents to SI similarly controls the short -wave set. pass quite readily.

Junior Rheostat No. 239 RADIO BROADCAST Laboratory Information Sheet November, 1928 When the leading manufac- turers of the country choose the Circuit for Short-Wave and Broadcast Reception Yaxley Junior Rheostat for their finest radio sets you are BROADCAST RECEIVER safe in following their good -r---1 judgment. sl t The Junior Rheostat is made to the highest Yaxley standards -a master instrument, with a smooth movement and lots of r _ - service stability. Diameter, SI 1,7íT inches; mounts in single -17(; inch panel hole. Junior Rheostats, with Bake- lite Knob, up to 400 Ohms, 75c; 1,000, 2,000, 3,000 Ohms, $1.00. Junior Potentiometers, 25c extra. tr SHORT-WAVE RECEIVER Switches for Junior Rheostats, Self- Contained and easily at- tached, 40c. No. 240 RADIO BROADCAST Laboratory Information Sheet November, 1928 Resistance Units Television ftrag"50 line at a level Absolutely dependable. Run true to DATA ON THE BELL TELEPHONE LABORATORIES' fled and delivered to the transmission METHOD of 10 milliwatts. The amplification from the photo- rating. Have convenient screw eye electric cell to the line was 130 TU. and lug for easy mounting THE demonstrations of television given by the (e) Synchronization was accomplished by the use soldering Bell Telephone Laboratories, associated with of synchronous motors containing 120 poles and and wiring. the American Telephone and Telegraph Company. having a synchronous speed of 1062.5 r.p.m. The rank higher, in our opinion, than any of the other angular phase displacement was above 0.07 de- Spacewound, 1 to 60 Ohms . 15c demonstrations so far given, in quality of the results. grees. This magnitude of phase displacement corre- the angular twist in a steel 100 25c In the following paragraphs are summarized some sponds roughly to to 400 Ohms of the most important elements of the apparatus shaft 6 feet long of 1 inch in diameter, operated at used by these Laboratories. full load. Tapped resistances, 6 to 64 Ohms 30c (a) The scanning discs contained 50 holes and (f) With regard to the effect of extraneous cur- 100 to 400 Ohms 40c revolved at a speed of 1062.5 revolutions per min- rents due to noise. it was found that satisfactory ute, giving 17.7 pictures per second. results were obtained if the average picture currents Grid resistances, 100 to 500 Ohms 25c (b) Theoutput voltage of the photo -electric cells were 10 times greater than the average noise cur- at the transmitter was about 10 microvolts. rents. 600 to 3000 Ohms . . 35c (c) The range of frequencies decided upon as This corresponds to 20 TU, or a power ratio of being essential for good quality extended from 10 to 100. In ordinary sound broadcasting the noise in Your radio dealer or jobber 20,000 cycles. Overall measurements on the final the telephone lines is kept at a level 60 Tu below 10 has them in stock amplifier indicated a frequency characteristic milliwatts, giving a power ratio of 1.000.000. It is constant within plus or minus 2 Tu over this evident that it is permissible to have the noise range. level much higher in television reception than in YAXLEY MFG. CO. (d) The signals from the transmitter were ampli- sound reception. Dept. B, 9 So. Clinton St. Chicago, Illinois

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(Are you a professional set builder') 1

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Push-pull Transformers with impedances to match power tubes and dynamic speakers Type "BX" Input Trans- former has extremely high primary inductance. Sec- ondary accurately divided. -POWER TRANSFORMERS Price, each $6.50 Type "GX -210" Output For the UX250 Power Tube Transformer. Especially designed for push -pull am- The General Radio Type 565 plifier using UX -210 or CX- Power Transformers consist of 310 tubes. Secondary two models for both half and connects directly to moving full -wave rectification utiliz- coil of dynamic speaker. ing the 281 type of rectifier Price, each 56.50 tube. The Type 565 -A Half- Wave Transformer illustrated Type "HZ -171" Output consists of one 600 -volt second- Transformer. Saine as ary, two secondaries of 7.5 above except impedance volts and one of 2.5 volts. It matches UX -171, CX -371, is designed for 105 to 125 -volt, or UX -250, CX -350 tubes. 50 to 60 -cycle lines. Price, each X6.50 Type 565 -A Transformer giving audio hook- (200 Watts) Free circular GENERAL up and complete information on request Price - $13.50 RADIO COMPANY SANGAMO Bulletin No. 931 will be ELECTRIC 30 State St. Cambridge, Mass. sent on request COMPANY 274 Brannan St., San Francisco, Cal. Springfield Illinois

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Used b y Leaders because The y ae fie Leaders intheir Field , -with man y typeses of resistances from which to choose, it is highly significant that the most important radio and electrical laboratories and manufacturers in this country have standardized on DURHAM Resistors, Powerohms and Grid Suppressors. The reasons are plain. First -there is a DURHAM Resistance unit for every practical need up to 100 megohms. Second -the DURHAM Metallized principle has proved its utter superiority for years. Third - DURHAM accuracy and uniformity can be relied upon regardless of the type of unit or the purpose for which it is used. Each succeeding year sees more manufacturers, laboratories, professional radio men and dealers and jobbers endorsing DURHAMS. Descriptive literature on the DURHAM line gladly sent upon request. ir METALLIZED RESISTORS & POWEROHMS INTERNATIONAL RESISTANCE CO., 2006 Chestnut Street, Philadelphia, Pa.

www.americanradiohistory.com 64 RADIO BROADCAST ADVERTISER The New Victoreen A, C. Circuit Is the Outstanding Success of the Year

HOOK-UP WIRE "THE BRAID SLIDES BACK" EXCELLENT FOR r ALL A -C WORK Vital improvements in Victoreen R. F. Transformers, together with Can Be Easily Twisted For changes i' the circuit itself, have still TROUBLE? Filament Leads and simplified a further perfected BRAIDITE is as safe as insulated wire has had no "Super" which for years your receiver or power pack refuses and as convenient as bare wire. BRAID - superior. to functiou as it should our Service If Department will repair it for you for ITE twists easily and holds its shape per- The New Victoreen is simply mar- thc nominal charge of from $5 to $10 de- bending. pending upon time consumed. manently after It's quick and easy velous. Here you have A. C. opera- to work with, cutting wiring time in half. as tion at its best. Tone quality such Economy To make a connection, simply shove back you have never heard before- selec- Set Building Why not have your dealer send us your the insulation. After soldering, the insula- tivity such as you never dreamed to kit so that we may wire it for you. The tion slides right back into place, leaving no be possible- simplicity of assembly amount you have probably already saved on the purchase of your kit coupled with exposed sections of bare wire and making developed to the point where anyone our moderate charge for wiring will appeal the neatest and most workmanlike looking can construct a set which is as nearly to you as a sensible and economical pro- position. Write us for rates, etc. job. perfect as human ingenuity has been At All Dealers able to devise. And remember, we guarantee either the 25 Feet Stranded 35c repair or wiring service. The heart of this new Victoreen 25 Feet Solid 30c circuit is of course the world famous We are equipped to build and repair the Red, Green, Yellow, Blue, Black Victoreen R. F. Transformer - SM Screen Grid Six, Sargent- Rayment Seven, Hi Q, LC -27, 28, Universal, etc., etc., Send us the name and address of your dealer greatly improved in efficiency, with etc. Our experience with Television also FREE and we will send you a sample package of binding posts located for maximum enables us to offer our workshop to build Braidhe FREE. Include Ric for postage. convenience in wiring. Each trans- any Television Kit you desire. former is individually tuned to a pre- For further details address CORNISH WIRE CO. cision of less than of one per cent. / 38 Church Street New York City by the Victoreen patented method. SILVER RADIO LABORATORIES These new Transformers, together 2114 Mapes Ave. New York, N. Y. 1 with the other Victoreen components which are used in this remarkable set, are literally years ahead of their time. To get the results which only & Victoreen gives, either build, or have Jenkins Adair built for you, a Victoreen Super. Condenser Transmitter Blue Print Free, together with full constructional details. Write for it to -day.

For the `Jbfost `Perfect Results from the Victoreen "Super" use the Victoreen "B" Power Supply

A Vitrohm 507-109 Unit installed on your radio set lengthens the life of the a.c. tubes by auto- Supplies 45, 9o, 18o, .and 45o volts, matically lowering the using a UX 210 or 250 in the last stage. Contains two voltage regulator tubes so filament voltage. For Broadcasting, Phonograph that the 90 and 18o volt taps are sup- Recording, and plied with a constant volt potential. It This unit costs only $2.00 Power Speaker Systems is the last word in "B" supply. For the -a small investment if transmitter is a small condenser which most satisfactory results you must PHISvaries its capacity at voice frequency, and one set of a. c. tubes is is coupled direct into a single stage of ampli- have it. fication, contained iu the cast aluminum case. Free Blue Print, with list of parts and saved. The output, reduced to 200 ohms, couples complete assembly instructions, will be to the usual input amplifier. The complete Write for free informa- transmitter may be mouuted on the regulation sent upon request. microphone stand. It operates on 180 v. B and tion on the complete line 6 or 12 v. A battery. The Geo. W. Walker Company of Ward Leonard Radio This transmitter contains no carbon, and is entirely free from background noise. lts yearly aferchandisers of Victoreen 'Radio Parts Products. upkeep is practically nothing. It is extremely rugged, and will withstand hard usage. 2825 Chester Ave., Cleveland, Ohio Price, complete with 20 ft. shielded cable, $225.00 F.O.B. Chicago. J. E. JENKINS & S. E. ADAIR, Engineers WARD LEONARD vE°UNNSITT 1500 N. Dearborn Parkway, Chicago, U. S. A. YORK ELECTRIC-CO. NEW Send for our bulletins on Broadcasting Equipment Qualty R.adio -":t Parts L__ www.americanradiohistory.com RADIO BROADCAST A1)VER'I'ISER (i5

Bring the games to the crowd -and they'll welcome your message

MIK 1 List Price $135.00 without tubes Pam 16 or 17 List Price $125.00 without tubes Where Crowds Assemble Use the Voice of a Samson You can reproduce with great volume any radio music on the air or recreate the best recorded music by using a PAM 16 or 17. For the radio music connect a PAM to the output of a detector tube of any radio set or tuning unit, and for recorded music connect it to a magnetic phonograph pick up.

You can make announcements before, during or For even greater volume use the PAM i9 or 20 after the game if you use a SAMSON MIK 1 (a 2' which has approximately 22 times the undistorted stage entirely AC operated microphone input am- output of the PAM i6 or 17. plifier) which uses the same high grade transformers Send for illustrated bulletin RBI describing these we have supplied many of this country's better units and other items showing why "PAM AM- broadcast stations. PLIFIERS are a Sound Investment."

amsonffctrise6:

Main Office: ME Eu Manufacturers Canton, Mass. F1..M'A Since 1882 Factories at Canton and Watertown, Mass.

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..,' +á41td"Ct

00 Ir2JUrer If you insist on yourA.c.Tu6er the best, they must hand you The Vitrohm 507 -109 Unit costs Televocals. $2.00. Installed on your radio set, it lengthens a. c. tube life by auto- matically lowering filament volt- All standard age. types. Ask for Attached in a moment -Nothing them at your combustible - Nothing to wear out -Does not get excessively hot. dealers. Lost Music It consists of a Vitrohm Resistor mounted within a perforated Televocal Corporation metal cage, a plug, and a recep- recaptured tacle. Televocal Building by the REMLER Write for free information on this Dept. B -4, 588 12th Street and other Ward Leonard Radio West New York, N. J. POWER AMPLIFIER Products. Today broadcast programs are far better than the receivers that make WARD LEONARD MOUNT them audible. The problem is -not better broadcasting but better recep- ELECTRIC CO. NEW YORK tion. This is the problem which is completely solved by the Remler Power Amplifier. Lost music is recap- tured when you make this wonderful new amplifier an integral part of your set. Build a Designed -not for louder music, but Daven Television DRESNER for more music -it brings orchestra Receiver details to your ears just as field glasses bring landscape details to your eyes. Complete Essential Kit, $60.00 SHORT WAVE or have THE first complete Kit. Furnished You can assemble it yourself it installed with either or by a professional set-builder at a trifling cost. T24, T36 T48 The coupon below -when you sign and mail Scanning Disk. Motor. Bushing. it- Rheostat. Daven Television Tube, CONVERTER will bring you full details. 3 Complete Stages of Daven Televi- sion Amplification and Instructions REMLER for Budding. Complete Twin -Rotor Daven Television Receiver, Com- plete, including Television Tube - CONDENSER $100.0o Less amplifier Tubes. For knife -edge tuning use this famous twin -rotor con- $22.50 denser. Specified in circuits DAVEN TELEVISION that demand extraordinary APPARATUS accuracy and efficiency. Price $5.00. Daven Television Scanning Disks Each SPECIAL 14 T'14 ...... S 5.00 36 T36...... 7.50 REMLER 10.00 Comb. Disc with 24.36 and 48 Apertures T.468 15.00 Wave Length Range Met Druin Daven Tele. Amp. ? T3...... 12.50 Daven Spec. Telev. Amp. T.4 for 1 Hi Mu Tubes DIAL and 1 power Tubes 171, 210, May be used with any type of broadcast Rigid, heavy construc- 250 Types... 17.5o Daven Telev. Neon Lamp, 2.0 to 8o Milliamperes receiver. Easily connected in just a few tion, smooth, no back- Striking Voltag= too lash, illuminated. Drum Plate rl "xt ? "...... 11.50 moments' time. No complicated wiring. Daven Telev. Motor ...... 27.50 fifteen inches in circum- Daven Bushing to 6t Simply plugged into the ference. t" ie and ë' Motor Shafts i.00 detector socket in Removable cali- Dawn Bushing for 48 Aperture bration strips. $4.50 disc 3.5o the set. Covers the entire range of wave Price Daven Rheostat. 3.5o Daven Telev. Photo Elect. Cell 1;" Bulb 10.00 lengths from IS to 5So meters. Maximum Use the caut."n below far full infer- Daven Telev. Photo Elect. Cell 3" Bulb 37.50 satisfaction from top to bottom. Don't motion an Render Pats and Units. Daven Television Couplers. 1st Stage No. 4115 D421xx miss the excellent programs now being Ind Stage No. 42111 D422ZZ broadcast on the short waves. Get a Dres- Remise Division, Gray & Danielson Mfg. Co. 3rd Stage No. 4235 D -423xx ner Converter. Five interchangeable coils 260 First Street, San Francisco, California. 5 Glastors are used for Grid and Plate resistors 1.15 xx Super Davohms in Plate and Glastors in Grid 4.65 furnished with each unit. Gentlemen: Please send me: Daven AC 71 for output tubes in series with : All the "dope- on the Power Amplifier. Television Lamp 3.5o If your dealer can't supply you, SEND fl Bulletin service for professional set builders. Daven AC to (for brighter illumination) 9.00 MONEY ORDER DIRECT and we ship Daven Mu 10 Hi Mu Tubes for Amp. Stages 2.15 Parcel Post Prepaid. GUARANTEED. Name...... Daven Mu 6 Power Tube 3.5o (When ordering unit make sure to specify Send 2c stamp for new Television Booklet Address...... whether to he used on A.C. or D.C. set) City...... State ...... THE DAVEN CORPORATION DRESNER RADIO MFG. CORP. Do you build and sell sets? R I3 -11 Amplification Specialists 640 Southern Boulevard, Dept. A., New York, N. Y. 190 Summit Street Newark, N. J.

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i I -7r/l..,í

I 11111 gat

irn1,1,

i/071 - qpnllll 1 IIII IIpUpIIIIIIIIIl01 ///_A 'WC%"''=

rlpii / 1 In the Modern Broadcasting Station And in quality radio receivers for home use, Faradon Capacitors play a very definite part in maintaining satisfactory service, meriting its widespread utilization. More than twenty years of the application of electrical engineering skill combined with highest quality mate- rials have made Faradon Capacitors the standard of electrostatic condenser long life and reliability. Our engineers stand ready to coöperate on special equip- ment which cannot be taken care of by the more than 200 types of Faradon Capacitors ready for prompt delivery. WIRELESS SPECIALTY APPARATUS COMPANY Jamaica Plain, Boston, Mass., U. S. A. Established 1907

Electrostatic Condensers for All Purposes

www.americanradiohistory.com 68 RADIO BROADCAST ADVERTISER

Trade, mark A Complete line of Volume Controls Exclusively Licensed by Technídíne Corporation Under U. S. Patent No. 1593659 MOOTII, gradual control of intensity under all conditions S will be your reward if you in- corporate the Tonatrol Volume Control in your receiver. Toua- trots are variable resistors of the famous Royalty type, especially designed with the requirements of different circuits in mind. Furnished in standard types or Linking e Ï4Torld with battery switch or power switch attached. From $1.50 to $300. Electrad specializes in a full witic a Lost Continent,, line of Controls for all Radio Purposes including Tele- vision. Radio now ties together in a close patches fromByrd's Expedition. They will be Write for Free Hook -Up Circulars network all the continents on the globe, received at the Times office in New York and from there given out to the press of the world. Dept. M -11, 175 Varick Street except one. New York Antarctica, larger than the U. S. A. and Of course these messages will be sent and received Mexico combined, is still almost totally un- on short waves. The receiving set known. Here lies the South Pole on a pla- used by the New York Times is the same E LECTRU. heard teau almost as high as Pike's Peak and above which Nobile's signals in the Arctic. It which tower still higher mountains and smok- relies for its operation on National Short- ing volcanoes. Here is utter silence and frozen -NV-aye equipment. desolation. Here dreadful tem- NATIONAL COMPANY, um, Ñ pests sweep for weeks at a time INC. has developed new and at 100 miles an hour and more. better equipment for the simple Commander Richard E. Byrd's construction of non- radiating Cle-Ra- Tone Antarctic Expedition, now just short -wave receiving sets em- embarked, will explore this ploying the 4 electrode 222 great continent for the first time. Tube. This equipment is de- Radio Sockets The New York Times has scribed in our Bulletin No. exclusive rights to the news dis- 131 -B. Write us for it today. National Screen -Gris( Short- Isla or Receiver NATIO N_ A L RADIO PRODUCTS NATIONAL CO.. INC. W. A. READY, PRESIDENT MALDEN, MASS. Specially Designed for With Naald adapters A. C. Detector Tubes and connectoralds CUSTOM SET BUILDERS you can put power Spring tubes in sets- change Browning -Drake has an interesting and supported, shock absorbing. The hattery sets to A. C. unusual proposition. Take advantage of tube -holding element "floats" on perfectly sets- attach electric the fact that more Browning -Drakes are balanced springs. Reduces microphonic pickups to A. C. or disturbances, life D. C sets -connect built than any other. Write today. tends to lengthen of radio sets to Victor tube, and lessens the possibility of short - Electrolas -testA C. BROWNING CORP. circuiting closely- spaced tube elements. - CONNECTORALD tubes and A C. -DRAKE sets with D. C Cambridge Massachusetts Y- Type, Green Top, for 5 prong A. C. = ADAPTER testers-make port- Tubes: for mounting on top of panel, able sets more power, $1.00; for direct attachment to panel, 75c. -. ful with bigger tubes \Vhy not suhscríhe to Radio Broadcast? By the year only $4 cc; SOCKET -make battery sets or two years $6 oo, saving $2 40. Send direct to Doubleday, Red Top, for Standard UX Type Tubes: a 75c.; alaary portable and host Doran & Co , has , Garden City, New York for mounting on top of panel, for for plop= of other things. Or- direct attachment to panel, 50c. der from your dealer or write for a corn, HOOK -UP BOOK FREE At all Radio and Electrical Dealers and Jobbers plete Naald catalog Naald has the only Improve your reception with complete line of Its Benjamin Electric Mfg. Co. kind in the world. CARBORUNDUM Stabilizing Detector Units, 120 -128 S. Sangamon Street, Chicago ALDEN MANUFACTURING CO. Grid Leaks and Resistors New York San Francisco THE CARBORUNDUM COMPANY Dept. RB 3 Brockton, Mass. 247 W. 17th St. 448 Bryant St. DEPT. D'2, NIAGARA PALLS, N. Y

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Increased Amplification Improved Quality with this new valve

PSEE R O N O--CO U N C E D IFLAID30 TUBES Harold P. Donle's IT'S performance that Latest Achievement counts! And it doesn't THE inventor of the famous take a critical ear to note Sodion Detector valve brings the great improvement a out this DA2 6 -volt amplify- set of CeCo Tubes make in ing valve which can be used in any type D. C. set with no reception. changes. It's a simple matter to Amplification for both audio avoid disappointing results and radio frequency are greatly by a CeCo increased, and the quality of making sure that your set vastly improved. Tube occupies each socket Full size illustration of the DA 2 amplifying valve. Those that have tried these of your set. Price 03.00 each. valves are enthusiastic about The exclusive CeCo method of them. evacuation is largely responsible Here is what some of them say: for their outstanding perform- "We seem to obtain far greater volume and clarity." ance and is directly responsible "Really, it is the most marvelous valve I have ever for their longer operating life for come in contact with." which CeCo tubes have gained "I have tried two of these tubes in my regular tuned a country wide reputation. radio frequency broadcast receiver, and I am delighted with the increase in volume and distance obtained." No matter what your tube re- "Received the four tubes ordered, to -day. Must say quirements may be-there are that they even exceed all my expectations." CeCo Tubes made to meet every "It is a pleasure to report that the three tubes I re- radio need in both A. C. and D. C. ceived from you Saturday have increased the sensitivity types as well as in "special of my Hammarlund- Roberts Hi -Q to a considerable degree. I also tried one in the R. F. stage of a Brown- purpose" types which are ob- ing -Drake and there too, the gain was considerable." tainable no where else. "Excellent for low wave sets"

Try a set of CeCo Tubes and you, too, will If your dealer has not yet received his stock, mail orders will be find how much better they improve reception. A CeCo dealer will gladly advise you which promptly filled upon receipt of check. types to use to obtain the best results. We Guarantee Every Tube

CeCo Manufacturing Co., Inc. PROVIDENCE, R. I. The Donle Electrical Products Corporation MERIDEN, CONNECTICUT

www.americanradiohistory.com 70 RADIO BROADCAST ADVERTISER

Be/iindthe POLYMET Potter SERVICE radeMark Condensers If you are interested in commercial T -2900 servicing of radio receivers, you and should investigate the unusual mer- its of the following Weston instru- T -2950 ments -each one a testing authority for in its specific field. 250 Type Power Tubes These condensers are built for flower ampli- fiers using two 281 type tubes for a full wave rectifier. Model 528 A. C. The T -2900 condenser is for operation with 3 volt- an amplifier equipped with a single 250 type Range meter power tube. The T -2950 condenser is arranged for push pull amplifier having two 250 type power tubes. The 'lathes of an obscure Scottish isle T -2900 Condenser each $20.00 This compact little instrument specialize in weaving t he finest of woolens. Taps at 2, 2, 2, 4, 1, 1 Mfd. be made only when a shown above has three ranges - Shipments can T -2950 Condenser each $22.50 for chance vessel calls. QUALI'T'Y? Yes, but 150 8 4 volts. It is designed delivery Taps at 2, 2, 2, 41, 1, 1 Mfd. line supply and filament voltage lacks dependability. fine By -Pass and filter condenser for all types of tests of A. C. Receivers. A handy A one -time manufacturer of very requirements are available. kit instrument, exceptionally ac- automobiles is no longer in business. curate, light and durable. Con- Again QUALITY, but owners lack service. tained in mottled red and black Behind the Polvmct seal there is Itugnes- Bakelite case. tioned QUALITY, and something more- the Polyinetorganizat ion, insuring thcut- Model 537 A. C. -D. C. Set most in SERVICE and DEPENDABILITY. Tester Send for the Polymer Catalogue that will A complete servicing outfit POLYMET MANUFACTURING CORP. quickly diagnose the trouble in any 597 Broadway, New York City type of radio receiver set made - without need for any additional equipment. The meters provided POLYMET Co. are equivalent to ten instruments: Potter Manufacturing North C61eago. W. A 3 -range A. C. Voltmeter -150/8/4 PRODUCTS 4 Natbrd Onward! . d Your Solace volts; a D.C. Volt Milliammeter with five voltage ranges- 600/300/120/ 60/9 volts, (all 1,000 ohms per volt); and two current ranges -150/30 milliamperes. FERRANTI AC Electric With this Weston Set Tester fila- Power Speaker ment, grid, plate and cathode volt- Audio Frequency ages are determined under actual GEMBOX operating conditions. It determines Transformers filament current requirements and plate current drain. It locates $65 without "shorts" between grid and plate as Tubes well as distortion in the audio sys- New It Dynacone tem due to tube overloading. $25 provides for filament circuit and gen- Crosley radio sets have always been good sets. In them eral continuity tests, and also serves the public has always received the utmost value. The AC as a rapid tube tester. Electric power speaker GEMBOX at $65 is the world's lowest priced power speaker radio. Every modem feature available, to insure good reception, is incorporated in the Crosley Gembox. 5 DAYS' FREE TRIAL Try the Gembox and the new dynamic DYNACONE in your own home. Test itl Compare! Its realistic tone and rich reproduction is amazing! are specified for the 8 -Tube A C Electric SHOWBOX $80 Genuine Neutrodyne with all modern improve- SKYSCRAPER ments. Principal parts for the SKYSCRAPER in- 6 Tube Battery Operated cluding aluminum base, three shields and BANDBOX $55 front panel correctly drilled, one Ferranti Genuine Neutrodyne for places Audio Transformer Type A -F 5, where electric current is not requency available for electric receivers. one A -F 5C and one O -P 8C for magnetic Dry Cell Battery Type. Write for descriptive circulars type speakers or O -P 4C for dynamic cone BANDBOX, Jr., $35 just off the press speakers and three special radio frequency coils. Complete instructions for building Weston Electrical Instrument with necessary photographs and drawings. List price $95.00. Instructions only, net MUSICONE $15 Corporation price $1.00. Improved -the world's greatest success in the field of magnetic type speakers. 604 Frelinghuysen Ave., Send 15c in coin for copy of Newark, N. J. the 1929 Ferranti Year Book FERRANTI, INC. &kEY TIIE CROSLEY RAI)IO CORPORATION 130 W. 42nd St. New York, N. Y. Dept. 'l0 WEBTON Poel Crosley. Jr. Pre, Cincinnati, Ohio FERRANTI, Ltd. FERRANTI Montana, Wyoming, Colorado, ,ew Mexico and west RADIO Hollinwood ELECTRIC, Ltd. grids slightly higher I NSTRtJMENTS England Toronto, Canada Prices of ('rushy receiver. do not include tubes

www.americanradiohistory.com RADIO BROADCAST AI)VER'I'ISER 71

Raythe®rC-: The New Knapp ccA "Power Kit as* KiI10-LanW

This is the "A" power after you have as- TWO PIONEER Magically sembled it. A professional job! Operates on 105 to 120 volts, 5O to 60 cycles AC. Supplies rippleless DC current for operating any set Silent using Standard S or 6 volt tubes and power TELEVISION tubes. ACCESSORIES Absolutely Dry The Raytheon Laborator- ies invite correspondence Greatly Improved and at a Lower Price from both engineers and amateurs in regard to these New Money - Making Plan for Set - Builders two accessories now in The new Knapp "A" Power has all of the features of the old model - successful operation. magic silence -absolutely dry -"B" Eliminator receptacle- voltage -Lamp is regulator- complete, tooled part kit, etc., etc., and also eight new Raytheon Kino which make it the finest "A" Power ever put out. the first television- recep- improvements tion tube developed to Compare the appearance, read the improvements -and remember work on all systems. that the price has been reduced! Raytheon Foto -Cell, an The Only "A" Power Adaptable Every hole is drilled -all you do is put Heterodyne the screws and nuts in place and extra sensitive broadcast- toShort Wave,Super- connect a few wires. Just follow in- ing tube, is supplied in and Television Reception struction sheet. No extras to buy. either hard vacuum or The Knapp "A" because of its supe- rior filter system and the special Elkou gas -filled types. rectifier is so silent and so steady that THE SET- BUILDER TAKEN it functions perfectly. CARE OF CO. RAYTHEON MFG. The 8 Improvements Regardless of what Kendall Square Bldg., Cambridge, Mass. the established trade 1. Larger Filter System -3 Elkon may think about it -I Condensers instead of 2. Ideal am going to cont' e for Super -nets, Short Wave sets to give you the maxi- and Television. mum discounts. The 2. Improved Choke Coils coupon will bring you full 3. Pendant Switch Controlling "A ", the details of both "B" Elimina tor and Set the new "A" Power and the special dis- 4. Dial for regulating voltage counts to set-builders. 5. Celeron Front Panel David W. Knapp, Pres. 6. Baked finish KNAPP ELECTRIC, Inc., Port Chester, N.Y. -Div. P. R. Mallory & Co., Inc.- 7. Heavier gauge metal cover 7 8. Die Cast lIase Pia te instead of wood Mr. David W. Knapp, President, KNAPP ELECTRIC, Inc., Dept. K -20 350 Madison Ave., N. V. t' COMPLETE KIT -EASILY Kindly send me complete Information ou the Knapp ":1" Power and your special direounts for fRaythe on t ASSEMBLED Set -Builders. The New Knapp Kit is a tooled job - Name Foto.Cell __- the parts seem to fall into place. Address

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r CARDWELL CONDENSERS $OTtII&R The Taper Type Unexcelled for Type "E" Short Wave Cardwell `Receivers

tam,o i

ti Completely wired Push - Pull Power Stage Stability Is HANDLES ample power Vital to faithfully reproduce in the short wave receiving circuit. ' The effect of a rising and falling note so often troublesome in ('W code reception, due to instabil- full frequency range with- ity in the circuit, seuil obviously play havoc with broadcast reception on the short waves, if at all Dg.Lee pronounced. Elim- 1 out tube overloading. CARDWELL TAPER PLATE CONDENSERS are rigid and vibrationless and will absolutely inates hum caused by raw hold their calibration, thus eliminating one of the important causes of circuit instability in short wave receivers. AC on filaments of Power The tuning curve is ideal, midway between SLW and SFL, attained without eccentrically shaped With the same creative enthusiasm that Tubes. plates, thus concentrating the weight of the rotor Increases clarity, close to the shaft. It will pay you to investigate. produced the first radio vacuum tube Transmitting Condensers for pourers up to 50K11' (1906) Dr. DeForest has now developed reality and volume. and more. Receiving Condensers in all standard capacities. Send for literature. the perfected Audion. a All good dealers carry Cardwell Condensers. If AmerTran gives you unit gour deal.r dors not, send to us direct. When you replace your tubes with in 4 types designed for prac- DeForest Audions you will experience . . *t . a new enjoyment in clarified reception. tically any combination of The Allen D. Cardwell Mfg. Corp. Send today for your free copy of speakers (including the new 81 Prospect Street the interesting booklet by the " Father dynamic types), and power Brooklyn, N. Y. of Radio." tubes. "The Standard of Comparison" Deforest Riclic(c. The type P - AmerTran JERSEY CITY N.J. power stage consists of a Type 15i Input and either a Type 15/, 271, Zoo or 36/ ;Fllre>tzrr eht=irmn Output transformer(depend - ., . .. . .` ing upon the combination of power tubes and speaker LETS DO LETS MAIL LETS PUT a OUR EARLY - AWAY desired) mounted on metal i CHRISTMAS TILL SHOPPING CHRISTMAS CHRISTMAS EARLY PACKAGES DAY !. base and wired to two power I. 28 tube sockets with necessary 5010 for Th( A.MERICAN soc rr FOR TME CONTRO,, OF CYKER 5 o,000 ohm resistance in the C DON'T let the "static" that conies in over the You may save -lead. house lighting system from motors, street Approximate cars, telephones and electrical appliances mar your shipping radio programs with blare, squeal, fry and scratch! VALUABLE LIVES Plug in a Falck Claroceptor between wall weight, zo lbs. For complete socket and set and have clearer A.C. reception. A wonderful new improvement by a pioneer radio information see any author- equipment manufacturer. Grounds and thus blocks by buying these out line interference noise and radio frequency ized AmerTran dealer or disturbances. Also improves selectivity and dis- write to us direct, mention- tance. Requires no changes in set. Measures just 3 %zx5,Axz/ inches. Tested, proved. I'raised by CHRISTMAS ing the speaker and tubes thousands. Get one right away -at radio parts dealers. Write for descriptive folder. LABELS you intend using. $7.50 complete with Price completely aired and ready to cord and plug install in set $36. oo without tubes. Mail a post card to Licensed under Patents owned or controlled by R. C. A. and may be boughr with tubes THE alCE) AMERICAN SOCIETY FOR THE CONTROL AMEANTRADE MARK REG.U.S.PAT.OFF. CLAROCEPTOR OF CANCER AMERICAN TRANSFORMER COMPANY Built by ADVANCE ELECTRIC CO. 34 East 75th Street Transformer Builders for more than 28 Years 1260 St. Los Angeles, Calif. 285 Emmet Street, Newark, N. J. W. Second New York City JOBBERS and DEALERS, GET OUR PROPOSITION

www.americanradiohistory.com RADIO BROADCAST ADVERTISER 73 "Yost Can Forget the Condensers -If They Are DUBILIERS"

Type PL 1120 especially designed for the Thor- darson types R -t80 and R -280 Power Compacts, used with 171 type tubes and the 280 type tube Rectifier or the Elkon E -80 metallic r e u Rectifier. Price $15.50 n sP n a ßd1!,rSteI11, oW Your radio receiver needs a high grade aerial system if you want consistently good reception. The Beldenamel There Aerial Kit contains all the parts of a fine antenna sys- tem -each part matched for is perfect results. Replace your old aerial with a Beldenamel No Aerial Kit. Your antenna Substitute for Qualit9 system will then be perma- nent-it cannot corrode! See No amount of lurid claims by Dubilier Light Socket Aerial your dealer, now. nimble- penned advertising writ- "A Moulded Bakelite Product" Bare Copper Beldenamel Aerial ers will take the place of quality Aerial W ire Wire is protected Corrodes against cor in the final analysis -the opera- Bring in programs with a mini- Rapidly /f rosion. tion in your power supply. mum of interference. Do away with the unsightly and trouble Ever since the advent of Radio, causing outside aerial and light- Dubilier has been the manufac- ning larrestor. Simply attach to turers' standard -and the set - the set and plug into the nearest builders' stand -by. Built in every light socket. Uses no current. Other Belden Radio Products Dubilier Condenser is a factor of Sold by all good dealers on a 5 Indoor Aerial Kits, Colorubber safety which is your safeguard for day, money -back basis. Price Hookup Wire, Aerial Accessories, years of service without failure. $1.50. Battery Cords, Extension Cords and a dozen other items are in- cluded in the Belden Line. Write to Dept. 30 for free catalog Ask your dealer to show you the newBeldenLoudspeakerExtension Cord that is flat and lies under the rug. No unsightly wiring around the room. Does not wear the rug. Belden Manufacturing Co. Dubilier 2312A S. Western Ave. CONDENSER CORPORATION Chicago

10 East is) New York 43rd Street ni?s' City Reg. U.S.PetOff

Fahnestock Clips RADIO'S GREATEST CONVENIENCE

Used by Manufacturers of Standard Seta and Parta -and by Manufacturers of High Grade Wet and Dry Batteries. NO. 502 ALL GENUINE ELECTRIC FAHNESTOCK CLIPS PICK -UP bear our imprint on the thumb Fits A. C. or piece of the clip. D. C. Sets WORLD'S LARGEST MAKER OF CLIP TERMINALS No. 502-Price $5.00 PRICE $5.00 48 different sizes and styles to meet all requirements. The Na -.tld Electric Pickup fits any radio set and will electrically amplity music from any phono- .Send for Catalog and Samples graph. Can also be attached to any power amplifier. It is the lowest priced pickup on the market and is sold on a fire -day money bark guarantee. Get one FAHNESTOCK ELECTRIC CO. from your dealer or write direct. I. ALDEN MANUFACTURING CO. L. City New York Dept. RB 4 Brockton. Mass.

www.americanradiohistory.com RADIO BROADCAST ADVERTISER End Radio Bothers DO YOU KNOW what's wrong when your radio set isn't working right ? Ten to one, you don't. Twenty to ane, you would If you had a copy of Positive Line Voltage Control Safe Hoff's Radio Trouble Finder Ever hear of M. M. Hoff. radiotriclan, of Philadelphia? He was one of the very first "radio bugs" and has heen building and studying sets ever since. And now, out of his your A.C. tubes The Centralab Radio Control Box broad experience, this man has written a book to tell radio owners how to keep their sets working right. from excessive filament volt- is the most advanced form of volt- He tells in plain words and illustrations how a set is PROTECT made, what the parts are called, what are the few usual age and insure maximum efficiency age regulator. It is so designed troubles and how to fix them. Then he lists 103 troubles that sometimes happen and tells how to detect and fix each from your new that it will pro- one. The book is a regular cyclopedia of radio information - A.C. receiver, vide absolute only it's in a language anyone can understand. Read it five minutes and you'll know more about radio than you ever which is designed positive and safe dreamed of. It will save you many a repair man. It will save you to operate at a control of line hours of guessing and fussing and fuming. It will help you to keep the tone of your set always sweet and strong. It will certain specified voltage. A sim- keep yuu from losing many programs. And, hest of all - IT WILL MAKE YOU STOP SWEARING-MUCH TO line voltage. To ple manual con- THE SURPRISE OF YOUR FAMILY-because radio re- pairs are expensive. Why hire them done when you can easily be safe, you must trol is the only learn how to keep your set from needing them? have some means adjustment. No All It Costs Is $1.00 Send cash with your order and you get also a Dictionary of controlling meters or tech- of Radio Terms and the latest list of Radio Broadcasting Stations with call letters and the new Federal Radio Com- the voltage from nical knowledge mis,ion wave lengths. Send your dollar today while the the light socket, required to oper- cop,. , last. Six copies for $4.00. which varies in different localities ate, although meter can be at- CHICAGO BARGAIN STORES and during certain times of the day. tachedat little extra cost if desired. 426 Quincy Bldg. Desk B, Chicago, Ill.

f 26 Keefe Milwaukee, Avenue Wisconsin NOW READY! CENTRAL RADIO LABORATORIES A New Practical Radio Book

At only one Why not build up a RADIO BROADCAST'S dollar a rear, profitable little busi- DATA SHEETS ness of your own? there is not a woman Containing 72 Pages of in your neighborhood «ith this new maga- Useful Technical Data on who w ould be without zine you will find THE :1.11ERICAN sales ease and quick- VACUUM TUBES 110.11E. practical and your profits POWER SUPPLY home- making service worth- while. Let, us DEVICES that, she can actually write you full details use and adapt to her of this dignified way SPEAKERS own home. she will to earn income. Agen- AUDIO SYSTEMS want to buy this cy Division, T Il E RECEIVERS magazine on sight -- 13 IERI C.1 N HOME, and can afford to. Garden City, N. Y. CIRCUITS and a hundred other radio subjects of interest to all radio engineers, set builders, service men, home construc- tors and amateur operators. Send one dollar now for a copy of Radio Broadcast 's Data Sheets. We will send book by return mail. If you are not satisfied you can re- turn book within ten days and we will refund dollar immediately. Use coupon below

% SET BUILUEKS DEALERS \I) DOUBLEDAY, DORAN & CO. INC. of The NEW 1929 catalog is crammed lull tür Garden City, N. Y. (R. B. D. S.) FINEST, NEWEST, Nationally known A. C. sets, consoles, cabinets, dynamic speakers, kits. GENTLEMEN: eliminators and accessories at LOWEST Enclosed is a dollar for a copy of Radio Broadcast's Data Sheets. If I am not sat- PRICES. Largest stock of radio parts Prompt isfied I will return book in ten days and delivery. No delay. you are to return my dollar. Write for our FREE catalog WESTERN RADIO MANUFACTURING CO. Name 128 M.. Lake St. Dept. RR -II Chic ae,, Address

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If It's Sponsored by Dongan It's O. K As an exclusive specialist in parts then runs the gauntlet of Dongan's engineering and manufacturing, Don - laboratory experiments; those merit- gan, for years, has occupied a key ing further trial are subjected to every position in the industry. New test. Only when finally approved tubes, new hook -ups -new ideas by by the chief engineer is a new design the hundred -come to Dongan for offered to the market -a finished consideration. Every single idea product. One of the most successful Developments of 1928 Power Amplifiers built around UX 250 Tubes Look for The following are Approved Dongan Parts for use with UX 250 tubes the LIST No. 7568-- Transformer for full wave rectification using 2 UX 281 tubes to supply B and C power to receiver and power for 2 UX 250 tubes $13.5o No. 8529-Transformer similar to No. 7568 with the addition of 2 on top of all low voltage windings, one for 226 tubes and the other for 227 tubes so that you can build a power amplifier for either radio receiver or phonograph pick -up 16.5o No. 6551- Double Choke, for use with above transformers ... i 5.00 D -600 Power Amplifier Condenser Unit 16.5o RADIO / TUBES D -3o7 -A Condenser Block, used in connection with D -600 . io.00 No. ri77- Straight Power Amplifier Output Transformer 12.00

No. i i76-Same as No. 1177, but of Push Pull type 1 2.00 CÙDHEN you look inside of your radio, be sure you see the monogram Custom Set 'Builders can secure any of these items direct from factory at trade "C" smiling up at you on the top discounts. Set Manufacturers are offered the full cooperation of Dongan en- of each radio tube. gineering department for their individual requirements. Thirteen years of experience and DONGAN ELECTRIC MANUFACTURING CO. tireless research combined with a 2991 -3001 Franklin Street guarantee against mechanical and Detroit electrical defect stand behind this simple monogram. A0 TRANSFORMERS of MERIT for FIFTEEN YEARS %z,9, Cunningham Tube quality has re- sulted in national leadership and

public approval, two assets we zeal- RADIO FANS, a one -years subscription to Radio Rioadeast will cost ously guard and is your assurance you four dollars, two years six dollars;. Consider this expenditur as being a necessary investment on your part for the future develop- of faultless modern reception. ment of your own knowledge of Radio. 425 Wee Charging Batteries Never use old tubes with new ones new tubes throughout Starts You -use Let me show you how to make big money WRITE right from the start. E. T. CUNNINGHAM, INC. TODAY I've prepared a FREE book explaining all details. First New York Chicago San Francisco Send for large, new, il- week's profit pays for all equip- ment. You can get all the battery lustrated Catalog "A -2," charging business in your community with my Manufactured and sold under rights, patents Service Station Charger and inventions owned and 'or controlled by showing the latest of -it's years ahead of or- Radio Corporation of America. dinary chargers - handles 50% to 70% more everything in radio at batteries. I explain everything -start you in a business of your own and put you on the way to wholesale prices. big money. Write for FREE BOOK. C. F. HOLMES. Chief Engineer, Dept. R B Independent Electric Works 5116 Ravenswood Ave. Chicago, tit. AlliedCORPORATION Radio 111 W. LAKE STREET, CHICAGO FREE BOOK Just Out

www.americanradiohistory.com 76 RADIO BROADCAST ADVERTISER

As i/you had u rínqside seat TWENTY -TWO thousand muffled thumps of the fighters' ments of radio design: for fight fans pack the Garden dancing feet. shielding, condenser blades and to see the big fight with their The tense voice of the an- frames, chasses, sub -panels, own eyes. . . nouncer comes over the air front panels and for many Millions clearly and distinctly, free other parts. sitting coin - from interference and without Look for Aluminum -you fortably at buzz or hum to blur the re- will find it in the finest of re- home "see" it from the ring- ception. ceiving sets. And if you are side seat of the radio an- That is the experi- building a set, use Aluminum nouncer. ence of the millions for the best results. They learn about each tell- whose receiving sets The booklet, ing blow almost as quickly, are Aluminum equip- "Aluminum for and much more accurately, ped. Radio," will be sent on re- than most of the fans seated No other metal com- quest. It explains the varied in the Garden. They hear the pares with Aluminum in ful- radio uses to which Aluminum thud of glove on body, the filling all the varied require- is adapted. Send for your copy. ALUMINUM COMPANY OF AMERICA

ALUMINUM IN EVERY c).)I COMMERCIAL FORM 1 2464 Oliver Building ®ó®" P it t s b u r g h, Pa. ALUMINUM `?he mark of QuaIitq iii Radio

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