Radio Broadcast (May 1928-Apr 1929)

FEB 13 1929 RADIO 9 ROADCAST WILLIS KINGSLEY WING .... Editor KEITH HENNEY . Director of the Laboratory HOWARD E. RHODES . . Technical Editor EDGAR H. FELIX . . . Contributing Editor I VOL. XIV, NO. 4> 1 ENGINEERING THE LABORATORY SERVICING Contents for February, 1929 Frontispiece Life Test Racks for Vacuum Tubes 226 A Figure in Radio Progress Edgar H. Felix 227 Measurements on Broadcast Receivers L. M. Hull 230 The March of Radio An Editorial Interpretation 233 The Davis-Dill Publicity Rarrage Progress in Long and Short-Wave Fitting Receivers to New Alloca Radio tions News of the Radio Industry Aircraft Radio Decisions of the Courts With the Broadcasting Stations The Business Side of Radio Servicing John S. Dunham 236 Strays from the Laboratory Keith Henney 239 Power, Efficiency and Energy A Test for Screen-Grid Tubes Power of Station Harmonics Duration of Engineering Jobs Three New Pamphlets Available How Useful Is a tube? Importance of Tube Voltages Accuracy of Variable Condensers Impedance of Standard Loud New High-Voltage Rectifier Tube Speakers New Regulation of the Commission An Efficient Push-Pull A. F. System Kendall Clough 241 Sound Motion Pictures ---- Carl Dreher 244 Broadcast Engineering ----- Carl Dreher 246 Transmitting Amateur Television Boyd Phelps 247 Are Filters Needed in A. F. Amplifiers? Keith Henney 250 Book Reviews Carl Dreher 252 "Radio Broadcast's" Home Study Sheets 253 No. 15. The Transmission Unit No. 16. Experiments with a Wave meter The Serviceman's Corner - - - - 255 An Economical Battery-Operated Receiver Howard E. Rhodes 257 Volume Control Systems - - - - 259 "Our Readers Suggest — " - - - - 260 A Short-Wave Super-Heterodyne Robert S. Kruse 262 Trouble Shooting in the Power Unit B. B. Alcorn 264 " Radio Broadcast's " Service Data Sheets 265 No. 17. The Philco Electric Re No. 18. The Browning-Drake Receivers ceiver 1 In The Badio Marketplace 267 The Remler "29" Super-Hetero The Junior Model "Hi-Q 29" dyne Manufacturers' Booklets - - - - 270 "Radio Broadcast's" Laboratory Information Sheets 272 No. 256. Three Types of Graphs No. 260. Voltage Gain in R. C. No. 257. Heater Connections for Amplifiers A. C. Tubes No 261. Where A. C. Hum [Origin No. 258. An Analysis of Filter Cir ates cuits No. 262. Advantages of Dual Push No. 259. Filter Circuit Character Pull istics No. 263. Wavelength Kilocycle Chart The contents of this magazine is indexed in The Reader j' Guide to Periodical Literature, which is on file at all public libraries . . . among other things r I "'HE unit heretofore employed by engineers to express -* power ratio — the TU — has been superseded by another which means the same thing, but has a more logical name The new unit is the Bel and the decibel, abbreviated DB, expresses exactly the same numerical relations at its predecessor, the TU, did. All references in this magazine from this issue on will employ the new term. For those who wish to refresh their memory on the point — and the whole question of the transmission unit — Home Study Sheet No. 15 on page 253 of this issue furnishes an unusually complete review. r 1 "'HE present issue contains a vast deal of interesting and useful information. In especial, Kendal Clough's article should prove of importance to those who are trying to solve audio problems requiring the use of an amplifier furnishing a large amount of undistorted power for such uses as publicaddress systems, etc. The article by Keith Henney on page 250 discussing the value of complete filtering in audio amplifiers is thoroughly practical and the conclusions are supported by careful measurements. The second appearance of Carl Dreher's department devoted to sound motion pictures contains information invaluable to those working in the field. And those who have followed Mr. Dreher's "As the Broadcaster Sees it" will recognize the same material under its new heading "Broadcast Engineering," a title which more properly describes his regular contributions. THE present issue differs in appearance from those which preceded it. The changes in the text pages make for increased readability. The cover, of which we are very proud, was designed in New York by A. B. Tobias, one of the best known and ablest of present-day designers. The typography of the text pages was done by W. B. Dutch er of the Art Department of Doubleday Doran & Company. RADIO dealers and servicemen are writing us in great numbers with the most enthusiastic praise for the sections of this magazine written especially to help them. Our plans for the coming months include many articles which no serviceman or dealer can afford to miss. Of especial interest is the article by John S. Dunham on page 237 of this issue on the business problems of service work. The March number will be a special tube issue with a wealth cf information in a very useful form. In addition are special articles on an ingenious r.f. distribution system for apartment houses, Prof. Terman of Stanford University on "Detection," K. S. Weaver of Westinghouse on the ux-250, Frank Jones on " Dynamic Loud Speaker Measurements," C. T. Burke on a " Discussion of Impedance," an interesting circuit for automatic volume control, and our special departments, packed full of useful information. Willis Kingsley Wing. TERMS: $4.00 a year; single copies 35 cents All rights resented. Copyright, 1929, in the United States, Newfoundland, Great Britain, Canada, and other countries by DOUBLEDAY, DORAN & COMPANY, INC., Garden City, New York MAGAZINES . . . Country Life, World's Work, The American Home, Radio Rroadcast, Short Stories, Le Petit Journal, El Eco, Frontier Stories, The American Sketch, West. BOOK SHOPS (Books of all Publishers) . . . New York: <Lord & Taylor, James McCreery & Company, Pennsylvania Terminal, 166 West 32nd St., 848 Madison Ave.. 51 East 44th Street. 420, 526, and 819 Lexington Avenue, Grand Central Terminal, 38 Wall Street> Chicago: <75 East Adams Street> St. Louis: <223 N. 8th St and 4914 Maryland Ave. > Kansas City: <920 Grand Ave. and 206 West 47th St. > Cleveland: < Highee Company > Springfield, Mass: < Meekins, Packard & Wheat. OFFICES . . . Garden City, N. Y. New York: 244 Madison Avenue. Roston: Park Square Ruilding. Chicago: Peoples Gas Ruilding. Santa Rarbara, Cal. London: Wm. Heinemann, Ltd. Toronto: Doubleday, Doran & Gundy, Ltd. OFFICERS . . . F. N. Doubleday, Chairman of the Board; Nelson Doubleday, President; S. A. Evebitt, Vice-President; George H. Doran, Vice-President; Russell Doubleday, Secretary; John J. Hessian, Treasurer; Lillian A. Comstock, Asst't Secretary; L. J. McNaughton, Asst't Treasurer february, 1929 page 224 ®