Radio Broadcast (Nov 1926-Apr 1927)

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426 RADIO BROADCAST ADVERTISER f by Radio k IL Leaders Ji lately? iTEW people realize what a remarkable improvement they can secure in tone quality by occasionally changing the Resistors in their sets. Remember that the characteristics of tubes and batteries constantly change. Even when you replace old tubes with new ones there is always a variance. Changing values within your set require Resistors of proportionately different values if you are to have the harmony and unison of all elements which affect perfect reception . Most internal Receiver noises are NOT from faulty tubes, "tV batteries or loose connections, but are purely the result of unstable grid Resistors. Wise radio owners keep several extra Durham Resistors, of various ranges from i to 5 megohms on hand and occasionally change them to meet varying conditions. Try it yourself and note the immediate improvement in tone quality. (.500 Ohms to 10 Megohms) RESISTORS INTERNATIONAL RESISTANCE COMPANY lhpt. I), 1936 Murkot St. Philadelphia, Pa. {Continued from page 420) R 385.5 Microphone. Microphone, Radio Broadcast. Dec, 1926. Pp. 183-184. Condenser. "The Condenser Transmitter," A discussion concerning the condenser microphone, its characteristics and.peculiarities, is^presented. It is compared to the carbon microphone, the latter having certain advantages over the condenser type, although both are used in broadcasting stations. R582. Transmission of Photographs. Television. Radio Broadcast. Dec, 1926. Pp. 139-143. "And Now, We See by Radio!" A. Dinsdale. A new system of transmission of motion pictures, called the Baird system, is discussed, and details relative to its operation and development are outlined. A comparison is made between the comparative effectiveness of the selenium cell and the photo-electric cell. The system is spoken of in the highest terms and said to be the only real practical system developed to date. Its accuracy in reproducing images and objects is considered to be far greater than that of any other system, this having been shown by actual demonstrations to others. Commercially, it is considered by many to be the only apparatus available at present. R402. Short-Wave Systems. Short-Wave QST. Nov., 1926, Pp. 9-13. Transmission. "General Electric Short-Wave Test Results," M. L. Prescott. In a summary article, the results of the General Electric Company's short-wave transmissions, covering a period of eighteen months, are closely compared. Six stations were operating at frequencies from 20,000 to 2750 kilocycles, at various times during the intensive test period of April, 1926. Experimenters of the A.R.R.L made observations and these are shown plotted as audibility curves. The curves show decided variations when comparing day and night transmission. R132. Amplifying Action. Amplification, QST. Nov. 1926 Pp. 14-18. R.F. "R. F. Amplification — A Re-Hash," E. B. Lyford. The problem of controlling oscillations in r.f. stages is summed up, four general methods of stabilizing being enumerated. (1) The potentiometer in the grid return, or in the plate circuit. (2). The losser method in the tube circuits. (3). Hazeltine neutralization method. (4). Reversed tickler method or the bridge compensation method. A variation of the Rice circuit of neutralization is shown and explained. Dimensional data are given for those who desire to experiment with this method of neutralization. R330. Electron Tubes. Relays' QST. Nov., 1926. Pp. 20 — 21. Electron. "A Sensitive Vacuum-Tube Relay," W. H. Hoffman and F. H. Schnell. A relay used in conjunction with a receiving set to operate sounders, bells, buzzers, etc., is outlined. A signal audibility of R-5, or better, will cause the relay to function. The parts required to build the relay, together with the circuit diagram, serve as a guide to the builder. R3 4.3. Transmitting Sets. Transmitter, QST. Nov., 1926. Pp. 22-25. Crystal-controlled. "A Shielded Crystal-Controlled Unit," J. M. Clayton. A crystal-controlled transmitter, with separate stages of a three-stage oscillator-amplifier circuit shielded, here described, is said to have solved several difficulties experienced in unshielded sets. Tubes of the ux-210 type are used throughout, a maximum of 500 volts being available for the plate potential. Two tubes operate in parallel in the last stage. Complete data on construction and operation, including the circuit diagram, are given. R220. Capacity. Capacity QST. Nov., 1926. Pp. 28-31. Standards. "The Uses of a Calibrated Variable Condenser," R. B. Roof. With a well calibrated variable condenser, seven possible uses for it are described: (1). Tofmdthe distributed capacity of a coil. (2). To find the inductance of a coil. (3). To match two dissimilar coils so that they may both be tuned by the sections of the same tandem condenser. (4). To find the capacity of fixed condensers. (5). To calibrate other variable condensers. (6). As a wavemeter in conjunction with an inductance. To measure decrement and r.f. resistance. (7). Various uses in oscillating vacuum-tube circuits. A vacuum-tube driver is needed for the first five uses. In order to indicate resonance several methods, as outlined, may be used. R113. Transmission Phenomena. Transmission QST. Nov., 1926. Pp. 32-33. Phenomena. "Horizontal Wave Experiments at 2aer," J. M. Hollywood. Data obtained and conclusions arrived at during a series of tests on horizontally and vertically transmitted and received waves on 40 meters (7496 kc), indicate that a number of theories may be looked upon as supplying information concerning wave propagation. The author speaks of the "pebble in the pond theory," "the radiant ray theory," and the "lines of force theory," all of them being illustrated. R124. Coil Antennas. Loop Experiments. QST. Nov., 1926. Pp. 36-40. Considerable experimental data obtained with a loop receiver-transmitter using tubes no larger than the ux-210, are presented. The circuit diagram of the set itself is shown, together with constructional and operating data, and photographs. The outfit was used mainly for portable work in cars and planes. A Heising modulating system can be connected to it for phone work, as illustrated. R120. Antennas. Antennas, The Transmitter. Oct., 1926. Pp. 7-10. Herl; Type. "Hertz Excitation. Something Different," K. M. Ehret. Whether an antenna will operate better when radiating on harmonics or on the fundamental depends on location, says the writer. A theoretical as well as practical discussion, pertaining to the Hertz form of oscillators, follows, wherein facts of current and voltage feed to the radiating system are clearly outlined. A "re-radiating" antenna (inductive coupling of the main antenna to a secondary oscillator) is suggested as giving very good results. SELECTED FOR R. B LAB. CIRCUIT ON SHEER MERIT • It gets that last mile" IRGAP SOCKE RADIO BROADCAST LABORATORY recommend Airgaos for THE R. B. LAB. CIRCUIT^ (November issue page 36) because, as there stated, they introduce a minimum of GRID' PLATE capacity and aid in prevent' ing objectionable feedback. At all dealers or direct, postpaid 60c. each AIRGAP PRODUCTS COMPANY Mfr. 9 Campbell Street Newark, N J Bradtepleak THE PERFECT GRID LEAK Provides a noiseless range of grid leak resistance from to 10 megohms. Assures most effective grid leak resistance value for all tubes. Small grid condenser (0.00025 ' is separate. Metal parts nickel plated. One hole mounting. ^jJgn-Brag^rCok Electric Controlling Apparatus 278 Greenfield Avenue Milwaukee. Wig. Type 612— $42.50 The "<B" Without a 'Buzz Also — Complete set of parts for homebuilders at reasonable prices. Write us. M A Y O L I A N RADIO CORPORATION 1 668 Webster Ave., New York, N. Y. 'Pioneers in 'Battery Elimination The 'Power of Niagara — The Quiet of an cArctic ^ight