Coronado Eagle and Journal, Volume XIV, Number 28, 13 July 1926 — >Radiu [ARTICLE+ILLUSTRATION]

>Radiu

By DR. ALFRED N. GOLDSMITH The quality of reproduction of rau■lc in the home depends on many elements at the transmitting and receiving stations. Acoustic synchronizing, or the accurate re-creation in the home of the sound waves produced In the studio. Is the determining factor In the enjoyment of radio programs. Kew people realize the very Important part played by vacuum tubes In the receiving set From the standpoint of securing real musical results In the home tubes must meet a number of difficult specifications. While high-grade tubes do, as a matter of tact, meet such specifications, It Is by no means uncommon to see the entire circle of broadcast transmission and reception broken and tone quality ruined by the use of unsuitable or unreliable vacuum tubes. Considering, drat, some of the electrical constanta of the tubes and without going Into the technical detalla of the matter, vacuum tubes have a certain characteristic which la known aa the amplification factor. If the amplification of the tubes used In the receiver la too email, weak and unnatural Bounding signals will result It on the other hand, the amplification Is too great In Ita relation to the design of the receiving set the receiver may "oscillate” or produce squealing or howling notea which cannot be conveniently eliminated or controlled. Internal Impedance. Another Important constant Is what Is known as the "Internal Impedance" of the tube. Roughly speaking, this Is a measure of the opposition of the tube to the flow of plate current through It. It Is the factor which limits the current drawn from the , 'B” battery. If the Internal Impedance Is too small there will be an excessive drain op the plate batteries without corresponding advantage and plate battery renewals will be uncomfortably frequent. On the other hand. If the Internal Impedance Is too high, weak signals of unsatisfactory character will be produced and tone quality on the average loud speaker will be distinctly unsatisfactory. Accordingly, Internal Impedance of vacuum tubes roust 'also be held within carefully considered limits. The elements Inside of modern vacuum tubes are close together, and they. In conjunction with the wires leading from them to the contact pins In the base of the tube, constitute what are known as electrical capacities. In other words, there are miniature condensers formed by the filament, grid and plate, the capacities of such condensers residing Inside of the tube, it Is a fact that In many highly efficient circuits these Internal tube capacities definitely Influence the electrical behavior of the set. Receivers which are "neutralized" or "balanced" against tendency toward oscillation (howling) are necessarily so balanced for a particular tube. If the Internal capacity of tubes varies too far receivers which would otherwise properly function will begin to produce uncontrollable noises, generally of a bussing or whistling nature, whereupon the musical enjoyment - of the audience Is destroyed. The Filament. Inside the vacuum tube Is a glowing element called the filament. It Is a sort of reservoir from which streams a current of electricity In the form of a myriad of tiny electrical charges called electrons. These pass from the filament to the plate Inside of the tube and their flow Is definitely controlled by the grid element between the filament and the plate, which acts as a sort of electric valve, turning on and off the flow of current through the tube and presumably In accordance with the shape of the sound originally ■ produced In the- broadcast studio. This, In general terms, Is the process whereby the original signal Is reproduced In the home. It Is clear that an essential portion of this process Is the emission of a sufficiently copious stream of electrons from the filament If the stream is reduced to a mere trickle the signals will become weak and distorted. In this case, even for a low volume of sound In the home,

there will be rattles and distortions In tone quality. Vacuum tubes used as amplifiers require a high vacuum. Unusual and apparently extravagant precautions must be taken to extract gases from the bulb and even from the metallic elements Inside the tube and the very glass Itself. The presence of gas In the tubes shortens Its life and causes It to be "noisy." The delicate elements Inside of a vacuum tube. If Jarred, will vibrate. Some makes of tubes are peculiarly sensitive to mechanical disturbance and easily produce a “ringing note” If the receiving set is touched or tapped. Particularly Is this the case If the tube sockets are not effectively cushioned and elastically supported. Vacuum tubes which produce a loud and prolonged ringing note when tapped will not give the same satisfaction as “nonmlcrophonlc tubes" which are tree from this defect In any case the vacuum tube mounting should be appropriate. Suitable Batter!ee. A brief mention of the Importance of suitable batteries In good condition*. In their relation to tone quality Is pertinent When the “A” or filament batteries of a receiver run too low the tubes will not light up fully and the signals, besides being weak, are frequently distorted or scratchy In quality. A run-down condition of 1 the “B” or plate batteries similarly causes a noisy or weak signal with distorted quality, or may even give rise to disagreeable howling,setands. The “O'* or grid battery also plays a great pan In the production of blgb-quallty music. ' The best rule is to select reliable tubes, each suited for the particular purpose to which It Is to be put in the receiver, and then not overwork these tubes nor neglect the upkeep of the batteries feeding the tubes

Dr. C. B. Jolllffe of the Radio Laboratory of the Bureau of Standards, With a 260-Watt and a Typo “N” Electron Tube.