Many of the multi-valve electric sets now sold, employ Indirectly-heated valves in the radio-frequency and detector position. Briefly, the indirectlyheated valve has an additional electrode called the cathode, which on account of its heat-retaining properties is insensible to the variations of the power mains from which the current is drawn, and the heat valve remains more or less constant. It can be likened to a heat reservoir, the heater element supplying a fluctuating supply to it, but the output, which influences the electron stream forming the conductive path in the valve, nevertheless being quite steady. The cathode being the electron-emitter it is coated with a substance that gives off electrons freely on being heated. The base of these indirectly-heated A.C. valves has five prongs, the usual plate! grid and two filament prongs, and the cathode prong.
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Sun (Auckland), Volume III, Issue 901, 19 February 1930, Page 14
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136Untitled Sun (Auckland), Volume III, Issue 901, 19 February 1930, Page 14
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