THE NEW A.C. TUBES

Radio Record, Volume I, Issue 16, 4 November 1927, Page 14

THE NEW A.C. TUBES

| TWO DISTINCT TYPES. | There are two kinds of a.c. tube, those that have filaments in the usual sense, and those that have heaters,, which operate from a.c., and which, in turn, heat a cathode, which supplies the electron stream which the radio set actually makes use of. : An American contemporary suggests that as this class of tube is somewhat in a state of development, there uced be no hutry to do away with present batteries and tubes, at least while they are still good. mo The heater type of tube is mow fairly well-known as regards its principle, but the filament type is a later development. ‘The stout filament type has a true filament, very leavy and’ rugged, heated by a lot of current at a low voltage. Riliminating the hum in this class of valve did not prove so formidable a problem in the radio aud audio amplifiers as in the detector, which calls for special arrangements. One system utilises the combined plate current of all other valves for heating the detector filament. As the rugged filament type cannot be used as a detector of the grid leak and condenser type, a heater type is recommended as detector. The rugged filament type may be used with a C-battery detector. The heater type may be used right through the set. Hum is kept at a minimum bv biasing the heater with respect to the cathode. One type of heater tube may be used in a fourprong holder, but most makes require a special five-prong holder, and one make has two heater terminals at the ton of the tube. This new departure appears to herald the production, at no very distant date, of a perfect hatteryless receiver. There are quite a number of makes of thie tubes on the American market, and, no doubt, any that are imported for sale in New Zealand will be those that haye heen proved to he the most efficient.