INCREASED VALVE LIFE

Hawke's Bay Tribune, Volume XIX, Issue 31, 23 January 1929, Page 5

INCREASED VALVE LIFE

One of the important services the devolpment vf the dull emitter type of filament did for wireless, apart from tho enormous economy in current consumption it achieved, was greatly to increase the life of wireless valves. In the early days of broadcasting, when the uld bright

filament valve was the only type available, tho effective life of the filament, if it escaped accident, was about 1000 hours. Owing to the fact that it was necessary at a temperature dangerously close to the melting point of the tungsten from which they were made, it was exceptional for a valve to “die of old age.’’ The tungs ten filaments were very brittle, and if they escaped burnout through a slight current overload, the filament was frequently fractured by slight shocks. It is probable that the average life of a valve used for broadcast reception was not very much more than fiOO hours. Since the development of dull emitter filaments, however, tho average life of a valve has ben extended to the life of the activating material in the filament. The filaments themselves are much tougher than the old bright filaments, and fractures occur very seldom. The very low-operating temperature eliminates the danger of burn-out, except by’ an accidental short-circuit of the high-tension battery. It is probable that the average valve used in a broadcasting receiver now has a life of from 3000 to 5000 hours, while cases in which valves are used for COOO hours and 7000 hours are not uncommon. It is interesting to note that there has also been a steady improvement in the quality of bright filaments used in transmitting valves. I have at present a large transmitting valve which was purchased more than three years ago, and which as been in constant operation, frequently under heavy overloads, ever since. Its filament emission and other operating characteristics are still quite normal.