LONGER-LIVED VALVES

Shannon News, 18 December 1928, Page 1

LONGER-LIVED VALVES

OVER 3000 HOURS COMMON. One of tin; most important ferviccs die d (.' v o lop i'll ent of the dull emittei tvpr of valve filament did for winder apart ' from tin 1 enormous economy u. cm rent consumption it achieved, wagreatly to increase the life of wirelosvalves. Tn the early days of broad-

misting, when the old bright iiiamen/ v-ive was the only type available/the' effective life of flic filament, if it sniped accident, was about 1000 hoars Owing to the fact that it was neces .-•ary for the old lilapients to be operat'd at: ti temperature dangerously close to the inciting point of the tungsten from which they were made, it was exceptional for a valve to “die of old age. - ’

The tungsten filaments were very brittle and if they escaped burn-out through a slight current overload, the filament was fmjuent,ly fractured by sfight shocks. It is probable that the average life of a valve used for broadcast reception was not very much than 000 hours.

Since the development of dull emitter filaments, however, the average life of a valve has been extended to the life of the activating material in 1 the filament. The filaments themselves | are much tougher than the old bright, filaments, and fractures ' occur very seldom. Th very low operating temperature eliminates the danger of burnt-out, except by an accidental ’short-circuit of the. liigh-tcnsion battery. It is probable that the average valve used in a broadcast receiver now has a life of from 3000 to 5000 hours, while cases in which valveij are used

*for OC'OO liouts and 7000 hours arc not uncommon. It is interesting to note that there has also been a steady improvement in tlie quality of bright filaments used in transmitting valves. As an example, a large transmitting valve which was purchased more than three years ago has been in constant operation, frequently . under heavy , .overloads, ever since. Its filament emission and other operating characteristics are still quite normal.