A NEW FILAMENT

Evening Star, Issue 20985, 26 December 1931, Page 4

A NEW FILAMENT

A new coated filament which has been produced has several advantages over the older types of coated filaments. This has a high electron emission per watt of filament energy _ supplied ; an electron emission which is lasting; non-micro-phonic properties all combined with rigiditv and - robustness. The'low thermal property, which gives the first advantage enumerated above, means a reduction in the amount of heating energy required to emit a given quantity of electrons from the filament surface. In the case of this new, filament the electron emission per watt of energy supplied from the accumulator i? higher than ever before obtained in respect of a 2-volt valve. This omission efficiency has a two-fold advantage; it effects a saving in the cost of running the valve from an accumulator by cutting down the accumulator charging expenses to a minimum, and it permits a very long filament to be employed even though the filament voltage is as low as 2 volts, and this has the effect of increasing' the surface area of the filament available for electron emission. The greater the emissive surface area available, the higher can be‘made the eletrical characteristics of the valve; thus the new filament, with its long length and largo area for emission, conduces to a very high electrical efficiency without the necessity for resorting to extremely close clearances between electrodes. A new 2-volt pentode is the first valve to be fitted with this type of filament. The filament has enabled a very high degree of mutual conductance (as high as 2.5 ma/v) to be obtained while, at the same time, adequate electrode clearances are still maintained so as to ensure rigidity and freedom from electrode contact. This last-mentioned feature is particularly important in the case of pentode valves with their complicated internal construction.