GB521850A - Improvements in and relating to thermionic electrodes for electric discharge devices - Google Patents

Abstract

521,850. Thermionic valves. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 26, 1938, No. 34472. Convention date, Nov. 26, 1937. [Class 39 (i)] Thermionic cathodes or arc discharge rectifiers &c. have one part rendered emissive by heating current and another part becoming emissive on being heated by power losses in the discharge so that the required heating current is reduced and the total emission increases automatically with the load, substantial variations in the arc drop being thus avoided. The cathode may comprise inner and outer helices 20, 21 connected across common leads 14, 15 transverse to the arc. Each helix consists of a refractory wire core overwound with fine wire coated with thorium oxide or alkaline earth or other emissive material. The inner helix 20 is heated by current supplied through the conductors 14, 15 to produce an arc passing through the outer helix which is heated primarily by this arc rather than by current from the conductors 14. 15 or heat radiation from the inner helix. In modifications, the outer helix 21 is replaced by two concentric outer helices or is connected at both ends to one only of the conductors 14, 15 or is so connected to the conductors 14, 15 that current flows through it in a direction opposite to that of the current in the inner helix 20, thus eliminating magnetic effects and producing a uniform distribution of discharge current along the length of the cathode. In other modifications, the outer helix 21 is replaced by an open ended imperforate or mesh cylinder coated with emissive material. The gas filling may be mercury with argon or helium.