GB536070A - Improvements in and relating to thermionic discharge devices - Google Patents

Abstract

536,070. Thermionic valves. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 30, 1939, Nos. 31133, 31134 and 31135. Convention dates, Nov. 30, 1938, March 11, 1939, and April 8, 1939. [Class 39 (i)] A thermionic cathode, especially for a gas filled valve, consists of an emissive surface or surfaces within a heat-shielding casing, which also encloses a heater, the emissive surfaces being heated substantially uniformly by radiation and reflection from the heater and casing, from both of which they are substantially insulated thermally. Figs. 1 and 2 show emissive surfaces 7 ... 12 made of wire net or of corrugated metal covered with net and arranged radially within the casing 18. The heater consists of a wire 1 wound on a refractory core 2 and separated from the emissive surfaces by insulating blocks 5, 15 but in electrical communication with them by a washer 13. The casing 18 is of thin perforated sheet metal coiled in several layers, the edges of the perforations being burred to separate the layers; it may be connected electrically to the emissive surfaces by a high impedence 46 as described in Specification 529,934. The whole cathode structure 29, Fig. 4, may be mounted by insulator 39 on rods 37 which also support a shield 35 carrying the grid 31, which may be a perforated graphite disc. In a modification the heater consists of a wire packed in a mixture containing emissive material enclosed in a wire net sheath. The mixtures may be 70 per cent barium oxide and 30 per cent aluminium oxide, and during operation the barium oxide evaporates and condenses on the emissive surfaces. Or the heating wire may be wound on a rod of such material. In other modifications the emissive surfaces consist of ribbons of wire net wound helically on vertical supports. Specifications 309,447, [Class 39 (i)], 380,025, 383,645 and 446,478 also are referred to.