GB862448A - Improvements in or relating to thermionic valves - Google Patents

Abstract

862,448. Thermionic valves. M-O VALVE CO. Ltd. June 15, 1959 [June 18, 1958], No. 19479/58. Class 39(1). In a thermionic valve of the kind including a cathode, having a planar electron-emissive surface 2, and a planar control grid 11 disposed parallel to and not more than 0.1 mm. from the emissive surface, the control grid and emissive surface are supported by a system which includes at least four parts joined together successively between the emissive surface and the grid, the arrangement being such that upon thermal expansion of the parts, the successive parts alternately tend to urge the emissive surface towards and away from the control grid whereby the clearance between the emissive surface and the grid, preferably about 0.025 mm., remains substantially constant despite any change in the ambient temperature or in the operating temperature of the cathode which may occur during operation of the valve. As shown, the support system comprises an impregnated, porous tungsten disc 3 and a molybdenum cup 4; a tube 15 of an alloy consisting by weight of 30% tungsten and 70% nickel; a nickel tube 18; and two annular members 21, 26 of an alloy consisting by weight of 42% nickel and 58% iron, a molybdenum shim 27 and a ceramic tube 23. The dimensions of the various parts are given. According to the Provisional Specification the valve is designed for insertion into two waveguides having a common wall. A foil of insulating material is wrapped round the cathode contact so that the contact foil and the metal tube, formed in the wall of the input waveguide, into which the contact is inserted, form a capacitive element which provides a radio frequency connection between the input waveguide and the valve while allowing a biasing potential to be applied to the grid.