GB570834A - Improved arrangement for adjusting small clearances between electrodes in discharge tubes - Google Patents

Abstract

570,834. Thermionic valves. LIEBMANN, G., and CATHODEON, Ltd. Nov. 20, 1941, No. 14912. [Class 39 (i)] [Also in Group II] In thermionic valves, particularly for high-frequency operation, the cathode is mounted on a rigid rod or tube which is linearly expansible by heat and has a heating element independent of the cathode heating element so as to enable fine adjustments of the cathode relatively to the other electrodes to be made after the envelope is sealed. As shown, in a valve having a grid 1 connected to a plate 2 sealed through the envelope 3, an anode 4 in the form of a cup sealed to the envelope on one side of the grid, and an indirectly heated cathode 7 on the other side. the latter is mounted on a tubular member 8. Heating elements 13 for the cathode, and 14 for the member 8 are connected in parallel with a source of current, and a resistance 15 in series with the element 14 is adjusted so that under operative conditions, the spacing between the cathode and grid is brought to the required dimension. The member 8 may be a metal or alloy having a ratio of specific thermal expansion to specific heat conductivity as high as possible. Metals such as nickel and iron, alloys such as platinum-iridium or nickel-iron, particularly the alloy having a composition of 24 to 27 per cent nickel, are referred to. The member 8 is welded to a thimble 9 sealed to the envelope. Alternatively, the member 8 may be glass or a ceramic material, which may have a conducting film when it is required to act as a lead. A lever system may be provided to amplify the expansion movements of the support. The resistance 15 may form a permanent part of the valve structure, and the leads to the heating elements may be arranged in an external extension of the heat expansion element which may form part of a concentric line circuit. Specification 553,350, [Group XXXVI], is referred to in the Provisional Specification.