GB698896A - Improvements relating to concentric keep-alive electrode arrangements in electric discharge devices such as t.r. switches - Google Patents

Abstract

698,896. Cold-cathode tubes. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 14, 1951 [Dec. 12, 1950], No. 30339/50. Class 39(i) In a T.R. switch comprising two coaxial main electrodes forming part of a resonant circuit and at least one of which is hollow and contains an auxiliary " keep-alive " electrode, the tip of the hollow electrode is of skeleton construction so that the operative end of the auxiliary electrode is visible and its separation from the main electrode can be readily determined, but at the same time the main gap is shielded from the auxiliary electrode. Figs. 1 and 2 show a known construction of T.R. switch, to which the invention is applicable, comprising a length of metal rectangular waveguide 1, electroplated internally with silver and/or copper, having end flanges 2 and 3 and hermetically sealed at each end by a metal plate provided with a slot 5 into which glass is sealed by fusion, the slot being tuned to preferably the mid frequency of the operating band. A single member having flanges which are brazed to the walls of the waveguide provides two partitions 7 forming an iris 6 which together with coaxially mounted main electrodes 11 and 12 constitutes a resonant circuit tuned to substantially the same frequency as the slots 5. The partitions 7 are separated from the side walls of the guide by spaces 8 to' facilitate chemical cleaning and/or electroplating of the envelope during manufacture. Electrode 11 is mounted on a flexible diaphragm 9 and is surrounded by a tube 10. Adjustment of the position of the electrode is possible by means of a screw 19 threaded into the tube 10, and a second screw (not shown) can replace the screw 19 to engage the thread in the electrode 11 for major retractions. Electrode 12 is fixed in the upper wall of the guide and is made hollow to receive an auxiliary electrode 14 which is sealed into the mounting tube 20 by a glass bead 21. The apparatus can be evacuated and filled with gas through an exhaust tube 22 which is sealed by a glass bead 23. Fig. 3 shows an electrode construction according to the invention wherein the hollow main electrode 12 is provided with a tip in the form of a wire loop 13 welded to the electrode. The auxiliary electrode 14 is covered, except at its operative end 15, by a glass coating 29 and the second main electrode 11 is solid. In an alternative embodiment both main electrodes are hollow and contain auxiliary electrodes, the wire loops forming the skeleton tips of the main electrodes being arranged at right angles to one another. Alternative forms of the skeleton tip comprise two wire loops, one wire loop and two short probes, a wire gauze, a plurality of straight or curved wires secured across two projections from the hollow electrode, and a bridge piece formed integrally with the electrode.