GB446860A - Improvements in and relating to gaseous electric discharge devices - Google Patents

Abstract

446,860. Thermionic cathodes. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. May 7, 1935, No. 13447. Convention date, May 8, 1934. [Class 39 (i)] A cathode for use in gaseous electric discharge devices, such as high pressure metal vapour lamps, comprises an elongated body of refractory metal having a curved configuration and contained within a loosely-mounted closely-wound helix of refractory wire, with the loose turns at the region of curvature containing the body eccentrically and bearing against the body at the inside of the curve, a thermionically active substance being disposed on the body and the helix, and in the interstices between them. In one form the cathode comprises a V-shaped portion 17, Fig. 3, projecting into the discharge space and surrounded by a single turn. The ends are connected together by a cross-bar 15 supported on the leading-in wire 13. In another form, for heavier currents, the refractory body is wound into a helix 22, Fig. 5, with its axis perpendicular to the lamp axis. The ends of the helix are brought out to separate leads 23. In each case the refractory body is surrounded by a closely-wound helix loosely mounted thereon, forming a store of electronemitting material, At the curved parts the helix bears on the inside of the curve, the turns on the outer side separating slightly and serving to facilitate starting where they project into the discharge space. A lamp is described for use with the cathodes, comprising a tubular envelope supported within an outer jacket by ring spacers at each end which are clamped together by two longitudinal braces one of which acts as the lead to the cathode at the far end. A starting electrode of metal gauze is wrapped about the envelope one-third of the length of the discharge from one electrode and is connected to the other electrode. The portion of the envelope near the ends of the tube may be of uranium borosilicate glass through which the electrodes leads are sealed, and which also absorbs infra-red radiation and maintains the ends of the tube at a higher temperature. The filling may be argon at 5 mms. pressure and mercury, sodium or cadmium in the unsaturated condition. The space between the inner and outer envelopes may contain nitrogen at a pressure of half an atmosphere. Specification 433,520 is referred to.