GB773580A - Improvements in or relating to cathode structures for electron discharge devices - Google Patents

Abstract

773,580. Thermionic cathode constructions. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Aug. 3, 1954 [Aug. 19, 1953], No. 22817/53. Class 39(1). An indirectly heated cathode structure comprises an insulating disc having an aperture, a cathode comprising a tubular body closed at one end and containing a heater wherein the edges of the open end of the cathode body are seated on the insulating member around the aperture, the heater extending through the aperture in the insulating member into the cathode body so that the end of the heater remote from the tubular cathode body is closely surrounded by the insulating wall of the aperture. In one form, Fig. 3, an insulator 1 of moulded and fired ceramic is provided on one or both sides with circular ridges 3 which prevent metal deposition occurring in operation from forming a continuous path from the centre to the edges, is countersunk at 4 and thickened at 5 and has a central aperture from which three longitudinal slots extend radially. The cathode 7 is closed at one end by an integral portion thereof or by a separate cap and has three strip legs 8,120 degrees apart which in assembly are passed through the slots and their ends bent over. A connecting tape 9 welded to the end of one of legs 8 is threaded through a hole 10 in the insulator. The heater 11 of " molytungsten " wire coated with insulation is thus enclosed partly by the cathode tube 7 and partly by insulator 1; it may contact insulator 1 but not legs 8. In an alternative construction holes can be drilled in the insulator around the central aperture and the cathode legs passed through them, the ends of the legs being bent away from the axis of the central aperture. The invention can be applied to cathode ray tubes, especially for television purposes, klystrons and travelling- wave tubes. The heater may be multiply folded instead of helical.