GB665468A - Improvements in and relating to electric discharge devices - Google Patents

Abstract

665,468. Electric discharge devices. ENGLISH ELECTRIC CO., Ltd. Oct. 21, 1949 [Oct. 27, 1948], No. 27933/48. Class 39 (i). The cathode of a metal vapour electric discharge device comprises a shallow pool of metal supported on a flat metal plate forming part of the envelope and provided with an upstanding marginal flange the edge of which is sealed to the vitreous or ceramic portion of the envelope, the seal being below the level of the cathode metal. As shown, Fig. 1, the liquid mercury cathode 4 is supported by a "Kovar" Registered Trade Mark) plate 1, and extends above the level where the flanged marginal portion of the plate 1 is sealed at 2 to the tubular glass envelope 3. The plate 1 is stiffened by a steel disc 7 copper brazed thereto and cooled by a metal radiator 5 having cooling fins 6 secured to the disc 7. A connection 8 for the grid 11 is brought through the cathode by means of a glass seal 9 and Kovar eyelet 10, welded to the plate 1, and above the cathode liquid level the insulation of the grid lead is effected by beads 13, the gaps between the beads forming a highly deionized path to the lead 8 to facilitate operation of the device. The lead-in 14 for the excitation arc supply is similarly brought through the cathode and is connected to a support 18 of a magnetically-operated ignition dipper electrode 19, as described in Specification 665,467. A cathode spot fixing plate 20 secured to the disc 1 projects from the mercury surface near the dipper 19, and increases stirring of the cathode liquid to enhance cooling. In another embodiment, Fig. 2, the Kovar cathode supporting disc 28 is annular in shape and is sealed to the envelope 23 and to an inner tube 24 through the closed upper-end of which are sealed the lead-in grid and excitation conductors 25, 26 and an exhaust and sealing-off tube 27. The disc 28 is stiffened by a Kovar plate 30 copper-brazed thereto, to which a mild steel radiator 31 is soldered after baking out. An annular steel or other body 37 of high thermal conductivity, provided with a spot fixing ring 38 is mounted beneath the cathode surface to reduce the quantity of mercury 22 required and to enhance cooling. The body 37 is slightly spaced from the plate 28 or may itself form the major portion thereof, in which case Kovar rings welded to its outer and inner peripheries are sealed to the envelope 23 and tube 24. In a further embodiment, the major portion of the Kovar cathodesupporting plate is made re-entrant, in order to reduce the amount of cathode material. The ratio of cathode diameter to depth of cathode material is between 6: 1 and 30: 1.