GB755985A - Improvements relating to electric discharge devices - Google Patents

Abstract

755,985. Thermionic valves. BRITISH THOMSON-HOUSTON CO., Ltd. (General Electric Co.). Feb. 17, 1954, No. 4694/54. Class 39 (1). The cathode 5 and grid 40, Fig. 6, are spaced from one another by an insulator 1 having two accurately formed bearing surfaces 17, 18 on the same side of the insulator, one surface 17 locating the cathode while the other 18 locates the grid. The valve generally is designed to be sealed together by soft solder and evacuated in one operation, being for this purpose formed of a cathode assembly, Fig. 2, an anode assembly, Fig. 4, and a grid assembly 36, 38, Fig. 6. The cathode assembly comprises cathode 5 mounted on the end of cylindrical cathode eyelet 3 which passes through central aperture in insulator 1 and is urged upwards by spiral spring 11 engaging respectively the turnedover end of the eyelet and cathode terminal shell 9 which enters a recess in the back of the insulator and is ultimately sealed therein by solder ring 10. Three lateral supports 3<SP>1</SP> are pinched between shell 9 and the insulator to provide a low inductance connection and, if made of spring material, may replace spring 11 in locating the cathode. Cathode shell serves as lead to the cathode and to one end 16 of the heater 14, the other lead 15 to which is secured to a central pin 47, Fig. 6, supported in insulator 42 sealed by solder rings 49, 50. The anode 25, Fig. 4, has a hollow stem 24 for evacuation which can be sealed at the end by dipping into a solder bath; the stem passes through central aperture in anode insulator 22 and is sealed by solder ring 26. Grid 40 is stretched across support 38 which rests on insulated locating surface 18 and is spaced from anode insulator by spacing ring 36. An external ring 34 surrounds the three assemblies and the space between it and members 22, 36, 38 and 1 is filled with solder when solder ring 41 is melted. The complete assembly shown in Fig. 6, is mounted in a bell-jar, Fig. 8 (not shown), which is evacuated. The solder rings are melted by induction heating to 800‹ C and, after the usual outgassing schedule, a pot of solder is moved up to seal exhaust opening 31. The appropriate surfaces of the ceramic insulators are painted with titanium hydride slurry to give a better bond to the solder. The insulators may alternatively be quartz or a glass capable of withstanding the processing temperature.