GB840310A - Improvements in or relating to thermionic valves - Google Patents

Abstract

840,310. Thermionic valves. STANDARD TELEPHONES & CABLES Ltd. Feb. 27, 1959, No. 6991/59. Class 39(1). In a thermionic valve an indirectly-heated cathode sleeve is locked in an upper electrodelocating-insulator and is free to move axially, due to thermal expansion, through a lower insulator. A cathode tail is secured to the upper end of the cathode sleeve and passes down inside the sleeve to make connection with a lead sealed through the valve base below the lower insulator. As shown the cathode sleeve 10, Fig. 3, of a triode is locked in an upper mica disc 5 by means of a projecting rib 11 and rolled down portions 12 of the sleeve. Since the cathode tail 15, of nickel tape, is welded to the top 16 of the sleeve, it is less liable to fatigue due to bending upon expansion of the sleeve. In an alternative embodiment the rolled-down portions 12 are replaced by an extension of the cathode tail which is brought out through the top of the sleeve turned over and made to bear against the top of the insulator 5. In this case the tail is pressed against the inside of sleeve 10 by heater 16, Fig. 6, and may be secured to the outside of the sleeve by welding at 17. The end of the tail 15 may be sandwiched between insulator 5 and a further insulator 18,