GB553188A - Improvements in vacuum tubes and method of manufacture thereof - Google Patents

Abstract

553,188. Thermionic valves. HAZELTINE CORPORATION. Jan. 5, 1942, No. 151. Convention date, March 5, 1941. [Class 39 (i)] The grid of a vacuum tube is supported solely by the cathode. In one form an indirectly-heated cathode 17, Fig. 2, is provided with longitudinal grooves into which fit semicircular insulators 29 engaging the support rods 28 of a closely-wound helical grid 25. Especially with valves of high transconductance, this enables the control grid and cathode to be formed into a unit before assembly and avoids damage to the cathode which might result in passing a cathode into a closely-fitting already mounted grid. The insulators 29 may be assembled on, or formed integrally with, either the cathode or the control grid before the insertion of the cathode into the grid, or the insulators may be slid into place afterwards. The cathode and grid may be circular, elliptical or rectangular cylinders. In another form, the grid supports rods 28 fit into insulating buttons 35, Fig. 6, at each end of the cathode, which is indented at 37 to receive the buttons. Recesses 38 in the buttons prevent the evaporation of continuous conductive films from the cathode. The insulating bridge 15 supports the cathode, screen and suppressor grids and the anode and is secured to a metal shield engaging a metal envelope.