GB491179A - Improvements in thermionic cathodes for electric discharge devices - Google Patents

Abstract

491,179. Discharge lamps. GENERAL ELECTRIC CO., Ltd., and PEARCE, A. G. July 29, 1937, No. 21033. [Class 39 (i)] An electric discharge device having a thermionic cathode which, in operation, is heated by the discharge only has a cathode comprising a helix of refractory metal made up of two parts, each substantially cylindrical, of which one part is relatively wide and encloses the body of thermionically active material while the other part is relatively narrow and is turned towards the path of the discharge. The device is of the high pressure metal-vapour type and the thermionically active material forms the starting electrode and the narrow helix of refractory metal the running electrode. For operation on alternating current the cathode acts as an anode for part of the cycle. As shown the tungsten wire of the helix is close wound and is À35 mm. diameter and the wide portion 1 is 1À5 mm. internal diameter and the narrow portion 2 of 1À0 mm. internal diameter. The rigid body 3 may be a rod of alkaline earth oxides enclosed in a tungsten wire helix close wound and of À15 mm. wire on a 1 mm. mandrel. The cathode may be mounted by one lead only and the rod may be retained in the helix by handing the lead 4 across the opening. The cathode may be degassed and activated by bombardment only or heating may be effected by current passed through the helix. Specifications 444,545, 472,658, and 491,176 are referred to.