GB473666A - Improvements in and relating to thermionic discharge devices - Google Patents

Abstract

473,666. Thermionic valves and relay circuits. BRITISH THOMSON-HOUSTON CO., Ltd. April 22, 1936, No. 11499. Convention date, April 23, 1935. [Classes 39 (i) and 40 (v)] In a discharge tube having an ionizing medium therein such as argon, at a pressure of 1 to 500 microns or mercury or caesium and wherein the initia tion of a discharge is controlled by a grid 15, this grid is shieldec against heat radiation electrostatic effects and sputtering from the anode 5 and the cathode 7 by cylin ders 20, 21 with punch ed out holes to allow for the discharge flow As shown the grid is formed of a number of rings 18 supportec by side rods which are also screened by the cylinders 20, 21; in a modification the gric is formed of a cylinder with punched out parts leaving cylinders con nected by vertica strips all shielded by cylinders such as 20 21. The electrodes and shields are carried be tween mica end plates 8, 10 held together by bolts 9, one of which serves as the anode connection to the lead 12 ; this also carries the getter plate 14, the getter consisting of an alloy of barium or strontium with aluminium. A filamentary cathode or an indirectly heated cathode as described in Specification 386,376 is used ; the filament may be coated with emissive material. The potential of the grid is determined by a photo-electric cell 45 in a bridge including resistances 47, 48 connected to a secondarv 41 of the transformer 40. Bias for the shields may be obtained from external sources or as shown is obtained from another secondary 42 through a circuit including a condenser 49 and resistances 50, 51 one side of the condenser being connected to the cathode ; heating current from the secondary 43 is supplied to the cathode through leads, one of which is connected to one side of the transformer to take the main discharge current. A load 44 is included in the anode lead. Specification 445,593 also is referred to.