GB293723A - Improvements in the evacuation of vacuum electric tube devices - Google Patents

Abstract

293,723. Robinson, E. Y., and Metropolitan-Vickers Electrical Co., Ltd. March 11, 1927. Vacuum tubes.-In the evacuation of vacuum tubes with oxide or other thermionic cathodes, one electrode only, for example the cathode, is first heated, after the tube has been pumped and sealed, to drive off gas therefrom and during or immediately subsequent to this heating a metallic getter, not on the cathode, is heated to combine with the evolved gas, another electrode such as the anode being then heated to drive off gas which is absorbed by a heated metallic getter during or subsequent to the heating of the anode. Two separate getters independently heated preferably by different heating means may be employed. Two discs not forming parts of electrodes and carrying getters may be located at different ends or sides of the tube or at rightangles : either or both may have several pieces of magnesium welded on. When an indirectlyheated cathode, such as a nickel tube coated with barium and strontium oxide and heated by radiation or conduction from a heater or by electron bombardment from an auxiliary cathode, is used, the cathode is originally coated with carbonate and is heated by an electric current to form the oxides after pumping the vacuum tube without heat-treating the electrodes and after sealing. The carbon dioxide is absorbed by magnesium supported on a disc and heated by high-frequency induction with or without vaporization and without heating the electrodes. The gas pressure is thus reduced to 0.1 mm. and the anode is then heated by electron bombardment to a dull, redheat to drive out occluded gases and to vaporize one or more pieces of magnesium welded to the anode. A final clean-up of gas may be produced by the vaporized magnesium or by lime on the pinch under the influence of positive-ion bombardment when the device is operated at normal or higher voltages. Reference has been directed by the Comptroller to Specifications 151,611, [as open to inspection under Sect. 91 (3) (a) of the Acts], and 231,467.