GB315094A - Improvements in and relating to electric arc devices - Google Patents

Abstract

315,094. Freedman, P. July 5, 1928. Vacuum tubes; low-pressure metallic-vapour apparatus.-In arc-discharge devices adapted to function as rectifiers, oscillators, or amplifiers in which the volt-ampere characteristic of the discharge is controlled by means of a grid electrode, and wherein all the electrodes are of refractory material the anode is situated between the cathode and the grid electrode. The envelope is filled with gases such as nitrogen, argon, neon, &c. or with vapour of mercury, rubidum, caesium, &c., or with a mixture of gas and metal vapour. The device is operated with the grid positive with regard to the cathode, the arc discharge between them having a negative characteristic, and the discharge between the anode and the cathode may have either a negative or positive characteristic. The device shown in Fig. 1 comprises an anode 7, a control electrode 8, and a cathode 9 consisting of a filament having a helical portion and a straight portion on which is threaded a tube of tungsten mixed with thoria or like oxides. The discharge is started between the anode and the heated coiled part of the filament but passes later to the tubular part of the cathode. The cathode may consist wholly of a helical filament, or it may be formed as a refractory bead 13, Fig. 4, in which case the anode 14 may be formed as a ring so as not to shield the cathode from the control electrode 15. A mercury pool 16 may be provided to supply vapour. A device for large power output is shown in Fig. 5 and comprises a control electrode 17 in the form of a refractory block, an anode 18, a cathode 19, and an auxiliary starting-cathode 20 consisting of a filament coated with emissive oxides. The device is started by using the cathode 19 as an anode with respect to the auxiliary cathode 20 and so heating it by bombardment to an emissive temperature.