GB223921A - Improvements in electric discharge apparatus - Google Patents

Abstract

223,921. British Thomson-Houston Co., Ltd., (Assignees of Prince, D. C.). Oct. 23, 1923, '[Convention date]. Thermionic generators.-In a discharge tube containing a gas or vapour which is continuously ionized during operation, a negatively-charged grid is mounted so that electrons passing to the anode must pass through the grid, and the grid openings are of such a size relatively to the number of positive ions in the neighbourhood of the grid and to the negative potential applied thereto, that with a small negative potential applied to the grid the current is interrupted even when the anode is charged to a high positive potential. The grid closely surrounds the anode at a distance equal to the mean free path of the electrons passing to the anode. In the arrangement shown for converting continuous into alternating current, two anodes 8, 9 are mounted in tubes 7 branched from a main container having a mercury cathode 2 and two mercury anodes 3, 4 for maintaining the arc. The positive supply main is connected through an inductance 19 and transformer windings 20, 21 with the anodes 8, 9, and the negative is connected with the cathode 2 and earth. The grids 10 are connected together through a winding 25, which has an intermediate point joined through a resistance 28 to earth, and is coupled with a primary winding 24 connected through condensers 23 with the windings 20, 21 which are shunted by a condenser 22. The anodes 3, 4 are continuously excited from a source 5 and an inductance 6 is inserted in the lead to the cathode. The circuit arrangement is similar to that described in Specification 206,837, and is such that if a grid is made negative at the instant when the current to the corresponding anode is zero, current will be prevented from starting up until the negative potential is removed. The resistance 28 reduces the current in the grid circuits. It is stated that a negative potential of 130 volts on a grid prevents current from starting even with a potential of 45,000 volts on an anode. Specification 5684/15 also is referred to.