Patent GB-347210-A (GB)
Title: Improvements relating to vacuum electric tube devices or valves
IPC: H03F1/54
Filed: 1930-01-20
Abstract: 347,210. Thermionic valves. DAVIS, N. R., Park House, Atkinson Road, Ashtonon-Mersey, BURCH, C. R., 12, Derbyshire Lane, Stretford, Manchester, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Bush House, Aldwych, London. Jan. 20, 1930, No. 1929. [Class 39 (i).] Relates to means for automatically " conditioning " one or more continuously evacuated values after shutting down, and particularly after dismantling so as to ensure a degasefication of the electrodes ; the cathode current is maintained below normal when the anode voltage is applied and is increased to normal by means associated with the excitation of the grid. The reduction of cathode current is effected by resistances having short-circuiting switches. The cathode current may be reduced automatically below normal when the alternating grid excitation falls below a predetermined value. Fig. 1 shows a bank of rectifiers 4, energized from a three-phase supply 1 through a circuit-breaker 2 for supplying the anode voltage to amplifier banks 13, 16. The motor-generator " drive " 33, 34 is applied to the grids of the amplifiers in push-pull, the output from these being applied in push-pull to the grids of the valves 16, which supply a furnace or other load circuit through a transformer 32. Grid-bias for the valves 16 is derived from a directcurrent generator 17 driven by a variable-speed motor 18. Alternating current filament current is supplied from sources 6, 19, 25, respectively, provided with low voltage relays 11, 23, 29. Fig. 2 shows in section A the circuits and hand-operable switches for the permanently running gear such as the pumps for supplying cooling water and backing and Langmuir evacuating pumps, in section B the preliminary starting gear, the automatic control gear and the hand-controlled " conditioning " gear, and in section C additional " conditioning " gear for use when more extensive " conditioning " is desired than is effected during the normal starting operation. In operation the switch 43 is closed, whereupon, if the permanently-running gear is working satisfactorily, a switch 61 closes to energize the bus-boxes 62. The "drive" set 33, 34 is started by hand through a rheostat 64, and the switch 98, Fig. 3, is operated to close the circuits of the filaments of the rectifier-valves through an auto-transformer 7, and of the filaments of the amplifier valves 13, 16 through dimming resistances 109, 110 and auto-transformers 20, 26, respectively. The " drive " voltage is applied to the grids of the amplifiers 13, the grid-bias generator 17 is started up, and the circuit-breaker 2 is closed through a switch 101. The resistances 109, 110 are short-circuited by contactor switches 111, 112 energized through a contact 115 closed by the arm of the rheostat 79 of the field of the " drive " generator 33 when the voltage of the generator reaches a predetermined value. The field winding 65 of the motor 63 and the field winding 78 of the generator 33 are controlled in the manner set out in Specification 347,34S. In order that more extensive " conditioning " may be effected than is provided by the normal starting operation, the output is reduced and bus-bars 117 are energized through switches 118 so as to provide an artificial load and to permit (a) operation of the grid-bias generator manually, (b) the application of a positive bias for degasefying the grids, and (c) opening of the switches 111, 112 short-circuiting the resistances irrespective of the position of the " drive " generator rheostat. The " conditioning " gear may be cut out subsequently by a press-button switch 131.