GB912414A - Improvements in or relating to apparatus employing electronic valve devices - Google Patents

Abstract

912,414. Valve supply circuits. COMMUNICATIONS PATENTS Ltd. May 31, 1961 [June 10, 1960], No. 20526/60. Class 40 (6). The anode of a magnetron 22 is fed via rectifier 19 from the secondary of a transformer 10 and its cathode heater 26 from the secondary of a transformer 23. A third transformer 13 has one secondary winding 15 connected in series aiding with the secondary of transformer 10 and a second secondary winding 16 connected in series opposition with the secondary of transformer 23. The primary of transformer 13 is fed from the slider of a variable auto-transformer 27 which is connected, in parallel to the primary of transformer 10 to the contacts of contactor 29. The primary of transformer 24 is connected, via series resistor 34, and in parallel to the input terminals of contactor 29 to the main control switch 30. Also connected to this switch is the coil 31 of a thermal delay switch having contacts 33 which connect coil 32 of contactor 29 into circuit and contacts 35 which short-circuit the resistor 34. Upon closure of the switch 30 and with the slider of auto-transformer 27 at minimum, the heater of the magnetron 22 is energized, resistor 34 limiting the heater current. After a time determined by thermal delay switch 31, this switch operates to close contacts 33, 35, thereby short-circuiting resistor 34 and applying full heater volts to the valve heater, and also energizing contactor 32 whereby its contacts are closed and anode volts are applied to the anode of the magnetron. As the slider of auto-transformer 27 is moved up, the anode voltage of the magnetron is increased but, due to the inverse connection of the winding 16 the heater voltage is decreased, thereby compensating for the additional heating effect produced by increased bombardment of the cathode. A further pair of contacts on the contactor 29 is utilized to short-circuit the primary of transformer 14 when the main contacts of the contactor are open, thereby preventing energization of the transformer 10 via the auto-transformer 27 and transformer 13, through the secondary 16 of which the heater current of the magnetron passes.