GB400976A - Improvements relating to oscillatory electric circuits, such as may be used, for example, in connection with cathode ray devices - Google Patents

Abstract

400,976. Valve generating circuits. ELECTRIC & MUSICAL INDUSTRIES, Ltd., Hayes, Middlesex, and BLUMLEIN, A. D., 32, Woodville Road, Ealing, London. April 4, 1932, No. 9651. [Classes 40 (iii) and 40 (v).] A generator of saw-tooth oscillations has two reactive circuits 7, and 7, 8, Fig. 1, with different reactive properties, and means 2, controlled by applied signals, for transferring the control of the form of the generated wave from one circuit to the other. Normally a positive potential Vg on the grid of the thermionic valve 2 keeps its impedance low, so that the voltage Vc across the controlling-coil 7 of a cathode-ray tube, due to a high-tension source 6, is substantially constant, and the current IL in the coil increases from zero at a uniform rate. When a negative synchronizing impulse is applied to the grid, the impedance of the valve increases and the current IL is diverted to the condenser 8. This starts an oscillation in the circuit 7, 8, which is stopped after half a cycle by the condenser discharging through a diode 3. The current IL is now in the opposite direction, and is reduced to zero at uniform rate by the battery 6, thus completing the cycle, Fig. 2 (not shown). A tuned circuit 9 prevents spurious oscillation. According to modifications, the amplitude of the synchronizing impulse is increased by backcoupling from the coil 7 to the transformer 1, Fig. 3 (not shown) ; the inversion of the diode is avoided by connecting it across a coil coupled to the coil 7 ; the controlling coil of the cathode-ray tube is coupled to the inductance 7 by a condenser ; the wave form of the synchronizing impulses corrects the effect of resistance in the circuits. As shown in Fig. 4, a condenser 14 across the controlling-plates of the tube is charged at a uniform rate from a high-tension source 17 through a large inductance 15. A positive synchronizing-impulse on the grid of a gas-discharge valve 12 makes it conducting to discharge the condenser through a coil 13. This starts an oscillation in the tuned circuit, but, after half a cycle, the condenser charges in the opposite direction and applies a negative potential to the anode of the valve 12, which ceases to conduct. The condenser is then discharged at a uniform rate through the inductance 15, thus completing the cycle, Fig. 5 (not shown). At low frequencies, mechanical switches may be used in place of the valves 2, 12.