Improvements in or relating to electron discharge tube circuits for generating electrical oscillations of sawtooth waveform

摘要

655,790. Sawtooth generating circuits. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Nov. 24, 1948, Nos. 30492/48 and 24321/49. [Class 40 (vi)] In a circuit for generating a sawtooth wave in an inductive load, of the type in which the return stroke is generated by allowing the load to execute a free half-cycle of oscillation and in which the initial and remaining part respectively of the forward stroke are generated by the current in a damping valve and a driving valve, negative feedback is applied to both valves. In Fig. 1 one valve is the driver and one the damping valve, the two valves being controlled by the push-pull outputs of a sawtooth source 5 and the negative feedback being obtained from a resistor 12 in series with the output coil 11. The damping valve may alternatively be connected directly across the secondary winding 10 of the output transformer (Fig. 2, not shown). In Fig. 3, the latter part of the waveform applied to the scanning coil 21 is generated by the output from a driver valve 13 and the first part by the current through a damping valve 14 resulting from the " resonant return" operation. Negative feedback is applied from the output circuit through capacitor 28 and a pair of cathode coupled amplifier valves 24, the first anode supplying the feedback for the driver valve and the second anode the feedback for the damping valve. The coupling capacitor 28 and resistor 31 are proportioned such that C28xR31=L21/R23 to produce a downward slope to the feedback pulse to compensate for the resistance 23 of the scanning coil. Resistor 46 in the second anode circuit of valve 24 is made smaller than resistor 35 in order that the damping valve is cut off slowly whereas the driver valve is brought into operation more rapidly. The flyback is initiated by negative pulses from a valve 55 which cuts off the driver valve, a rectifier 38 being provided to prevent the absorption of the synchronizing pulse by a capacitor 44 which is inserted to prevent selfoscillation due to phase shift in the feedback path. A potentiometer 33 adjusts the slope of the output wave. The linearity of the wave may be improved by connecting a resistor 57 in series with the anode of the damping valve, the value of the resistor being equal to the effective anode impedance of the valve (i.e. as modified by the negative feedback) so that the anode is substantially a point of zero impedance.