GB522165A - Improvements relating to time base circuits - Google Patents

Abstract

522,165. Valve generating circuits. KOLSTER-BRANDES, Ltd., SMYTH, C. N., and SHANNON, D. S. B. Dec. 2, 1938, No. 35165. [Class 40 (v)] A time-base circuit of the non-self-running type for television systems, oscillographs &c. includes means for applying to a control electrode of a discharge tube for periodically charging or discharging a condenser a bias which changes to render the tube more susceptible to triggering pulses as they become due. In the circuit shown in Fig. 1 a resistance R1 and condenser C1 are connected in parallel in the anode circuit of a grid-controlled valve V, to the grid of which synchronizing impulses are applied over a condenser C2. On receipt of an impulse the valve conducts, the condenser C1 is rapidly charged through the valve, and then slowly discharges through the resistance R1 until the next impulse is received. To reduce the effects of interference the control grid is connected to the slider of a potentiometer R. While the condenser C1 is discharging the anode voltage rises, and a fraction of this rising voltage is applied to the control grid in addition to the constant bias from the network R3, C3. Over the greater part of this time the grid bias is too negative to allow interference pulses to trigger the valve. Alternatively a discharge tube of the deflection control type may be used for charging and discharging the condenser as shown in Fig. 2. The electron tube V2 comprises a cathode K, focussing electrode F and two anodes A1 A2, with a deflecting plate A3 for deflecting the stream from one anode to another. A relaxation condenser C is connected between the cathode K and the main anode A2, in series with which is a condenser-charging resistance R4. A current limiting resistance R5 is inserted in the connection to the auxiliary anode A1. Television signals are applied to the plate A3 and normally deflect the beam to the auxiliary anode A1 so that the condenser C charges over the resistance R4. On the arrival of a synchronizing pulse the potential of the plate A3 becomes less negative and allows the beam to fall on the main anode A1 and discharge the condenser. A fraction of the anode voltage is applied to the deflecting plate A3 which is thereby prevented from becoming highly positive, due to the arrival of an interfering pulse, until the condenser C has become charged. A pentode amplifier may be incorporated in the envelope of the deflection control tube as shown.