GB697819A - Automatic-control apparatus - Google Patents

Abstract

697,819. Television. HAZELTINE CORPORATION. July 5, 1951 [July 21, 1950], No. 15987/51. Class 40 (iii). [Also in Group XL (c)] In a television receiver in which the signal from the video amplifier 16, Fig. 1, and a gating pulse from the line amplifier 23 are applied to a stage 19 to produce an A.G.C. voltage on line 25, variations in output due to the change in relation phase of the inputs to stage 19 are minimized by the provision of a further shortergating pulse. Normally non-conducting valve 30 has a pulse A, Fig. 2, applied to the anode, at the time of occurrence of the synchronizing pulse B. A further pulse C is derived from pulse A over the differentiating circuit comprising capacitor 50 and resistor 37 so that the input to the grid of valve 30 appears as in curve D. Due to the bias network 32 only a small part of curve D is effective to produce conduction in the valve, curve E. The capacitor 47 is thus charged negatively to give the A.G.C. voltage while the network 32 biases diode 42 which only conducts during synchronizing signals. If the line time-base should run slow and give a pulse A<SP>1</SP>, the corresponding pulse D<SP>1</SP> is still as effective as D and gives a current pulse E<SP>1</SP>. In a modification, Fig. 4, the differentiated pulse is fed to the outer grid of the heptode 70 over the differentiating circuit 50, 71, 72, and the valve is held in a non- conducting state by the divider 62, 63. A pentode may replace the triode 30, Fig. 3 (not shown). Specification 697,821 is referred to.