GB759565A - Improvements in or relating to circuit arrangements for use in television receivers - Google Patents

Abstract

759,565. Television. PHILIPS ELECTRICAL INDUSTRIES, Ltd. July 9, 1954 [July 10, 1953], No. 20174/54. Class 40 (3). [Also in Group XL (c)] In a television receiver of the type in which the D.C. component of the signal is not applied to the cathode-ray tube, the gain of the receiver is controlled in dependence upon the brightest portion of the picture signal containing the D.C. component. The picture signal of the polarity shown at 5 is applied to the grid of a video amplifier 6, the anode of which is connected through a capacitor to the grid of the cathode-ray tube. The waveform 14 at the cathode of the amplifier is applied to the cathode of a normally non-conductive valve 15 to cause it to conduct and discharge a capacitor 19 on the occurrence of the brightest parts of the picture. The capacitor is charged through a rectifier 17 by pulses derived for example from the line time base and the voltage at the anode of the rectifier depends upon the amount the capacitor 17 is discharged and accordingly upon the brightest part of the picture. Part of this voltage is applied through lead 20 to control the gain of the receiver. A switch 22, 23, ganged with a station selector switch (not shown) feeds the video signal to the grid or cathode of a cathode-ray tube according to whether the signal is positively or negatively modulated. In the latter event the A.G.C. potential derived from the synchronizing signal peaks.