GB713011A - Improvements in or relating to cathode ray tube circuits - Google Patents

Abstract

713,011. Television receivers. CINEMATELEVISION, Ltd. Aug. 28, 1952 [Aug. 29, 1951], No. 20404/51. Class 40 (3). [Also in Group XL(c)] In order to prevent damage to the screen of a television receiver cathode-ray tube when either or both of the timebases fail, negative pulses coincident with the foreward strokes of the line and frame timebases are applied respectively to the screen and control grids of a normally conductive pentode 4, the circuit being such that the pentode is cut-off only if line and frame pulses are present simultaneously and the resultant chopped positive pulse, Fig. 2C, at the anode is applied through a low-pass filter 16 ... 18 (cut-off frequency 5 kc/s) to the grid terminal 22 of the cathode-ray tube to intensify the beam during the forward strokes of the frame timebase. The negative frame sawtooth waveform is applied to terminal 1, the required pulse waveform, Fig. 2A, being produced by capacitor 2 and resistor 3, and positive line timebase pulses, Fig. 2B, are applied via terminal 10 to the grid of a triode 8 whose anode is directly coupled to the screen of V4 whose anode is also coupled directly to the grid of V8 so that V4 and V8 constitute a trigger circuit. The maximum potential of the grid of the cathode-ray tube is limited by the diode 20 and brilliance control 21.