GB864933A - Improvements in or relating to cathode ray tube circuits - Google Patents

Abstract

864,933. Cathode-ray tube circuits. BUSH & RANK ClNTEL Ltd. Dec. 2, 1958 [Dec. 2, 1957], No. 37444/57. Class 40(7) Relates to circuits for preventing the production of a focused beam in a cathode-ray tube in the absence of both or one of two scanning generator outputs. The frame time-base potential at terminal 1 is amplified by valve 3 and fed to voltage-doubling peak-rectifier 12... 15. The rectified signal is fed to triode 17 together with the line time-base signal from terminal 18. The cathode of triode 17 is so biased, from divider 21 . . . 24, that a relay 20, which controls the production and/or focus of the C.R.T. beam, and which is in the anode circuit of the triode 17, is operated only when both inputs are simultaneously present. A small inverse current is passed through relay 20 from resistor 31 to render the circuit more sensitive to changes in the operating signals and to reduce its release time. Upon first energising the circuit, positive surges at the anode of valve 3 are by-passed from the rectifiers 12, 13 by a rectifier 25 which, after an interval, becomes non-conducting due to the application of a positive potential to its cathode from voltage-divider 27, 28 which includes a time-constant condenser 26. Such surges are also reduced by the provision of a time-constant cathode biasing circuit 6, 7 and screen grid supply circuit 29, 30. The gain of valve 3 is stabilized by a feedback circuit 9, 10, 11.