GB505490A - Improvements in or relating to cathode ray tube television and like apparatus - Google Patents

Abstract

505,490. Television. WHITE, E. L. C., and FAUDELL, C. L. Oct. 11, 1937, Nos. 27657/37 and 2084/38. [Class 40 (iii)] A cathode-ray is cut off if either deflecting force fails. The current passed by a controlling valve V4 is regulated by potentials derived from scanning oscillators V1, V3. An additional winding 10 on the frame scanning transformer TF supplies current through a rectifier 11 to a load resistance 12. The potential across this resistance is applied through a filter 14, 15 to the controlling grid of the valve V4, and, if the scanning currents decrease, the anode current so decreases that a coil 4 releases a contact 3 to break the mains supply to the cathode-ray tube CR. The current for the coil 4 and the valve V4 is obtained from the potential developed across a resistance 16 in a resonant return circuit 17, V2, 19, which, in conjunction with a valve V1, produces the line-scanning oscillations as described in Specification 400,976. If these oscillations fail, the current through the valve V4 is insufficient to maintain the relay 3, 4 closed. This decrease in anode current also renders a valve V5 conducting to discharge a high-tension lead 9 to the cathode-ray tube. According to modifications, both scanning oscillators affect the grid circuit of the control circuit of the controlling valve, which has a separate high-tension supply and cuts off the high-tension supply to a transmitting cathode-ray tube through two relays in series, Fig. 2 (27557/37) (not shown) ; potentials derived from the scanning circuits are applied respectively to two controlling grids of a a hexode, which controls a relay to disconnect the high-tension supply to the cathode-ray tube and discharges the high potential on the accelerator or first anode of the tube, Figs. 1 and 2 (2084/38) (not shown) ; rectified outputs from sources of line-frequency and framing-frequency signals are applied through resistances to the grid of a double-diode triode with the relay 3, 4 in its anode circuit, and the diodes limit the maximum of the rectified outputs to the potential of the grid-bias battery, Fig. 5 (not shown). Specification 423,213 also is referred to.