GB706005A - Improvements relating to cathode ray tube apparatus - Google Patents

Abstract

706,005. Cathode ray tubes. ELECTRIC & MUSICAL INDUSTRIES, Ltd. June 28. 1950 [July 1, 1949], No. 17401/49. Class 39(1) [Also in Group XL(b)] In cathode ray apparatus in which the beam is focused and deflected over a screen, and in which the E.H.T. voltage for the final anode is derived from a poor regulation power supply 7 so that the E.H.T. voltage varies with variations in the beam current, particularly due to the beam modulation in television receivers, and in which the E.H.T. power supply is fed with current from a relatively low voltage source 1, consequential variations in potential of the current fed to the E.H.T. power supply are fed from point 21 to a grid of an amplifier tube 11 to vary its gain and so to -set up compensating variations in its output current which is fed to deflecting and/or focusing means. As shown the output of tube 11 is connected to focusing coil 9, and, through transformer 18, to line scanning coils 17. The relatively low voltage is defined as a voltage suitable for supplying the anodes of amplifier valves in the apparatus and may be 200-400 volts while the E.H.T. voltage may be 4000-8000 volts. A further tube similar to 11 may be provided for energizing the frame scanning coils in a similar manner, Fig. 2 (not shown). A rectifier 1 feeds a D.C. voltage to converter 7 via smoothing condensers 4, 6 and resistor 5 the converter 7 preferably being a high frequency oscillator, the applied voltage controlling the amplitude of the oscillations, and having means for rectifying the oscillations, and the rectifier 1 is also connected via focusing coil 9 and smoothing inductance 10 to the anode of tube 11; the coil 9 has a shunt condenser 13 to reduce ripple and inductance 10 and condenser 14 also serve for smoothing purposes. A grid electrode of tube 11 is fed via decoupling circuit 15, 16, from the junction of resistance 5 and converter 7. Electron discharge tubes represented at 12 are for amplifying the incoming picture signals and for applying them to the modulating electrode of the cathode ray tube. Due to the internal resistance of rectifier 1, the variation in output voltage thereof due to variation in the current input to converter 7 is compensated to some extent by the variation of current through coil 9. Specification 623,037 is referred to.