GB566835A - Cathode ray beam deflecting circuits - Google Patents

Abstract

566,835. Valve generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 30, 1943, No. 10652. Convention date, June 30, 1942. [Class 40 (v)] In a magnetic deflecting system for a cathoderay tube, linear deflection and high efficiency consequent on the use of a large percentage of current from an inverted suppressor tube is obtained by applying to the inverted suppressor tube a potential derived from the deflecting coils through a passive coupling network. The arrangement is such that the driving tube operates without substantial regeneration. Fig. 5 shows a control tube 10 feeding deflecting coils 62 and an inverted suppressor tube 66 arranged to pass current in opposition to that passed by the tube 10. Tubes 10, 66 are preferably beam power tubes. Centreing of this beam is affected by varying the currents in the coils 62 by resistance 64. The tube 66 is connected across the coils 62, resistance 70 being provided, if necessary, to limit the anode volts. The heater winding of the valve 66 is insulated and preferably of low distributed capacity. Control of the tube 66 is effected by varying the screen potential by potentiometer 68. Grid bias is produced by grid current in the elements 74, 76. The controlling voltage is derived from the voltage across the deflecting coils 62 by differentiation in the circuit 78, 80 and 81. Capacity 80 may be comprised wholly by the self capacities 80<1>. A large condenser 73 is provided to maintain the anode voltage of the tube 66 constant. In a modification, Fig. 6 (not shown), a bleeder resistance is provided so that the whole anode voltage may be applied to the tube when the grid bias is controllable. Fig. 7 shows a modification in which the inverted suppressor tube 86 is isolated from the control tube 10 by a transformer 88 which passes the lower frequencies, a condenser 90 being provided for the higher frequencies. Centring in this case is affected by a potentiometer 92. In the cathode circuit of the inverted valve 86 bleeder resistance 110 is provided and the grid is connected through a network comprising a variable condenser 112 in parallel with the interelectrode capacity 114 and the elements 106, 108 to the deflecting coils 62. The screen grid voltage is substantially that across the deflection coil adjusted by a proportion obtained from the potentiometer 68 or by a series resistance. Fig. 8 shows a modification in which the inverted suppressor tube 116 is isolated from the tube 10 and control grid bias is obtained from the source 118 through a choke 122. Diode 130 is arranged to open the screen grid circuit during the retrace period and a condenser 134 forces the cathode of the diode to follow the cathode of tube 116 and so guards against the screen grid emission current, bombarding the control grid in the tube 116 and also prevents the circuit acting as a relaxation oscillator.