Patent GB-663034-A (GB)
Title: Improvements in cathode ray tube apparatus
IPC: H04N3/185
Filed: 1947-08-08
Abstract: 663,034. Automatic regulation. RADIO CORPORATION OF AMERICA. Aug. 8,1947 [Aug. 10, 1946], No. 21990/47. Class 38 (iv). In a cathode-ray tube, such as a television receiver in which the signal-modulated beam is scanned over a luminescent screen, variations in the potential of the final anode caused by the beam modulation (due to poor regulation of the power supply) are compensated by a controlling circuit which varies the anode potential in accordance with the average signal amplitude so that as a result the anode potential is maintained substantially constant. In one form, Fig. 1, the supply circuit comprises an oscillator valve 1 with control electrodes 3, 5 coupled via coils 7, 9 to rectifiers 13, 17 the output of which is applied through resistance-capacity filters 21, 23; 25, 27 to the final and first anodes respectively of the cathode-ray tube. A beam focussing control 19 is provided for adjusting the relative values of the output voltages E1  and E2. The voltages E1 and E2 are controlled to maintain them constant by applying video signals to resistance-condenser circuit 33, 35 so that a voltage proportional to the mean amplitude of the picture signals is applied to control grid 29 of amplifier 31, and the amplified output from 31 is applied via resistor R and condenser X to control electrode 5 of tube 1 so as to vary the mutual conductance thereof. In another form, Fig. 2, the saw-tooth deflecting current is applied to coils 45 and when flyback occurs the collapse of current in coils 45 provides a high voltage pulse which is rectified by rectifier 47 and the resulting D.C. voltage is smoothed by resistance-capacity device 48, 49, 51 and applied to final anode 43. The final anode voltage is controlled by applying the video signals to resistance condenser circuit 63, 65, the output from which is applied to control grid 61 of valve 57 which acts as a variable impedance. Since the output circuit of 57 is connected to the smoothing device 48, 49, 51 by resistance 59 and the voltage of 43 is determined in part by the flow of current in 59 and 57, the desired controlling effect is achieved. In another form, Fig. 3 (not shown), the final anode voltage is derived from the horizontal synchronizing pulses which are applied to an amplifier, the output of which is applied to an auto-transformer and the peak voltage thus obtained is rectified, smoothed, and applied to the final anode. The final anode voltage is controlled in a manner similar to that of Fig. 2. In another form, Fig. 4 (not shown), synchronizing pulses are applied to an amplifier, the output of which is applied to an auto-transformer to produce a peak voltage which is then rectified and smoothed and applied to the final anode as in Fig. 3, and the final anode voltage is controlled by applying the video signals to a resistance-condenser circuit, the output of which is applied to a second amplifier. The output from the second amplifier is applied to the first amplifier to vary its amplification factor. In another form, not illustrated, the anode supply circuit includes an iron core step-up transformer fed from 60-cycle mains, the output of which is fed to a rectifier and then to a smoother, and the anode voltage is controlled in a manner similar to that of Fig. 2.