GB1427250A - Assembly for the rejuvenation of cathode-ray tubes of tv-sets and for the visual check of cathode conditions - Google Patents

Abstract

1427250 Cathode-ray tubes SAFE ELECTRONIC SYSTEMS SA 15 Aug 1973 [25 Sept 1972] 39566/73 Heading H1D [Also in Division H4] An assembly for the rejuvenation of cathoderay display tubes and for the visual check of cathode conditions comprises first and second voltage converters S1, S2, the former, S1, having input terminals A, B connected to the primary of a mains transformer for, e.g. 220 V A.C. operations and the latter, S2, input lines 1, 2 connected either to the primary of the transformer in converter S1 or, alternatively, to a voltage source in the range 220 to 6000 V. Each converter has a plurality of output terminals to which controlled voltages may be supplied and converter S2 is additionally connected via further input lines 3, 4, to output terminals C and D of converter S1. In operation, when it is required to rejuvenate the tube, terminal C is connected to the tube cathode terminal D is connected to the first grid and terminals E and F are connected to the heater. An A.C. voltage in the range 6 to 12 V is then applied to terminals E and F and the heater is overheated for a period between a few seconds and a few minutes. A voltage in the range 50 to 5000 V is then applied to terminal D for a period ranging between one minute down to a quarter of a second (depending on the magnitude of the applied voltage) and the tube is thus rejuvenated. When the tube is a threegun colour tube each gun may be treated as described above or the converter S1 may be fitted with three separate sets of terminals. When a visual check on the cathode condition is required (even after it has been rejuvenated) terminals E1, F1 are connected to the heater, terminal C is connected to the cathode, terminal H, to which a voltage of between 0-50 V is supplied, is connected to the first grid, terminal L to which a voltage of between 150 and 400 V is supplied, is connected to the first anode, terminal M to which a voltage of between 100 and 300 V is supplied is connected to the second anode (focusing anode) and terminal AT, to which a voltage of between 4000 and 7000 V is supplied, is connected to the main anode. By manually varying the above voltages within the ranges indicated a disc-shaped image of the cathode is produced on the screen and if such image is luminous and uniform the efficiency of the tube is considered to be very good. If the image is speckled, the tube should be subjected to one or two rejuvenation cycles as described above. The various voltages produced by the converters S1, S2 may be either direct, alternating or pulsating and the converters are provided with either manual or automatic control devices controlling the magnitude and durations of the voltages applied to the tube.