GB783719A - Improvements in or relating to signal storage cathode ray tubes - Google Patents

Abstract

783,719. Television pick-up tubes. ENGLISH ELECTRIC VALVE CO., Ltd. Nov. 1, 1955 [March 17, 1955], No. 7778/55. Class 39(1). In a cathode ray storage tube with separate reading and writing beams, grids 9, 10, Fig. 2, are interposed in the paths of the respective beams and are given different D.C. potentials. Writing takes place at or below the second cross over point (S.E. 7, 1) and reading at or near the maximum of the SE-primary voltage curve, between the first and second cross over points. In writing the secondaries generated at the target by the signal modulated electron beam cannot pass suppressor grid 9 which is 100 volts negative to signal plate 7 and the discrete storage areas 8 can therefore charge negatively by varying amounts up to the potential of grid 9; the latter is so close to the target that SE redistribution and the consequent production of shading signals is prevented, the secondaries returning approximately to their point of origin. Collecting grid 10 associated with the reading beam is earthed so that the voltage between the discrete areas of the mosaic 8 cannot exceed 100 volts, i.e., the voltage difference of the two grids. The grids 9, 10 are of fine mesh and are spaced about 4 mils. from the target, and the signal plate area is less than that of the mosaic so its capacity is small. The discrete mosaic elements have areas of 8 x 0À06 mm. and are spaced apart by 0À005 mm., and are formed on glass plate 6. The wall coating 12 and signal plate 7 are both earthed the latter via output resistance 11. The invention thus minimises secondary electron redistribution, prevents temporary or permanent breakdown of the insulation between the discrete mosaic areas and improves reading and writing efficiency secondary electron redistribution causes shading signals and temporary breakdown of insulation between discrete mosaic areas can cause generation of spurious signals.