GB472861A - Method of and apparatus for modulating electron streams - Google Patents

Abstract

472,861. Cathode-ray tubes. FARNSWORTH TELEVISION, Inc. June 23, 1936, No. 17420. Convention date, July 6, 1935. [Class 39 (i)] In cathode-ray tubes such as television image - dissectors, an intense, composite electron stream corresponding to an optical image is produced by means of a grid having a continuous photo-electric surface on one side and an insulating surface on the other side. The grid may be formed by uniformly coating a wire foundation 25, Fig. 2, with insulation 26 and then adding a photo-sensitized silver layer 27 on one side, or a silver foundation 29, Fig. 3, may be coated on one side with insulation 26 and photo-sensitized on the other side 30. In both cases, the insulation is applied by smoking with burning magnesium and the silver is photo-sensitized by oxidizing by a glow-discharge in oxygen and applying caesium, excess of caesium being removed as by baking the tube at 60‹ on the pump. The grid 4, Fig. 1, so prepared is mounted with its photo-electric surface facing a window 2 and a cathode 7 producing electrons flooding the grid. When an optical picture is projected through the window 2, corresponding charges are produced on the insulation 26 of the grid and an electron image is produced and deflected over an apertured anode 17 containing a more positive electrode 19 to produce television signals. Discharge of the charge image on the insulation 26 may be produced by leakage or the presence of gas, but preferably by secondary electron emission consequent on bombardment of the insulation by some of the faster electrons from the cathode 7. Other of these faster electrons may produce secondary emission from the photo-electric surface, some secondary electrons and the photo-electrons producing charges on the insulating surface of the grid. The grid 4 may be positive with respect to the cathode 7 and a separate accelerating anode may be used. Wall coatings 12, 14, 22 form an electrostatic lens. The electron stream flowing from the grid 4 towards the anode 17 may be focused and deflected magnetically. Specification 472,859 is referred to.