GB539419A - Improvements in or relating to electron discharge devices - Google Patents

Abstract

539,419. Cathode-ray tubes. BROWN, W. S. Feb. 5, 1940, No. 2184. [Class 39 (i)] In a television device comprising a perforated screen on which a charge image corresponding to an optical image is formed, and which is scanned by a cathode ray which is modulated by the charge image, the ray is caused to impinge on the screen in a direction parallel to its'original direction by a magnetic field, in the manner described, for example, in Specifications 530,409 and 542,219, Fig. 1 shows an arrangement with a photo-electric or photo-voltaic screen 6, such as that described in Specification 510,696, which receives an optical image from a projection device 7 and is scanned by a ray from a cathode 2 so deflected by plates 9 and a coil 8 as always to strike the screen 6 perpendicularly. The signal may be transmitted by electrons passing through the screen and collected by an electrode 10, or by electrons repelled and collected by an anode 5, or the electrodes 5, 10 may be connected in push-pull. The screen 6 may also be made of photo-conductive material on a foundation which is biased slightly above cathode potential. In a modification an electron image formed by projecting an optical image is focused on to the screen 6. In this case the arrangement may be such that the necessary potential distribution on the screen 6 is produced by the emission of secondary electrons, either greater or less in number than the primary electrons. In the la.tter case the screen is of semi-conducting material on a conductive base kept at a slightly higher potential then the cathode. In a further modification the screen 6 is scanned by a second cathode-ray modulated in accordance with an optical image to be received and the first cathode-ray, modulated by the screen 6, falls on a fluorescent screen.