GB493543A - Improvements in or relating to ikonoscopes, television cathode ray tubes and the like - Google Patents

Abstract

493,543. Cathode-ray tubes. RADIOAKT.-GES. D. S. LOEWE. Jan. 8, 1937, No. 624. Convention date, Jan. 11, 1936. [Class 39 (i)] In a cathode-ray tube containing screening or accelerating electrodes made of wire net, thin electrodes are prevented from casting an objectionable shadow on the screen either by placing them at the place where the ray has the greatest practicable breadth, i.e. as close to the electron lens as the deflecting electrodes will permit, or by so choosing their potential and by making them of such material that the secondary electrons emitted just compensate for the electrons absorbed. The Figure shows the invention applied to a tube in which a mosaic screen 5, on which an optical image is projected as described in Specification 489,362, is scanned by a cathode-ray, an aperture in a diaphragm 2 being focused on the screen 5 by means of an electron lens formed of the tube 3 and diaphragm 4. Arranged as close as possible to the deflecting plates 8, 9, is a wire net electrode 6a, the potential of which with respect to the electrode 4 can be adjusted. This electrode may, in addition to acting as a screen electrode, serve to collect secondary electrons emitted from the screen 5. An accelerating electrode 6b at a positive potential of 8000 volts relative to the screen 6a may also be provided. Alternatively a net 6c may be arranged near the screen 5 and made of such material, e.g. tungsten, that the secondary emission from it compensates for the electrons absorbing by it. In a modification the net is arranged across the end of a cylinder.