GB543890A - Improvements in television transmitting tubes - Google Patents

Abstract

543,890. Cathode-ray tubes. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 24, 1940, No. 10829. Convention date, June 24, 1939. [Class 39 (i)] A television tube comprises a mosaic or like screen for converting an optical image into an electron image, a coil producing the axial field for focusing the ray on the screen, which it strikes with a very small velocity, electrodes cooperating with the magnetic field for scanning, and other deflecting electrodes which shift the ray parallel to itself and also shift the ray composed of electrons returned by the screen in the same manner and other electrodes deflecting the latter ray in opposition to the original scanning so that it is received by an electron multiplier or other collecting device of comparatively small area. In the arrangement shown electrons from the gun 3are scanned over the screen 2 in a direction perpendicular to the plane of the paper and by the co-operation of a coil 27 and plates 28, 29. Between the plates 28, 29 and the screen 2 are plates 33, 34 which deflect the beam as shown so that under the influence of the coil 27 it proceeds parallel to its original path 35 as shown at 37. The electrons returned by the more negative portions of the screen retrace their path as shown at 40 and are deflected by the plates 33, 34 to pass between the plates 29 and 30. The plate 30 is connected to the plate 28 so that the returning electrons are deflected in the opposite direction to the scanning deflection and are collected by an electron multiplier 4 of the screen type. To ensure that the electrons passing between the plates 33 and 34 shall pass through a region of approximately constant potential for different scanning potentials the plates are connected across a resistance 44 a centre tap on which is connected slightly on one side of a resistance across the plates 28, 29. A modification is described in which only the original ray passes between plates corresponding to 3, 34 and the collector is behind the gun instead of beside it.