GB953881A - Low-power-deflection cathode ray tube - Google Patents

Abstract

953,881. Cathode-ray tubes. RADIO CORPORATION OF AMERICA. June 27, 1960 [July 7, 1959], No. 22514/60. Heading H1D. In a cathode-ray tube comprising an elongated neck 14 in which an electron beam is produced, a faceplate 16 and an interjacent cone 18, a multi-apertured electrode 46 is disposed across the beam path immediately following the deflection region 48, so that the beam may be projected through the deflection region at low velocity and immediately afterwards accelerated towards the faceplate by a radially divergent electrostatic field between electrode 46 and a conductive coating 44 on cone 18. The grid 46 may be flat, but as shown, it is hemispherical and produces, in conjunction with wall coating 44 and aluminium layer 27 on phosphor layer 26, a radial electrostatic field which supplements the principal deflection field provided by yoke 42. However, by suitable shaping, grid 46 may also be used to correct various forms of raster distortion. In particular a grid of the shape shown in Fig. 6 corrects pincushion distortion. Furthermore, a grid curvature can be established for any particular tube to achieve invariant picture size with screen potential variation, e.g. in a colour kinescope which depends upon differences of electron penetration of a plurality of phosphor layers to produce colour modulation. By varying the voltage on anode 36, the beam focus may be varied without effect on deflection sensitivity, so that an inexpensive permanent magnet may replace the electrostatic focusing lens and a touch-up signal voltage can be applied to anode 36 so that the focus force varies with the beam spot position on the raster. Instead of being secured to glass rods 40 which support the electron gun electrodes, grid 46 may be supported by the faceplate end of a frusto-conical ring secured to the envelope. Grid 46 may comprise a woven mesh or a late formed with apertures tapering towards anode 36 so that secondary electrons are confined to the electron gun side of the grid and are collected by anode 36.