GB1256507A - - Google Patents

Abstract

1,256,507. Electron-beam tubes. RANK ORGANISATION Ltd. 9 April, 1969 [10 April, 1968], No. 17262/68. Heading H1D. An electron gun having purely electrostatic beam shaping means, and which is stated to permit control of the size and shape of the image, produced on a screen, of the gun aperture, independent of beam current and modulation depth, includes a flared electrode 16, Fig. 1, mounted around the periphery of the cathode 10; an accelerating electrode 17-e.g. at 5 volts positive with respect to the cathode-and the aperture of which preferably either has a penetration factor less than. 0À70 or is covered with wire mesh; a screening electrode 15 which screens the space between the cathode and electrode 17, and to which a modulation signal may be applied; and, optionally, two further accelerating electrodes 21 and 22 at e.g. 1030 volts positive with respect to the cathode. The screening electrode 15 may either, as: shown, be of substantial thickness, or may be constituted by two spaced electrodes held at the same potential, or may be a thin electrode the aperture in which is covered by a wire mesh. As described, the gun. is incorporated in a cathode ray tube, Fig. 2, having- further spaced electrodes 29 to 37 interconnected in two groups held at 1030 and 320 volts respectively, the final electrode being connected to a continuous graphite envelope coating 38, which may itself be connected to a graphite high resistance helix 42, which further accelerates the beam. To enhance focusing of the beam, the tube includes an electron lens, which may be-formed by a pair of coaxial cylinders, or by spaced conductive envelope coatings-e.g. by the end turns, nearest the gun, of the helix 42, if the latter is of sufficiently high resistance. Otherwise, the end turns may be electrically isolated from the remainder of the helix, to permit the application of a potential difference therebetween. Reference, without further description is made to a gun providing a plurality of beams, and to the use of the gun in a vidicon, orthicon, travelling-wave tube, or storage tube.