GB685821A - Improvements in or relating to cathode ray tubes or the like - Google Patents

Abstract

685,821. Cathode-ray tubes. RAULAND CORPORATION. May 18, 1951 [May 19, 1950], No. 11645/51. Class 39(i) In a cathode ray tube the offset anode 21 has a beam defining aperture 24 and a fluorescent coating is provided on a surface shielded from direct impingement by the beam but disposed so that when the beam strikes the interior surface of the anode 21 the coating fluoresces and can be observed through a transparent neck portion of the envelope and adjustable beam deflecting means such as the magnetic means shown enable the beam to be directed through the aperture 24. It is state( that the fluorescence is due to impingement by primary electrons reflected at anode 21 and/or by secondary electrons ejected from anode 21 under primary electron bombardment. The fluorescent coating may be on the external wall of anode 21 at 31, and/or on the interior surface of the neck 10 at 32, or at any other suitable place adjacent the gun electrodes, such as on rods 13 or lugs 22. The device preferably incorporates an ion trap, the mixed beam of electrons and ions being deflected in one direction by a transverse electrostatic field component between offset electrodes 18, 21 and restored to the axis by a magnetic field produced by permanent magnet 27. A second permanent magnet 28 is preferably provided to correct any overshooting of the beam, and the two magnets 27, 28 which have oppositely directed fields are mounted on a member 26 which may be rotated or moved axially to adjust the magnetic deflection so that the electrons but not the ions pass through aperture 24. The electrodes 14, 18, 21 are carried by lugs 15, 19, 22 from glass rods 13 held in the envelope by suitable means (not shown) and terminal connections 25 connect the anode 21 to the internal wall coating. 14 is the control electrode and cathode 17 is mounted within it and spaced therefrom. Specification 678,546, is referred to.