GB803221A - Improvements relating to electron guns - Google Patents

Abstract

803,221. Cathode-ray tubes. GENERAL ELECTRIC CO. July 14, 1955 [July 14, 1954], No. 20450/55. Class 39(1). An electron gun for a cathoderay tube consists of a concave cathode 9, Fig. 2, a focusing electrode 12 and a first anode 14 to focus the electrons to a crossover beyond the anode, a second anode 20 which is electrically connected to the first anode and spaced from it to define a fieldfree region, and a modulating electrode 18 which is located in the field-free region. The first anode 14 has a conical aperture 15 and a frusto-conical protuberance 14a with a cylindrical aperture 17. The focusing electrode 12 may have a frusto-conical portion, Fig. 4 (not shown), surrounding the protuberance 14a. The main lens is formed by the second anode 20 and a third anode 23. The electrodes are held by rivets 30 embedded in glass members 29. Suitable dimensions are given for the various electrodes, apertures and electrode spacings with suitable voltages. In another embodiment, Fig. 6, an intermediate anode 32 and a second control electrode 34 are provided in the fieldfree region between the first and second anodes 14, 20. Control electrode 34 may be used to impress a second modulating signal on the beam or as a gating electrode to cut off the beam as it is swept from one portion of the screen to another, e.g., in producing a series of discrete images.