GB421051A - Cathode arrangement for braun tubes - Google Patents

Abstract

421,051. Cathode-ray tubes. RADIOAKT.-GES. D. S. LOEWE, 10, Wiesenweg, Steglitz, and SCHLESINGER, K., 39, Friedrichstrasse, Friedrichshagen, both in Berlin. May 13, 1933, Nos. 13931, 13932, and 13933. Convention dates, May 14, 1932, June 27, 1932, and Jan. 12, 1933. [Class 39 (i)] Electrons emitted at right angles to the axis of a Braun tube are controlled by an electrode between the axis and the emissive surface and near the latter, and the space between the emissive surface and the control electrode is screened from the anode. In oscillography, the control electrode is maintained at a positive potential relatively to the cathode, the potential being below the ionization potential of the filling if the tube is gas-filled. In television, the control voltages are applied between the control electrode and the cathode. In one arrangement, Fig. 1, a bifilar filamentary cathode 1 surrounds a cylindrical grid 5 at a distance of 2 mm. and is surrounded by an enclosure 9, the end plate 7 of which screens the cathode from the anode 6. Electrons pass inwardly through the grid 5 and are accelerated towards the anode 6, and ions move to the left and do not reach the cathode. Alkaline earth metal 28, 29 may be atomized by eddy-current heating or by a filament 30 to improve the vacuum and to activate the cathode, or the cathode may be an alloy or oxide coated. In a modification, Fig. 3, electrons are emitted from the upper, inner surface of an equipotential cylinder 1 and are controlled by a grid 5, of pitch equal to half the grid diameter, before emerging from the aperture 26 of À5 mm. diameter in the screen 7. The tube 1 is heated by a filament 21 in an insulator 13 and fits into a porcelain tube 12 itself fitting into an outer metal tube 25 carrying the parts 5, 7. The cathode lead 24 embraces a lower insulator 14 joined to the insulator 13 by a pin 20 and containing the leads to the filament 21. This filament may be doubly wound and may be shielded from the emissive surface 1 by a metal cap above the insulator 13. The leads to the filament 21 may also be screened. In another modification, Fig. 6, an auxiliary anode 8 is arranged on the opposite side of the axis to a cathode 1 and grid 5. The electrodes 2, 5, 8 are constructed and operated to give a steep, straight characteristic for the grid control. The main anode 6 draws electrons from the cathode 1 through the screen 7. The anode 8 may alternatively be a grid-like cylinder surrounding the axis and surrounded by cylindrical control grid itself surrounded by a cylindrical, equipotential cathode heated by an outer winding. The electrons may be concentrated between the screen 7 and the anode 6 by biassing and shaping concavely the screen 7 or a separate electrode 37, or by a cylindrical electrode between the parts 7, 6.