GB461235A - Improvements in or relating to braun tubes, preferably for television purposes - Google Patents

Abstract

461,235. Cathode-ray tubes. RADIOART.-GES. D. S. LOEWE. May 8, 1935, No. 13525. Convention date, May 9, 1934. [Class 39 (i)] Highly evacuated, television or other cathode-ray tubes comprise in succession a cathode 2, an apertured control plate 7 close to the cathode and with a cylindrical extension 8, an apertured diaphragm 10, an electrostatic electron-optical system 12, 14 including at least one apertured plate and an electrostatic deflecting system 16.. 19, the diaphragm 10 being spaced from the plate 7 to such a distance, preferably 10 mm. or more, and its aperture 9 being only to such extent larger than the emissive surface of the cathode 2 that any straight lines drawn from the edges of this emissive surface through the edge of the aperture 9 pass unobstructedly through the systems 12, 14 and 16 .. 19. Most electrons from the cathode thus pass through the aperture 9 and leave it in a narrow cone not intercepted by the remaining electrodes. The cathode 2 is an indirectly heated nickel hood with a small shallow recess into which oxide is painted and is centred in the cylinder 8 by a cylindrical fitting. The part of the diaphragm 10 adjacent its aperture 9 is of molybdenum or other metal of high melting point freed from gas and welded to a bronze plate forming the main part of the diaphragm 10. An electron-optical system as described in Specifications 457,757 and 457,846 reproduces the aperture 9 on the picture screen. The lens field is shielded by the tubular formation of the anode 14 and by the bronze tube 11 which is arranged as described in Specification 455,084 and biassed by a potentiometer 46. The cathode ray is shielded by a silver coating 36 on the wall of the tube connected through springs to the anode 14 and by an earthed magnetic screen 37 surrounding the,part of the tube from the cathode to the system 12, 14. The deflecting plates are operated in phase opposition as described in Specifications 423,427 and 452,650, and are supplied by the twin-tube relaxation apparatus 20 described in Specification 456,208. The deflecting plates are inclined and have screening electrodes 16<1>, 171. To secure a bright image on the screen, the diaphragm 10 is connected to the main anode 14 and a further diaphragm may be provided at 38 to act as first accelerating anode, an intermediate cylinder 39 being then added. The electrodes are all connected to contacts on the base of the tube, are supported by glass rods which pass through them or through discs such as 5, 6, and are steadied by springs bearing on the tube. Dimensions and voltages are specified.