Patent GB-420667-A (GB)
Title: Improvements in and relating to cathode ray tubes for television purposes
IPC: H01J29/52
Filed: 1933-04-03
Abstract: 420,667. Cathode-ray tubes; television. RADIOAKT.-GES. D. S. LOEWE, 10, Wiesenweg, Steglitz, and SCHLESINGER, K., 39, Friedrichstrasse, Friedrichshagen, both in Berlin. April 3, 1933, Nos. 9914/33, 25,274/34, 25275/34, and 25276 /34. Convention dates, April 4, 1932, July 27, 1932, Nov. 26, 1932, and Dec. 16, 1932. [Classes 39 (i) and 40 (iii)] A television cathode-ray tube comprises a cathode 19, an electrode 3 with an aperture 17 in front of the cathode, an electrode 2 for controlling the emission from the cathode by space-charge control, a picture screen and an electrostatic electron-optical system reproducing the aperture 17 on the screen, means 6, 7 being provided to cause the ray to scan the screen. The light spot on the screen thus has the shape of the small aperture 17 and does not vary as its brightness varies. In a modification the electron-optical system reproduces on the screen an image of the emissive surface of a cathode. The cathode is not pin-shaped and may comprise an equipotential body with a rectangular recess filled with emissive material. The face of the cathode may be flat or convex and may be of curvature equal to or less than that of the zero equipotential surface near the cathode. The electron-optical system comprises a cylinder 4 negative with respect to the electrode 3 and a positive plate 5. The cylinder 4 is mid-way between the plates 3, 5 or nearer the plate 3. The plate 3 is positive with respect to the cathode. Dimensions and voltages are specified. The electrode 2 may be a negatively biassed Wehnelt cylinder concentrating the electrons on the aperture 17 or a grid in the cathode dark-space, the control voltage being Œ 5 volts. The electrode 3 may carry a metal tube on the side facing the cylinder 4. The picture screen may have a thin metal coating connected to the plate 5 or to a higher potential, or a metal ring or coating may be provided on the wall near the screen. The tube may be filled with gas at a pressure of 5 x 10-<3> mm., or 5 x 10<-4>-5 x 10<-6> mm. In the latter case, the concentrating effect of the gas increases with increasing ray currents and the potentials of the electrodes are adjusted so that the image is sharp for small currents, the decreasing sharpness of focusing of the electron-optical system for heavy ray currents being compensated by the gas. The gas pressure may be maintained by elements or compounds with corresponding saturation pressure ; caesium, rubidium, potassium or sodium or hydrides are arranged in side-tubes which are of capillary form or which are joined to the cathode-ray tube by a capillary tube. Specification 395,529 is referred to. The Specification as open to inspection under Sect. 91 comprises also the subjectmatter of Specifications 422,041 and 420,881. Explanation of the focusing action of electrode systems comprising apertured plates and cylinders is included and modifications of detail are specified, including an auxiliary electrode between the deflecting plates and the picture screen, a wall coating extending from the deflecting plates towards the screen and biassed negatively with respect to the anode 5, and an arrangement in which the ray enters obliquely into the deflecting system. This subject-matter does not appear in the Specification as accepted.