Patent GB-442511-A (GB)
Title: Braun tube
IPC: H01J29/62
Filed: 1934-06-09
Abstract: 442,511. Cathode-ray tubes. RADIOAKT.-GES. D. S. LOEWE, 10, Wiesenweg, Steglitz, Berlin. June 9, 1934, Nos. 17112, 17113, and 17114. Convention dates, June 10, 1933, June 20, 1933, and July 14, 1933. [Class 39 (i)] A Braun tube, more particularly for television, comprises an electron-optical system which is adapted to reproduce on the screen the electron-emitting surface, or an aperture in a diaphragm through which the electron beam passes, and is formed by an electrode 6, Fig. 4, which consists of a perforated plate and by an electrode which consists of a perforated plate 19 provided with a tubular abutment 18 or of a funnel-shaped member 7, Fig. 3. The electrode 6 is positively biassed and the electrode 7 or 19 is positively or negatively biassed with respect to the electrode 6 when the larger aperture therein is nearer to the cathode or to the screen respectively to form a dispersing or concentrating lens. A third electrode, which consists of a perforated plate 8 and is positively biassed with respect to the electrode 19 is provided when the larger aperture in electrode 19 is nearer to the screen. The third electrode may be provided when the larger aperture in the electrode 19 is nearer to the cathode. Dimensions of the electrodes and the potentials thereon are given in the Specification. The distance between adjacent electrodes may be 1 mm. The electrodes 6, 8 may be connected together, and the focus may be adjusted by varying the potentials on either of the electrodes 8, 19. A tube is provided with an indirectly-heated cathode 1, Fig. 1, a control electrode 2 which, when the tube is gas-filled is located in the cathode dark space, a concentrating lens 3, the electronoptical system 11, inclined deflecting plates 9, 10, and a positive electrode 12 for preventing the return of secondary electrons. All of the electrodes are connected together through insulating means to form a unit. The electrodes 4, 6 are secured together by a screening cylinder 5, which may be connected to the electrodes or to earth, and the arrangement is such that the aperture in the anode 4 is reproduced on the screen. The anode 4, Fig. 2, consists of a plate of copper or phosphor-bronze adapted to support a plate 16 which, is provided with an hexagonal or rectangular aperture 17, is formed of tungsten, tantalum or molybdenum and is coated with soot on the side nearer the cathode to reduce secondary electrons. The portion 13 of the tube may have a metallic coating which may be used for concentrating the ray. The deflecting plates are negatively biassed to reduce " cross-current " error. Thermal overloading of the anode 4 is minimized by arranging the concentrating system 3 in such manner that the maximum concentration occurs where the ray is at maximum intensity. The spot produced on the screen may be smaller or larger than, or the same size as, the aperture which is to be reproduced and the diagonals of the picture produced on the screen may be equal to the diameter of the neck of the tube. In another form, a tube is provided with a cathode 1, Fig. 6, having an electron-emitting surface 25, a Wehnelt cylinder 2 having a controlling plate 26, a system 29 acting as a condensing lens, a system 33 acting as a dispersing lens and a system 7 which is constructed in the manner described to reproduce the aperture 27 in the electrode 4 on the screen. The plates 4, 28, 31 are positively biassed and earthed, the cylinder 30 is negatively biassed and the cylinder 32 is positively biassed with respect to the electrodes 4, 28, 31. The focal point of the lens 33 may coincide with the point of intersection of the rays from the system 29. In other forms, the length of the tube is reduced by deflecting the ray through 180‹ one or more times. An electron beam from a cathode 2, Fig. 7, passes through a control electrode 4 and a preliminary concentrating system 10, is deflected by a magnet 13 and is concentrated by the system 11. The system 10 comprises an electrode 5 which may be concave or consists of a perforated plate provided with a tubular abutment. The system 11 is constructed in the manner described to reproduce the aperture 14 in the electrode 6 on the screen. The electrodes 6, 7 and 5, 8 may be structurally united. The magnet for deviating the ray may comprise semicircular pole pieces between which the ray passes. An iron tubular screen is located within or externally of the tube and extends between the aperture to be reproduced on the screen and the electron-optical system. The tube may be provided with a number of collecting and dispersing lenses. The Specification as open to inspection under Sect. 91 comprises also subject-matter which is contained in the Specification 442,427. This subject-matter does not appear in the Specification as accepted.