Patent GB-545689-A (GB)
Title: Improvements relating to the construction and arrangement of electrodes in electron discharge devices
IPC: H01J21/36
Filed: 1940-11-08
Abstract: 545,689. Cathode-ray tubes. ELECTRICAL RESEARCH PRODUCTS, Inc. Nov. 8,1940, No. 16256. Convention date, Dec. 2, 1939. [Class 39 (i)] In a cathode-ray tube using pairs of electrodes for modulating, collimating or focusing, a potential distribution along the axis of the tube is predetermined and the adjacent surfaces of the electrode pair are shaped to conform to the equipotential surfaces of the corresponding field ; with a modulating electrode near the cathode and at zero potential, the shape of the electrode surface will be a cone such as M, Fig. 3, and the first accelerator electrode has a surface shaped in the form of curves B which are asymptotic to the cone M. With a focusing lens the first electrode M, Fig. 4, may be cylindrical. Formulae are given for determining the shapes of the curves, and the selected potential increases from cathode to the screen so that the second differential coefficient of the potential with respect to distance along the axis is positive. If the cathode is of substantial size its emitting surface also follows the appropriate equipotential surface. The coned modulating electrode 21, Fig. 1, is carried by a sleeve 25 from an insulator 26 which also supports a cylinder 28 in which the curved electrode 22 is mounted ; this has a constricted orifice 24 formed by a metal insert. A cylinder 29, which with the curved electrode 34, forms a focusing lens, is carried by rods 32 from the stem 15. The curved electrode may be carried by a glass standard 54, Fig. 6, sealed to the main envelope. Pairs of deflecting plates 40, 41 are mounted above the electrode 34, a plate 36 acting as a screen to this electrode from the deflecting potentials. A shield 37 surrounding the plates 40 has stays 39 bearing on the envelope wall ; this may have a graphite coating. The stem 15 has an attached contact carrying cap 49 ; the leads 42, Fig. 6, to the deflecting plates may be taken to prongs 68 in a ring 67 on the tube. The cathode electrodes 21, 22, 29 insulating spacer 26 and coupling member 55 between the electrode 29 and cylinder 28 are carried as a unit from bands 31 on the stem 15. The deflector plates are carried by an insulating disc 71 seated on the shield 37. The electrodes 41 may be enclosed in a shield 78, Fig. 9, secured to the top of the shield 37 ; spring fingers 39 attached to brackets 82 on the shield 37 and bearing on the graphite coating may be used to apply a potential to the coating when it is used as an accelerator electrode. In a modification a separate pair of deflector plates may be used with the plates 40 the extra pair being coaxial but independently connected to terminals for applying potentials. In a modification using a ribbon shaped beam the cathode 93, Fig. 12, is mounted in the modulating electrode 94 ; the accelerator and focusing electrodes 95, 96 and the cathode have suitably formed surfaces 110, 111, 114, 99 to direct the beam on the fluorescent screen 117. The electrode 94 has two U-shaped parts 104 at its ends ; intermediately it has triangular cut away parts and in consequence it may be used to suppress emission from the ends of the cathode and thereby vary the length of the image on the screen. The electrodes 96 may be used as deflector plates.