Patent GB-715683-A (GB)
Title: Improvements in or relating to unsymmetrical electrostatic deflection systems for cathode ray tubes
IPC: H01J29/74
Filed: 1950-10-20
Abstract: 715,683. Cathode-ray tubes. SIEMENS & HALSKE AKT.-GES. Oct. 20, 1950 [June 23, 1949; June 23, 1949; June 23, 1949; Oct. 21, 1949], No. 25667/50 Class 39(1) An unsymmetrical electrostatic deflection system for television tubes and oscillographs comprises a single deflection space having a cross section normal to the beam of a right angled isosceles triangle, the two deflecting voltages being applied respectively between the corners at the ends of the hypotenuse and the third corner of the tringle which is at a fixed reference potential and the arrangement being such that the field in the deflection space is substantially uniform. The boundaries of the deflection space may or may not be defined by plate members. In one form, Fig. 1, the deflection device is a hollow triangular prism the side faces of which are at least partly of resistance material, and the deflecting voltages are applied to edges 1, 2, a return lead at earth potential, anode potential or some other suitable potential being attached to edge 3. The prism walls may be of insulating material with a low conductivity layer, or of semiconductive material in which case strips of higher conductivity reinforce or form edges 1, 2, 3. Alternatively the prism walls may be of metal if the resistance layer and leads are separated from the metal by an intermediate insulating layer of enamel. The prism is surrounded by a conductive screen 4. The beam when undeflected preferably passes through the system midway of the height above the hypotenuse, but may pass through at any other point. Four such deflecting systems may be assembled together within a rectangular screen, Fig. 2, the adjacent apices of the triangular prisms bearing against a central conductor 6. The electrons start as a single beam and are split up into four parts by the deflecting system; the beam is preferably made initially convergent by an electron lens adjacent to the cathode. The device has a luminescent screen. Biasing potentials may be superimposed on the deflecting potentials or applied to conductor 6, along edges 7, 8, 9, 10, or to screen 11 to decrease the loss of electrons at the centre of the system but this is unnecessary if the beam has a large cross-section. The deflecting system as a whole may be used to apply symmetrical or unsymmetrical deflecting potentials. For example, by connecting two diagonally opposite deflecting elements together the device may be used to apply symmetrical deflecting voltages to a two-beam system. In such a system a single beam is first split into four parts at the deflecting system and then two pairs are united to form two separate beams. Four triangular deflecting arrangements may be arranged one above the other, Fig. 3 (not shown). In such a tube the gun generates a convergent beam which is made flat by a cylindrical lens, passed through the deflecting arrangement and then through a multiple cylindrical lens and final accelerating electrode, and then produces four separate images on the luminescent screen. The deflecting arrangements may be arranged in pairs one above the other, Fig. 4 (not shown). The multiple deflecting arrangements are useful for multi-beam tubes with separate cathodes where the brightnesses of the beams are required to be independently controllable. An apertured diaphragm may be arranged in front of a single triangular deflecting prism, Fig. 5 (not shown). The diaphragm may be connected to two voltage dividers, (a) a tapping on resistances connected across the deflecting supply circuit, giving a small voltage variation (b) a voltage divider connected between the tapping point and earth, which is optional. The diaphragm may be an end face of the triangular prism, in which case it is formed of resistance material. The edge of the diaphragm aperture may be made of conductive material to make the potential distribution uniform. In another form, Fig. 6, the short sides 30, 31 are resistance layers and two plates 33. 34 are substituted for the hypotenuse. The deflecting voltages are applied to conductive plates 33, 34 and a common return lead at zero potential is attached to conductive edge 32. The plates 33, 34 may be exponentially curved and at least parts thereof may serve as the anodes of two triode amplifier valves also enclosed within the cathode ray tube envelope, Fig. 7 (not shown). In another form, Fig. 8, the deflecting voltages are applied to opposite edges of the resistance face 47. Conductive plates 52, 53, 55, 56 complete the deflecting arrangement. Apertured diaphragm 58 is connected to a tapping on divider 59, or alternatively the resistance face 47 can be used as the voltage divider. In modifications, (Figs. 9-12, not shown), the resistance face 47 is omitted and flat or curved plates may or may not be attached to edges 48, 49. In another form, Fig. 13, conductive faces 73, 74, 80 are associated with grids 78, 79, 81 of non- uniform mesh as indicated by the dots. The deflecting voltages are connected to edges 75, 76 and the earth return to grids 78, 79 at edge 77. In a modification, Fig. 14, faces 82, 83 are earthed, grid 87 is connected to face 86, and the deflecting voltages are applied at the junctions of 86, 87 and 89, 90 respectively. The grids may be formed of parallel bars as shown, or alternatively the whole deflecting arrangement may consist of insulating plates with a uniform metal coating on their outer sides and conductive coatings in the form of spaced strips on their inner sides. In another form, Fig. 15 (not shown), the triangular prism is made up of three members with interengaging serrations in the flat sides of the prism, the deflecting voltages being connected to two members respectively and the third member being earthed. The width of the serrations is chosen in accordance with the desired degree of homogeneity of the field; for accurate homogeneity the serrations are fine and comb-like. Other forms of interengagement with progressive linear or non-linear reduction in width can be used. The deflection members may be of sheet metal or of thin conductive layers secured to insulating supports. Instead of varying the grid mesh, the distance between the plates and the grids may vary.