Patent GB-451574-A (GB)
Title: Improvements in or relating to cathode ray tubes, preferably for television purposes
IPC: H01J29/46
Filed: 1934-11-05
Abstract: 451,574. Cathode-ray tubes. RADIOAKT.-GES. D. S. LOEWE, 10, Wiesenweg, Steglitz, Berlin. Nov. 5, 1934, No. 31682. Convention date, Nov. 8, 1933. [Class 39 (i)] The electrostatic focusing electrodes for forming a small spot on the screen of a highvacuum tube for television reception are formed by a metallic coating on the inner wall of the tube, extending from near the cathode to near the screen, but interrupted by one or more annular gaps 8, 19, one of which is nearer the screen than the deflecting means for causing the spot to move over the screen. The deflecting means are entirely magnetic or, if electrostatic deflecting plates are used, each plate of variable potential is associated at its edges with shields earthed or maintained at a fixed potential to prevent the variable potential from affecting the field beyond the edges of the plates. As shown, one plate 11 is earthed and the other plate 12, to which the scanning potentials are applied, has a shield 13 covering its edges transversely to the ray and, if necessary, its other edges also. Alternatively, the plates may be operated in push-pull and both then have shields. The edges of the shields are turned back for about 5 mm. Interference with the focusing fields and trapezoidal distortion of the picture are avoided. The lead to each deflecting plate at variable potential is surrounded by an insulating tube 14 with a silver coating at constant potential. Electrons from the cathode 1 controlled by the modulating plate electrode 4 pass through a plate accelerating anode 5, a cylinder 6 and a diaphragm 7 the aperture in which is focused on a reduced scale on to the screen. The cylinder 6 is. biassed negatively or connected to the cathode so that most of the electrons pass through the aperture in the diaphragm 7. The aperture may be focused on the screen by the lens formed by a single gap 8 in the internal coating, the spot on the screen being smaller the nearer the gap 8 is to the screen. The coating 9 on the left of the gap 8 is earthed and the cathode 1 and coating 10 on the right of the gap are maintained respectively negative and positive by a potentiometer 17 with earthed tapping for adjusting the focusing. The potentiometer 17 is shunted by two series-connected condensers 15, 16 with the common terminal earthed. An earthed shield 18 of non-magnetized, ferromagnetic material is provided outside the conical part of the tube. In a modification, a second annular gap 19 is formed in the internal coating to form two lenses in series. The central part 20 of the coating surrounds the deflecting platos and is connected to the shields 13 of the plates and at a lower potential than the end parts 9, 10 of the coating. Dimensions and voltages are specified. Specifications 393,826 and 427,090 are referred to. The Specification as open to inspection under Sect. 91 comprises also the provision, on all insulators required for mounting electrodes, of metal coatings connected to the adjacent wall coatings and separated by narrow gaps. This subject-matter does not appear in the Specification as accepted.