GB493790A - Improvements in or relating to cathode ray devices - Google Patents

Abstract

493,790. Cathode-ray tubes. BRITISH THOMSON-HOUSTON CO., Ltd., and RUSHFORTH, L. April 30, 1937, No. 12413. [Class 39 (i)] An electron-optical system, such as an electron gun, for cathode-ray tubes, comprises metallic electrodes insulated and spaced from one another by ceramic parts, so that the axial spacing is determined by the thickness of the insulators, whereas the relative transverse alignment of one or more electrodes is maintained solely by frictional forces set up by clamping the electrodes and insulating parts together ; in the absence of such friction the parts would not maintain the alignment of the electrodes. In one form, the tubular second anode 1 encloses a cathode 15, modulating electrode 8 and first anode 5. Insulators 4, 7, 9 support the electrode 8 and a flange 14 on the anode 5, the whole being held together by cups 2, 10 which are welded to 1 after clamping in a press with a suitable jig aligning the electrodes. The spacing of the cathode from electrode 8 may be observed through windows 11, 12, cut in the anode 1 and a groove 24 in insulator 9. A mica washer is interposed between members 2 and 4. To reduce surface leakage between the electrodes, gaps are left between them and the insulator which are so narrow that sputtered material cannot enter them. In a modification the modulating electrode is a cap surrounding the cathode. An electron microscope objective is also described, in which the first electrode is spaced from the anode by an accurately ground ceramic tube ; the cathode is made movable to vary the magnification. The gun may be assembled with insulators of unfired material, such as soapstone, which is then fired in vacuo or in a suitable neutral or reducing atmosphere, e.g. at 900‹ in hydrogen. Specification 444,633 is referred to.