GB503126A - Improvements in and relating to electron discharge tubes - Google Patents

Abstract

503,126. Cathode-ray tubes. PYE, Ltd., and LIEBMANN, G. Aug. 25, 1937, No. 28007/38. Divided out of 503,074. [Class 39 (i)] Electrons from the cathode pass successively through two electrodes each with several perforations and through a further electrode which is maintained at or near the potential of the cathode or final anode of the tube and which has an aperture electronoptically reproduced on the fluorescent or other screen. Defocusing effects of the perforations are thus avoided and a straight or other desired control characteristic obtained. An indirectly heated cathode 10, Fig. 2, held in an annulus 13 as described in Specification 503,125 is close to a modulating electrode 26 and a first anode 27 both having similar and correspondingly placed perforations 33, Fig. 3. Electrons passing through these perforations are focused by an electrode 28 and coil 29 towards a small aperture in a stop 32 in the final anode of the tube, and this aperture is focused on to the screen 25 by coils 30. The final anode is formed partly by a wall coating 23. Magnetic shields 31 may be arranged between the coils. The electrodes are spaced as described in Specification 603,074. In a modification, the electrodes 26, 27 each have a single aperture covered with gauze, the stop 32 has an internally stepped aperture to assist concentrating the electrons through it and is at cathode potential, and an electrostatic lens formed by second and third anodes produces on the screen an image spot of the same size as the aperture in the stop. The second anode is tubular with perforated diaphragms and the third anode is a wall coating. Electrons may be concentrated on to the stop electrostatically by short cylinders or discs of decreasing diameters and increasing potentials. Electrode dimensions and voltages are specified.