GB652267A - Improvements in or relating to cathode ray tubes and like devices - Google Patents

Abstract

652,267. Cathode-ray tubes. GENERAL ELECTRIC CO., Ltd., and ALLARD, L. S. Dec. 30, 1947, No. 34751. [Class 39 (i)] A circuit arrangement comprises a lowvoltage cathode-ray tube (i.e. a tube wherein the energy of the electrons reaching the target is about 100 volts so that the secondary emission ratio of the target is approximately unity) provided with a plurality of electrodes to change the velocity of the electrons after their deflection, the arrangement being such that one or more of these electrodes other than the final one near the target is maintained at a higher potential than the final electrode. The electrons thus have a higher velocity through the deflecting system and are subsequently decelerated, which enables one to obtain better focusing. The potentials of the electrodes are preferably so arranged that the electric field is substantially constant along the axis between the first electrode and the target surface. In the Figure the electrodes 6, 7, 8, 9, 10 are in the form of conducting bands on the envelope and may be of graphite or of metal; the width of the bands progressively increases in the direction of the electron beam. The potentials of electrodes 6, 7, 8, 9, 10 may be 1500, 1000, 500, 200 and 100 volts positive respectively with respect to the cathode. To reduce distortion the envelope may be in the form of a cylindrical portion joined to a cylindrical neck of smaller diameter. The invention may be applied to tubes'with a fluorescent screen, or to storage tubes using a target comprising a mica sheet covered with a plurality of discrete photo-electric particles. Specification 652,255 is referred to.