GB553131A - Improvements in cathode ray tubes - Google Patents

Abstract

553,131. Cathode-ray tubes. COSSOR, Ltd., A. C., SHELTON, E. E., and MOSS, H. July 23 1940, No. 12050. [Class 39 (i)] In cathode-ray tubes of the kind in which the beam issuing from the gun is divided by a plate 3 between the first pair of deflector plates 4, 5, as described in Specification 505,026, provision is made for making the secondary electron current between the plate 3 and one of the deflector plates independent of the potential of the other. This consists in making the plate 3 of a material of low secondary electron emission such as metal with a carbonized surface or in shielding the field on one side from the other or both. The shielding effect is obtained by extending the plate 3 in the direction of the cathode to an apertured disc 2a which is at the potential of the second anode 2 and may form part thereof. The deflector plates 4, 5 and the plate 3 are carried by mica discs 29, 30, which carry an apertured rectangular metal plate 21. The edges of the aperture parallel to the deflecting plates have turned up lips 21c, and deeper plates 22a are attached at the transverse edges. The outside edges of the plate 21 have deep flanges 21a, on which and the plates 22a rests an apertured mica disc 28 carrying a metal plate 24 electrically connected by a lead 23 to the flange 21a of the plate 21. A tubular shield 25 surrounds the deflecting plates. By these means, the plates 3, 4, 5 are shielded from the straight portions of the additional deflector electrodes 6, 7 which are cross-connected to the deflector plates, and from the supporting and lead-in rods, such as 9, 14 by which the pairs of deflector plates 4, 5 and 20 are mounted. Secondary emission from the fluorescent screen are collected by a metal sleeve 27, which has a push fit over the mica discs 28-31, and is given a potential of about 35 volts positive to the final anode through a lead 17.