GB693956A - Improvements in or relating to storage electrodes for use in signal converting electron discharge tubes - Google Patents

Abstract

693,956. Cathode-ray tubes. RAULAND CORPORATION. Nov. 15, 1951 [Nov. 15, 1950], No. 26764/51. Class 39(i) A storage electrode for a signal converting tube comprises a foraminated structure such as a mesh 12, Fig. 3, covered on one side with an insulating film 13 of which the portions covering the interstices of the mesh are coplanar with the central plane thereof, and on the other with photoemissive material 14, leaving the insulating film exposed. The mesh may be of gold or chromium, possibly plated on to copper. The photoemissive material may be a conventional caesium/antimony or caesium/silver-oxide mosaic structure, and the film 13 may be any suitable insulating material although silicon dioxide is preferred. One manufacturing technique consists of forming an antimony layer on one side of a fine gold mesh, which is then covered with an organic film such as nitrocellulose, this film being drawn into the interstices of the mesh by surface tension. Silicon dioxide is then evaporated on to the other side of the mesh, completely covering mesh and interstices, as at 13, to a suggested thickness of 1000-8000 Š: after which the nitrocellulose film is dissolved away. The mesh electrode is then mounted within the tube, and photosensitized in the normal way. The mesh should be as fine as possible, since this determines the resolution, and the gold mesh of the above example has a thickness of .0002 in. and 400 openings per in. The storage electrode is used in tube 10, comprising cathode 22, control grid 25, first anode 29, second anode 33 closed at one end by a wide mesh screen 37, decelerating electrode 16, accelerating electrode 17, further accelerating electrodes 44, 45, which may be formed as wall coatings, and a metal-backed fluorescent screen 41. The secondary emission ratio for the insulating film 13, and hence the storage electrode as a whole, may be greater or less than unity, according to the voltage of the primary electrons. In order to condition the storage electrode for recording, its potential is raised, by tap 38 on potentiometer 31, to a value which gives a greater than unity value, so that a positive charge is built up. A charge pattern is established on the storage electrode by signals from a source 23 in the cathode circuit, or by causing the incoming signals to vary the potential of control grid 25. The photoemissive side of the storage electrode is illuminated from a source 42, so that an image pattern of photoelectrons is projected to impinge on fluorescent screen 41. Alternatively, the storage electrode may be conditioned by a flooding beam or a focused scanning beam from a separate gun. The tube is particularly suitable for half-tone storage and reproduction. Specification 677,300 is referred to.