Patent GB-501375-A (GB)
Title: Improvements in or relating to television transmission tubes
IPC: H01J31/48
Filed: 1937-10-15
Abstract: 501,375. Cathode ray tubes. STANDARD TELEPHONES & CABLES, Ltd. Oct. 15, 1937, No. 28113. Convention date, Nov. 6, 1936. [Class 39 (i)] A television transmission tube comprises an evacuated vessel having disposed therein an electron collecting electrode, a screen consisting of a metallic grid coated with a photo-conducting layer, a source of electrons disposed on the opposite side of the screen to the collecting electrode; means for projecting a luminous image on the photo-conductive surface of the screen and means for causing an electron beam from the source to scan the screen. A light image is focused upon a photo-sensitive screen 8 which is scanned by a cathode-ray beam from a gun 4. The beam, which is retarded by a grid 10 and is modulated by the charge on the screen 8, falls on the first electrode of a multiplier 5, giving rise to signals in the output resistance 15 of the multiplier. A grid may be provided before the multiplier. In a modification; the screen 10 is in the form of a continuous photo-emissive layer deposited on a transparent plate which is situated in an envelope and is scanned by a luminous ray generated by the fluorescence produced by a cathode-ray tube arranged adjacent to the envelope. The latter contains the multiplier and the photo-sensitive screen 8 which is then illuminated by the image from the other side so that an electron beam from the screen 10 scans the screen 8 and passes to the multiplier. The screen 8 comprises two perforated conducting plates 51, 52, each coated on one side and in the perforations with insulator 54, placed with their insulated faces together, the outer face of plate 52 coated with the photoconductive material 55 (such as selenium or mercurous iodide) and of plate 51 with a resistance material 56, and the whole then enveloped in a transparent conductive coating 57, as by vaporization in a vacuum. A difference of potential is applied between the two plates and between them and the grid 10, so that the coating 57 assumes a potential varying as the illumination of the' layer 55. If the resistance along the surface .57 is insufficiently high, it may be broken up into a number of segments so that the potentials will not " spread." In a modification in which a single plate is used, the difference in potential is imposed between the screen 51 and. the conductive coating 57. The Specification as open to inspection under Sect. 91 comprises also the features : The screen 8 consists of a wire gauze covered with insulating material having photo-emissive material superimposed thereon. The gauze may be formed by covering a metal plate with a resist pattern and etching the gauze, or an aluminium plate may be covered with oxide by anodic oxidation or compressed locally by hammering prior to etching. Conducting particles are then applied as by a photographic process, the aluminium plate being impregnated with oil prior to treatment, the oil being subsequently evaporated. Iron, nickel, aluminium or copper may be used for the plate.. The multiplier may be replaced by a simple collecting anode and an external amplifier or multiplier. The photo-conductive surface may be chosen to respond to different wavelengths and the screen may be adapted to unidimensional, scanning. This subject-matter does not appear in the Specification as accepted.