Patent GB-381306-A (GB)
Title: Improvements in or relating to picture telegraph and television systems
IPC: H01J29/80
Filed: 1931-09-08
Abstract: 381,306. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.-(Assignees of Zworykin, V. K.; 416, Warwick Road, Haddonfield, New Jersey, U.S.A.) Sept. 8, 1931, No. 25224. Convention date, Sept, 25, 1930. [Classes 39 (i) and 40 (iii).] In a television or picture telegraph receiver comprising a cathode ray tube 10 in which a ray 12 of electrons is directed on a structure forming part of a television or picture reproducing system and is deflected so as to scan the picture area, means are provided for increasing the velocity of the electrons at a point in the path of the ray shortly after the point at which deflection is effected, and a substantial distance from the end wall of the tube, whereby the greater part of the path of the ray is traversed by electrons at high speed, while the deflection is effected while the electrons are moving at a relatively low speed. The ray is developed from an electron gun 11 comprising a heater 15, cathode 16, grid 17 and anode 18. The receiving circuit shown comprises an antenna 19 connected to earth through a tuning condenser 20 and inductance 21. This circuit is coupled to amplifying circuits 23, 24, the output of which is connected through filters 25, 26 and amplifiers to supply scanning frequencies to coils 28, 29 arranged to cause deflection of the ray 12 in two directions at right-angles. The picture impulses are impressed on the primary winding of a transformer 27. A second anode in the form of a cup-shaped structure 31, made of fine wire mesh, is disposed in the tube 10 with its open end extending towards the electron gun 11 and in contact with a silver coating formed on the interior of the tube between the lines 33, 34. The bottom 35 of the structure 31 forms a screen through which the electrons pass to the end wall of the tube. In the form shown in Fig. 1, this end wall is coated with a thin transparent layer of silver or other conducting material supporting a fluorescent screen 14 ; a thick coating of silver 37, in the form of a ring, overlaps the edge of the thin layer and serves to connect the same to a battery or other source of high potential 39. The screen 35 and structure 31 are maintained at a high potential intermediate between that of the anode 18 and the fluorescent screen. In operation, the resultant field of the coils 28, 29 deflects the ray 12, as the electrons are emitted from the gun, at a relatively low velocity determined by the potential of the anode 18. As soon as the electrons pass beyond the influence of the coils their velocity is accelerated under the influence of the second anode 31, and they reach the screen 35 while travelling at a high velocity. The velocity is further increased between the screen 35 and the fluorescent screen, causing the production of a very bright spot at the point where the ray strikes the latter, the brightness being further increased by secondary emission from the screen 35. The image developed on the screen 14 may be projected through a lens system 42 to an observation screen 43. In a modification the fluorescent screen is replaced by a Wehnelt window, the electrons passing through which may be made to fall on a photographic plate or film. In a further modification, Fig. 5, the distance between the screen 35 and the fluorescent screen 14 is increased, to minimize difficulties in insula. tion, and a focusing coil 47 is arranged about the tube between the screens. A water jacket 48, with inlet and outlet connections 49, 50 may also be arranged on the end of the tube. The velocity of the electrons between the screens 35 and 14 mav be increased in a series of steps by the provision of additional anodes at intermediate points.