GB743431A - Improvements in or relating to picture and/or picture signal producing electron discharge tubes - Google Patents

Abstract

743,431. Television pick-up tubes. COMPAGNIE GENERALE DE TELEGRAPHIE SANS FIL. May 19, 1953 [May 27, 1952], No. 14079/53. Class 39 (1). An electron discharge tube comprises a photo-conductive layer with a metallic back-plate at near cathode potential, a permeable decelerating electrode near the target and at a high potential relative to the cathode of the gun and a scanning beam producing secondary electrons and reflected primary electrons at the target to form pictures on a fluorescent screen or develop video signals or both. A very thin metallic back-plate 3, e.g. of platinum or glass supports the photo-conductive layer 4 and the very fine mesh planar grid 10 which lies close to the layer and at a high potential, e.g. 1000 volts, i.e. the potential of a wall coating 2 and the anode 8 of the inclined gun 6, 7, 8. The electron lens 11 is at a lower potential, e.g. 500 volts and its focal plane passes through the centre of deflection C of the gun. Beam electrons reflected from the charge image produced on the target 4 by the image of the object cast by lens 5 which may be of infra-red or ultraviolet radiation, are accelerated and focused through a diaphragm 16 to give a visual image. Alternatively, as in Fig. 2, (not shown), they are focused onto the first element of an electron multiplier, the final electrode of which gives a video output signal. In another modification, the primary electrons reflected at the target pass to a symmetrically placed electron multiplier to give the output signal. Fig. 5 shows an arrangement combining the two systems to provide a visual monitor, the reflected electrons being received by the electrode 12 of the multiplier 13 and the secondary electrons being accelerated along the axis on to the fluorescent screen 16.