GB530409A - Improvements in or relating to television transmitting tubes - Google Patents

Abstract

530,409. Cathode-ray tubes. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 22, 1939, No. 18254. Convention date, July 30, 1938. [Class 39 (i)] In television transmitting tubes utilizing low velocity electron beams for scanning a mosaic target, the electron beam deflecting system is such that the electrons not reaching the target are returned along different paths to a collecting electrode in front of the electron gun. The tube shown in Fig. 1, comprises a gun consisting of an indirectly heated cathode 3, a control electrode 4 and first and second anodes 5, 6. The screen 2 consists of a transparent insulating plate 8 with a backing signal plate 9 and a photo-electric mosaic surface 10. A concentrating coil 13 surrounds the tube throughout its length, and the beam deflection means for scanning the screen comprises a pair of electrostatic plates 14 and a pair of magnetic coils 15. After deflection by the plates 14, the electron beam is returned parallel to its path before deflection, and in the case of a low velocity electron beam, the electrons returning from the screen take a different path from their outward traverse and are caught up by an apertured electrode 16 disposed between the gun and the deflection plates. A second pair of electrostatic plates at right angles to the first may be used instead of the deflecting coils. The signals may be taken off the plate 9, or the electrode 16 and may be amplified by an electron multiplier consisting of a series of mesh plates of secondary electron emissive material and a collecting electrode (Fig. 3, not shown). The photoelectric mosaic may be replaced by target electrodes of the photo-conductive or photo-resistive type.