GB434942A - Improvements in or relating to cathode ray tubes and television and like transmitters incorporating the same - Google Patents

Abstract

434,942. Television ; cathode ray tubes. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Vance, A. W. ; 324, South 11th Street, and Branson, H. ; 5931, Frontenac Street, both in Philadelphia, U.S.A.) May 24, 1936, No. 16170. Convention date, May 24, 1934. [Classes 39 (i) and 40 (iii)] A television transmitter or like cathoderay tube comprises a mosaic of light-sensitive elements mounted upon and insulated from conducting means in electrostatic association therewith, an anode common to the elements and means including a source of relatively low-velocity electrons for causing said elements to assume a negative potential with respect to the anode to increase the sensitivity of the device. An iconoscope comprises an electron gun consisting of a cathode 3, Fig. 1, a control grid 5, negatively biassed by means of a battery 11, and an anode 7 maintained at a positive potential by a battery 9. The electrons are accelerated and concentrated by an anode 13 which consists of a metallic coating and is connected to earth and maintained at a high potential by. a battery 15. The mosaic 17 is formed on one side of a mica sheet, the other side of which is provided with a metallic coating connected to earth through a resistance 27 and battery 29, and to the amplifier 25 of the picture signals. The mosaic may consist of silver globules each of which is coated with a film of silver oxide which is covered with caesium; alternatively it may consist of a continuous film so thin that the resistance between the individual small parts is large, or it may consist of a continuous film divided into elements by a ruling machine. The mosaic is sprayed uniformly with electrons from a cathode 41 which, together with a control grid 43 is connected to variable tappings on a resistance 47 connected across the battery 15. The auxiliary anode 45 may consist of a metallic coating and be connected to the anode 13. The potentials on the grid 43 and the anode 45 and accordingly the velocity of the electrons sprayed upon the mosaic are so adjusted that the number of secondary electrons is less than the number of primary electrons. With a mosaic, which consists of caesium coated silver oxide globules, the velocity of the electrons should be less than 65 volts, e.g. 45 volts. The electrons may be sprayed. continuously on the mosaic or only when a scanning line or picture frame has been completed. In a modification, the scanning is effected by deflecting coils 21, Fig. 2, which are supplied through a coupling condenser 57 with voltage impulses of saw-tooth wave form which are also supplied through a condenser 55 to the primary of a transformer 53. The control grid 43 is connected through a tapping on a resistance 49, connected across the secondary of the transformer 53, and through a battery 51 to the cathode 41, and to a tapping on a resistance 47. Normally, the negative bias on the grid will suppress the emission of the electrons, but upon the application of the voltage impulse, which returns the electron beam at the end of a scanning line, a positive potential is applied to the grid to release the electrons.