GB484574A - Improvements in or relating to television or like systems - Google Patents

Abstract

484,574. Cathode - ray tubes. BAIRD TELEVISION, Ltd., and JONES, V. Nov. 5, 1936, No. 30096. [Class 39 (i)] In a television or like system an electrondischarge device is provided having a photoelectric cathode 2 upon which an image to be transmitted is projected, the photoelectrons emitted being arranged to form a charge image on a single - sided photoelectrically sensitive mosaic electrode 3, which comprises a plurality of discrete photoelectrically sensitive elements 4 at least partially insulated from one another and which is scanned by a light spot. The cathode 2 and elements 4 may be sensitive to light of different wave lengths so that the mosaic may be scanned with light different in colour from that forming the image on the cathode 2. The electrons emitted by the cathode may be multiplied by secondary emission from one or more secondary emitting grids as described in Specification 469,404 and the electron stream is focused upon the mosaic 3 by a magnetic coil 8 which may produce an intense focusing field immediately in front of the mosaic so as to prevent diffusion of the image charges and in this case the anode 6 is in the form of a grid parallel with the mosaic 3. A transparent metallic layer 5 is provided on the back of the mica sheet forming the support for the elements 4 of the mosaic, this layer being connected through a resistance 9 with the cathode 2. The mosaic 3 is scanned by a light spot which may be projected from either side of the electrode assembly, whereby electrons are emitted therefrom proportionally to the intensity of the electron image incident thereon, thus giving rise to image signals in the resistance 9. Suppressor grids may be provided between the anode 6 and the mosaic 3, and also adjacent the cathode 2. Image signals may also be obtained from a load impedance connected between the electrodes 3 and 6, or the photoelectrons emitted from the mosaic 3 on scanning may fall upon an electron multiplier consisting of a series of grids at gradually increasing potentials or the multiplier may comprise a series of coaxial cylinders of decreasing diameter arranged within the ring-shaped anode 6 which is then of larger diameter than that shown. The light spot for scanning the elements 4 may be obtained by covering the electrode 5 or the mica sheet of the mosaic with fluorescent material, this being scanned by a cathode-ray gun mounted within the envelope 1.