Patent GB-425267-A (GB)
Title: Improvements in or relating to cathode ray tubes
IPC: H01J29/52
Filed: 1934-06-11
Abstract: 425,267. Cathode-ray tubes. FERNSEH AKT.-GES., Goerzallee, Zehlendorf, Berlin. June 11, 1934, No. 17232. Convention date, June 10, 1933. [Class 39 (i)] The brightness of the light spot on the screen of a cathode-ray tube for television &c. is modulated by controlling the number of electrons impinging on luminescent portions of the screen by means of fields transverse to the ray in the immediate neighbourhood of the screen. The screen may comprise spaced fluourescent strips parallel to the scanning lines, a cathode ray of half the width of the scanning lines being deflected on to the fluorescent strips according to the brightness of the picture points. Disturbances due to fluorescence of the glass between the fluorescent strips may be avoided by covering the glass with conductive strips or by painting opaque strips on the viewing side of the screen. The screen may have a continuous luminescent coating with superposed spaced strips of conducting material. To avoid dark strips in the image, the screen is viewed through lightdiffusing discs ; the screen may be deposited on the polished side of a matt disc or on the translucent glass end of the tube. The screen is accurately adjusted relatively to the ray, for example, by magnets outside the tube. In a modification avoiding this adjustment, the ray 7, Fig. 1, is the full width of a scanning line and is reduced to half width 8 by a grid 1<1> .. 51 before deflection by the modulating field, as shown at 6, on to conducting strips 1 . 5 and off the intervening fluorescent strips. The modulating electrodes are outside the picture area or a separate pair of electrodes for each line are provided in the form of strips of copper foil supported by wedge-shaped glass plates. In a further modification, these electrodes are highly positive relatively to the cathode to absorb deflected electrons and make the strips 1 .. 5 unnecessary. In one such arrangement the strips 11 .. 51 are also omitted and the positive deflecting strips 9, Fig. 2, are connected together alternately. The modulating potentials are applied to the two sets of strips to deflect the full-width ray 7, the maximum deflection being shown. The Specification as open to inspection under Sect. 91 comprises also the following modifications. The modulating potentials are applied to the deflecting plates which produce scanning. Saw-toothed contacts struck by the ray at the end of each line control deflecting fields determining the position of the ray relatively to the strips of the screen. The masking grid is inclined or at a right angle to the scanning lines, the beam being traversed in the direction of the scanning lines at variable velocity. The masking grid comprises stretched wires in front of the screen of a gas-filled tube at a position where the ray has a smaller width than at the screen. The number of electrons reaching the screen may be modulated by fields parallel to the ray, the modulating potentials being applied to a control grid between the positive luminescent screen and an accelerating grid, which may be at the same potential as the screen. Screening grids may be added. This subjectmatter does not appear in the Specification as accepted.