Patent GB-779564-A (GB)
Title: Colour television apparatus
IPC: H01J31/20
Filed: 1955-05-13
Abstract: 779,564. Colour television tubes. STANDARD TELEPHONES & CABLES, Ltd. May 13, 1955 [May 18, 1954], No. 13918/55. Class 39(1). Deflecting plates divide the beam of a colour tube into at least two beams and control the angle of approach onto a perforated target electrode, behind which is a mirror electrode reflecting the beams back onto a pattern of at least two different phosphors arranged on the face of the target electrode away from the cathode. The beam from cathode 2 is focused and modulated by electrodes 3, 4, 5, 6, and are offset at and divided at the sets of deflecting plates 32, and 29, 30, 33, respectively. The divided beams are scanned by deflecting coils 17 and bent back into normal incidence with the target 22 by means of focusing ring electrodes 9, 10. The metal target 22 is perforated and spaced from a transparent conductive film 12 at negative potential which reflects the beam onto blue, red and green phosphor strips 24, 25, 26, Fig. 4, the blue strips coinciding substantially with the rows of apertures 23. By offsetting the beam by means of the deflection plates 29, 30, 32 to angle of approach may be altered to cause impact wholly or partially on the red, blue and green phosphors strips as determined by the chrominance circuits 40 applying signals to the plates. Luminance signals are applied to grid 3. The displacement of the beam giving partial or mixed colour of luminescence (including white) are indicated at 34a, 34b, 34c, 35a, 35b and 35c, Fig. 4. An optical analogy of the lens effect produced by the anode 6, the ring 9, 10 and the wall coating 8 is discussed in the Specification, Fig. 8 (not shown). In a modification, Fig. 9, the anode 48 carries three sets of triple plates 46, 47, 48 arranged at 120 degrees to each other, with their central partitions 49, 57, 58 designed to divide the beam into six portions. The central set may be omitted to give only three portions. Each partition is connected to a separate colour input circuit and fed with chrominance signals. The target 13A, Fig. 12, has colour strips 61, 62, 63 located in lines at right angles to the planes of the electrodes 46, 47, 48 with an aperture 60 at each intersection and bare patches 74 between the strips. The amounts of offsetting and the proportion of each beam falling on a colour strip are determined by the modulating potentials on the electrodes 46, 47, 48, as shown at 65a, 66a, 67a 68a, 69a, 70a. Each colour develops two spots on the phosphor plate. The beam splitting is stated to reduce the effect of noise, non-linearity and spherical aberration. In order to bring the three centres of deflection of the colour selecting electrodes into virtual coincidence sets of three electrodes are provided, Fig. 13 (not shown) and each colour selecting unit comprises two sets of electrodes, as shown diagramatically in Fig. 15, the centre plate 79 of one set being connected to the outer plates 81, 82 of the other and vice versa. The plates are spaced in ceramic mounts. The plates and partitions of the three electrode sets are arranged so that the backward projection of each beam 90, 91 passes through the same point 92, i.e. by varying the spacing or size of the plates or the potentials thereon or the parameters of the other lens elements.