Patent GB-721199-A (GB)
Title: Improvements in or relating to cathode ray tubes for colour television
IPC: H04N9/26
Filed: 1951-02-15
Abstract: 721,199. Colour television tubes. CHROMATIC TELEVISION LABORATORIES, Inc. Feb 15, 1951 [March 20, 1950], No. 3645/51. Class 39 (1) In a colour television receiver in which the phosphors are excited in definite sequence by the selective impingement thereon of the beam, one of the phosphors is a translucent layer on the picture area and at least one other phosphor coating is deposited on or supported by a plurality of conducting strips mounted close to and approximately edge on to the translucent layer, the strips being so connected that when they are all at the same potential equal to the layer potential the beam passes between the strips and strikes the layer, while when one strip is made more positive than an adjacent strip the beam passing between them strikes the more positive strip to excite the phosphor coating deposited on or supported thereby. Preferably the translucen layer 23, Fig. 11, is the green phosphor, and may be on the tube end wall or on a separate glass sheet within the envelope and the strips 27' 29', 27', 29' carry alternately red and blue phos phors. The strips are connected in two alternate sets. Other primary colours may be used or in a two-colour system the strips carry phosphors of only one primary colour. The strips may be supported at intervals along their length by glass fibre cords 37, Fig. 4, and the ends of the strips may be held in slots in insulating supports 39 Fig. 3, members 31, 33 acting as leads and sup ports for the structure. In alternative constructions the strips may be notched, Fig. 5 (not shown), and spaced apart by correspondingly notched insula tors. Glass fibre cords pass through the notches and secure the assembly; the notched insulators are slightly wedge-shaped so the beam enters parallel to all the strips. In another form, Fig. 6 (not shown), the strips have corrugations secured to adjacent strips by insulating beads fused thereto. In another form, Fig. 7, glass beads 53 space the strips apart and glass threads 51 hold the assembly together. The beads at the front and rear of the strips are of slightly differen diameter to give the correct tilt to the strips In another form, Fig. 8 (not shown), the strips are wound into spiral form and it is stated that concentric circular or elliptical forms may also be used. In another form, Fig. 9 (not shown) the strips are wedge-shaped, and in a modification, Fig. 10, the strips 27", 29" are wedge shaped and glass beads carrying the red and blue phosphors are fused to their apices. In all forms the strip spacing is not greater than and preferably one-half or one-third of a picture element size and their width about 10 times their spacing. The scanning lines may be parallel, perpendicular or diagonal with respect to the strips. The devices may use field, line or dot sequential systems or simultaneous systems. The density of the phosphors on the strips may be varied so as to compensate for loss of light which would otherwise result for excessive deflecting voltages between the strips, i.e. the density is greater further away from the end wall of the tube. The green phosphor layer may or may not have a thin conductive coating of metal, e.g. aluminium; if there is no coating, the layer takes up a suitable potential by secondary emission. The tube may be of glass, metal or 'glass and metal' and has electrostatic or electromagnetic deflecting means for scanning. If the strips are not edge on to the gun, means, e.g. auxiliary focussing means, must be provided for deflecting the beam just before it enters the grating to make it parallel to the strips of the grating. The tube has modulating grid, first and second anodes, and may have internal electrostatic or external magnetic focussing. The end wall of the tube may be frosted before deposition of the green phosphor to diffuse the light uniformly.