GB712237A - Improvements in or relating to cathode ray tubes for color television - Google Patents

Abstract

712,237. Colour televsion tubes. CHROMATIC TELEVISION LABORATORIES, Inc. March 30, 1951 [April 25, 1950], No. 7395/51. Class 39(1) A colour television receiver has a target 25, Fig. 4, formed with a plurality of recesses 27, each recess having a phosphor 35 emitting one colour at the bottom thereof and further phosphor coatings 35<SP>1</SP>, 35<SP>11</SP> emitting other colours deposited successively on the sides thereof, the distance between the centres of adjacent recesses is as small as or smaller than the area of a picture point, and deflecting electrodes 37 additional to the scanning means are provided adjacent to the target for colour switching. The electrodes 37 are narrow strips and are preferably alternately positive and negative. The beam will normally impinge on the green phosphor at the bottom of each recess but by applying a moderate potential difference between pairs of adjacent electrodes 37 the beam contacts the red phosphor and with a higher potential difference contacts the blue phosphor. Electrodes 37 are energized by an oscillator which may or may not provide an additional D.C. bias to modify the rate and sequence of the scan. In modified forms the recesses may be of triangular form and a separate apertured mask disposed in front of the screen, Fig. 5 (not shown), or the mask may be formed integrally with such a screen, Fig. 6 (not shown). The strip deflecting electrodes may be fused at one end to the screen and be formed with mask portions at the other end, Fig. 7 (not shown). One or more positively biased focusing electrodes may be disposed between each pair of deflecting electrodes, the collecting electrodes having a relatively negative and varying potential, Figs. 8, 9 (not shown). in which case the mask may be dispensed with. The strip deflecting electrodes, and focusing electrodes if provided are carried by glass supports 38, Fig. 3, and the structure is strengthened by mica combs 40. Members 44 serve as supports and leads. The tube has one or more focusing and accelerating electrodes and horizontal and vertical scanning coils and the scanning lines may be horizontal, vertical or diagonal. The colour controlling potentials applied to the strip deflecting electrodes may be in field, line or dot sequence. For line or field sequences square wave oscillators, preferably with a D.C. bias, are used. The screen may or may not form the tube end wall. The mask may be formed with Lenard windows of thin foil instead of aoertures, and the screen recesses, permeable mask portions and mica combs are given different inclinations so as to all face the centre of deflection. Instead of a single piece of glass with roundbottomed recesses as in Fig. 1, the screen may be made of alternate wide and narrow strips as indicated by the dotted lines 33 in which case the bottoms may be rounded or flat. A filter may be disposed between the red phosphor and the glass screen as a ruby' coating 46 to correct the colour which by itself is unsatisfactory. The screen may have a reflecting coating of aluminium between the phosphors and the gun e.g. it may be applied to screen faces 31, Fig. 4. Total internal reflection in the screen may also be used to increase the light output.