GB1430119A - Cathode ray tube devices - Google Patents

Abstract

1430119 Cathode-ray tubes RCA CORPORATION 28 June 1973 [28 June 1972] 30744/73 Heading H1D [Also in Division H4] In a cathode-ray display tube having a pastdeflection focus grill 30 formed of parallel conductive elements adjacent a phosphor screen 26, e.g. a colour television tube having three guns and a phosphor strip screen, compensation for the variation of focusing which occurs between different vertically spaced regions of the screen is effected by the use of a modulated grill voltage (Fig. 5, not shown) of parabolic form and having a period equal to that of the vertical scan, and which may, as shown, be derived from the vertical scan oscillator 62. Defocusing at the outer side edges of the screen, resulting from the effect of the modulating voltage, on the electron trajectories, is prevented by applying the modulating voltage to the centre member of the grill via line 50, maintaining the two outer edges of the grill at a constant potential, and connecting successive adjacent grill elements to one another through successive taps on resistors 64 and 66. Alternatively, the resistors may extend only part-way to the edges of the grill (Fig. 3, not shown), the remaining outer members being started together. The resistors 64 and 66 may be uniform or non- uniform, and formed by resistive material incorporated in the glass frit seal between the funnel 18 and the faceplate 16, in which seal the ends of the grill elements are embedded.