GB1339970A - Method and apparatus for adjusting the colour purity of a colour picture display tube - Google Patents

Abstract

1339970 Colour television tubes PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 19 April 1971 [10 April 1970 12 Sept 1970] 26468/71 Heading HID [Also in Divisions H3-H5] A method of adjusting the colour purity magnet of a colour television tube comprises scanning the screen with one or more unmodulated beams whilst a magnetic field is provided adjacent the screen, and adjusting the purity magnet until there is a constant colour over a predetermined area. Prefereably the field is provided by a coil 2, Fig. 9, which is centrally disposed over the screen 1, and with only the "red" electron gun operating the purity is adjusted until a red ball appears at the centre C. If the tube construction is such that the electron landing areas should not be centrally positioned on the luminescent spots in the centre of the screen, the adjustment may be such that the red ball appears on the 5 o'clock- 11 o'clock axis at a predetermined point which may be indicated by reference marks. A similar process may be used to position the deflection yoke using two circular coils positioned with their centres on the ends of the horizontal axis of the screen (Fig. 7, not shown); the yoke is adjusted until the red balls lie on the horizontal axis. To avoid coils overlapping the edges of the screen, the auxiliary coils 2<SP>1</SP> and 2<SP>11</SP> may be made semicircular, as shown in Fig. 9, and a further coil 2<SP>111</SP> amplifies the action of coils 2<SP>1</SP> and 2<SP>11</SP> to locate the red balls as near the edge of the screen as possible. Two guns may be operated to produce a yellow ball so that the deflection unit is correctly aligned for two colours. After the adjustments have been made to the purity magnet and to the deflection yoke, the coils may be energized through a thermistor with alternating current to degauss the shadow mask (Fig. 10, not shown). Permanent magnets may be used instead of coils.