PURPOSE: To increase the aperture of a main lens, and reduce the aberration of a cathode-ray tube by installing plural magnets so that they are symmetrical to the center of a focusing electrode, performing a static focusing with these magnets, and supplying a dynamic focusing voltage to the focusing electrode.
CONSTITUTION: Two doughnut-shaped magnets 6 and 7, each of which is magnetized so that its ends have opposite magnetisms, are installed outside a cathode-ray tube 1 so that they are symmetrical relative to the center of a fourth grid (G4), which is a focusing electrode, and so that end surfaces of the magnets 6 and 7 facing to the fourth grid (G4) have the N polarity. The aperture of a main lens can be increased by carrying out a static focusing by means of the magnets 6 and 7, and carrying out a dynamic focusing by means of the fourth grid (G4). As a result, the spherical aberration of the tube 1 can be reduced.
WATANABE YUZURU
TOOYAMA TAKASHI
