Abstract: To prevent the formation of a corona (2) in a known in-line color picture tube with an automatic-focusing deflection system and four grids (G1-G4), a rectangular opening is provided on the side of the second grid (G2) facing the first grid (G1). As a result, the luminous spot (1) formed by the electron beam at the center of the screen is converted to a vertical ellipse and the ratio of the axes of the lateral ellipses on the edge of the image is reduced, thus improving the sharpness of the edges. The openings (5) in the first grid (G1) are elongated in the in-line direction, in particular rectangular, the adjacent openings of the second grid (G2) are also rectangular and all the other openings in the other grids (G2, G3, G4) are circular. In this way, the ratio of the axes of the luminous elliptical spot (11) produced by the electron beam at the center of the screen is reduced without adversely affecting the sharpness of the edges.

Abstract: In a cathode-ray tube with a thick grid No. 2 (24) in the electron-gun system, current transfer into grid No. 2 (24) may result in a lack of picture sharpness. To avoid this error, the aperture (4) in grid No. 2 (24) has a widening (6) of conical shape or stepped diameter.

Abstract: An electron-gun system is described in which the segments of the particularly long electrode neighboring the other electrodes are made of a material having a temperature expansion coefficient differing from that of the other electrodes.

Abstract: The electrodes of an electron-gun system of a color-picture tube are heated less as their distance from the cathode of the system increases. The electrode materials are so chosen with respect to their coefficients of expansion that no mechanical stresses are caused in the system structure despite the different temperatures.

Abstract: The cathode support of an indirectly heated cathode for picture tubes is commonly mounted in a ceramic disk by cold riveting. With sheet thicknesses below 0.1 mm, the support cracks during riveting. According to the invention, that portion of the support which projects beyond the ceramic disk is first rolled over by wobble-riveting, after which the support is braced by hot-pressing. This insures that the cathode support is securely held in place and prevents cracking.