Cathode-ray tube for displaying pictures.

摘要

A cathode-ray tube comprising in an evacuated envelope a diode electron gun for generating an electron beam, which electron gun comprises a cathode placed on an axis and the emissive surface of which extends substantially perpendicularly to said axis, and an anode which extends substantially perpendicularly to the axis and has an aperture opposite to the cathode, said electron beam being focused on a target by means of at least one focusing lens. If said cathode-ray tube according to the invention is a picture display tube and the target is a display screen and the spacing between the anode and the cathode of the diode electron gun is smaller than 200 µm and the electron beam generated in the operating tube viewed in the direction of propagation is focused to form a cross-over immediately after the anode by a positive electron lens, which cross-over is displayed on the display screen by means of the focusing lens and in which cross-over the current density on the axis is larger than three times the current density in the point of intersection of the axis with the cathode, a target is formed at comparatively large electron beam currents (1-5mA) on the display screen having a diameter which is smaller than the diameter of the spot in the so far known cathode-ray having triode electron guns. The part of the anode comprising the aperture preferably consists of a thin metal foil which extends perpendicularly to the axis and the thickness d of the foil divided by the radius r of the aperture is smaller than 1(a/r < 1). Such tubes are particularly suitable for use as a projection television tube or a D.G.D.-tube