In a glass front-panel for a cathode ray tube, whose surface layer contains more potassium ions than those in the interior thereof, and whose flange is stuck to a rear panel to form a vacuum vessel, only the surface layer of the flange portion is substantially removed, or in a glass front-panel for a cathode ray tube, comprising an image displaying portion, a side wall portion and a flange portion, a belt-like electrode for making a gradient of electric potential easier is disposed on a surface of the side wall portion, so that the cathode ray tube is prevented from being damaged due to dielectric breakdown.

A method of manufacturing a display tube comprising an envelope having an envelope portion and a display window. The quantity of X-rays released from the envelope portion is determined, after which discrete X-ray absorbing means are provided in those places of the envelope where the quantity of X-rays released exceeds a limiting value. In a display tube manufactured according to such a method and comprising, in particular, a substantially rectangular display screen and a cylindrical neck portion having an electron gun the diagonals of the envelope of which are provided with discrete X-ray absorbing means, the desirable quantity of X-rays is absorbed in a simple and cost-effective manner.

In an electron tube grounding device, an image display unit includes an earth plate for grounding an electron tube, and a degauss coil for magnetic erasing, which is improved to prevent the deformation of the earth plate for grounding a chassis frame which shields the electron tube and its periphery. The damage of the degauss coil can be caused by the assembling of the electron tube and the chassis frame. The electron tube grounding device includes an electrontube, a chassis frame for surrounding the electron tube, and an earth plate for grounding the chassis frame and the electron tube. The chassis frame includes a penetration aperture formed on one side thereof, and a rail means protrudently formed on the back portion of and outside the penetration aperture where the earth plate is inserted to be fixed. The earth plate includes a fixed end portion fixed at one side of the chassis frame, an intermediate portion with elastic force which makes it contact with a band of the electron tube in case of assembling, and a free end portion inserted into the rail means after coming out of the chassis frame through the penetration aperture.

A surface treatment film composed of a conductive film with a surface resistance of 1.times.10.sup.3.OMEGA./.quadrature. or more and an antireflection film is provided on the surface of a glass panel. A ground electrode is provided on the surface treatment film so as to be electrically connected with the conductive film. The ground electrode is grounded in a circuit manner. An area of the surface treatment film covered with the ground electrode is set at 500 mm.sup.2 or more. Thus, even in the case where the conductive film has a resistance of 1.times.10.sup.3.OMEGA./.quadrature. or more, an effect of suppressing a leakage electric field to 1.0 V/m or less, which satisfies the TCO guideline, can be realized.

Human bodies are shielded from an alternating electric field radiated from a deflection yoke of a cathode-ray tube device to prevent the alternating electric field from adversely affecting the human bodies. For an alternating electric field traveling forward in the direction of a tube axis 28 of a cathode-ray tube, a cone section 1b is formed with a conductive film 17 for shielding an electric field and/or a face panel 2 is formed with a transparent conductive film 21 for shielding an electric field and the transparent conductive film 21 is grounded or an optimum potential is given only to the transparent conductive film 21 for shielding an electric field.