A new cathode-ray tube for monochrome and colour television

Abstract

A flat, thin television cathode-ray tube for monochrome or colour, whose thickness is only about one-quarter of its screen diagonal, has been developed by the authors to the point at which the feasibility of its essentially novel features could be tested singly, and partly in combination. In the flat tube the electron beam—and in the case of a colour tube, three beams—issuing from the same gun is launched vertically downwards. A line-deflection system imparts to it a pendulating motion in a vertical plane, and a reversing lens turns this plane by 180°, increasing the deflection angle by a factor of about 4. Just before reaching the screen region the beams are turned into the vertical direction by a magnetic collimator. The beams now enter a narrow space between the phosphor screen and a ‘scanning array’, consisting of parallel, horizontal conductors, arranged in a plane parallel to the screen. At a certain level the beam is thrown against the phosphor screen by an electric field, which travels downwards with the speed of the frame scan. This travelling field is produced by the beam itself, which, in the intervals between line scans, falls on the conductors of the array in a narrow zone, discharges them, and thereby pushes the field to a lower level. Recharging of the array after the frame scan is also effected by the electron beam, making use of the secondary emission of the array conductors. This is the principle of self-scanning. Colour is produced by shooting three beams on parallel lines and close together into the screen region. The deflecting field between screen and array acts as an efficient short-focus lens, and unites the three beams in one small spot at the screen, which they approach at different angles. Colour discrimination is produced by a line shadow mask about 0.5 mm only from the screen, and fixed to it by means of small, invisible bridges. This also serves as a mask in producing the colour-phosphor strips by a powder-settling process in air. The extensive electron-optical development work is described in detail, and mention is also made of special technological problems raised by the new c.r.t. design, and of their solution.