Home Projection Television: Part I. Cathode-Ray Tube and Optical System

A comparison of direct-viewing with projection tubes leads to the conclusion that the latter are better suited to provide a picture of adequate dimensions. The characteristics of a 2.5-inch cathode-ray tube for television projection in an average living-room are described. Some details of the tube are as follows: a very small spot size, achieved by unusually close tolerances in neck and gun dimensions; a narrow neck, reducing the energy required for the magnetic focusing and deflection to a value about equal to that for direct-viewing tubes; a face plate ground to meet the optical requirements of the projection system; and a metal backing for the screen so that high reflectivity and good electrical conductivity aid in the achievement of an adequate brightness. For projecting the image on the viewing screen, a modified Schmidt-mirror system was adopted. The different possible modifications and their advantages and disadvantages are discussed. A simple and flexible method for preparing aspherical correction plates is described; it consists in molding the correctors on a glass plate from a gelatine solution and drying them afterwards. The design and performance of the projection system are discussed briefly.