The symboltron - A character writing tube

It has long been known that the triode of a CRT when operated under temperature limited conditions can project a very sharp image of the cathode surface. The portion of the cathode capable of being projected without appreciable distortion approximates one quarter of the grid hole diameter. This simple CRT triode immersion/projection lens is applied to produce a very simple and effective character writing tube which requires only a pair of electrostatic orthogonal fields for character selection and a magnetic deflecting field for character positioning. The selecting and deflecting fields are totally independent of each other and no compensating fields are required.