High Current Electron Gun for Projection Kinescopes

One of the problems in the art of reproducing a scene by television is to obtain an image of adequate size. Because of this there has been considerable interest in projection systems where a small, high intensity image reproduced on the face of a projection Kinescope is thrown onto a viewing screen of the desired size by a suitable optical system. The light output and the definition of these systems has been limited by the inability of the electron gun to provide a sufficiently large beam current in a small spot. This paper describes an electron gun giving large beam current in a small spot. The design of this electron gun is based on the results of the present investigation which shows that the ratio of the current in the first crossover inside the radius r to the total space current is I/Is=1-ε-ar2E where E is the voltage applied to the first crossover forming system and a is a constant for any given cathode temperature, potential distribution, and geometry. Inasmuch as the total space current varies approximately as E^3/2, the concentration of current in the first crossover increases very rapidly with voltage. A description is given of an electron gun based on this theory. All available voltage is used to form a small intense first crossover whose edges are sharply defined by a first crossover defining aperture. A magnetic final focusing lens reimages this first crossover on the fluorescent screen. This electron gun gives beam currents of 1.