An electrostatic printing tube for electronic duplication

When the electron beam of a cathode-ray tube strikes the ends of a linear array of parallel wires passing through the faceplate, the wires begin to charge toward cathode potential. If a sheet of dielectric material backed by a ground plane is placed close to the other ends of the wires, a discharge will take place when a given wire has reached a critical value of voltage. The resulting spot of charge on the dielectric can be made visible by application of charged powder. If the beam is scanned along the array of wires, an appropriate signal put on the grid of the electron gun and the dielectric pulled past the wire array, the tube can be used to print letters or reproduce line drawings with great, rapidity.