The Beam-Power Tetrode

Author: N.H. Crowhurst

Tube construction. Left: pentode, right: tetrode

Another method of preventing secondary emission a specially shaped electrode between the screen grid and the plate. It is called a beam-forming electrode and consists of two pieces of metal placed in a different direction from the grid wires of the normal grid. (The normal grid wires are wound around the cathode at a constant radius; beam-forming electrodes run parallel to the cathode in specially selected positions.) It is connected to the cathode in just the same way as the suppressor grid of the pentode, and its effect on performance is very similar to that given by the addition of a suppressor grid. It succeeds in squeezing the last ounce of efficiency out of the tube, by extending the voltage and current swing to the maximum possible degree.

Effect of beam-forming plates on the tube characteristics