The Triode

Author: E.E. Kimberly

If a mesh screen or grid be placed between the cathode and the plate of a diode, its presence will not materially affect the migration of electrons. However, if the grid be charged negatively with respect to the cathode, some of the electrons migrating from the hot filament will be driven back in accordance with the law of repulsion of similar charges, and the current flow in the plate circuit will be diminished. Conversely, a positive charge on the grid will accelerate the migrating electrons and will increase the plate current.

Because the grid is much nearer to the cathode than it is to the plate, a small change in grid potential may be made to cause a great change in plate current. This action is called amplification. The three-electrode tube is called a triode. By use of the triode a small amount of power may be made to control a large amount of power. Such a high-vacuum tube is known as a pliotron.