Grid and plate currents in a grid-controlled mercury vapor tube

Abstract

An oscillographic and quantitative investigation of the grid and plate currents of a grid-controlled mercury vapor tube, operating in an a.c. circuit, as functions of grid voltage and resistance, plate voltage and phase displacement between grid and plate voltages. It is shown that the direction of grid current depends not only upon the instantaneous polarity of the grid but also upon the magnitude of the grid voltage and upon the plate current. The grid current wave may consist of positive loops only, of positive and negative loops of varying areas or of equal areas, and of negative loops only. The various factors affecting the form of grid current wave are considered in detail. Inverse plate current occurs whenever the grid current is concurrent with the negative half-cycle of the plate voltage. The minimum value of inverse plate current occurs when there is no grid current coincident with the negative half-cycle of the plate voltage. It is caused by the lag of deionization of the mercury vapor furnishing a small amount of ionization when the plate voltage becomes instantaneously negative. With a constant average grid current the magnitude of the inverse plate current varies approximately sinusoidally with phase displacement between grid and plate voltages.