The dependence of the inter-electrode capacitances of valves upon the operating conditions

The results of the measurement at a frequency of 1 million cycles per sec. of the effective inter-electrode capacitances under working conditions of a variety of valves are tabulated, together with an estimate of the net capacitance residing between the active elements themselves. The grid-filament capacitance shows an increment which increases with anode current up to the point at which grid current flows. The increment diminishes at a given value of anode current as the anode voltage is increased. Experiment shows that this increment in capacitance is not a simple function of anode current, neither of anode-filament nor of mutual conductance. It is augmented the higher the filament temperature and is probably a function of the initial velocity of the electrons. The effective grid-anode capacitance suffers a reduction as the anode current increases, but the reduction is much smaller proportionately than the increase in grid-filament capacitance. Every type of valve examined displays the effect¿even the small acorn triodes and pentodes, in which the increment represents a 50% augmentation of the ¿cold¿ value of Cfg