The Measurement of Direct Interelectrode Capacitance of Vacuum Tubes

A method of measuring direct capacitance in the range 10^-10to 10^-15farads by a charging current at radio frequencies is described. A low resistance current indicator is shunted across one of the direct capacitances. The charging current I = ωEC is a measure of the direct capacitance provided that COE is maintained constant. A simple circuit arrangement provides an apparatus giving reliable results measured visually by substitution with a standard. The method has been practically applied in the measurement of direct capacitances present in vacuum tubes providing data for design purposes and for control of product uniformity. The method is specially advantageous in its ability to measure exceedingly small direct capacitances present in screen-grid tubes.