The measurement of the grid-anode capacitance of screengrid valves

Two methods of measurement of the grid-anode capacitance of screen-grid valves are described. In the first the working value of this capacitance is deduced from measurements of the change in the input capacitance of the valve upon reducing the anode load from a known value to zero. It is necessary to know the amplification factor of the stage. A description of the bridge employed for its measurement is given in Appendix 1. The second method measures the grid-anode admittance with the filament cold. The result is obtained in terms of the ratio of the readings of two voltmeters and the settings of a variable air condenser covering a range of capacitance over which it can be calibrated directly.