The Exact Measurement of Electron-Tube Coefficients

Abstract

The analysis of the conventional bridge circuits (Chaffee, Thermionic Vacuum Tubes) for the measurement of electron tube coefficients has been extended to include the effect of grid current and tube and battery capacitances. It has been found that the addition of an auxiliary capacitance bridge to the usual circuits permits annulment of the quadrature component of voltage introduced into the detector circuit by the tube capacitances. In every case in which one or more of the tube capacitances form one arm of the auxiliary bridge the conditions of balance show the expression for the tube coefficient to be independent of the capacitances of the auxiliary bridge. If all the tube capacitances are considered it appears that a single balancing condenser in the auxiliary bridge will always suffice to give an exact null balance, although the expression for the tube coefficient may contain a correction factor, usually negligible, involving the capacitances. This capacitance balancing method has been applied to circuits suitable for measuring both positive and negative values of the plate and grid coefficients and the exact expressions for the coefficients are given under the general condition that electron current flows to both grid and plate.