Equivalent Electrostatic Circuits for Vacuum Tubes

A method of field analysis by conformal transformation is used to demonstrate that the electrostatic properties of a triode may be represented by three capacitances in star, whose magnitudes are related to tube geometry in simple fashion. The method is then extended to the construction of an equivalent electrostatic circuit for multigrid tubes. It is shown how there can be derived from the electrostatic circuit (a) good approximations to the potential distribution in various parts of the tube and around these first approximations more accurate determinations of the local potential distribution; (b) a simple and rational expression of the dependence of cathode-current flow upon the various electrode potentials, for both parallel-plane and cylindrical geometry; (c) the ordinary interelectrode capacitances, as far as these are affected by the structure of the active portions of the electrodes. The application of this general method to structures having non-regular geometry and to other problems of current and potential distribution is discussed.