A Low Grid-Current Vacuum Tube

Abstract

The various factors that may cause a current to flow to the control grid of a high vacuum tube are outlined. The magnitudes of the separate components are experimentally determined, and methods are given by which these currents may be greatly reduced. A tube is described which has a grid current of ${10}^{\ensuremath{-}15}$ ampere and a mutual conductance of 25 microamperes per volt. As an input resistance of 4\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ohms may be used, a current of ${10}^{\ensuremath{-}17}$ ampere may be detected when a galvanometer having a sensitivity of ${10}^{\ensuremath{-}10}$ ampere per millimeter is used in the plate circuit. Under this condition the sensitivity is 250,000 millimeters per volt.