Vacuum Tube Characteristics in the Positive Grid Region by an Oscillographic Method

A method of determining "complete" plate and grid characteristics of vacuum tubes in the positive grid region by means of oscillographic recording has been developed. A condenser of high capacity furnishes a single pulse of grid excita tion which can be made to cover the entire region from any desired positive grid voltage to zero. Due to the rapidity of this excitation instantaneous power input to the tube of twenty to thirty times nominal rating has been recorded without danger to the tubes. Several typical complete charts of plate and grid characteristics obtained by this method for an experimental tube of the so-called "50-watt" type are given. The experimental procedure in obtaining these characteristics is discussed in detail. Also the circuit for obtaining oscillographically the highly important "composite diode line," with Ep= Eg, is described. The inadequacy of the usual logarithmic extrapolation of zero-grid characteristics into the positive grid region is discussed. The complete plate and grid current charts, which can be obtained accurately only by an oscillographic method, are practically indispensable in precalculation of class B and class C performance. The method has been successfully used in studying the characteristics of the smallest and the largest existing tubes in this country.