Some Considerations concerning the Internal Impedance of the Cathode Follower

The behavior of the cathode follower working into a load consisting of R and C in parallel is investigated for step-function and sine-wave input. It is found that the tube is easily cut off for applied voltages which are decreasing functions of time. The conditions for which the tube is conductive for decreasing applied voltages are derived. They are severe for step-function input but not for sinewave input. The influence of tube parameters, supply voltages, applied-voltage wave form and amplitude, and load conditions are analyzed. Design recommendations are suggested which increase the conductive range. It is pointed out that these recommendations are of value even if conditions for conduction during all operating situations cannot be satisfied.