Some Aspects of Cathode-Follower Design at Radio Frequencies

Pertinent high-frequency design data including the circuit gain, the gain phase angle, the input impedance in resistive and reactive components, and the maximum allowable input signal voltage may be determined quickly from simple design charts derived by approximations which are applicable over a wide range of frequency and circuit parameters. The only circuit quantities required for use of the charts are the magnitude and phase angle of the cathode load impedance, the internal tube capacitances, and the grid-to-plate transconductance of the tube at the operating point. A discussion of the effects of the grid-to-cathode capacitance on circuit operation at high frequencies is presented, including a critical analysis of the source impedance. It is shown that the source impedance may be greatly affected by the impedance of the grid driving source unless remedial measures are taken. Various circuit changes which reduce or eliminate the undesirable effects of the grid-to-cathode capacitance are offered with discussion and analyses.