Power Amplifier Design Fundamentals: More Notes from the Pages of History

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  • Author: Andrei Grebennikov
In early radio-frequency vacuum-tube transmitters, it was observed that the tubes and associated circuits may have damped or undamped oscillations depending upon the circuit losses, the feedback coupling, the grid and anode potentials, and the reactance or tuning of the parasitic circuits [28]. Various parasitic oscillator circuits such as the tuned-grid-tunedanode circuit with capacitive feedback, Hartley, Colpitts, or Meissner oscillators can be realized at high frequencies which potentially can be eliminated by adding a small resistor close to the grid or anode connections of the tubes for damping the circuits. Inductively coupled rather than capacitively coupled input and output circuits should be used wherever possible.