Some Simple Oscillators
Author: J.B. Hoag
A three-electrode vacuum tube may be used to produce electrical oscillations of frequency from a fraction of a cycle each second to many million. The ability to generate oscillations resides in the amplifying property of these tubes, i.e., the energy developed in the plate circuit is greater than that applied to the grid circuit. The additional energy comes from the plate power supply. If part of the amplified energy is "fed back" from the plate to the grid by resistive, magnetic, capacitive or electron coupling devices, and has the proper phase or polarity with respect to that of the grid, there will be continued amplification sufficient to overcome the losses in the circuits and produce sustained oscillations.