Harmonic generation by grid circuit distortion

THE USUAL vacuum tube harmonic generators are fundamentally high distortion amplifiers operated under conditions of grid bias and plate voltage which, to distort the input voltage wave, utilize the non-linear relation between plate voltage and plate current. A paper published in the June 1931 issue of the A.I.E.E. Transactions (see footnote) gives the result of an investigation into the possibilities of using the non-linear grid voltage-current characteristic to produce harmonics. Grid distortion can be utilized by operating the tube so that the grid goes positive for a part of each fundamental frequency cycle and then inserting in series with the grid lead an impedance across which the grid current impulses produce a voltage drop rich in harmonics, which then is amplified in the plate circuit.