The California Instruments 800T Series of Variable Frequency Oscillator provide a pure sine wave output for driving the California Instruments Solid State Invertrons, These oscillators incorporate a unique amplitude regulator circuit which prevents amplitude overshoot as the frequency of the oscillator is varied or as the decade range of the oscillator is changed This prevents possible damage to a sensitive load connected to the output of the Invertron as a result of excessive output voltage amplitude. The multi-phase versions of the 800T Series Oscillators are used to drive two or more Solid State Invertrons connected so as to provide either two phase or three phase power.