sentences:  The purpose of the valve is to act as a switch which will allow energy to pass into the oscillator at the correct time to maintain the oscillations.In order to time the switching, a small amount of energy is fed back to the grid of the triode effectively blocking or firing the device or allow it to conduct at the correct time.This so-called grid bias can be derived, either capacitively, conductively or inductively depending on whether the oscillator is a Colpitts, Hartley oscillator, Armstrong tickler or a Meissner.