An oscillator of extremely high inherent frequency stability that is used to drive a power amplifier in order to supply a substantial power output to the load. This arrangement is used where substantial output power is required with a high degree of frequency stability, as in the generation of a carrier wave, since the frequency of an oscillator is partially dependent on the load supplied by it. The master oscillator ‘sees’ a constant load from the buffer between it and the multistage power amplifier and hence the frequency stability is maintained.