An Automatic Frequency-Controlled Oscillator and Amplifier for Driving Mechanical Vibrators

Abstract

An oscillator system has been developed for driving mechanical sound generators or other vibrating mechanical systems which require that the vibrating member be driven at its resonant frequency. The oscillator is a vacuum tube type in which an automatic frequency control, similar in principle to that employed in radio receivers, is used to keep the frequency at or very close to the resonant frequency of the vibrator. The change in phase of the vibrator motion relative to the driving force is used to supply a potential proportional to the difference between the driving frequency and the resonant frequency of the vibrating member, and having a polarity dependent on whether the driving frequency is less than or greater than the resonant frequency. This voltage is used to control a reactor tube which in turn controls the frequency of the oscillator circuit. The circuit is very effective, changes in either oscillator or vibrator frequency, or both, of approximately 500 cycles per second in 12 kilocycles, being followed automatically so that the oscillator frequency will not deviate from the resonant frequency of the vibrating member by more than 0.1 cycle per second.