Bill Hewlett's Prototype Resistance-Capacity Oscillator, 1938
An audio oscillator is an instrument that generates one pure tone or frequency at a time. Through the years, HP oscillators were used to design, produce and maintain telephones, stereos, radios and other audio equipment.
Bill Hewlett designed the prototype for what eventually would be called the Model 200A audio oscillator as a thesis subject while working toward his electrical engineering degree at Stanford University in 1938. The Model 200A would become HP's first product.
Bill felt there was a real need for a new type of oscillator that would combine the stability of the coil-condenser type and the flexibility of operation of the beat-frequency type, and still be light and portable as well as simple in construction and adjustment. His was a new type of oscillator in which the frequency-determining element is a resistance-capacity network.
What made Bill’s oscillator design unique?
In simple terms, Bill's unique contribution to the oscillator design was to achieve excellent performance at a low cost by adding a small light bulb to act as a "negative feedback" element in the oscillator circuit.
The small light bulb is set to be partially on. If the oscillator's signal strength becomes stronger or weaker, the light bulb turns on more or less to cancel the unwanted variations. This allows the oscillator to maintain a nearly constant output over its designed operating range.
This is the original prototype resistance-capacity oscillator built by Bill Hewlett while he was a graduate engineering student at Stanford.