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Bill Hewlett's prototype resistance-capacity oscillator, 1938


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Click to go to larger photo of Bill Hewlett's Prototype Resistance-Capacity Oscillator.
This is the original prototype resistance-capacity oscillator built by Bill Hewlett while he was a graduate engineering student at Stanford.

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.

How did Bill's prototype end up in the HP Archives?
The prototype was discovered in 1985 by a Stanford student who was working part-time at HP. His Stanford dormitory had an archives room in the basement. While cleaning out the basement room, someone discovered original electronic equipment from the 1930s and 40s, including Bill's resistance-capacity oscillator. The student decided the oscillator belonged at HP and wrote a letter to Bill asking how he could donate it. Eventually the oscillator made its way to the HP Archives. Bill wrote a letter to the student, saying:

I would like to say "thank you" for your thoughtfulness in bringing this to my attention, and I am glad that you have joined HP as a manufacturing engineer.

How do we know this is Bill's prototype?
An article in the September 1955 Watt's Current (the original HP company magazine) describes how Cy Elwell, an early HP employee, located and borrowed what is identified as Bill's prototype from Oscar Villard, Jr., professor of Electrical Engineering at Stanford University. At the time it was used in a historical exhibit at the WESCON show. A photo of the oscillator made it possible for HP's archivist to identify the oscillator currently residing in the HP Archives as Bill's prototype. After borrowing the machine, HP had returned it to Stanford, where it was found years later in the dormitory basement.

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