The HP 200 Series, R-C Oscillators
The HP 200C quoted by Bob DeVries, was an evolution of the basic HP 200A/B Audio Oscillator which was itself the first measuring instrument manufactured by Hewlett Packard in 1939.
At the origin, this very first audio oscillator prototype was built by Bill Hewlett for his Stanford University thesis project in 1938. It was a resistance tuned oscillator covering from 35 cps (frequency unit was the cycle at this time) to 35,000 cps in 3 ranges. The major problem with such a resistor / capacitor tuned Bridge was to obtain a constant level output over a full decade frequency range. Bill Hewlett solved the problem by inserting a non-linear element (a simple 3 Watts light bulb) in the feedback loop of the oscillator.
The HP 200C, shown below, was one of the very early evolution in the Model 200 Series.
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