HP 200A

The HP 200A Audio Oscillator, first built in 1938, was the first product made by Hewlett-Packard and was manufactured in David Packard's garage in Palo Alto, California.

It was a low-distortion audio oscillator used for testing sound equipment. It used the Wien bridge oscillator circuit, that had been the subject of Bill Hewlett's masters thesis. It was also the first such commercial oscillator to use a simple light bulb as the temperature-dependent resistor in its feedback network. The light bulb was an inexpensive and effective automatic gain control that not only kept the oscillator output amplitude constant, but it also kept the oscillator's loop gain near unity. The latter is a key technique for achieving a low distortion oscillator. Earlier, Larned Meacham had used light bulbs in bridge circuits to stabilize and linearize oscillators in 1938.

The product code was chosen to give the impression that HP was an established company. A variation, the HP 200B, was customized for Walt Disney, which bought eight units for use in the production of Fantasia.

The circuit diagram is shown in Hewlett's 1939 patent.