The HP 200A 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 An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillators convert direct current (DC) from a power supply to an alternating curre ...

used for testing sound equipment. It used the

Wien bridge oscillator A Wien bridge oscillator is a type of electronic oscillator that generates sine waves. It can generate a large range of frequencies. The oscillator is based on a bridge circuit originally developed by Max Wien in 1891 for the measurement of imp ...

circuit, that had been the subject of

Bill Hewlett William Redington Hewlett ( ; May 20, 1913 – January 12, 2001) was an American engineer and the co-founder, with David Packard, of the Hewlett-Packard Company (HP). Early life and education Hewlett was born in Ann Arbor, Michigan, where his ...

's Masters thesis. It was also the first such commercial oscillator to use a simple

light bulb An electric light, lamp, or light bulb is an electrical component that produces light. It is the most common form of artificial lighting. Lamps usually have a base made of ceramic, metal, glass, or plastic, which secures the lamp in the so ...

as the temperature-dependent resistor in its feedback network. The light bulb was an inexpensive and effective

automatic gain control Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the inpu ...

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 Larned can refer to: * Charles Larned (died 1834), lawyer, military officer, and politician * Josephus Nelson Larned (1836-1913), American journalist, educator, librarian, historian * Larned B. Asprey * Scott Larned (1969–2005), keyboardist * ...

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. Walt Disney bought eight of them for use in the production of '' Fantasia''. The circuit diagram is shown in Hewlett's 1939 patent.

Development

Through the 1940s and into the 1950s, the subsequent versions of the 200A covered different and wider frequency ranges. The latest version was the 200CD; it covered from the subaudio 5 Hz to the low end (Long Wave) of the AM radio band at 600 kilohertz. The 200CD became a ubiquitous audio generator in engineering laboratories worldwide from the 1950s to the 1990s.

References

External links

HP200A manual (1951) at HP archive
Hewlett-Packard products Electronic oscillators Products introduced in 1939 {{electronics-stub