HP 200A

HP 200A front panel
Insides of the Hewlett-Packard HP 200A. The light bulb repurposed as a positive temperature coefficient resistor is to the right of the upper section of the variable capacitor, which is the large structure in the center.

The HP 200A, first built in 1938, was the first product[1] 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.[2] 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.[3]

The product code was chosen to give the impression that HP was an established company.[4] A variation, the HP 200B, was customized for Walt Disney, which bought eight units for use in the production of Fantasia.[5]

The circuit diagram is shown in Hewlett's 1939 patent.[6][7][8]

Specification:[9]
HP 200A HP 200B
Frequency range 35 Hz-35 kHz in 3 range
X1: 35-350 Hz
X10: 350-3500 Hz
X100: 3500- 35 000 Hz		 20 Hz-20 kHz in 3 range
X1: 20-200 Hz
X10: 200-2000 Hz
X100: 2000- 20 000 Hz
Scale of dialer 35-350 20-200
Calibration accuracy less than 2% less than 2%
Output power 1 W 500 Ω load 1 W 500 Ω load
Distortion less than 1% between 35 Hz and 15 kHz less than 1% between 35 Hz and 15 kHz
Output impedance less than 75Ω under 15 kHz less than 75Ω under 15 kHz
Power voltage 115 V 50-60 Hz 60 W 115 V 50-60 Hz 60 W
  1. ^ "Hewlett-Packard's First Product: The 200A - HP History".
  2. ^ Gordon Laing (2004), Digital retro, The Ilex Press Ltd, ISBN 9781904705390
  3. ^ Meacham, L. A. (October 1938), "The Bridge Stabilized Oscillator" (PDF), Bell System Technical Journal, 17 (4): 574–591, doi:10.1002/j.1538-7305.1938.tb00799.x, archived from the original (PDF) on 2014-04-14. Frequency and amplitude stabilization of an oscillator with no tube overloading. Uses tungsten lamp to balance bridge.
  4. ^ Pasiuk, Laurie (2006). Vault guide to the top tech employers. Vault Inc. p. 111. ISBN 978-1-58131-339-0. Retrieved 2010-05-10.
  5. ^ "The 200B Oscillator and Disney Fantasound - HP History".
  6. ^ US 2268872, Hewlett, William R., "Variable Frequency Oscillation Generator", published 11 July 1939, issued 6 January 1942 
  7. ^ "Variable Frequency Oscillation Generator, US patent 2,268,872" (PDF).
  8. ^ "Model 200A audio oscillator, 1939".
  9. ^ "User manual for Model 200A Audio Oscillator, Serial 30223 and Above" (PDF). July 9, 1951.