Wien Bridge (HP 200a)

While doing research on the Twin-T oscillator, I came across
this fascinating tidbit. Hewlett-Packard's first product was a
sine-wave audio oscillator (the HP200A) based on William Hewlett's
1939 Stanford University master's degree thesis.

Hewlett's inovation was to use an incadescent bulb as
a variable resistor to stabilize the output level.

ARRL Code Practice Oscillator and Distribution Amplifier
using a Wien Bridge [PDF]

WikiPedia Wien Bridge article
HP Virtual Museum: Model 200A audio oscillator
Art's theremin Page: The Wien Bridge theremin