>Radios in the 1930s used an incandescent lamp as a volume expander.

I have also seen them used as a compandor - the particular example I
remember was in a series of articles that Electronics Australia ran many
years ago, where they built an electronic organ. A suitable 6.3V 300mA dial
lamp was used from the speaker output to drive a spring reverberation unit.
As the output volume got greater the lamp glowed brighter, so a lower
proportion of the output signal was fed to the reverb channel.

>HP used incandescent lamps in their first audio generators
>to stabalize the feedback gain. Too high an output level
>(headed towards clipping) would increase the lamp resistance,
>decreasing the oscillator loop gain.

I believe the later glass-vacuum encapsulated thermistors give a faster
response and flatter output level as frequency is changed.

>I've used incandescent lamps as current limiters in an electric
>vehicle battery charger.  A near constant voltage source is
>applied to the battery string through an incandescent lamp.

I currently have an old car battery on float charge like this. Also the
technique was used in power supplies for kids toys, such as model railway
controllers - the lamp doing double duty as an output short circuit
indicator, as well as being the current limiter.

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