In 2012 I decided I needed a simple, fixed audio oscillator. I had some parts in my junk box and quickly put it together. I wanted a simple, bulb stabilized Wien oscillator because of its low distortion and simple construction. The schematic (nicked from stackexchange) is very simple:
R1=R2=3.9k, C1=C2=0.1uF and Rf is 150R. The bulb is a miniature leaded device of 6 V/50 mA (estimate). A transformer, bridge and two electrolytics completed the setup. As the low noise opamp I used, LM833, has two opamps I used the second as a buffer. Output resistor of 100R and it is pretty much fool proof. No voltage stabilization is used, the LM833 had a SVRR (Supply Voltage Rejection Ratio) of more than 100 dB and I think that's quite enough.
Construction was also simple:
The operation is as expected. At switch on the circuit has to stabilize itself and gyrates wildly. Eventually things settle down because the thermal inertia of the bulb is much slower than the oscillating frequency (about 400 Hz):
First 0.2 s
I used it off and on for years but the open transformer connections and power socket made me a bit nervous. I found a suitable boxie and put it in it:
The funny thing now is that the bulb doesn't seem to be glowing. I had to use a very long exposure (minutes) and high ISO (12800) to see it: