In my textbook, the Wien-Bridge oscillator and the Twin-T oscillator needs a tungsten lamp as the self-adjusting resistance:
The lead-lag circuit connected to noninverting input has a gain of 1/3 on its center frequency. Since the lamp started with low heat (less resistance,) the starting close loop gain is big. As the output oscillation builds-up, the lamp heats up and thus close loop gain decreases until it reaches the point where gain is 3 so that \$A_{V(CL)}*\frac{1}{3}=1\$. This ensures stable oscillation. (Well, that's how I understood it.)
How can I make sure that the tungsten lamp resistance will remain constant?
Won't the oscillation decay immediately if the resistance of the lamp increases even just a little bit since \$A_{V(CL)}*\frac{1}{3}\$ will now be less than one?