A light bulb has negative resistance, and it is relatively linear. The more current you put through it the higher its resistance.
In the Wien Bridge oscillator, if the signal increases the resistance increases, and drops the gain of the circuit, lowering the signal. It is a form of AGC loop. The light bulb does not even have to glow, or be near its rated voltage for the effect to manifest.
The down side is if the frequency of the oscillator gets too low, where the filament begins to warm and cool with the waveform, severe distortion sets in. Otherwise a very pure sine wave is the result, as the filament achieves an RMS temperature.
You could use simple diodes to get much the same effect, or just set the gain of the circuit without an AGC, though it not nearly as good. Just adjust the sine wave with an Oscope.
In the Wien Bridge oscillator, if the signal increases the resistance increases, and drops the gain of the circuit, lowering the signal. It is a form of AGC loop. The light bulb does not even have to glow, or be near its rated voltage for the effect to manifest.
The down side is if the frequency of the oscillator gets too low, where the filament begins to warm and cool with the waveform, severe distortion sets in. Otherwise a very pure sine wave is the result, as the filament achieves an RMS temperature.
You could use simple diodes to get much the same effect, or just set the gain of the circuit without an AGC, though it not nearly as good. Just adjust the sine wave with an Oscope.