The Wien-bridge oscillator is reborn

Posted on Jul 25, 2012

To keep the gain constant, the circuit used an incandescent pilot light to provide AGC (automatic gain control). As is true for all incandescent bulbs, the pilot light has nonlinear resistance. When you turn on the circuit, the cold lamp`s resistance is low, resulting in high gain. As the gain increases, the resistance of the warming lamp increases. Thus, the lamp provides an AGC function.

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