Wien-Bridge Oscillator Using Incandescent lamp Stabilizer

Incandescent lamp has been used to reduce harmonic distortion in sine oscillator circuit. The nonlinear resistance characteristic of the lamp filament help the circuit to shape the signal to approximate the ideal sine wave. Here is the classic Wien-bridge oscillator circuit using the incandescent lamp:

You can change the frequency of the oscillator by modifying the R1 (and R2), or C1 (and C2).  [Source: National Semiconductor Application Note]