The main problem with your Wein Bridge oscillator is that there is no Automatic Gain Control. Minimum gain required for oscillation is 3.000+Δ. If gain is just slightly more, then the amplitude builds up, and the sine wave becomes a clipped sine...
Drs Hewlett and Packard solved that problem with their entry product, call a HP200 sine wave oscillator in the 1940s. They used the non-linear resistance properties of an incandescent lamp to stabilize the amplitude of their Wein-Bridge Oscillator.
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