On my Wien Bridge oscillator, a dual 365pF variable capacitor (from an old AM radio) tunes the frequency, and resistors are switched to change the range. The two sections in the dual variable capacitor match extremely well (much better than a stereo pot) and even have trimmer capacitors for exact matching and frequency calibration.
I think the switched resistors are 40M each for the 10Hz to 100Hz range. I selected matched 20M resistors from many of them.
It has a FET-input opamp so 40M isn't loaded down.