I love the 386 power amp chip. It is incredibly versatile. As the engine behind the Ruby, Little Smokey, and Noisy Cricket amps, it is the best bang for the buck single-chip amplifier.
But it is more than that: it is also used widely in distortion effects.
Basically, the Tufnel is two cascaded JRC386 gain stages with individual gain controls, a tone control, and a volume control.