Many thanks to SWLing Post contributor, James Patterson, who writes:

Has anyone ever thought of changing the Tuning knob on the PL-660?

Putting a larger knob on it makes for much easier turning instead of the very small fiddly knob Tecsun supply.

Finding the right plastic knob maybe a problem, needing to insert it over the tuner cam. But modifying another knob off something else is what I did.

Tricks of the trade!!

That looks like a very simple and effective mod, making the 660 more tuner-friendly for you! Thank you for sharing, James!