[morzh]

It was my belief that if you drive the output transformer and want to make the tone ctl as the bypass to its primary, you need lower capacitance and lower resistance. In other words, the impedance of the RC should be comparable to the primary's.
I suspect that no matter what cap you use, at the pot set to 10 kiloohms and up to the full scale resistance the effect is small. And when the cap is fully on (pot is shorted) 0.22uF is too much to be in parallel to the primary.

I remember one radio with such tone ctl, I think the pot was wirewound and fairly low in ohms. Maybe 2K or so.