Adjusting the PI 10K pot?

[Mark]

So far I have adjusted the amp till it clipped and then I adjusted the pot to try and get the amp to clip evenly.

The tubes I'm currently using are an old set of Winged C 6L6's. They were once matched, but now are 10mA's apart.

As you'd imagine I ran out of travel on the pot.

I dare say the -C- will have to go, is there a better way to adjust this pot without using exotic test equipment?