Switch out pots? - Advice needed

If the guitar is equipped with humbuckers, it likely has 500K pots for the volume control. If left in with P-90s, it will likely be bright. Once you disconnect the humbuckers from the guitar (and any other leads on those pots) put a meter on the original pots and measure to be certain of their values. But I'd bet you'll read 500K +/-.

300K linear taper is a common value for P-90's. I like audio taper 300K for P-90s. To each their own.

 

Try the P-90s with the 500ks, they usually sound good that way. If you want to mellow it out a little, that's what the tone knob is for.

 

Ditto. It's harder to get signal than it is to attenuate some of it...I avoid setups that permanently throw signal away. If the tone knob as-is doesn't float your boat, try some different caps to see if you get closer to what you want. BTW, I have GFS Dream 90's in an Epi LP with 500K pots. Just too pretty set of pups to go back to the 300Ks that were in it. Spent a little time swapping caps on the tone pots till I got it right, total joy to play now. Would love to give the Mean's a whirl sometime.

--Ray