Up for sale here is this vintage 1958 Centralab 250k potentiometer with power snap switch attached.  I am pretty sure this is a linear taper pot.  It is labeled "Centralab USA" on the front and "134844 8G17 250K" on the side.  The "844" means this was made the 44th week of 1958.  I measured this and it tests right around 250k.  The back has a power snap switch attached, so you can wire this as a combination power switch and tone/volume/whatever control.  If you wanted, you could remove the snap switch from the back.  This has a short 1/4 "D" shaft, so any standard "D" knob should fit, or any 1/4" round shaft knob with set screw should fit. This is guaranteed to work great for you, though it may need some Deoxit.  The terminals have a little vintage solder and wire bits on them.  This is a pretty rare potentiometer and would be great on your amp.  Please see my pictures for details.

US shipping and handling is $4, and international is $12.  I accept Paypal.  If you have any questions, please ask.

I have a number of other vintage parts, collectibles, Magic cards, and vintage electronics listed--feel free to take a look!