Up for sale here is this used vintage Allen-Bradley #202105 1 meg ohm linear taper potentiometer, from the 1950s or 1960s and Made in USA. It tests around 1.316 meg ohms on my multimeter.

This has a very short 1/4" shaft that adjusts with a flathead screwdriver (not included).  This is guaranteed to work great for you. This is a pretty rare potentiometer and would be great on your amp. Please see my pictures for details.

All my small parts are set up for combined shipping, so just use the "add to cart" feature and then check out all at once, and it will combine shipping. If you have any questions, please ask.

I have more pots and other vintage electronics listed--feel free to take a look!