This has a power switch attached to the back, and it turns on/off when you pull out the shaft or push it in. The power switch is rated for 3A 125V, so it should be fine for most tube amps. This is guaranteed to work great for you, though it may need some Deoxit. This is a pretty rare potentiometer and would be great on your guitar amp. Please see my pictures for details and measurements.
US shipping and handling is $7, and international is $21, no matter what quantity you buy. 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 many more vintage pots and other vintage electronics listed--feel free to take a look!