Fender Bassman T100?

Where the volume knob is at physically compared to another amp doesn’t mean much.

 

It's 100 watts into any impedance that the amp supports. Number of cabinets does not matter, and it doesn't behave like a solid state amp, where lowering impedance increases power.

And like @inthevelvet said, knob position isn't a universal indicator ... Many amps reach max volume with knobs at noon to 3:00, while some are calibrated to use the whole range.

But there's another thing about this amp: there's a quarter power setting, which removes some of the tubes from the circuit and drops output to 25 watts. Check to make sure that's not engaged. I don't recall where that setting is, but I'm sure the owners manual is online somewhere.

Edit to add: I'm assuming it's this amp, the 100T ... if not, the quarter power thing night not be accurate
https://www.musiciansfriend.com/amplifiers-effects/fender-bassman-pro-100t-100w-tube-bass-amp-head

 

You're welcome, and good luck. And I'm kinda jealous ... I like the 100T a lot, though I've only played it in stores, and I've always been curious about the Earth tube amps. You've got some cool tubey goodness going on!