I have a 400+ and never need to turn the master up all that much.. great amp. You could try a THD "Hot Plate" but they're made for amps that only have a few 6L6s in them. You could also trade your 400+ for a 400 (has 6 tubes instead of 12), a d-180. or a buster.
Try asking mesa these questions (and when they answer, please try to let us know too
)
1. Will a THD Hot Plate (or any other attenuator) work with the Bass 400+ amp? Can two attenuators be used with two cabinets?
2. Can the 400+ safely run with less than the 12 tubes? If so, which tubes? How many?
3. Can the 400+ be easily modded to have a switchable mode to run in Class A mode? (the amp might be about 50 watts instead of 500)
4. Can the 400+ operate without a speaker load (volume turned down and dummy cab hooked up) and use a mesa 2:50 as a power amp?
best of luck!
If you want to play around with a different brand, try a 1970s Ampeg V2 (its only 2 power tubes) they're usually pretty cheap ($150-300)
Ampeg also made a V4 (4 7027 power tubes) in the 70s and more recently the V4BH (90s/00s) with 4 6L6s in the power section.
