I'd never had any experience with this model, but a buddy gave me his because it didn't work. It's a '73, bone stock. I rebuilt the power section (filter caps were shot to hell), reworked the power connections (no more ground switch, rerouted the power leads so they don't go right through the power tube wiring), new power cord, clipped the snubber caps on the power tubes, got the bias where it needs to be (factory bias was way cold), increased the grid stoppers and screen grid resistors on the power tubes, removed the negative feedback loop, and that's about it, pretty much basic stuff. Checked the signal path resistors and coupling caps, but they seem fine; I don't think this thing's been played much. wow, this thing sounds good! I love the bass channel with the deep switch on, it's huge, fantastic dynamics, breaks up real nice too. Haven't checked power output yet, but it's painfully loud. Thinking about leaving the bass channel alone and doing the Rock/Jazz switch thing on the other channel, make it a little more versatile. Overall, it's been a really pleasant surprise.