IMO the reverb shouldn't hum when you turn it up. That needs to be repaired, or replaced if there's still time to do that. There's new-owner chatter on other forums, mostly centered around idle hum noticed by folks who have never had a single-ended amp, before. They aren't dead quiet at idle. The only gut shot I've seen showed heater wires that weren't twisted together and weren't long enough to disconnect, twist, and reconnect. So far, no one with an opinion has wanted to void the warranty by rewiring.