Hum isn't an issue on this amp...I'm overly anal about my amps; and dig into them constantly. This thing is dead quiet, I spent A LOT of time balancing the 12ax7, and biasing the 6v6 to get it how I like it.
However, it's just missing that extra bit you get out of a P/P amp. Power/volume of the Champ is just fine. If I mess with it more I may change out a few coupling caps to a higher value, but that's about it.
BTW I have a 20-20-40 filter cap set-up on it.