EvLoutonian said:and does it matter if the second mic only sees 102v instead of 105v?
I would not worry about 3v difference. Each tube draws different amount of current, so that's probably where the 3v come from. That's also why you should keep power supplies with there respective microphones. So you set up the correct voltage for that particular tube/mic once and leave it (except for checking it every few months) until you change the tube again.
Concerning the gain difference; that could also be the tube. Maybe swap the tubes and see if the gain changes with it.