Scott Tube Amp volume drop

So i've been successfully using my new restored Scott 299A tube amp for about a few weeks (bought on ebay) and when i first got it i wasn't going past vol 2 (live in a fussy apt bldg). Anyway, now i noticed that i need to push it to vol 3-4 to get similar sound and vol. What could this be?
Probably a Input or driver tube 12 AX7 or other small tube.
also work the Tape Mon switch back and forth about 30 times
Best John
Thanks i'll give it a try. What's the best way to see rule out which tube it could be if i don't have spare tubes?