Two things for the OP. 1. Play the amp as it is until the tubes give out 2. when the tubes give out, get the amp serviced by a tech who actually knows how to correctly bias an amp and get a good set of quality brand tubes. Forget all the hype and BS, stick to svetlana, JJ or EHX for your 12's and for the power amp you want a properly matched set - and fwiw, I have seen TAD "matched" sets be nowhere near the goalposts, so I would stay away from them and literally stick to EHX gold pin 12's or svetlana / JJ's and for the power tubes, EHX or groovetubes. Quality on all of them are generally good, and you want to buy from a reputable agent or get your tech to supply and fit. in the meantime, play it as it is and stop worryong about how it might sound, when you aren't even familiar with this particular amps nuances. The valves that are in there might be the best ones that you ever had. but you won't know that unless you play the amp as is and get used to it.