Simply replacing 12AU7s by 6SN7s would double the filament current drawn (3.6 amps vs 1.8 amps for 6 tubes). That could easily burn out the power transformer if its rating is marginal.
The above statement is correct. Unless you can measure this yourself, and are capable of modifying your amp yourself, then don't try to swap out the tubes. Overall the amp would operate but you don't know how the current will effect the other parts in the amp. Most tubes will operate in a range and obviously if it all matches, the better the unit should sound. Therefore, the manufacturer should know what is best for their design.
Happy Listening.
The above statement is correct. Unless you can measure this yourself, and are capable of modifying your amp yourself, then don't try to swap out the tubes. Overall the amp would operate but you don't know how the current will effect the other parts in the amp. Most tubes will operate in a range and obviously if it all matches, the better the unit should sound. Therefore, the manufacturer should know what is best for their design.
Happy Listening.