This amp put the "harsh" in Harshall. Its bright and brassy unless you put something to "brown" it down. I have some Mullard fx2 EL34 biased in mine and run Mullard 12AX7 in V3 and V2. V1 is home of the gain in this amp and depending on my luck in Ebay, I run a NOS Telefunken, or Mullard. Sometimes I hit it right and grab an RCA blackplate NOS or used and its heaven after the amps been on and played 45 minutes and everything is up to temp. It's like sonic butter!!
All amps have thier own character and you may find other tubes better in yours. My son's JMP sounded aweful with Mullards and we switched back to the Chinese tubes. However in the V1 position we took out the Sovtek and dropped in a NOS telefunken 12AX7 and the amp came alive!!
In an amp with less tubes, the quality and type make a bigger difference. Have fun with your new amp!!!