That's what I read about replacing the stock with Siemens CCa & E88CC, which raises the sound to the next level.
I am still not ready for that for obvious reasons, but somewhere in the future, I will.
Even with stock tubes, the sound is fantastic!
I bought it for the use of CRBN, but if I had bought it before other tube amplifiers, there is a chance it would have been my only tube amplifier.
Enjoy!
Cheers!
P.S. I am not keen on opening threads. But if you are, you could start a thread. I will gladly participate and follow.