I know that there is some break-in audio, because I have built different amp kits and rebuilt vintage tube amps,I thought I did something wrong when listening for the first few hours, I been it sounded like crap, then between 10 and 20 hours everthing starts to fall in place and sound great. Also if you use Auricaps in your amp you better wait 50 hours for the thing to sound good. I know this is true because I can hear it, and other people hear the same thing. I know there are people out there that don't hear the same things because about three years ago I ran into a old TV and Radio repair man, and he was the only man in East Texas that still repaired old tube stuff still around and he worked in the bussiness since the second world war and he really beleived that all 12ax7's sounded the same, no matter if it was telefunken, RCA, or Mullard they all sounded the same, and that went for any type of tubes and caps too. The only thing I could figure was he didn't listen to any Hi-end audio in his life time or he didn't have good hearing, maybe all he heard in tube audio were the old five tube AM table Radios.