I’ve rolled a pair of NOS and I didnt noticed a break-in so far on either set. However on some new modern tubes I’ve definitely noticed a break-in. So I guess it’s not placebo for me or else all my tubes would have broke in. I think it’s important to not tell other what they hear or don’t hear as it only leads me to believe nah sayers are using a lesser system perhaps flawed with bad synergy. As I know mine has great synergy and is resolving and I hear every change from speaker positioning to interconnects to different styluses with the only exception being that of the NOS tubes as previously stated. And even then I wasn’t the original owner and have no proof they weren’t partially used since 1942 and have already been broken in so who really knows. What I do know is what I hear and I’m not interested in convincing myself something sounds good ad I have pulled the plug on many systems as good as they were bcs they just couldn’t climb that last 5%. For the changes I heard after break in it was not subtle, rather significant. So sorry if your not hearing your gear break in then i truly believe likely your rig is masking sound. Fix it or move on from it, you shouldn’t live with something that’s not reaching its full potential. Best of luck.
Vacuum Tube Break-in
Is there such a thing as tube break-in? I been laying with many tubes in about 20 tube amps for 40 years and never heard a difference in a new tube vs same tube with 50 hours use. I always bought and used NOS tubes, not used. I believe if a difference is heard with break-in, it is the placebo effect.