I will run things in with FM in the background. I believe speakers have break in , but it's short. Electronics, I'm not so sure. I think it's a mix of maybe a slight change and you as a listener acclimating to the new "sound" .
I know this about tubes, you can take a bunch of like ones and they all test different. New, NOS , doesn't matter. Some are simply better than others.
I have some new tubes that sound fantastic and I found some to be weak or triodes don't match.
I have some NOS that were from a large hoard. All from 1956. Some are great , some are ok , and two had shorts. Thankfully I rooted those out before damaging my amp
The problem with tubes is that the "tone" is so subjective. I happen to like JJ 6l6gc, they could sound horrible in your amp.
I paid a little extra the last time I bought 12ax7 and au7 to have them matched and to be screen for noise. That's what I would recommend, the remainder of the tubes that don't pass end up at Guitar Center and mom and pop music shops
Trust me on that one. I had purchased a few tubes in a pinch at a mom and pop , yes they worked but they were not strong, matched emmisions
Buy from Brent Jessee or someone with real knowledge of tubes
