You will have to evaluate each of the many components of the system in order to figure this one out, but the one thing that could affect all is your AC supply. Is your line voltage constant? Otherwise, this is a DIY question. Got a meter? Check AC voltage out of that step down transformer as it heats up.
Tube stereo sounds -smaller- after being on
Ok here is a weird one. I’ve been into tube audio for the last 20 years or so and I have one system I leave as is and one system I mess around with and change things out. For the most part, these days, I’m happy with both. Except I’ve been noticing something I thought I was imagining. Which is my experimental system starts out sounding great and after being on for a couple of hours sounds worse. Small soundstage, compressed highs and lows. Just over all enh. I have two turntables -
Gates and an EMT 930. The mixer is a great sounding one hand built in Austrailia called a Condesa Lucia. The amp is a Line Magnetics 2a3 amp LM 217. The cartridges are an EMT and a Denon 102. The tt preamps are by sun valley and auditorium 23. The one thing I can think of is the amp is a 220 version and goes through a power converter. Perhaps this is a sonic wrecker when it gets hot. Any other ideas? Thank you.