After 1700 fine hours with a pair of Baldwin 12AU7 (probably made by Sylvania USA), I’ve rolled to a newly manufactured pair of Slovak Republic JJ 12AU7. I’ve got an estimated 5000 hours in 2 years on the preamp.
I enjoy the heck out of a new pair of tubes. I enjoy the process of learning how they change the sound. They all sound pretty darn good, just a little different.
These are starting out a bit fuller in the bottom end but I suspect they will tighten up with a bit more time. The Baldwins with 1700 hours were getting just a touch soft on top, very pleasing, but a bit down on energy in the region. JJ has picked it back up and appears to be headed to a solid performer. Not bad for $20/pair shipped.