I’ve got a few RCA 12AU7 variants including a clear top, a grey plate, and a black plate 5963. They all sound great with my TS/Chatham 2399. The clear top is a little bright with my GE 6080, but good with the 2399 and 6AS7G. I think what I’m looking for changes from time to time. Sometimes a dark recording needs that little top end boost. The other day I plugged my Sennheiser HD600 directly into my NAD C740, which I can’t remember doing since building the Crack almost ten years ago because why would I, and was pleasantly surprised.