@curiousjim
I am using a single 12AU7 in a Hagerman Baritone tube buffer. So far, the new Tung Sol tube is working well for me in this circuit. I've tried:
new Tung-Sol 12AU7W
new Mullard 12AU7 (stock tube)
nos RCA 12AU7 cleartop
nos RCA 5814a black plate tri mica
nos GE 5814a grey plate