Nothing surprises me. I've had new units ship DOA right after my quality inspection. Or go bad once in the consumer's hands. Parts parts parts... 
Edited by Silent One - Today at 9:15 am
Nothing surprises me. I've had new units ship DOA right after my quality inspection. Or go bad once in the consumer's hands. Parts parts parts... 
I have used some nice Tung Sol 12SN7 round plates, RCA 12SN7 gray glass, and Hytron 12SN7.
They all sounded fine.