Thank you to all for the informative replies--much appreciated.
A quick question related to Amperex Bugle Boys
(And specifically, 5AR4s.) I've seem them listed from different countries--Holland and Great Britain. Is one desirable as compared to the other? Also, a couple of examples of testing that were listed was "94/95" & "97/98." From that, can the remaining lifespan of a tube be estimated? Thanks/Matt