Tubes for a pre stage... matched NEW or unmatched identical NOS?

12au7’s in usa or european old stock form are plentiful and relatively inexpensive, even for well matched sets 

The problem is what is 'well matched'? At the datasheet params? NONE of my tubes operate anywhere near them.

I've bought plenty of NOS 'matched' 12AU7 & commercial variants. NOT one came close to the claimed Gm when operated at the amplifier parameters. NOR were the Gm matched at datasheet parameters. 

NOS tubes often have significant gas after ½c. on the shelf and need a while for the getter to clear it. Some advocate baking, but others say never. Induction heating may be the answer.

Expect any NOS tube to change significantly over the first number of hours.

Methinks Confirmation Bias accounts for a fair portion of NOS enthusiasm.

$30 new production tubes, or $20 RCA Clear Tops…..no comparison 

Agree with  @vthokie83 RCA Clear Tops are a fantastic tube at an amazing price.  Way better than any new production that I have tried

Just dropped (2) RCA 12au7 "Clear Tops" in my Line Magnetic DAC. Pleasantly surprised - they are terrific so,... I agree with the hype 

I think many of you know that Brent Jessee is one of the most reputable providers of NOS tubes out there. He will have one of the largest selections, and the tubes go through a rigorous testing before being sold.....and he warrants all of his tubes for 30 days, and many for up to 2 years (not sure of the difference)

This link will take you to the best page I have ever seen on 6DJ8/12AU7/6922/7308/ECC88/E88CC/CCA/6N23P(Russian)/etc. He explains the difference in tube suppliers and their country of origin, and what to expect sound wise from each version of the tube, even how to translate date codes to date your tubes. NOTE: He focuses mostly on Euro tubes, with some information on American and Japanese tubes as well. It's a long read, but should definitely be bookmarked and printed out for future reference....especially for tube rollers.

http://www.audiotubes.com/6dj8.htm