Does a tube need the break-in hours?

12AT7 tubes can be called different things, but I am not aware of any substitutes.  For example, 6201 is US mil-spec AT and ECC81 is euro designation.  .

I have a bunch of US ATs and a fair number of Amperex/Philips/Valvo.

You might want to post a wanted ad with the specifics of what you are looking for.  The admins don't want us dealing direct.  I would be happy to post a listing if you let me know what you want.

For any Amperex/Philips/Valvo tubes, the late 50's to mid 60's production are the very best.

I have hundreds of tubes from the 50's and 60's.  No problems.  Much better than most current production.