The only answer I can think of off hand is to thoroughly explore current production tubes before you venture off into NOS. You might be surprised that in many instances the differences are not that great and perhaps not worth the extra money. I've found that I'm able to use mostly current production stuff, except for a couple of critical places.
Vintage tubes skyrocketing in price
Anyone else think that the skyrocketing prices of NOS tubes is unreasonable? They seem to be continually increasing in price weekly. It makes tube rolling exclusive to the wealthy. I am not happy. Comments?