Give Brent Jesse a call 847 496 4546, he's the best "font of information" on NOS tubes. I will also add that in my preferred tubes are usually medical/broadcast/military......not always, but usually. The fact that those types of tubes are supposed to last longer does not hurt
Do military/industrial tubes sound better than regular ones ?
Or they are usually just more rugged and longer lasting? I am particularly interested in 12AX7 and 12AU7 RCA blackplates from early and late 50s.
They are often double the price, but that would not be my main concern in this case because even regular ones should last for a very long time.
In other words, I would like to have best sounding RCA blackplates in my VAC Avatar SE, and longer lasting would be a bonus.