Russia also has their military grade tubes. The Russian Rockets Reflektor 6N23P are a popular tube still used by many especially in heaphone amps. These tubes were used by the Russian Space program back in the 70's. I still have a set in an old tube amp. I'm sure there are many others.
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.