The finest 6N3P tubes were selected at manufacture for military use, with up to 5000 hours life expectancy and printed with an additional code (Cyrillic 6Н3П-ЕВ). The rest were for domestic use, and with the ability to operate at over 200Mhz, the 6N3P was used in many East European VHF radios, televisions and in several beautiful radiograms in the 1950s and 1960s. The basic, domestic quality thermionic tubes have codes for a projected life span of either 1500 (6Н3П-Е) or only 500 hours (6Н3П). Many were used and then stored for over 50 years, so life expectancy may be questionable, both for the tubes and for me! The Tube Computer integrates 920 thermionic triodes in 460 tubes with 5 Backplane boards into a functional general purpose computer. It is still a work in progress, and it does need a lot of tweeking. But that's half the fun!!