6N2P
The 6N2P, (Russian: 6Н2П) also sometimes spelled in English "6H2Pi" is a miniature 9-pin dual triode vacuum tube manufactured in USSR, Russia and China with characteristics similar to the RCA 12AX7. The most significant difference between the two is that 6N2P has its two filament elements connected in parallel, unlike the series filament connection of the 12AX7, and it is thus only possible to operate it from a 6.3 volt, 340 mA filament supply (whereas a 12AX7 may be operated from either 6.3 or 12.6 volts, at 300 mA or 150 mA, respectively.) The 6N2P also has slightly lower gain than a 12AX7. The 6N2Pslightly lower-gain and higher filament draw is similar to the 5751 tube (introduced in the mid '50s)and sold in quantity to the US military. The 5751 tube may be operated from 6.3 volts at 350 mA (the higher current draw is for increased reliability) for use in avionics.
In the 1970s an improved and more rugged version of the 6N2P was introduced, designated 6N2P-EV (Russian: 6Н2П-ЕВ) The 5751WA tube is a ruggedized military version of the 5751, and is the closest equivalent to the 6N2P-EV. Currently, a 12AX7 variant derived from the 6N2P-EV is being produced by Sovtek, under the designation 12AX7WA.
A Chinese version of 6N2P exists, labeled in Latin lettering (instead of Cyrillic) 6N2.
In the 1990s a (now extinct) line of "Red Bear" guitar amplifiers was being produced in Russia by Novik Ltd. and distributed in the United States by Gibson Guitar Corporation. These amplifiers used 6N2P tubes instead of the much more common 12AX7, prompting user modifications of the amplifier to 12AX7, because the original Russian 6N2P was scarcely available outside of Russia.
On the photo, from left to right - 6N2P produced in USSR in 1967, 1974, 6N2 produced in China and Soviet 6N2P-EV (left), produced in 1980.
References
(6n2p-ev Rugged version of 6n2p Data sheet)