Double triodes 6N1P-EV OS (6H1П-EB OC) are 6N1P tube modifications with extended lifetime (not less than 5000 hours) and improved reliability. Tubes with suffix or stamp OS (OC) are specially selected based on parameters to meet very strict requirements for the aerospace industry and space research. So these are elite pieces of the highest quality, which was ultimately confirmed during the testing itself (only one system (triode) out of 38 tests in total had plate current of 7 mA, what is around 93% of nominal, the other triodes had all higher plate current results , the tubes were also very nicely balanced). 6N1P-EV OS tubes are direct replacement for the chinese 6N1 and they definitely offer better performance. It may be also used as a replacement for ECC88/6DJ8/6922 tubes. But you have to be careful, because there are some important differences. The 6N1P-EV OS's are drawing considerably more heater current: about 600 mA, comparing to the ECC88/6922/6DJ8 tubes, where it is about 365 mA. in some cases, direct replacement without any discussion with the manufacturer, may end up with damaging of your equipment. Please discuss this with the manufacturer of the equipment. Measured on a precise Russian tube tester L3-3 in real connection (full power), so some white stamps caught a yellow-brown tinge, what is understandable in case of longer testing (each triode at least 5 minutes at full power). Pairs were selected from a larger number of tested pieces. Manufacturer: Voskhod. Years of production: 1982 and 1983.
