Platinum Grade 6N3P-E (cyrillic 6Н3П-Е) vacuum tubes tested and macthed by Riverstone Audio. You will not find a more rigorously tested pair of vacuum tubes anywhere. To determine stability, tubes are subjected to multiple test cycles and are matched within 5% for both mutual conductance (Gm) and tube gain (µ). FEWER THAN 40% of the 6N3P-E tubes we test meet our high standards for audio use and are chosen for our Platinum Grade pairs. The tubes you receive will exhibit low noise and excellent audio sound quality. 6N3P-E tube is the high reliability version ("E" suffix in the tube code) of this tube and is a great upgrade for Chinese 6N3 tubes. ***Please Note: We carefully inspect all tubes we use and to the best of our knowledge the 6N3P-E tubes we use in our Platinum Grade sets are NOS tubes. We also guarantee that the tubes will test at NOS levels when received.*** To protect the tubes during shipping and storage, the tubes are supplied in Riverstone Audio's own custom-designed "tube cradle" boxes. As a US seller we have confidence in the quality of what we sell. We back all vintage vacuum tubes we sell with our no-nonsense TWO-YEAR money-back warranty - the best warranty in the audio tube business. 6N3P-E (6Н3П-Е) tubes should only be used as a direct replacement for Chinese 6N3 and Russian 6N3P (6Н3П) tubes, but are generally suitable as a substitute for US/European 5670 / 5670W / 396A / 2C51 tubes. PLEASE NOTE: AMPLIFIER DAMAGE CAN OCCUR IF YOU SUBSTITUTE THE WRONG TYPE OF TUBE. Before ordering CAREFULLY determine the type of tube used in your amplifier (this information is typically printed or etched on the tube).