Our Platinum Grade 6N6P (cyrillic 6H6П) vacuum tubes are the most thoroughly tested available. To determine stability, each tube is subjected to multiple test cycles. The minimum test duration (not including tube burn-in) is 10 minutes. Tubes are matched within 8% for plate current (ip) and and within 5% for tube gain. Data labels with measured plate current and tube gain are provided for each tube. As a final quality check, all matched tubes are auditioned in an amplifier to determine sound quality. You will not find a more rigorously tested pair of 6N6P vacuum tubes anywhere. We have confidence in the quality of these tubes and back them with a no-nonsense two-year money-back warranty. We offer two versions of the 6N6P tube. The first version, which have the original "CCCP" designation on the tube were for export from the former Soviet Unibion and have a single getter support-post. The second version, which was a mil-spec version of the 6N6P tube, utilizes two getter support-posts have Ni-plated tube pins. Other than the getter support, the structure of the tubes is the same. To-date we have tested over 2500 6N6P tubes and do not find a discernible difference in audio sound quality between the two tube versions. The difference in price we charge for the two versions is based entirely on our initial procurement cost for the tubes. Both the CCCP version and the mil-spec version are equally suitable for high-fidelity audio applications. **Please Note: To the best of our knowledge, the 6N6P tubes we use in our Platinum Grade sets are NOS tubes. We 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 custom "tube cradle" boxes.