The 6SN7GTB are guaranteed NOS and as such will test with a tester reading plus or minus 5%, 3000 to 3300 micromhos. The 12AX7 tubes will be in the range of 1400 to 1600 micromhos. The exact tester readings will be supplied on special labels affixed to each box, as our tubes are hand selected and hand matched to each order. Each triode will be within 5% Gm of the other, and each tube will also match within the same percentage to the other. These tubes are NOS and will be expected to have 100% of life, which is minimum 5000 hours when operated at rated voltages and with proper ventilation. Our tubes carry a 30 day satisfaction guarantee.