Got a few PM tubes to test, try out, and give some opinions on. I use all kinds of tubes, from NOS, used vintage, new, newer, and whatever is kicking around in the parts drawer. My tube tester is a Hickok 6000A, a portable used by techs in the field "back in the day". It was calibrated before I bought it, and I trust it. I use a set of tubes to test just for calibration only and it is running within spec. I have not played the tubes yet, here is my test results and opinion thus far: Tube Test: Hickok Model 6000A Dynamic Mutual Conductance tester First tested expected sample Fender branded Chinese 12AX7A for calibration sample. Normal Mutual Conductance: Normal is 1250. Sample Tested at 1400/1425. Life test good, stays in the positive 1/3 range, -4 mark drop. NOTE: Life test is subjective, I measure by the amount of drop under load. Hickok manual indicates if it stays in the green, it is OK. PM 12AX7A #1: Strong silk screen. Pins were bent, straightened to fit in the tester socket. Marked “Made in China”. Filament Continuity: OK Triode #1: Tests Good 1350 Mut Cond. Life test –3 mark drop (Good) Triode #2: Filament: OK Test: Good 1325 Mut. Cond. Life test –5 mark drop (good). Conclusion: Tube tests “moderate”, stronger than most premium NOS, softer than most Chinese. PM 12AX7A #2: Weak silk screen. Pins also bent, all over to one side. Straightened. Filament: OK Triode #1: Tests Good (Low) 1075 Mut. Conductance (Low) Life test –3 mark drop (Good) Triode #2: Filament: OK Test: Good (Low) 1100 Mut. Cond. (Low) Life Test: -3.5 drop (Good) Conclusion: Significant difference between the two 12AX7 tubes. Although they should last a long time there should be a noticeable difference in gain characteristics. Both were well balanced from one triode to the other. Either tube could be used as a phase inverter. Not sure why the pins were bent, the boxes look good and the tubes were not bottomed out in the boxes. PM6L6GC: Base looks cheap, sharp corners on the top of the base. Has an appearance of plastic rather than bakelite. Silk screened, no other markings other than the silk screen on the tube glass. No indication of manufacturer or country of origin on the tube or on the box. Shipped in a duet. 6L6GC #1: Filament: OK Test: Good Expected Mut Cond: 5000 Tests 5250 (Good) Life Test: -2.0 (Good) 6L6GC #2: Filament: OK Test: Good Mut Cond: 4950 (Weak) Life Test: -.5 (Excellent) Conclusion: 6L6 is near the top of the range of the tester. Although it tests accurately I depend on actual amplifier conditions to detect any mismatch. Mutual conductance is always borderline at this range. I can tell more from current draw on the line test, which was within 5%, which usually indicates a good match.