PM Tubes @ GPDUSA

[GPDUSA]

Amazing tubes that come stock in Orange, Hiwatt and some Marshall Amps. Check 'em out!

PM Tubes by GPDUSA.COM

 

[GPDUSA]

Hey folks, forum member Cygnus X1 did a comparison test with some PM Tubes we sent him. Not many people know about these tubes so it was great to see a real live test with these vs. other high-end tubes. Check it out!

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.

If anybody has any questions about these tubes feel free to PM (no pun intended) me.