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In Reply to: RE: "Matched" power tubes, what am i missing? posted by Laudanum on July 05, 2016 at 04:14:49
Matching is only for the conditions under which the tubes are tested.
Were they "matched" for both Gm and current draw?
Matching is usually considered within 10%. If they were matched for a target of 90 mA current draw, then a 9 mA difference may be considered matched.
The # of hours on a tube will also have an effect.
Did the tubes come marked with the test conditions and results?
If it is a reputable dealer, I would let them know and see if something can be worked out for an exchange.
Follow Ups:
Thanks for the reply.
GM is the transconductance, right? So yes, they are matched for GM and current draw. According to his numbers, the tubes tested within 10% for GM. Current draw was listed as just under a 1ma difference.
Already contacted the dealer. He asked that I swap sockets to see if the difference followed the tubes. I had already told him that it did in my original message to him. He missed it. Waiting to hear back.
Ask for replacement. IME, "unmatched" tubes can become even further apart with use. You paid for "match" --- and maybe a lot of $$$ for NOS EL34 tubes. Get your money's worth.
If you are in the 40-45mA per tube range, should be less than 3mA difference, to be matched. IMHO.
Good luck!
I agree, and I am working through it with the dealer. Of course, to the dealer I'm the idiot until proven otherwise. I can deal with that if it gets me to a resolution.
In the meantime, I'm posting here to make sure I didn't miss anything that could be related to my gear (or my being an idiot). They aren't NOS but I still paid for a matched pair. I have a pair of Valve Art (Chinese) EL34's that were dead on when I first put them in and they are only 2ma apart after 30 or 40 hours. JJ's were about 1.5ma apart when I first got them and after probably close to 100 hours were about 3.5ma apart.
At any rate, based on the above, and common logic that if it stays with the tube when I swap sockets, it must be the tube, I don't think I'm missing anything. But I wanted to check here with folks who are smarter than I am.
Thanks
If you've bought "matched" tubes before and they match-up using your amp and measuring devices --- I'd say the pair you have now are not matched.
You did the correct things to test the tubes. Get another pair.
JOC... what brand and era manufactured are these tubes?
They're current production Svetlana.Since the dealers rep. is pretty good, I'm guessing he may have dropped one of the tubes in the wrong box. He doesn't label the tube bases, just the boxes.
Thanks.
Edits: 07/05/16
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