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Old 16th November 2012, 04:09 AM   #1
MGH is offline MGH  United States
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Default Are these tubes really matched?

Hi, just bought some pairs of "matched" Golden Lion reissue 12AX7, NOS Telefunken 12AX7 smooth plate diamond bottom, and NOS milspec Mullard CV4024 (12AT7).

Mullard CV4024: Mu 51.8/42.1 53.1/45.2
Golden Lion: Mu 97.2/95.5 96.7/99.0
Telefunken: Mu 91.5/91.5 91.0/91.8

My questions:
1) I'm not a tube expert but the Mullard is wildly off internally, 20% mismatch for one and 16% for the other. Between tubes seem relatively close, but still imbalanced internally. Would you return these for better matched pair?

2) I suppose the Golden Lion is pretty close. Is this acceptable?

3) The Telefunkens are almost perfectly matched. But absolute values seem a little low for NOS. Should be close to 100 according to specs. Is this acceptable? Especially given, I paid over $100 each for these.

Thanks for your input.
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Old 16th November 2012, 04:37 AM   #2
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Acceptable on what basis? An instrumentation application might fail them, but then, an instrumentation amplifier would contain enough negative feedback to overcome such differences with room to spare.

For audio purposes, even the worst '4024 halve vs. the best Golden Lion halve is not a huge difference: a mu-stage will differ by 7.4dB, which means you'll change the volume control once and forget about it (the 12AT7 distortion may be noticable, but that depends on design). You won't discern the differences between Golden Lion and Telefunken devices at all: the worst mismatch is only 0.73dB.

All in all, I'd be very concerned if you had a circuit that was so knife-edge unstable that 0.73dB variance was enough to make it malfunction. That's not a tube problem, that's a fundamental design issue!

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Old 16th November 2012, 04:45 AM   #3
MGH is offline MGH  United States
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Thanks Tim. I get your point about the Golden Lion and Telefunken. But the Mullard seems pretty far from being "matched", which I paid extra for the service. If I didn't pay for the matching service, I would accept the Mullard as is.
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Old 16th November 2012, 05:06 AM   #4
20to20 is offline 20to20  United States
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Quote:
Originally Posted by MGH View Post
Thanks Tim. I get your point about the Golden Lion and Telefunken. But the Mullard seems pretty far from being "matched", which I paid extra for the service. If I didn't pay for the matching service, I would accept the Mullard as is.
Check the description of the matching method. They may say that a matched pair is considered a match if they are close tube to tube only, and not matched first section to section internaly. That would be double matching.
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Old 16th November 2012, 05:17 AM   #5
MGH is offline MGH  United States
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Tube to tube, section to section was not specified. However, even tube to tube, it's off by 7%. I thought most consider 5% or less tube to tube as matched.
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Old 16th November 2012, 05:37 AM   #6
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Almost every pair of tubes listed on ebay claim to be "matched" even rectifiers...
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Old 16th November 2012, 05:52 AM   #7
20to20 is offline 20to20  United States
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Quote:
Originally Posted by MGH View Post
Tube to tube, section to section was not specified. However, even tube to tube, it's off by 7%. I thought most consider 5% or less tube to tube as matched.
AES won't even do a 12ax7 match or for other dual triode preamp tubes. Internally or tube to tube.

Power tubes, yes. But small imbalances in drivers can be compensated for with balance control. Do you have a unique need for 4 perfect sections?

Last edited by 20to20; 16th November 2012 at 06:00 AM.
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Old 16th November 2012, 08:22 AM   #8
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it is the job of the circuit designer to come up with designs that are not critically affected by tube mismatches, i believe it is not the job of the end user to match tubes....
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Old 16th November 2012, 11:03 AM   #9
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Quote:
Originally Posted by MGH View Post
1) I'm not a tube expert but the Mullard is wildly off internally, 20% mismatch for one and 16% for the other. Between tubes seem relatively close, but still imbalanced internally. Would you return these for better matched pair?
I'd return them to get my money back, then buy some JJs. Better consistency, lower distortion, ten times lower price.
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Old 16th November 2012, 11:29 AM   #10
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Mullard CV4024 are often poorly matched. I'm not sure if that means they were built to optimise something else (CV4000 series are supposed to be 'better' than earlier versions), or just that we are now left with the dross.

For good section matching try RFT, although they may be branded as something else (e.g. Mazda foreign).
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