Preamp Tube Comparison Claims

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Preamp Tube Comparison Claims

Postby JMPGuitars » Sat 08/24/19 9:34 am

I was looking at random stuff on tubedepot's site the other day, and I came across their preamp tube comparison page. Frankly, none of it makes sense to me. Rating Gm and Mu from 1 to 5? What does that even mean?

None of the questions marks (aka more info buttons) next to the measurements actually give additional info on how they came to any of these measurements or conclusions regarding "tonality" or noise.

So I wasted a few dollars on some new tubes and ran some tests. Here's my comparison of their comparison:
TD-EH-12AX7.jpg
QT-EH-12AX7.jpg
EH-12AX7.jpg
TD-JJ-ECC83S.jpg
QT-JJ-ECC83S.jpg
JJ-ECC83S.jpg
TD-JJECC803S.jpg
QT-JJ-ECC803S.jpg
JJ-ECC803S.jpg
TD-Mullard-12AX7.jpg
QT-Mullard-12AX7.jpg
Mullard-12AX7.jpg
TD-Sovtek-12AX7WA.jpg
QT-Sovtek-12AX7WA-7025.jpg
Sovtek-12AX7WA-7025.jpg
TD-Sovtek-12AX7WB.jpg
QT-Sovtek-12AX7WB.jpg
Sovtek-12AX7WB.jpg
TD-TungSol-12AX7.jpg
QT-TungSol-12AX7.jpg
TungSol-12AX7.jpg
TD-TungSol-ECC803S.jpg
QT-TungSol-ECC803S.jpg
TungSol-ECC803S.jpg

As I suspected, their charts are meaningless. Tubes have datasheets with curves for a reason. Sometimes manufacturers flub their datasheets to make mediocre tubes look better, but that's why you never look at only one datasheet for a tube type to get your data. The curve traces show how the tubes behave in the real world, with real voltages, and there is a variance of performance there.

The "tonality" of the tube is highly subjective, and also subject to the circuit it's tested in. If you blind test 100 of each tube with a room of 100 people listening, I would be surprised if the data collected actually produces meaningful results.

Thanks,
Josh
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Re: Preamp Tube Comparison Claims

Postby crgfrench » Sat 08/24/19 10:40 am

Plus 1 for science!

Thanks Josh this is awesome.
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