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List of Audio Tube Measured Noise Performance

I have begun to post and maintain a list of the measured noise performance of the types of vacuum tubes typically used in phono stages and other low-noise audio equipment. It might be of interest to any audiophile replacing or upgrading tubes in a phono stage.

So far the list is modest, with samples of twelve different brands and/or types, and a total of 58 tubes measured, but it is updated regularly. It includes tubes such as the 12AX7, 12AT7, 5751, 6922 / 6DJ8 / E88CC, and 6SL7GT. And it includes a sampling of tubes from all three major current production tube factories, as well as some new, old-stock (NOS) tubes.

I don’t sell tubes (or own stock in any tube factories), and the list is strictly measurement-based, so I believe it is completely objective. And I explain in detail how the measurements are made, for anyone who would like to repeat them.

You can see the list at:

http://tavishdesign.com/pages/downloads

I’d be interested in hearing about other tubes or brands you think should be included.

Scott
tavishdad
elevick
2,636 posts
 
Nice start. This is going to get really deep. I think that you need a lot more samples to accurately test a manufacturer. My guess is that a minimum of 30 tubes to get an accurate sample. Different run dates and factories make a huge difference on some. I know that some companies like Shuguang actually pick the best out at times and sell them as superior tubes.

Also, did you buy matched pairs/quads? That would mean the dealer already took out the garbage.

Finally, instead of giving the high and the low let's get down to real sampling: Use Standard Deviations. It's a much better number to judge by. Then if you get into variances you can compare different kinds of tubes not just different manufacturers...It will let us know things like the best overall consistency from a single manufacturer regardless of tube type.
kirkus
502 posts
 
Hi Scott - I applaud your efforts on the start of a very interesting and relevant project. I thought I'd just bring to the attention of interested readers an AES paper I saw a while ago on this very subject, by Merlin Blencowe of AMS-Neve:

http://www.aes.org/e-lib/browse.cfm?elib=17071

This paper is focused more on the influences of tubes' operating conditions on noise performance, but deals tangentially with some of the stochastic variability of different samples. Also some excellent information on specific noise mechanisms, as well as measurement techniques.

Sorry that (like all AES publications) it's not free, but this is an excellent one on a subject that rarely covered anymore. Thorough bibliography, too.
tavishdad OP
11 posts
 
Those are all good comments and suggestions. The current production tubes I tested were not pre-selected in any way. They were purchased in small lots from 3 different retail online tube vendors in the US.

Next time I update the list, I'll include standard deviations (either in addition to, or in place of min/max). I agree that is a better way to judge consistency of a manufacturer. And it is needed to calculate the statistical significance of the measured difference between tubes.

I've read Merlin Blencowe's paper, which is excellent. He also saw a lot of variation between tubes, but did not try to break it down by manufacturer, I believe. His paper has convinced me to test the D3a and similar Russian 6J52P, which I'll add to my list in the future.

We'll see how the list evolves as I test more tubes in the future - I'll post to this forum whenever I update the list.

Scott
swampwalker's avatar
swampwalker
5,138 posts
 
This is a great start, Scott. Maybe the manufacturers will start paying attention to these results, once they are more statistically robust. I know I will, my active gain MC phono stage uses 12AX7s. Well done.
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