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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
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.
lewm
12,472 posts
 
I don't get this. Noise from tubes is in my experience a variable related to sampling, and of course high gain tubes will tend to have more noise those that afford less gain, when used in a gain stage. Then too, the circuit design is critical and so are the voltage and current chosen to run the tube. These elements and more constitute a calculation of noise that has so many variables as to make the outcome unpredictable in advance. IMO, you have to measure noise in-circuit and experiment to determine whether substitution of one 12AX7 (for random example) with another 12AX7 results in audible or measurable improvement.
swampwalker's avatar
swampwalker
5,138 posts
 
"High gain tubes will tend to have more noise than those that afford less gain"

Truer words were never spoken but the real question is how much noise is introduced by different types of the same tube (high or low gain).
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