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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
lewm
13,030 posts
 
Scott, Re the ECC99, If one uses it as a driver, i.e., a cathode follower, would the noise be so important? Thanks for taking the trouble to both purchase and measure several of them.

I am using them in my very hi-gain phono stage as gain tubes; no obtrusive issues with noise, although I am sure there is noise at some level.
tavishdad OP
11 posts
 
Hi Lewm,

Intrinsic noise is not important if a tube is used at high signal levels. It is only important in the first stage of an amplification chain, where it can set the signal to noise ratio of the system.

You mentioned that you use the ECC99 in the first stage of a phono preamp, as the upper device in a hybrid cascode. In that location, intrinsic noise would definitely matter, although not as much as the lower device in the cascode. The ECC99 is a good performer, within a couple of dB of the best current production tubes I've measured.

I've updated the project page on my website again, to include the actual noise measurement histograms for the JJ 5751, JJ E88CC, and Tung Sol Reissue (Reflector) 6SL7GT. It is interesting to compare the three different plots - they tend to suggest that JJ is having some trouble getting consistent noise performance for their E88CC. The JJ 5751, on the other hand, shows fairly tight distribution and pretty consistent low noise performance.

Scott
tavishdad OP
11 posts
 
The list of tube noise measurements on our “Downloads” page has had several updates since my last post here. It now includes measurements on the Toshiba 2SK209 JFET, which is an interesting comparison to the tubes and provides a sanity check on my measurement technique.

The list also now includes the Sovtek 6C45, which has the lowest measured noise of tubes on the list, but the samples tested were also microphonic.

Samples of the Sovtek 6H9C / 6SL7GT have shown very low intrinsic noise, comparable to the best 12AX7s tested, and 3dB lower than the Tung Sol Reissue 6SL7GT. I’ve only tested 3 samples of the 6H9C but intend to test more.

I’ve also recently tested the RU-6H6, a NOS Russian tube comparable to the JJ ECC99. And there are additional samples of many previously tested types, so the statistics are becoming more meaningful.

Scott
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