List of Audio Tube Measured Noise Performance

Hi Everyone,

I updated the measurement list on my website "Downloads" page to include additional samples of the JJ 5751, and also an additional tube type, the JJ ECC99.

http://tavishdesign.com/pages/downloads

The JJ 5751 continues to be one of the most consistent and low-noise tubes in my study. But I’ve noticed that as more tubes are measured, the average input-referred noise tends to rise. This is true for all tube types, and it is because as more tubes are measured, it is more likely to get a high noise tube that raises the average. The noise distribution is actually not Gaussian – while there seems to be a lower limit for the noise of a given type, there is no upper limit, so there is a tighter distribution on the low side of the average and a wider distribution on the high side of the average. In the future, I may begin reporting the median as well as the average for each type.

The ECC99 is a high transconductance tube that I believe was originally intended for RF applications. I’ve experimented with it as a driver tube for my hybrid amplifier, but had not considered it as a low noise tube until Lewm on this forum suggested it to me. The ECC99 has transconductance comparable to an ECC88, but without the extremely tight electrode spacing or wide bandwidth.

I’ve only measured 4 samples of the ECC99 so far, but it seems promising. The average input-referred noise of 0.711 µV RMS puts it in the middle of my list, and I intend to measure more. One of the 4 samples had “popcorn” noise and was discarded.

Scott

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.

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

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