List of Audio Tube Measured Noise Performance

Hi Bdp24,
Good question. The intrinsic, input-referred voltage noise of a tube (EIN) should be the same regardless of how it is measured. On my “downloads” page, I’ve provided a lot of technical details about how I made the measurements, so that anyone who wants to repeat them can do so. I’ve also compared my results to other tube noise measurements in the technical literature, which have shown comparable numbers. So I believe my measurements are correct and reproducible, and anyone who measures the same thing should get the same answer.

I visited the webpages for RAM Tube Works and Upscale Audio, and although I may have missed it, I did not see any technical details about how their noise measurements are made. I also did not see that they are posting the actual EIN or noise figure of the tubes they sell (again, I may have missed it). What they seem to be doing is selecting and grading the noise levels of tubes of a given brand and type, which is fine. Other tube vendors do the same. But since they do not specify the actual noise level in a technically precise way, you can’t make comparisons between the various tube types and brands.

It is an odd situation – no one would buy a low noise transistor unless the manufacturer or vendor specified the EIN or noise figure. But no manufacturer or vendor that I know of provides this data for tubes.

If these sites (or other sites) are actually providing measured tube noise data, please point me to it, I haven’t found it yet.

Thanks,
Scott

Tavishdad, I find the ECC99 to be very useful in a variety of applications, partly or mostly because it has the same pin-out as do the 12AX7/AT7/AU7, etc, family, whilst having a much lower Rp and higher Gm than any of those do. I use it as a CCS and as a follower in some cases in gear that was previously wired for a 12AT7 or 12AU7. However, in my phono stage, I use ECC99 as the top tube in a hybrid dual-differential cascode topology at the input to my phono stage, a very critical application, as you point out. Because of the very very high Gm of the bottom transistor, the gain at the input is enormous and the S/N is very good, enabling me to run just about any very low output MC cartridge with room to spare.

Hi Lewm,
I'll put it on my to-do list. The only current-production ECC99 is JJ - is that what you use? What bias current do you run the ECC99 at?

Scott

JJ invented the tube and is the only maker, so far as I know. So, yes, that's the brand I use. I typically run them at 5-6mA per section, but I also feel that is not necessarily optimal; a little more current probably would be better. I have been constrained from using more current by the limitations of the rest of the circuit, in the 2-3 devices where I've implemented them.

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