List of Audio Tube Measured Noise Performance

Hi Lewm,
Thanks, another good question. If I understand correctly, you are asking if the intrinsic noise (EIN) of a tube really makes any practical difference in your audio equipment. It will only matter if the tube is the first active device in a signal chain, that is, the first tube in a phono stage, the first tube in the analog section of a hybrid DAC, or the first tube in a line amplifier or power amp. In that case, the tube EIN should determine the signal-to-noise ratio of the equipment (unless the equipment is poorly designed and has, for instance, a lot of hum).

Whether the signal-to-noise ratio matters depends on your signal source. Let’s take a phono stage as an example. The best signal-to-noise ratio achievable on an LP is around 70dB, I believe (it is often much worse). A tube phono stage using one of the lowest noise tubes on my list should have an 80dB signal-to-noise ratio, the way such things are usually measured (A-weighted and referred to an input level of 5mV at 1kHz). But one of the noisier tubes on my list may give a signal-to-noise ratio 8 – 10 dB worse, comparable to the surface noise on a very quiet LP. You wouldn’t want that. So it could make a practical difference, yes.

I haven’t measured the ECC99, but I have some on hand and could do so. I had not considered the ECC99 as a preamp tube, but it might be worth measuring. Thanks.

Best regards,
Scott

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.