List of Audio Tube Measured Noise Performance

Hi Everyone,

I updated the measurement list on my website.

1. I included a few more samples of Shuguang 12AX7B and Shuguang 12AT7.

2. I included new measurements made on the JJ EF86 (they call it EF806S). I've read in many places that pentodes are noisier than triodes, but I've never measured it before and was very curious to see how much. The EF86 measurements make it one of the higher noise tubes I measured, but not the highest. I also measured it as a triode, because I've read that a triode-connected pentode should produce less noise. At least in this case, it did not seem to be true. Within the accuracy of my measurements, it was the same. Hmmm......

3. Finally, I have begun to compute sample standard deviation (sigma) instead of posting the min & max for each type. Standard deviation is a better way to compare data sets of different sizes.

Scott

Since my last post here, I’ve updated the list on my website to include more tube types (such as the European D3a), and many more samples of the original tubes. The list at this point includes 95 samples and 15 different brands and types, along with some comments on the measurements and on specific tubes. And it includes the average noise, standard deviation, and number of samples of each type, so statistical significance of the measurements can be computed (if you are so inclined).

You can see the list on my “downloads” page at:

http://tavishdesign.com/pages/downloads

I’d be interested in hearing about other tubes or brands you think should be included.
Scott

Tavishdad, Thanks for pointing out the logical inconsistency in my generalization to the effect that "High gain tubes will tend to have more noise than those that afford less gain". After posting, I kind of wished I hadn't said that, for reasons you state; it's a matter of semantics, and I got the semantics wrong. But how about the other variable factors that to my mind also determine noise, at the practical level, which is to say when listening to music?

Thanks for posting your results, and keep at it, please. Have you tested ECC99?

Is the tube noise data significantly effected by the equipment used to measure it? Will your results pretty well match those of Roger Modjeski (RAM Tube Works) and Kevin Deal (Upscale Audio) if the same tube was to be tested by all three of you? Or is it more a matter of the relative noise levels of a group of tubes obtained by each tester?

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