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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

Showing 5 responses by lewm

lewm
12,560 posts
 
I don't get this. Noise from tubes is in my experience a variable related to sampling, and of course high gain tubes will tend to have more noise those that afford less gain, when used in a gain stage. Then too, the circuit design is critical and so are the voltage and current chosen to run the tube. These elements and more constitute a calculation of noise that has so many variables as to make the outcome unpredictable in advance. IMO, you have to measure noise in-circuit and experiment to determine whether substitution of one 12AX7 (for random example) with another 12AX7 results in audible or measurable improvement.
lewm
12,560 posts
 
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.
lewm
12,560 posts
 
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?
lewm
12,560 posts
 
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.
lewm
12,560 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.
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