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In Reply to: RE: How about the new 45 by EML? posted by drlowmu on April 06, 2014 at 14:54:18
Hi Jeff,
I'm sure the metallurgy of all 3 components influence the sound. In the past I've compared gray and black double plate 2A3s, both RCA branded, and they sound different. In general I preferred the sound of the black plates.
How can you say with such certainty that the symmetry and size of the cathode is responsible for the most differences? That's not obvious to me and doesn't correlate with what I have heard.
I have not A-B compared EML versus NOS American 45s, but I have compared EML 2A3 meshplates versus many other new production and NOS American units. One is not categorically better than the other and I hear strengths in both.
Donald
Follow Ups:
The EML mesh WILL sound different than the solid plate EML, or a JJ 2A3-40 solid plate. I am not so sure you get a true picture comparing a "meshie" to other solid plate 2A3s. A meshie is a different presentation.Also, the better the 2A3 amp, the wider band it plays ( not necessarily measures, but how it plays the speaker voice coil ) the easier it is to hear these differences. My buddy Dennis Fraker easily makes the best there is in 2A3 amps these days IMHO, so, we can get a handle pretty well on these tube performance differences, modern single plates with large symmetrical cathodes versus dinky NOS biplates with asymmetrical filaments. You should have him build you a pair of 2A3 SE DC amps, to have as your reference, while you can. It will easily be the best audio purchase you will ever make, IMHO.
Jeff Medwin
Edits: 04/07/14 04/07/14
I've listened to the EML solid plates too but spent more time with their meshplates, finding their sound more preferable to me of the two.
Thanks for your amplifier recommendation, but I'll keep enjoying what I have ;)
Well, transconductance depends largely on cathode-grid spacing, or at least the length of the electron path within that spacing. Since this is the smallest critical dimension in the tube, it is not unreasonable to ascribe a majority of the variability of performance with operating point to this variation. And in fact the curves of the modern designs are especially linear. Whether curve linearity is the major influence on subjective sound quality is I believe unknown and unknowable.
I personally am more suspicious of the cathode substrate and coating. It is reasonably well known that excess noise increases with cathode current, while Johnson noise decreases (because of increased transconductance) - hence the cathode size affects the current density and you might reasonably expect a quieter tube to have a larger cathode, all else being the same which it never is. Alternatively, (Jeff will love this) you might reasonably expect a tube to be quieter when run at a lower than maximum current.
The other known effect is that of the cathode substrate (the filament wire itself for DHTs). It's traditionally nickel, and certain impurities (silicon for example) are known to result in eventual formation of cathode interface, increasing noise. Silicon (again, just an example) also makes it easier to "form" the cathode, making it cheaper to manufacture tubes - no free lunch.
I have not even touched on the cathode oxide coating, about which I know practically nothing. But speaking as an engineer, I am certain that the things I don't know are even more important than the ones I do!
It's also "well known" that increasing the current lowers the Rp and as a result, lowers distortion and raises power. Can anyone hear the "extra noise" of a 2A3 run at 75ma compared to 43ma (except Jeff) ? Not "sound quality" but NOISE ? ? ?
It's a great question, but as far as I know there are no studies or measurements to guide us. Perception of low-level noise in music is not at all easy to understand; it often is perceived as something else like grain or listener fatigue. Digital studies have shown that the character of low-level nonlinearity is perceived even with large amounts of masking randomness, for an example of something that "should" be too small to hear.
I agree, there are several more plausible explanations of what Jeff hears - but there is not enough data available to completely discount this one.
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