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I've not heard any, but a friend whose ears I trust says they're somewhat edgy and not very musical sounding. What he says leads me to believe that they sound about as unattractive as the Sovtek 'N7s--thin and edgy, exactly the opposite of the sound I like.
BTW both of us love the sound, overall, of the Ken-Rad copper-post-hollow-filament-tube blackplates, staggered or not--slightly warmly balanced, NOT edgy in the treble, and very musical and attractive. He LOVES the sound of the similarly warmly balanced (and expensive) Brimars, altho they're a little edgy in the treble for me. I find the black-T-angleplates by Tung-Sol and Sylvania to be slightly thin and edgy. RCA black-ladderplates seem to do nothing right and are just boring.
I stumbled into 1 Raytheon-branded Tung-Sol roundplate but haven't listened carefully to it, as I'm looking for a mate for it. They're VERY expensive (as in over $100 each if they test strong), and I may sell the single.
Have you seen this rather-comprehensive thread on 'N7s? http://www4.head-fi.org/forums/showthread.php?t=119638
For an inexpensive new 6SN7, I obtained superior results (in the same amp Arthur mentions above) with the Chinese "Ruby" version (Shuguang factory I believe) than the Russian Sovtek (Reflektor factory, same as EH, though I don't know if or how they might differ beyond the pins) -- and I haven't often liked Chinese tubes.
I have a Wright WLA12A, and find the EH 6SN7s very listenable and a bargain at $8.95/ea. They're far superior to the Sovteks I own, both the 6SN7s and the supposed "milspec" 6H8Cs. If all NOS tubes went away and I could only get new production tubes, I could easily live with EH.
That said, there are definitely NOS tubes that sound better. I have Sylvania GTBs that are my current favorite, and GE GTBs with the top filament that are a close second. I didn't have to pay a lot for either, and I've never tried any really expensive tubes - not sure my preamp or the rest of my system warrant them.
I'm interested to try the Shuguangs...with the metal bases, you can dream that they're $400 Sylvania Ws...
Jppenn, Do yourself a favor, you don't have a huge tube roll here. Don't mess with the non NOS tubes. It's a waste of time and money. Go for the old valves. Experiment a little. For me all of the Sylvania's the W(40's), GT & GTA(50's), and GTB(50's to 60's) are wonderful and are far superior to the current manufactured tubes such as the Electro Harmonix you mentioned. Sylvania has it all sonically, few could argue. The Sylvania 6SN7 IMHO is the finest American tube ever made, bar none. In general they are progressively better the further back you go by some measure but that said the GTB's have smoked any current production tube I've ever heard in my applications. Just keep in mind that the price goes up with the scarcity and age of the tube. I run ten of them in my Atma-Sphere OTL MA-1 amps and have never heard these amps sound better. I have a friend that runs them in his phono amp and loves them.
Thank you for all the input. The reason I asked the question is because the older, good sounding vintage tubes are relatively expensive, i.e., a tung sol round plate for 125.00+ etc. So I thought I would ask about the EH. For my preamp I have found nothing that gives me the detail and smoothness as the TS round plate, everything else is a compromise. I do like the sylvania W's, the Raytheon WGT's and the sylvania vt-231's. One has to wonder why noone has duplicated the architecture of some of these great old 6sn7's?
"...the older, good sounding vintage tubes are relatively expensive, i.e., a tung sol (sic) round plate for 125.00+...". Indeed, but your example is the MOST-expensive 'N7* I'm aware of. And going to the EH could be viewed as moving from the best to the worst (or close to it; I think the Sovteks are the worst-sounding 'N7).
So what did your preamp cost? What do you have invested in your system. Do you enjoy listening to it? (I sure enjoy mine.) How long does the great sound from a pair of tubes last? If the RP TSs are a little rich for you, try the Ken-Rads. Seems to me there are enough alternatives out there to please you woithout spending $125 per 'N7.
On building tubes, it's not just the physical architecture. Apparently, tube manufacturers had secret formulas for materials, etc., and even those varied from one tubemeister to another, and I think that's one reason why one tube's sonics varied over the eras--another tubemeister was building them.
* I've stumbled into ONE TS RP, and it tests very well and operates well, but I've not listened carefully to it (without a mate). Probably I'll sell it.
At ~$9 a tube, the EH is priced right. I find them toward the yin side of neutral while lacking the depth of tonality I hear in a nice '40's RCA 6SN7GT. They are not as etchy, ringy, and bright as the Chinese varieties I've tried. The EH neither sheds any particular magical light nor grossly offends. If you've only one 6SN7 to buy, why not spring for several used NOS types like you mention and find out what you like - it should be fun. I'll second Andy at Vintage Tube Services as a great person to talk to about that 6SN7 in your preamp.
Here is a link I find helpful: THE 6SN7 ARCHIVE THREAD