How do the Electro Harmonix 6sn7's sound?

"...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.
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* 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.
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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

Cheers,
Tim

Dgclark0007, To answer you on the thread and we can talk more about it off line I use both Sovtek 6AS7G's or Svetlana 6H13C with the flying "C" for my power tubes. Cheers!