Maybe tube preamp

Wolf_Garcia: I run both 6SN7s and 6SL7s -- the 6SN7s are in my mono blocks and the 6SL7s are in my preamp. This decision was made to take advantage of the fact that the 6SL7s bring a little more gain than the SNs, which I wanted. With respect to the "Red Base" -- I believe that it is, in fact, important. I have rolled a lot of both the SNs and the SLs in order to be able to say that. New production, NOS/NIB, it doesn’t matter, nothing sounds like a red base 5691 which was RCA’s Premium version of the 6SL7 or a red base 5692 same for the 6SN7. Premium because both included extra support rods between the top and bottom mica spacers making the structure more rigid, and in doing so, eliminating microphonics; and long life cathodes rated by RCA at 10,000 hours.
                                                                                                                           RCA also made both in a Black base as well and I must say I find it very difficult to tell them apart. The Black base seems to be easier to find and they command less money.

Great info there tubepower…after reading endless "headfi" posts about the Freya I'm very curious about the tubes they ship with. I've also noticed RCA "black plates" and they do seem less pricey, so based on your experience I may just get a couple of those…I'm absolutely certain that if the Freya passes the test to earn a place in my gear pile I'm going to go after lots more 6SN7s.

Thanks Wolf, just to be clear, it's "Black Base" rather than "Black Plates."

I did mean "Black Base"...oops...and saw several on Ebay last night. Any recommended sellers you might have used? Otherwise I'll go with the Ebay rating score.

What claudebond said.  The tubes4hifi SP14 takes a back seat to nobody at any price.  Exceptional.  You do see them pop up on the used market if you're patient enough, but you have to be diligent and willing to wait.  Most people build one and never buy another.