Telefunken vacuum tube E88CC-TK; NOS versus brand new.

Thank you JJ. I know for certain that RCA NOS 12AU7 deliver good value.

You've confirmed my opinion of very high priced tubes before I purchased any.

While I agree that "tube rolling" can make an audible improvement in SQ, I think of it as something one can do if one has no further understanding of electronics or skills on the workbench, the use of which can effect much bigger and more permanent positive results.  More permanent because tubes age, and in doing so they change characteristics.  So, for example, "matched pairs" of tubes usually will not stay matched for long.  And any tube will change sound over time. But a better sounding film capacitor is for all intents and purposes, forever.

While searching for three matched pairs of early Sixties (grey shield/external date code*) Siemens CCa’s, for my BAT CDP’s output stage, I purchased a matched pair each, of the same generation/iteration E88CC and E188CC (only those found with close balance between triodes and high mA, etc).     As most probably know; the CCa was a specially tested/selected, low noise designation, used by the German and Dutch Post (more on the link).      Bottom line; they all sound almost identical, in the CDP (low noise not being as critical).        Nice thing about these 10K hour tubes; they just continue to test very closely balanced, between triodes and their matched-pair partner, after ten years.       Makes them worth every penny, in my estimation.                 *The silver shield/internal date code CCa’s always sounded too zingy, to me, whether in my ARC SP-9, SP-14 (when I owned them) or- the CDP.                  https://www.tubemuseum.org/ProductDetails.asp?ProductCode=SH%5FCCa%5Fsingle                                Yeah: low supply and high demand (there’s a reason).

@orpheus10 - If you get to try Frogman’s Teles, please: post your impressions.

Typically, in a CDP, tubes are used as cathode followers at the output of the CDP.  A cathode follower does not add any gain to the signal voltage and therefore is fairly neutral in its sonic signature.  If done well, it can be completely neutral.  I think there are or were a few CDPs that did use tubes for gain, such as the Raysonic's.  In that latter case it might be worthwhile to use the expensive Siemens CCa's in a CDP. 


Here we go with more pure "opinion":  I don't like 12AU7s at all.  Whenever possible I have replaced them with 6CG7 or 6FQ7, which are identical electrically.  Among 12AU7s I have used, Amperex Bugle Boys, real ones, were the best, but still not quite as good as a 6CG7. (You can't just plug a 6CG7 or 6FQ7 into a 12AU7 socket; some re-wiring is required.)  I'm talking about gain stages; 12AU7 is probably OK for cathode follower use. It's just my opinion, and I was wrong once back in 1965, maybe.  (Kidding.)