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

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.)

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.

Guys used to buy obsolete Tektronix oscilloscopes, in order to harvest from them the Telefunken 6922s, for use in their audio systems. I suppose they are all gone by now. In my one piece of gear that uses 6922s, I have been very happy with Siemens CCa types.

Many years ago I compared several brands of 12AT7 type tubes. To my surprise, by far the best sounding was a Chinese made variant sold to me by Billington in the UK. Since Billington is now out of business, I don’t know where I would get more of them, if I needed them, but fortunately I do not need them. My point is, don’t sell Chinese made tubes short if SQ is the major criterion. (The Chinese 12AT7s didn’t last long in use. Second best in my experiment w 12AT7s were GE 5-star gold pins.)

To anyone's knowledge, are there counterfit TFKs with the diamond stamped in the glass on the bottom of the tube, or can one assume that if the diamond shape is there, we have a genuine TFK?  Seems to me by now someone must have copied it, so you can never be sure what you have.  In my case, I have ECC83s that I personally bought new in the mid-1970s.  Only because of that, I am fairly confident they are real.