The Russian 6P14P (EB and EP) are absolutely the best EL84 variant I have found for the Doge 6210.
For about a week I had been using a pair of NOS (although I have my doubts) Mullard EL84's with the JJ/Tesla ECC83S (which is the near-replica of Telefunken ECC83S). Immedietly I noticed a decreased volume, but that does happen from time to time depending on the combo and not just from poor pin contact. The combo didn't sound bad at all but I didn't like having to turn the volume up to hear the same output I was used to with the Russian 6P14P and GE 12AX7 Lp's. So, after a week I thought maybe the Mullards were bunk and not allowing the JJ/Tesla's to perform optimally. I then tried EVERY pair of Mullard EL84s' I own with the same pair of JJ/Tesla's, and every time the same result, decent sound but low volume. I then tried an NOS pair of Bugle Boy 12AX7's with the Mullard EL84s, same result. At this point I was convinced that all my Mullards were swag and I had been ripped off, but once I calmed down I realized what Doc Art had said, or written, about good and bad combos; I have not yet tried the Mullards with the Sylvania 12AX7's, I have a couple of NIB pairs on the way. So before I jump off a bridge with my Mullards I will try them in every possible combo of 12AX7/ECC83/6BQ5 I have, including the EH and Ken Rad 12AX7's.
However, last night I was still ready to jump, so I just switched everything out and put in an entirely new combo: Russian 6P14PEP with the JJ/Tesla ECC83S gold pin. It sounds fantastic! Wether it sounds as good or better than the 6P14P & GE 12AX7 combo I have yet to discover. But Charles Mingus' "East Coasting" and Herbie Hankock's "Takin Off" sound pristine. When it comes to bass I like to hear the instrument and not just an overall increased presence of the low end, I like to hear the finger slide and slap off the acoustic bass' strings; I like to be able to separate the brass and woodwinds when they are all playing a chorus; you know, fruit-on-the-bottom, not low fat custard.
At this point, my preliminary amatuer conclusion is this, almost any pre-amp tube sounds good with the Russian "Reflector" 6P14P EB or EP (the EP is the military version with a little more plate voltage than the EB, but in a headphone amp application, like the Doge 6210, I find it hard to believe that anyone would be able to hear a difference). I'm going to give the current combo a week or so, and when my final batch of tubes arrive I will try all the combos I have yet to try, re-evaluating my pennultimate conclusions, and come up with what I hope be a modest amateur apendege to Doc Arts professional findings.
