Here is my daily update. I put in the 6J3P-E for burn-in and tested them again after about 10h (which imho is enough to have a feel for the "tone" and capabilities of a tube, even if the bass might still improve and highs might tame a bit, and other minute improvements; I just can't justify burning in every mystery tube for 50 hours...).
I would say the 6J3P-E is a bit cozy and warm, it sounds kind of like a higher gain warm 6AK5. Treble is pleasant and not too spiky, but not rolled off either. Mids are a bit grainy, lush, warm, and could use a bit more microdetail and separation. Bass is you typical average good tube-y bass, with a slight lack in punch, but OK for most music. Overall, a solid all-rounder C+ grade tube (at this point I think I need some objective grading system, as random words and comments just don't enable real comparisons), good overall but never excellent, and a bit too mellow for my tastes. This being said, I could imagine these tubes being very nice for listening to singer songwriter type music where you don't want too much microdetail, but warmth and mellowness with more grain, kind of like a more powerful M8100 with less instrument separation and detail. And they might improve after 100+h of burn-in the Voskhods, but that shouldn't add detail or change the tube's performance.
After the -unburnt-in- GE 6AG5 that were way below these 6J3P-E, I'd say I might just try one last special quality/military 6AG5 and be done with testing this tube family for the time being -or until someone else makes an awesome breakthrough.
Speaking of "grading" tubes, I would tend to grade on an relative scale not an absolute one, meaning that an A++ tube that suddenly pops up would mechanically make all the other tubes go down one grade and become my de facto new A+ reference. So right now, for me, the GEC CV4014 would be my A+ tubes, and my Mullard CV4015 would be an very solid A as well (probably A+ in some setups). Voskhod 6J1P-EV would have been a solid B+ tube and the Mullard CV4010/M8100 an A- (B+ for electronic music). The best Mullard M8083/CV4014 would hover between an A- and a B depending on the version tried, there's just way too much variety in that family.
After 9-10h of burn-in, the Military GE (non-JAN) 6EW6 tubes seem to have matured to the point where giving an opinion would be reasonable. These are some very good tubes, considering they're not a special quality or military tube (which doesn't exist in that family). Bass slams down on you in a powerful way and gives music a body and impact that is very enjoyable, it extends enough that wouldn't think anything is missing, not especially fast but not slow either, just visceral and well grounded. Background is not quite as black and empty as my best tubes; instruments, while very well rendered, don't stand out as clearly as they could, but they are all there, just sort of in each others face (like somewhat superimposed, but not in a bad way and still each audible). Soundstage is your average 300mW+ heater current large stage, not a mile-large like some EF91s but enough to not sound too squeezed, and is noticeably extended vertically, and very good in depth -big 3D bubble- in your head kind of stage but never in your face; the sense of space is definitely there, but again not quite as much or well as the best tubes, but very very close. Mids are ever-so-slightly warm but not as much as a GEC CV4014, I'd say in between these and the CV4015 or the more recent analytical 8136. The transients scream of realism and almost reach the best of the best, decay is just a tad slower than my fastest -analytical- tubes, but that's not necessarily a bad thing. Highs are well extended and sound like "it's all there" without ever being grating, airy without sounding silly or surreal. Overall, this an excellent tube, which I'm starting to think may still evolve a bit with an extra 10h of burn-in; a very solid A tube imo, that might get an extra point at 50 hours.
I'll try to *finally* formulate an objective opinion on the 6CB6A/6676, 8136, 6GX6/6GY6 at some point, and the 6GM6 when I get a chance to actually plug them.
Edited by Audiofanboy - 3/8/13 at 4:56am