Sorry for the long silence, I had been waiting for my Sylvania 5751 to arrive and it finally showed up yesterday (1 day to get from Sweden to New York, and almost two weeks to get from NY to Baltimore - ~200 miles - bloody post office).
So, right now I've got a TungSol 5998 and a Sylvania 5751 in my Jade, and I'm loving it. Sorry I don't have any HD650's to try it with... anyone want to loan me theirs for a while? If I had infinite cash, I'd buy some HD650s and W5000s to try out (and hell, a Darkvoice or something to compare with while I'm at it). But I don't see that happening soon for me... sigh.
I'm still evaluating whether I can hear the difference between different tubes. So far it's pretty subtle to me - more subtle than the difference between the two outputs on the Jade. But I'm new to this so take everything I say with a big grain/pile of salt. I did find one track - solo Renaissance recorder music - that has all sorts of weird distortion/echo/harmonics on it, and I was in a half-panic thinking my tubes were messed up. But it was the same, though less noticeable, with the stock Chinese tubes, and I could also hear the same thing through my regular HT receiver, both with the K701s and my loudspeakers (good ones in an acoustically treated room). So I'm satisfied that it's just something weird on the recording itself, and not a problem with my gear, that's a relief! And it seems to support the notion that the better quality the system, the more revealing it is of weaknesses in a recording.
Both the 5998 and 5751 are NOS, so I'm gonna burn them in for a few days before I do any more tube rolling (the Sylvania had a definite hum at first, but it cleared up within ~10 minutes). But even with the stock tubes that I've been using for the past several weeks, I think the Jade is an impressive little machine. I'm totally satisfied with the purchase.
I found the Jade to mate very nicely with my HD650 and Grado HP2. It is a great bang for the buck IMHO. I put a Telefunken in it which helped a bit but didn't greatly change the overall character of the amp.
Jade will have 10Pcs finish on next tuesday. (3~5 Units at end of this week).It can upgrade to have 2 Input , Zero feedback & -3db switch in option. Cathode output improved low frequency response to much lower by increasing capacitor value from 100u to 1000u due to I found cathode voltage is much lower than plate. So I change to 1000u/35V in cathode out coupling.