I just received my set of tubes consisting of:
National Union VT-229 (heavy graphite covered glass)
Sylvania JAN-CHS-6SL7GT VT-229
RCA 6SL7GT (VT229?) light smoked glass, black base, round plates
Tung Sol 6SU7GTY, brown base, black glass
Tung Sol 6SL7GT (stock tube, current production)
First off the bat, nearly all the tubes had better synergy with the GS-1K cans than the stock tube. The stock tube by comparison is really unrefined, weak and cold mid-range, aggressive highs, and really dry sounding. It did have better synergy with the HD650s; though I have yet to try the HD650 with the rest of the tubes as my main concern was the GS-1K,
Now with the GS-1K+NU VT-229. This was probably the best combo, but the other tubes may benefit from burn in. Really beautiful, clear, articulate, and crisp vocals. Great mid-range which is fairly neutral, maybe with a pinch of warmth. Handles sibilance really well. Highs are extended, airy, and detailed without being etched. Bass has good impact, but can be a touch more defined - though it's not a huge problem; it's a bit on the acoustic/organic side (which is a good thing sometimes) versus coming out of a super tight vise. Overall very balanced sound, great all around imaging, excellent dynamics. Very very enjoyable, and unfatiguing tube to listen to, without sacrificing detail. I should also add that this tube reproduced the best musical timbres, expecially of brass (adding "bite" to the brass when needed) and piano.
I had a post in another thread ranking the GS-1K, HD650 synergy with Zana Deux, and Grace 901 amps. I gave the ZD and GS-1K an 80 and the HD650+ZD a 95 . With the NU-VT-229, the GS-1K is about tied at 95 now.
RCA black base, light smoked glass: I'm not sure if this is a VT-229, though the seller says it is, but is not indicated on the tube. In any event, I was least impressed by this tube (especially after listening to the NU VT-229).
If you really have a problem with the highs being edgy and aggressive with the GS1K and the bass bloated which I often read, this will completely counter all of that. No more of any of that in fact. However, it didn't have the dynamics and refinement of the NU VT-229. After listening to this tube, I had the opposite problem of before, the mids are too dominant over the bass and treble. My least favourite of them all.
The Sylvania had a lot of good characteristics. And I didn't find it to do much wrong, but I found the NU VT-229 better, so I didn't pay as much attention to this one for the time being. I have a feeling burn-in may improve this tube more. It's a more upfront presentation overall. However, I found the highs although not aggressive, were a bit more pronounced, and weren't as balanced at least on the GS-1K. May be an interesting candidate for the HD650 (untested at the moment). It also wasn't as airy as the NU VT-229. Vocals were good, but not seductive like the NU.
Tung Sol 6SU7GTY. A good all rounder. Balanced sound, more so than the JAN-CHS (w/ GS-1K). But at least for the music I listen to Jazz, Classical - I'm heavily drawn to the NU. Really good imaging and soundstage. My impressions are not as detailed for this tube, as I tried it a bit earlier on, and have yet to swap it back in. Overall, it was good, but not OMG good of the NU VT-229.
Tung Sol 6SL7GT - stock tube, current production. Good synergy with the HD650. A write-off with the GS-1000. Timbres don't show very well with this tube as the JAN-CHS, NU, or TS6SU7. For the price, it's a bargain if you listen to HD650s. Bass is articulate and tight. Imaging and soundstage are very weak on the GS-1K, and acceptable on the HD650. Again, great for the price with HD650s, but there certainly is better for more money.
