With the Darkvoice and W5000, there is only one tube that has satisfied me in every aspect: The grey glass RCA 6SN7GT (or VT-231, identical tube). It's the tube I loved with the K501, and I dunno why the hell I didn't try it on the W5000 sooner. I've been going back and forth between it and my other tubes the last few days, and I can't really find any aspects where it doesn't win in my system. It's a little thick in the midbass, with less low end slam, which is the exact opposite of the W5000, so it fills out to the perfect combination of bass slam and warmth. The sound is very lush and smooth, with some kind of almost magical ability to counter the weird frequency response on the W5000. It's great with fast & clear phones like the W5000 and K501, but probably your last choice for any headphone that starts off too warm or recessed (I don't even want to imagine how thick and syrupy this tube would sound with the HD650
). The highs seem to have a bit of a slow rolloff compared to other tubes, so you need a good, strong treble response on your phones to avoid problems there.
Neither the Darkvoice nor the W5000 have what I would call a big soundstage, so the RCA's smaller, more intimate sound isn't a problem for me, and works great because it doesn't try to make the W5000 do more than it actually can for soundstage.
It is by far and away the most "musical" tube I've used. I can't even analytically listen to it if I try, I just get lost in the music for several hours at a time, even if I only meant to check how one track sounded. The music just
flows.
I've also been using a Svetlana 6H13C for the output tube, which I haven't had any complaints about at all. Both of these tubes are easy to get real cheap, so that makes me even happier about the combo!
I
really wish I could give my thoughts on this tube with more common phones like the K701.
