Singlepower tube rolling thread

You knew this was coming, didn't you?

I'm going to post a couple of fast impressions of some tubes, and fill in gaps as time goes by. I'm hoping that others will also report tube-rolling experiments, so we can build a database of what tubes work best with Mikhail's amps.

I also want to point out that tube construction changed over time. If you don't have NOS tubes with dates on the box, it becomes important to look at the tubes really hard. Find matching date codes if you can. There are some small differences in construction from year to year that do affect the sound of the tube. If you've got a mismatched set, the sound won't be as coherent as it should. IMO it's more important that the tubes be the same construction than that they be matched electrically. IME the Supra sounds better with slightly mismatched tubes that are identical than with electrically matched tubes that may be from different years.

OK, I'll start with the standard. Sylvania VT-231, 1940's production. Also known as Sylvania 6SN7GT, or JAN-CHS-6SN7GT. If they were made at the same time, they're all the same tube, regardless of label. And they all sound good. However, there was a change in contruction around 1953 or so, and tubes made before that are considered more desireable. If this is the only tube you've heard in one of Mikhail's amps, it may be all that you will ever need. A good set has the complete package. Good high end extension, a warm and full midrange and decent bass extension. Imaging is precise and the perceived staging is wide. What could be better?

JAN-CKR-6SN7GT aka Ken-Rad VT-231. Clear or dark glass doesn't matter, but it must be the staggered plate version. Here's where it gets weird. I didn't like this tube early on. I thought it had a hard area in the midrange that gave the Sylvania a clear edge. I was wrong, I think. I've now tried two sets in the past week, and there's no trace of the hardness I heard before. My suspicion is that the amp had not fully burned in when I tried them, and that what I was hearing wasn't the tubes, but the amp itself. It's also possible that it was a cabling or source issue, since there have been a lot of system changes since the early tuberolling attempts. Right now, these tubes are heaven. Extended highs, a crystal clear midrange lacking some of the Sylvania's warmth, and an extended bass response. Interesting, actually, since these were also the tubes I eventually settled on with the MicroZOTL when I had one. They've got something that eventually brings me back to them. The level of detail seems higher than it is with Sylvania's, and the bass impact of these tubes really comes through on the R10.

So, at least for these two tubes, I'd go with the Sylvania if midrange warmth is critical, and with the Ken-Rads for a more balanced presentation. I'm a big fan of balance, and right now the Ken-Rads seem to be hitting the spot. But I'd always have a set of the Sylvania's nearby...

more to come...

I have indeed been using a 6SN7A in the driver position with the VT-231's lately, but was going to report on that in a later post. One of those went on Ebay this morning at $107 for a single tube

The tube combinations are where it's going to get interesting. I had tried the RCA VT-231, and thought the high end didn't cut it compared to Sylvania's. However, I heard CD44hi's MPX3 with a Ken-Rad in front of RCA's, and it was a different story. Nicely balanced sound. The key tube does indeed appear to be the driver (right hand tube). I've been able to get away with a lot as long as I keep a good tube there.

I like the 6SN7A metal base as the gain tube a lot. It seems to add a bit of texture and really maxes out the detail of the amp. The downside is that the sound gets a bit dark. The tube I have is fairly low Gm, and dynamics seem to suffer a small amount.

Another interesting tube is a weird Sylvania 6SN7GT from 1950-52. Unlike most bottom-gettered Sylvania's of the time, it doesn't have the T-plates. It uses slightly staggered flat plates, looking very similar to an RCA tube. There are both black and gray plate versions. The gray plates are very dynamic, and throw a huge image, but ultimately I found them fatiguing. The black plates sound nothing like the gray plates, and are very close to the VT-231, IMO. These tubes transmit an enormous amount of detail. I had initially thought that they might be slightly dark, but am not sure anymore. I've done a much more careful job of date matching, and switching tubes around until I've got the right tube in the gain position (the only way I know how to do this is to use my test results as a first attempt, then just move them around and listen until it's right). I still don't have the full measure of these tubes, but they are a lot of fun to listen to.