Hmmm. I was getting really tempted by all this 596 talk, but it looks like you guys have snatched them all up off ebay!
Just as well, since I have my doubts the tube physically works in the WA6 due to its width. I'm more than content with the GZ33 anyway, which I've decided I like better than my EML274B overall. I'm trying to break the idea that I have to buy a backup as soon as I find a tube I like, because its expensive to fuel such paranoia and the Mullards have a reputation for being very hearty and long lived. I can't help but fear, though, that if I find myself needing one a few years from now it will no longer be possible to find one.
I've gone through nearly every 6SN7 driver tube I have with it now except for the BGRP (still considering it). The National Unions were more of a fluke than anything, since no other tube had such a Jekyll and Hyde sort of reaction the way they did. Not every tube became more dynamic and lively either, which was another interesting surprise. The way it broke down more or less is like so:
Tubes I thought sounded better on the GZ33 vs. the EML274B overall:
- National Union Blackglass 6SN7GT
- Sylvania Chrome Dome 6SN7GT
- Sylvania 6SN7W
Tubes I thought were more or less a wash overall:
- Raytheon VT231 ladder plate
- Brimar 6SN7GTY
- Sylvania "Bad Boy" 6SN7GT
- Sylvania 6SN7GTA
Tubes I thought sounded worse:
- RCA VT231 Greyglass
- Tung Sol 6SN7GT Mouse Ear
In the case of the Mouse Ear and the Greyglass both tubes sounded dull on the GZ33. The Tung Sol was the biggest surprise with a strongly subdued top end where as these tubes usually are pretty bright and sparkly up top. It shifted the focus into the lower mids, but something about the overall balance felt off. The Greyglass just came across as veiled and lazy sounding, which was totally not what I was expecting.
For the tubes in the middle group, there was always something gained and something lost which ended up balancing out. Well, except for the Raytheons which sounded nearly identical to how they behave on the EML except for a slightly more pulled in soundstage. The Syl GTAs improved considerably, but gained a harsh glare in the upper mids that was hard to look past. The Brimars didn't sound that different, but again they sounded more forceful in the upper mids, so the small gain in focus wasn't really worth it. I think I like this tube better with the Brimar 5R4GY. The Bad Boys have their bass tighten up quite a bit, something they really need in my experience. It also sharpens their transient response and makes them less romantic sounding. But this is a double edged sword, because when you take that romanticism away they don't really feel special anymore. I found myself a little bored listening to them, desperately wanting to roll the Chome Domes in in their place.
As for the winners, the Syl W's simply improve all around. Bass gets faster and tighter, the veil is lifted for the most part, and they display the big lively sound they are known for. I found the treble a little more peaky than usual, but the other gains make it worth dealing with.
The National Unions, like I wrote about before, sound radically different. They absolutely come alive, with huge powerful bass that grabs your attention and big bold dynamics. The sound is rich and vivid without sounding overdone or or exaggerated in any one area. I like the NUs when they are a laid back and romantic tube, but I love them like this. A new favorite pairing for me. Finally, the Chrome Domes, which I love anyway, gain a little more of everything on the GZ33. The soundstage even grows wider, which was surprising. My only gripe about this tube, that it has light bass, is not a problem here. It has quantity and weight to go with the amazing speed and drive it always had before. Everything sounds true to life, with a "your are in front of the recording microphone" sort of realism. They pick up a very slight unwanted edginess in the low treble range, but nothing that can't be forgiven. The only bad thing I noted was that their tonal balance doesn't feel as uncolored and neutral on the GZ33, there is definitely a flavor there now even if it is subtle.
So far the Chrome Dome + GZ33 combo is the most lifelike sound I have ever gotten from my amp. I wasn't going to try the Tung Sol round plates before, but now I think I'll have to. The most consistent improvement was in bass speed and drive. Neither of these things are strong points of the EML 274B, and because of this I think if I ever have to replace it I will go with an EML 5U4G next time.