Hey jb26, how are you liking your GB 5751?
I just recently picked up a Sylvania GB 5751 triple mica black plate, but it doesn't have the gold pins. I don't think the black plates were ever made with gold pins, that's the grey plate GB 5751. So now I have tried three tubes in my 901 with Dodd Buffer and battery:
The stock JJ ECC-803S
Sylvania JHS 12AX7
and the GB Sylvania above.
I think my hopes were too high for the GB 5751. I'm also realizing just how many other factors go into finding the right tube for each system, what works for one won't for another.
I started with the JJ tube and loved it and used it for the first 3 months or so that I had the amp.
Then a couple of weeks ago I put in the JHS 12AX7 and I noticed less leaf rustle on the volume pot and a fuller, warmer, very engrossing bass. Donald Fagen's Morph the Cat was awesome! Not only was the bass hard hitting, deep and totally satisfying, it also had texture that I hadn't heard before, a growl that was really cool.
But the vocals weren't sounding as natural, they sounded more processed and I lost the feeling that they were in the room. The dynamics seemed to increase and the vocals seemed a little farther back in the soundstage.
A couple of nights ago I put in the GB 5751 and it was weird. I'm finding that it does some things better than the other tubes and some things worse.
Much more leaf rustling in the volume pot then either of the others.
Instruments are more natural sounding, particularly in the high end, cymbals are outstanding. They were more separated and identifiable.
There's a longer room decay, yet it's tighter or faster, so hard cut outs and attacks are more noticeable.
There's no edginess in the mid highs that I've been getting from the other tubes.
I was playing a cut from the West Side Story movie soundtrack which sounded better than I've ever heard it, and I heard a cello behind the vocals that I hadn't heard before.
In an Aimee Mann song there's a strange aural illusion for a few bars in the backing vocals, they seemed to come directly from the sides of the room, I mean the space directly to my right and left... very cool. But with the other two tubes the illusion seemed to happen only on the right side.
While the vocals sounded a little more natural than the JHS, they seemed to be a little veiled and rounded off. Diana Krall doesn't have the same growl in her voice that is so engrossing.
The low end is very...polite... i.e. not much there. On some cuts it seems really tight and on some others pretty messy. That seems weird...
The dynamics seem even a little wider, yet there seems to be dips or holes at certain frequencies.
The other tubes seemed to have a more consistent character than this one, this one is confusing me. I'll have to listen some more to fully understand what I'm hearing.
I think so far I'm leaning back towards the JJ tube mainly because it feels a little more evenly balanced and the vocals totally draw me in, they're more realistic and believable to my ears. However, all I can definitely say at this point... is that more research is needed
I think I'll try to track down one of those Sovteks and I heard good things about the Raytheon.