100th post (101th...), at last I feel like I'm finally credible here lol.
I let my 6EW6 burn in for about a business day while I was at work today, but even listening after this, I feel that I can't quite reach a conclusion on these yet. I tried the GE 6AG5 really quickly earlier (which I don't expect to be using anyway as they aren't physically matched), my only conclusion would be that this family could show great promise, but not necessarily these old world 6AG5s. Still, I noted a nice slightly tube-y sound signature, and imagining a more selected/military model, I'm sure that family could reach great performance. Again, 6AK5 jumper settings for the 6AG5.
Speaking of changing jumpers, as I had to go from the EF92 setting to the 6AK5 one and back, I gave myself quite a scare testing my GE 6676/6CB6A earlier... I put them in, turned the amp on, heard a slight noise, and the driver tubes filaments took like 10 seconds to begin lighting up, and the power tubes also. I listened for a bit, and found similar impressions compared to my other CGE 6676 tubes. When I switched the amp off, it made a loud BZZZZZ sound for a few seconds, that had me pretty worked up. So I tried switching the amp on again with the same tubes, this time the filaments lit up right way but as soon as I tapped the amp with my finger, the 4 filament just went dark. I was literally convinced I had killed my amp by burning in a 400 mA filament current tube for the whole day... So, I reached for the plug to try and troubleshoot the issue, and it turns out the plug had come loose after fiddling with the amp to change jumpers twice. I put the plug back in, started the amp back up, it worked perfectly, I started breathing again. Lesson learned, check cables after putting the amp upside down a couple of times...
Anyway, after that heart-stopping problem, i resumed testing other tubes, and tested my fourth pair of tubes, the very odd spec-ed 6GX6/6GY6 (which actually has 6GY6 etched in the glass). Very high heater/filament current draw at 450 mA, but very un-audio like specs with transconductance and plate current (the specs I've convinced myself have the highest influence on "power") lower than a 6AK5, and meant to be a "dual control pentode" for FM detection, a far cry from nice sharp-cutoff pentodes well-suited for audio -as a pentode that is. It turns out these dual control pentodes once triode-strapped work very well in audio circuits for some mysterious design reason (look it up on google).
So, after a couple of hours with these tubes, I can say these are the best in my latest batch of non-LD certified tubes; outrageous performance for $3 a pair... And they aren't even burnt-in yet, holy schiit... Apart from the bass -which is a bit lacking in slam- and the volume (which is as high as a 8136 or a 6676, just low for a 450mA filament current draw), these are some of the best tubes I've put in my LD amp. They're just natural, basically. Sounds come in the most natural and detailed way from logical directions around your head, and proceed to give you constant small eargasms, that themselves sound like the most natural thing to be having while listening to music with these tubes. I'll hold off on describing these with real audiophile words until they're burnt-in, but seriously these are quite a discovery!
As a matter of fact, it's the use of "crappy" TV-intended very specifically designed dual control pentodes -and not signal pentodes- in audio systems that is interesting (again, google it), as they make extremely linear -and very inefficient- triode-strapped pentodes. I'll be looking for more tubes with specs like this, as there have been many made throughout the years, apparently
The last tube I intend to spend time with is the 6GM6 I got (high transconductance, very high plate current), which should sound glorious triode-strapped. That might have to wait until this weekend, as I end up not having enough time to actually test all my discoveries ;) ...
GE 6AG5 (two different structures)
Military GE 6EW6
Edit: my only worry with the 6GX6/6GY6 triode-strapped is that I'm pretty sure it's way over its heat dissipation specs (it is meant for 1.7W plate dissipation, which is like half of a 6EW6) as the control/suppressor grid(s) no longer serve their purpose as they are tied to the anode. Just food for thoughts.
Edited by Audiofanboy - 3/6/13 at 12:15pm