6SJ7 to 12AX7 ??

[blodviol]

GrooveTubes have a product called SubstiTubes, and one of the versions claims you can use this and a 12AX7 in place of a 6SJ7.

How is this possible?

Can the 12AX7 be run as a pentode? Or how does it work?

In case of the 6SN7, 6SL7 and 6SC7 versions it's just a matter of changing the pin-outs, I guess. But i just don't get how you can run a double triode in place of a pentode. Maybe i just haven't understood how a pentode works...

Can anyone shed some light on this?

Tríste

[Daver]

I think that besides reconfiguring the pins, the 12AX7 is set up as a cascode in that Substitube to approach the gain of a pentode. You're correct that you can't make a pentode out of two triodes.

[blodviol]

Originally Posted by Daver

I think that besides reconfiguring the pins, the 12AX7 is set up as a cascode in that Substitube to approach the gain of a pentode. You're correct that you can't make a pentode out of two triodes.

I suppose you mean cascade. So if i understand you correctly, one triode stage is fed into the other. Wouldn't that sort of defeat the purpose of a pentode..? What I don't understand is why not use a readily available pentode, like EF86, for instance..?

Tríste

[Daver]

Nope, cascode. One triode is the plate load for the bottom triode. There are several ways to set up the circuit. One type is attached here.

[Arthur B.]

Originally Posted by Daver

I think that besides reconfiguring the pins, the 12AX7 is set up as a cascode in that Substitube to approach the gain of a pentode. You're correct that you can't make a pentode out of two triodes.

I wonder what they do with the screen supply? You obvously can't connect the second grid to that supply because even if you pulled the grid up to the original screen's voltage, it would conduct more than the bottom tube.

[Daver]

My guess would be that they don't connect the screen supply to anything and leave it unused. Maybe one of us should email Groove Tubes and see if they will answer our questions. I'll try.
Daver

[arnenym]

http://picasaweb.google.se/arnhed/ED...98556629436514
I love it!

[blodviol]

Originally Posted by arnenym

http://picasaweb.google.se/arnhed/ED...98556629436514
I love it!

6SJ7 is very different from 6SL7, which is a double triode like 12AX7. The 6SJ7 is a single pentode. And don't put one in your amp!!

Is that the swedish 5E3-lookalike?

[blodviol]

Originally Posted by Daver

My guess would be that they don't connect the screen supply to anything and leave it unused. Maybe one of us should email Groove Tubes and see if they will answer our questions. I'll try.
Daver

Did you get a reply from GT?

Tríste

[arnenym]

Originally Posted by blodviol

6SJ7 is very different from 6SL7, which is a double triode like 12AX7. The 6SJ7 is a single pentode. And don't put one in your amp!!

Is that the swedish 5E3-lookalike?

Sorry, i mixed up SL, SJ and SN,, A letter could mean so much...
Yes ,it is my Edgar audio-amp, a "sortof" 5E3 from sweden. It got some improvements and is totally free from hum and got this little speciallity..

[Daver]

No, no reply. Sorry. Anyone out there know a distributor or someone else that carries them that might be able to get some info?