6SJ7 Rocket?

[andrew]

Has anyone built a Rocket using a 6SJ7 for V1?

[Cliff Schecht]

Are you using it as a pentode or triode? In my experience 6SJ7's sound quite different than a triode in any position but do have a great distortion sound.

[andrew]

I would like to set it up like http://www.aronnelson.com/gallery/main. ... h.GIF.html. I would like to use the Rocket tonestack and Rocket power section with KT-66s and a Pacific 6.6k OT.

[M Fowler]

Lot of stuff on that link but I didn't fint the Doug H stuff unless you mean the Ocatal Fatness he built?

[andrew]

Yes.That's the one.

[M Fowler]

I would rather use the EF86 or 12AX7 then the Octal tube in a Rocket but anything can be done. I have built a few octal preamp projects and they have a nice tone all their own. The Gibson EH150 finished last weekend has a lot of volume 375-0-375 PT and 4k3 OT 50w rating. Running three 6SQ7 in the pre, mid-amp, and overdrive. The PI is 6N7.

The Fender 5b6 uses a great set of octal preamp tubes as well. Two 6SC7 in pre and PI and two 6L6 nice sound tone too.

[andrew]

I wasn't looking forward to drilling an octal hole in my Rocket chassis anyway. How about a 12ax7 wired up as SSRP? I have not had any experience doing that but I have read that it sounds similar to an EF86.

[andrew]

Sorry--SRRP

[Cliff Schecht]

Looks like they are using the 6SJ7 to make up gain that is lost with the elimination of the PI section. Funny how similar this circuit is to something I developed about 6 months back using the same idea..

That design is going to sound radically different than a normal Rocket though. A 6.6k SE transformer isn't too common, me thinks you're better off with a standard 5k unit. I've used 3k-10k on quite a few designs and 5k seems to be the best trade off between the amount of distortion you can get in the PA and the amount of power you can get at the output.

[andrew]

Sorry I wasn't clear. It would be push pull with the usual rocket power section.

[Cliff Schecht]

Well in that case you are looking at eliminating one of the triodes to shove in a pentode I assume. I think the "problem" here is that a pentode can easily have 5 times the gain of a triode so you'll have to adjust the circuit accordingly and may change the sound of the amp considerably. If you stick with the datasheet biasing values (or similar) for the 6SJ7, you'll be able to get a fairly linear stage and could just drop the screen down pretty low (voltage-wise) to get the gain to a more usable level. Or you could try to squeeze a LOT of gain out of the pentode and maybe eliminate V1 completely. Just some thoughts..