Octal Express

[surfsup]

For my next build I am doing a Rocket, Express or Express 4gainstage. Thinking about it I have an x10 clone which is supposedly like an AC30 (rocket?) so maybe a rocket is too much duplication?

Anyone done an octal poweramp on an express?

I have seen references to "all octal" and "octal fatness". As I understand it:

all octal - octal preamp, I don't wanna do that
octal fatness - SE express pre with a single octal PA, I don't wanna do that

I assume if I do this, to "drive" the tubes harder, I will need to bias the PI to output more signal? If I go for it, what else do I need to think about?

[Lonely Raven]

I'm confused...the Power section on an Express *is* an Octal.

I still have my Rocket, which (IMHO) is pretty damn accurate. Feel free to swing by and compare it to your X10. I do think you'll find some overlap with the X10.

I also have an adapter to put a 6SL7 in place of a 12AX7. We can try out an Octal in different parts of the amps we have and see if you like it.

[Cliff Schecht]

I'm debating between an octal Rocket and an octal Express myself (leaning towards the Express, I have enough Rockets!). It seems minus V1 (I'd stick with AX7's for noise/microphonics reasons) the latter would be helluva fun amp to play and would have an interesting character. Maybe voice the thing (Rocket or Express) for KT66 or other big bottles instead of EL34's.. Or a 6550 Rocket? So many choices, so little iron...

FWIW I think a 4-gainstage Express would be utterly useless!

[Lonely Raven]

FWIW I think a 4-gainstage Express would be utterly useless!

I was thinking the same thing.

Your other ideas have merit!

I forgot who it is, but this one builder builds amps in ammo cans, and uses 6SL7 preamp tubes. It's the most greasy, complex overdrive I've heard in a long time...and that's what's got my head thinking about an all Octal Express.

Though I too worry about a noisy octal V1. However, there are military grade 6SL7 that are graded for lower noise.

[surfsup]

Hmm okay so it seems my googling skills are still pretty good and this hasn't been done yet. I am thinking of regular 12ax7 pre with only octal PA.

[M Fowler]

FWIW I think a 4-gainstage Express would be utterly useless!

Perhaps an octal preamp 4 gain stage Express would be useless but not with 4 12AX7s. It is a fantastic sounding high harmonics content gain pleaser to my ears Should have done this to my Ceriatone Express years ago.

Added a serial loop and running Boss DD-3 and Boss RV-4 through it for some coloring.

I still have my nice Distortion's (Larry Mann) Maple Cab Express with Pacific Iron when I want traditional Express tone.

Mark

[Zippy]

Hmm okay so it seems my googling skills are still pretty good and this hasn't been done yet. I am thinking of regular 12ax7 pre with only octal PA.

You have a lot of us confused. What Express are you looking at?

The Express has 12AX7 pre and EL34 output.

What changes are you proposing?

[surfsup]

The Express has 12AX7 pre and EL34 output

Funny, but you're right! For some reason I always thought it was an el84 amp.

Well this is gonna make it simple. I'll just do the layout with one more noval socket.

Mark I've already downloaded those two pics you put up a while back of your 4 gain stage express. I think my mind is set. Rocket will come later. Express4G dataplan is going to start tomorrow. Going to draw up the cad tonight.

[Cliff Schecht]

Can you post the threads? I don't remember seeing those (or caring at the time ).

[surfsup]

Cliff I assume you mean the Express 4G?

https://tubeamparchive.com/viewtopic.ph ... c&start=30

[Zippy]

The Express has 12AX7 pre and EL34 output

Funny, but you're right! For some reason I always thought it was an el84 amp.

If an Express has El84s, it is a Liverpool.

Well this is gonna make it simple. I'll just do the layout with one more noval socket.

FWIW and just so you know going in to the project, the Express has proven demanding of good lead dress. If you try to get clever with an Express, you may be hating it before you get to love it.

G'luck!

[surfsup]

Zippy thanks for that reminder. I wanna do something different. How about an Express with two octal sockets where each has a 6sn7 and each tube has both halves paralleled? I figure that would be about 5W output.

Would 4 gain stages be too much for a 6sn7 tube? I figure if I don't like it I could just rewire the octal pins and put in two el34s since I have both sockets already there.

[Zippy]

Seems like there have been some low power Express experiments also although I tend not to follow them. I'm sure you'll find them if you browse or search the Trainwreck forum. Key on "low power Express".

[surfsup]

Looks like the 6sn7 has a max plate V of 450 on the datasheet and the TWExpress schematic calls for ~390 on the plates so they *should* work...hmmm...I would like a lower power studio amp. Maybe I'll do that, a low power Express 4G.

[ampgeek]

Also take a look at the 6SL7. This is the more "common" octal replacement for a 12AX7. It will give you less gain (~15% to 20% IIRC) than a 12AX7.

That might work in your favor if you are considering a 4 gain stage Express.

They are prone to hum so you might consider a regulated DC heater supply for V1 and V2 right from the git-go to avoid having to roll lots of tubes to find tolerable ones. Specifically, in the V1 slot.

I would retain the 12AX7 in the PI slot to assure that the Express PA "magic" remains intact.

Cheers,
Dave O.