Help me design this amp

[Nathan]

Hi all, I have me a little chasis that is begging to me modified into a little tone machine. I have a few ideas, but could really use some help. Here goes:

It's a 2 EL84 amp with 2 12AX7 in a 1x12 cab.

I would like to scrap the circuit board, keeping the tubes and trannies. Can you recommend a schematic that would sound amazing with these tubes? If there's a design with reverb out there (single knob) it would be a plus!

P.S. I have a Hoffman Plexi 100 board all wired up. If that could be used in part (or for parts), it would be cool too.

**I really appreciate your help!**

 

[stekks]

you could make Marshall 18W copy, with just one channel. Maybe use only the treble/mid/bass pre-amp version (TMB) which uses one preamp-tube and the PI uses one.

www.18watt.com

 

[loverocker]

If you like the EL84/18Wer tone, go for that.

Otherwise - if that 100 board fits - I'd widen the EL84 socket holes to octal, put a pair of 6V6s in which'd free up some heater current for another preamp valve, and then I'd use the 100 board with almost no mods (just a Post-PI MV) to make a Baby 20Wish plexi.

I.E. I wouldn't bother with reverb

 

[Nathan]

Hmm I like that idea. I have some 6V6's lying around doing nothing too. My big question is regarding current and matching stuff.

1)Why 6V6?

2)Would I need to use filter caps for the 6V6's or caps from the EL84's?

Someone did a 6V6 Plexi mod to a Traynor amp and posted the details online.

Please list all details if you know what to do! And keep the suggestions coming!
Thanks a bunch!

 

[hasserl]

Naw, go with the 18 watt lite. Two gain stages, a volume and a tone control in between them, a LTPI and the power tubes. A simple uncluttered circuit, easy to build, you have all the main components, and tone to die for. Match that with the right speaker and you'll have likely the best sounding amp you'll ever come across.

 

[Boogie92801]

Make it a Lightning.

 

[Nathan]

Sounds good guys -I'll probably go for whatever looks the most straightforward. I am still a novice even though I built an Allen Tonesavor from a kit. Please point me to the schematics or detailed pointers! Thanks

 

[doctord02]

www.18watt.com

sign up, then go to the downloads section. You want the 18wattLite2 schematic. The direct link is here:

http://18watt.com/Storage/18wattLite2.gif

edit-

Better yet, use this updated one:

http://18watt.com/storage/18wattLite2b.gif

 

[hasserl]

My bad, I thought there were two stages cascaded, not parrallel. Sorry for the misinformation, and thank you good Dr. for clarifying it.

 

[loverocker]

If you want to keep it really simple and fast to build, you can't beat the 18W Lite. Here's my version with solid-state rectifier (you didn't mention whether your donor had a valve rectifier):
* Schematic - http://www.ampmaker.com/pp18guide/pp18sc2.jpg
* Board layout - http://www.ampmaker.com/pp18guide/pp18tb4.jpg

If you want more gain from the 18Wer, there's a simple way of rewiring the front end to cascade the preamp stages (search 18watt.com for 'hotswitch'.

My 6V6 idea was just a way of using your board to maximum effect. It's quite a lot more complicated to layout than these 18W circuits.

 

[Nathan]

Hey, I can try both. I have a Texas Heat in the 1x12 combo and a 2x10 extension cab that might sound even better. That color diagram makes it dead simple loverocker. Thank you!

-How hard is it to add bass, mid, treble to the 18watt Lite2? I have aq whack of knobs there now and don't want to leave bare holes in the chasis. Might as well use them.

-Another question: is it possible to use the Plexi 100 board with the EL84's?

-I noticed Mark Huss did the schematic for the 18watt lite. He did the 6V6 plexi that I found as well!

-Any idea of the difference in soudn between the 6V6 idea and the 18w Lite?

 

[hasserl]

Running a full tone stack will eat up a lot of gain, the 18 watt circuit really won't support that. You need another gain stage to include a cathode follower to get the traditional marshall style pre-amp. You don't have enough gain stages with two 12ax7's to do that along with a long tail PI, which is essential IMO for this style amp. However, I have a schematic here of a Carvin Vintage 16 amp with my modifications, this is an excellent sounding amp, very Marshallish with more gain than an 18 watt when you use the Raw control. Ignore the Reverb and connect the tone stack out to the PI in. Controls are Volume, Bass, Mid, Treble, Raw and Master Volume. You may not have enough spaces for all those. In that case I would leave off the Mid and use a resitor in place of the pot. If that's still too many I would drop the MV.

http://members.dslextreme.com/users/rlhasse/CarvinMods/HasseV16modschem.pdf

 

[Nathan]

This is really good stuff everyone. Thanks! I believe the way to go is to begin with simple (one of the 18 watts) followed by the 6V6 plexi if I'm not totally satisfied, and then the Crate! I'm very excited. I have lots to work from here! Super cool.

 

[loverocker]

Originally posted by Nathan
-Another question: is it possible to use the Plexi 100 board with the EL84's?

Well, the Plexi board with EL84s might be marginal on the amp's power transformer. If it was specced for 2xEL84 and 2xECC83 and no more, an extra ECC83 in the preamp (needed for the plexi circuit) could be too much (which is why I suggested the 6V6 which would free up some heater current for the extra valve).

It may be OK with 3xECC83 and 2xEL84s, though. That allows you to use the Plexi 100 board, and is very close to one of the well-documented www.ax84.com projects (the November, I think).

Originally posted by Nathan

-Any idea of the difference in soudn between the 6V6 idea and the 18w Lite?

Well, like for like I associate EL84s with a brighter distortion, with 6V6s being less aggressive, creamier. But you can tweak either circuit to compensate anyway.

And like hasserl says, if you want a TMB tone stack, you need an amp with more gain than the 18W (like the plexi, or the TMB version of the 18W over at www.a18watt.com).