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Unread 01-20-2011, 04:05 PM   #1 (permalink)
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In Search Of a simple 18 Watt Schematic

Trying to save a little design work.

Looking for a schem for a 2xEL84 18 watt TMB (no tremolo), with just a single channel.

Master volume would be good as well.

I have a transformer set from an RCA console I am thinking about converting.
Current tube compliment is 5Y3, 2x12AX7, and 2xEL84.

I've looked around the usual sites and have only found two channel versions.
Thought someone might know about something already designed that I could save some time with.

Thanks!
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Unread 01-20-2011, 04:17 PM   #2 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Aren't most of the 2 channel ones, just splitting V1? Instead of 2 channels, why not make the first gain stage a dual triode, like the high input on the normal channel on a 18watt or LiteIIB. I did one like that years ago, with a master volume. Ceriatone used to have a layout for one with an ef86 channel and a 2nd channel wired up like a dual triode. You can use that as a reference, just leave off the ef86 channel. That was years ago so, I don't know if it would still be there though? ***edit I didn't notice, you had 2x12ax7's. The one I was talking about used 3.
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Unread 01-20-2011, 04:18 PM   #3 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Just leave out the second channel. If the two channel schematic uses mix resistors and goes into one side of the PI, just omit the second channel. If the two channels go into opposite sides of the PI, just omit the second channel and have the now unused side of the PI go to ground through a .1uf cap.
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Unread 01-20-2011, 04:30 PM   #4 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

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Originally Posted by Lyle Caldwell View Post
Just leave out the second channel. If the two channel schematic uses mix resistors and goes into one side of the PI, just omit the second channel. If the two channels go into opposite sides of the PI, just omit the second channel and have the now unused side of the PI go to ground through a .1uf cap.
First channel is vol/tone, second is TMB.
I glanced at the Ceriatone and my tired brain said "whu"?
Vol 1 runs to V2, Vol 2 runs to V1, and an appearance of a cross-mash in between.
I'm really trying to cut down on one of the 12AX7's here.



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Unread 01-20-2011, 04:43 PM   #5 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

There are tons of 18W schematics out there.

Have you tried AX84.com - The Cooperative Tube Guitar Amp Project?
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Unread 01-20-2011, 04:48 PM   #6 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

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Originally Posted by Lyle Caldwell View Post
There are tons of 18W schematics out there.

Have you tried AX84.com - The Cooperative Tube Guitar Amp Project?
Yes.
P1 extreme and Hi Octane don't match my idea of the PP EL 84.

But tying in only the P1 preamp might be the ticket.
Hmmm.
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Unread 01-20-2011, 04:53 PM   #7 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Haven't looked at the Ceriatone but it sounds like a cascaded input.

Roll your own.

Just take the 50W Plexi schematic and adapt it to a cathode biased 2 EL84 output stage (you can pretty much use the AC15 output section adding in the 50W Plexi's negative feedback and presence control instead of the Vox "Cut" control).

If you don't want the dark/bright inputs of the Plexi just run V1 in parallel and omit the unused input/volume section.
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Unread 01-20-2011, 05:00 PM   #8 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Man Lyle you are FULL of info, I havnt seen you post a reply that hasn't helped someone out...fair dues and nice work

good luck cyg, I was looking for a kit that was an 18watt marshall with 1input and tmb and a master volume. I gave up after a while.
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Unread 01-20-2011, 05:04 PM   #9 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

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Originally Posted by Lyle Caldwell View Post
Haven't looked at the Ceriatone but it sounds like a cascaded input.

Roll your own.

Just take the 50W Plexi schematic and adapt it to a cathode biased 2 EL84 output stage (you can pretty much use the AC15 output section adding in the 50W Plexi's negative feedback and presence control instead of the Vox "Cut" control).

If you don't want the dark/bright inputs of the Plexi just run V1 in parallel and omit the unused input/volume section.
That was my first impression.
Then the fog overtook me.

I'm somewhere halfway between a "paint by numbers" guy and a "designer".
I'm just way too familiar with the Fender circuits and my own Cygnus-7 (SEL).

Thank you Lyle, keep it rolling...
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Unread 01-20-2011, 05:08 PM   #10 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

http://www.el34world.com/charts/Sche...s_spitfire.pdf

How about this?
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Unread 01-20-2011, 05:13 PM   #11 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

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Originally Posted by moldymealworm View Post
Great minds think alike...I have already built it.
I played it for about a year and then tweaked it literally to its demise.
I was trying to get rid of a hum I couldn't track down, and she is sitting on the far corner of my "bench of doom".



Wait, I found something.

What do you all (y'all) think of this?
Not TMB, and not really Spitfire.
MV should be easy enough to throw in.
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Unread 01-20-2011, 05:34 PM   #12 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

That's not ideal at least as shown. No grid resistor on the input, no presence control, I think that's wide of the mark.

Thanks viva-la-punk!
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Unread 01-20-2011, 05:48 PM   #13 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Here ya go!
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Unread 01-20-2011, 05:49 PM   #14 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Quote:
Originally Posted by Lyle Caldwell View Post
That's not ideal at least as shown. No grid resistor on the input, no presence control, I think that's wide of the mark.

Thanks viva-la-punk!
True, and I think I want more gain.
P1 preamp married to an EL84 P-P seems to be the mark.

I had a heck of a time getting a tone I liked out of the Spitfire...it sounded too much like a thin saturated AC15, not a good sound to me.
It spooked me until I got the EL84's down to realistic operating specs.
I think it went from some 360 volts on B+ to around 325.
Closer to their design.
I read the filament design of the EZ81 may have been the source of the hum issue.
It needs the filament separated from the rest of the tubes?

For all that I'd rather just go with a diode setup to avoid the headache.
But then I'd have some trouble getting the B+ where it needs to be, keeping in mind I'm using old iron.
Might stick with the 5Y3.
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Unread 01-20-2011, 05:51 PM   #15 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Yeah, no need for the hassle, heat, and current requirements of a tube rectifier. Diodes for this amp.

And I really recommend a 10H choke.
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Unread 01-20-2011, 05:51 PM   #16 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Quote:
Originally Posted by Cygnus X1 View Post
Great minds think alike...I have already built it.
I played it for about a year and then tweaked it literally to its demise.
I was trying to get rid of a hum I couldn't track down, and she is sitting on the far corner of my "bench of doom".



Wait, I found something.

What do you all (y'all) think of this?
Not TMB, and not really Spitfire.
MV should be easy enough to throw in.
I think you're selling yourself short here...
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Unread 01-20-2011, 05:53 PM   #17 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Quote:
Originally Posted by NSCS View Post
I do like that idea, but there is no way a power transformer designed for only four tubes could support all of that current.
And my planned chassis is only 13.5x5x2 inches.
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Unread 01-20-2011, 05:54 PM   #18 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Quote:
Originally Posted by moldymealworm View Post
I think you're selling yourself short here...
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Unread 01-20-2011, 05:57 PM   #19 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Quote:
Originally Posted by Lyle Caldwell View Post
Yeah, no need for the hassle, heat, and current requirements of a tube rectifier. Diodes for this amp.

And I really recommend a 10H choke.
Good point on the choke.
It would thicken the tone in the recipe.
I have a 9H/120ma kicking around, which should be perfect.

But without looking, don't diodes have minimal voltage drop?
The B+ would be whatever the PT puts out wouldn't it?
That's why I was thinking about staying with the 5Y3 that ran with that RCA transformer.
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Unread 01-20-2011, 06:01 PM   #20 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Quote:
Originally Posted by Cygnus X1 View Post
I do like that idea, but there is no way a power transformer designed for only four tubes could support all of that current.
And my planned chassis is only 13.5x5x2 inches.
It is only 4 tubes, aside from the optional tube rec of course. 2x 12ax7 and 2x EL84
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Unread 01-20-2011, 06:03 PM   #21 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Hmm, it's really hard to get a good range of drive and a usable tonestack with just two 12AX7s.
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Last edited by Lyle Caldwell; 01-20-2011 at 06:52 PM.
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Unread 01-20-2011, 06:04 PM   #22 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Quote:
Originally Posted by NSCS View Post
It is only 4 tubes, aside from the optional tube rec of course. 2x 12ax7 and 2x EL84
I was looking at the schem.
I must be seeing double, or not looking at the splits correctly.
I thought I saw eight preamp tubes or sumpin' there.

Allow me to return to your excellent post...I'll report back if I return from that realm.


Edit.
OK, yes...(duh), I remember now, it's all coming back in a rush.
Reading the text is a BIG help!

Lyle, to our amazement the higher gain TMB is indeed available with just two triodes.
All we have to do is look at the SEL which I tweaked into my "Cygnus-7" and the answer lies within.
Tweaking meant swapping out parts and pieces...and values until I was happy with the tone/drive of the amp.
I certainly didn't gain much useful knowledge in the process, just good, quiet tone.

Everyone, take a break.
You (and the coffee) have stirred my sole surviving Brain Cell to condense this down to fit the parts.
Thanks!
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Unread 01-20-2011, 06:59 PM   #23 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

It's always a trick. One good schematic you should check out is the Dr Z Stang-ray. EF86, phase inverter, power section.
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Unread 01-20-2011, 09:36 PM   #24 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Cyg, how about this? It's the build I am currently working on. I'm sure you have some old iron that will work. Use a beefier rectifier and adjust the voltages as you like. This build is 12 watts as I'm using the Bell iron.

It has an OD toggle on V1 which you could ditch if you want to keep it simple. I haven't designed the NFB circuit as I'm not sure what I want to do with it. I put it in for experimentation. The MV may require some tinkering as I'm trying something new.


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Unread 01-22-2011, 04:28 PM   #25 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

I agree with everything Lyle has said here (Specifically running V1 in parallel. Perhaps even have it switchable for a "thick boost" type thing). Man you're a wealth of correct info.. Definitely adding value to the community here.
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Unread 01-22-2011, 04:31 PM   #26 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Thanks Mike! I like places where I can be a total music geek without getting the weird looks (my girlfriend's eyes kinda glaze over when I talk about my work).
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Unread 01-23-2011, 07:38 AM   #27 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Quote:
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Definitely adding value to the community here.
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Unread 01-23-2011, 07:50 AM   #28 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Quote:
Originally Posted by MikeM View Post
I agree with everything Lyle has said here (Specifically running V1 in parallel. Perhaps even have it switchable for a "thick boost" type thing). Man you're a wealth of correct info.. Definitely adding value to the community here.
+1. Really enjoying your input on all things amp related, Lyle.

Is parelleling V1 the same as jumpering the two channels in my 5E3, cause if it is it makes for a great sound; much thicker.
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Unread 01-23-2011, 07:56 AM   #29 (permalink)
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Re: In Search Of a simple 18 Watt Schematic



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Unread 01-23-2011, 08:05 AM   #30 (permalink)
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Re: In Search Of a simple 18 Watt Schematic

Check out the TMB superlite.

18 Watt Community Center - Access Denied

I suggest you get a login for the 18watt.com forums.

18 watt marshall clone, need suggestions please

I will PM you the email.
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