36w JCM800?

JohnnyCrash · Post by **JohnnyCrash** » Sun 07/23/06 9:20 pm

After completing the AX84 Hi Octane and being shown the similarities between it's preamp and the JCM800's, I started thinking "why not a 36w power section with a JCM800 preamp?".

Any thoughts on this? Technical or otherwise?

I love the normal 36w build, but I'm a metal junkie and would like several cool amps for different things... perhaps I should string one together.

I know it may not be an original thought - I thought I saw a 2203/2204 thread in the By The BBQ section... I assumed this was for the normal 50 or 100 watt "stock" versions though.

Chubsman · Post by **Chubsman** » Sun 07/23/06 9:37 pm

Only prob is that a jcm800 uses both sides of the 1st 12ax7... so you would have to add a 4th 12ax7 to your 36w.

JohnnyCrash · Post by **JohnnyCrash** » Sun 07/23/06 11:57 pm

If it's the full front end of a JCM800 going into four EL84s, it should still only need the two preamp tubes and the phase inverter. Well, I'm guessing...

I need to crack out the schems again

phsyconoodler · Post by **phsyconoodler** » Mon 07/24/06 12:24 am

If you build the 2204 and lower the plate voltage to 36 watt specs and use the appropriate resistors to keep the preamp voltages the same as the 2204,it would work just fine.A normal 2204 runs anywhere from 420 to 470 plate volts and thats usually too much for an EL-84.The reason I say 'usually' is because there are many EL-84 fixed bias amps out there that do use up to 420 plate volts.
So you need to use an appropriate PT and use basically the same layout for the rest of the amp as the 2204.If you were to use a tube rectifier instead of diodes like the 2204,you would have an easier time getting near the correct voltages.There are also several mods for the 2204 circuit that gets you almost into scouped metal zone like a boogie.One more preamp tube would get you there and then some.
Now take a 2204 and use 6V6's and there are a minimum amount of changes you need to do.And then if you really want to,take a 2204 and set it up for 6550's and use TAD yellow jackets and you've essentially got a class A EL-84 2204.Grindy little bastard of an amp.

Chubsman · Post by **Chubsman** » Mon 07/24/06 8:55 am

Then why does my 36W use one side of the 1st 12ax7 for the norm chan and the 2nd side for the TBM side...

And my 2204 use both sides for 1 channel only?
If I could slap a 2204 preamp into my 36w and keep the normal channel... i would be in heaven.... Doable?

Post by **rjgtr** » Mon 07/24/06 9:30 am

Chubsman wrote:Then why does my 36W use one side of the 1st 12ax7 for the norm chan and the 2nd side for the TBM side...

It is just a different design. On the 36w and the 18 watt the phase inverter is used to mix channels. On the 2204, there's really only one channel, so it all goes to one side of the phase inverter.

And my 2204 use both sides for 1 channel only?
If I could slap a 2204 preamp into my 36w and keep the normal channel... i would be in heaven.... Doable?

To do this you'd need to add another tube or you could convert the cathode follower of the TMB channel into a gain stage and use a plate fed tone stack. This would get you very close to the sound of a 2204 on a 36w platform. You'd just copy the the 2204 preamp up to the CF and leave it off. Then just feed the tone controls from the plate of the last tube. I'd change the 500p treble cap to a 250p in this case to keep the tone control response similar to the cathode fed one.

phsyconoodler · Post by **phsyconoodler** » Mon 07/24/06 1:25 pm

Just install a post phase inverter master volume into your 36 watt and add Doug Hoffman's hot switch to cascade the gain stages and you don't have to radically change your circuit at all.Or just use a series/parallel input arrangement like the lite 18 watt uses.
I am assuming you want to get it to grind at lower volumes?Or are you thinking you need a better EQ section?

JohnnyCrash · Post by **JohnnyCrash** » Wed 07/26/06 9:59 pm

I'm looking for more grind.

I've got a Hi Octane I just finished and it is a BEAST.

I like the 36 watt, but it's much more "classic rock" sounding. Still I don't want to "fix" something that aint broken. I like it fine, just contemplating another build.

Chubsman · Post by **Chubsman** » Wed 07/26/06 10:29 pm

Thanks rjgtr

I will try this...!!! I might bug you for assistance...

rollingelbow · Post by **rollingelbow** » Mon 09/11/06 1:30 pm

Am I the only one who doesn't like their High Octane? Is it the AX84 HO? Cause mine just blows for me. Muddy..as per my other thread in by the bench. Flubs out.

JohnnyCrash · Post by **JohnnyCrash** » Sat 09/16/06 2:03 am

rollingelbow wrote:Am I the only one who doesn't like their High Octane? Is it the AX84 HO? Cause mine just blows for me. Muddy..as per my other thread in by the bench. Flubs out.

I am not super happy with mine when it's in low volume settings...

BUT, with a 6EZ5 power tube and cranked up (power tube cookin) it sounds KILLER.

It sounds very very similar to my older 80's JCM800s (which I sold like a dumbass)... no bass flub-out for me whatsoever.

Mauri · Post by **Mauri** » Thu 12/14/06 7:16 am

hey I am very interested in building an amp with the normal channel of the 36W and a jcm800/high octane channel ( http://www.18watt.com/modules.php?name= ... ic&t=14285 )
and make it footswitchable too. Has anyone got any layout or schematics for this? *hint hint Chubsman*

phsyconoodler · Post by **phsyconoodler** » Wed 01/10/07 7:50 pm

Ok.here's the deal:build a 2204 and put in 4 9 pin sockets for EL84's.Make the amp fixed bias and be prepared to have your ears pumelled by a wall of grind.Run them at 400+ volts and drop the screen voltages to acceptable levels.there are so many mods out there for 2204's that your head will spin.It will kick some serious ass and then some.

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36w JCM800?

36w JCM800?