18W Plexi or JCM800?

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M Fowler
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18W Plexi or JCM800?

Post by M Fowler »

I see people build 18w plexi with PP EL84's and I have as well but has anyone built the JCM800 as PP EL84 18W or did you just use 6V6's for 22W?

Mark
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Reeltarded
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Re: 18W Plexi or JCM800?

Post by Reeltarded »

Dunno about the 84s, but that circuit blasts off with 6V6s for sure.
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guitardude57
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Re: 18W Plexi or JCM800?

Post by guitardude57 »

I rebuilt a Blues Jr into a 1986 Plexi bass circuit. It came out absolutely wonderful. Of course, because of the nature of farty bass syndrome in this circuit, I would just turn the bass down. You could adjust things, or build the 1987 or 1959 circuit and get some more
guitar tuned bass tones.

I did the single input with the individual bright and bass channel volumes to blend. Duane tone all day long. Clear define notes... with just a bit of hair. If you put a mild boost in front, all the gain and fat you could want.

Even using the original iron from the Jr,
I really liked it. It was cathode biased EL84. It could easily keep up with a Hot Rod Deluxe, bass and drums with no more than half up on the volumes.

I have always been more of a Plexi fan than later versions like the 800 etc.
Mike


I am never surprised and always amazed
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Colossal
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Re: 18W Plexi or JCM800?

Post by Colossal »

Mark,

I dabbled in 6V6 Plexis for a while (killer tone!), then that inevitably became 6V6 JCM800 variants, and as you know, that's sort of mutated into EL84 modded Marshall variants.

I'm pretty smitten with the EL84 for its magical midrange, sparkling clarity, and that softer pentode knee. You can get some remarkably tight low end out with EL84s and they do perform well in a high gain circuit. I think it's important to keep the grid leak values 220k or less to keep the fizz down.

Some of the guys on 18Watt built 2xEL84 plexi variants as well with great results. There is also the Brownnote Dirty 18 which has a cascaded preamp.
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M Fowler
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Re: 18W Plexi or JCM800?

Post by M Fowler »

I built a 18w EL84 plexi but want to build the JCM800 with lower wattage such as PP EL84's but most are using PP 6V6 so I wanted to find out if anyone had built a JCM800 PP18w EL84 version.

Also, what did you do with the high/low inputs keep it stock, go to single jack, or modify low for more usuable gain?

Thanks for your replies guys.
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Richie
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Re: 18W Plexi or JCM800?

Post by Richie »

If its 18 watt, its probably been done, or tried before. I have built both,EL84 and 6v6 versions. Some SS rectos some half and half, or with An added pentode channel. So, just depends on what someone like or what they are after.Might even do an AFD type 84 amp or have the input for that to use one or the other. Or even footswitch could be used. I don't like useing a jack as a more switch type thing. If they get dirty, they make noise. I'd rather have a switch actually do that.
Also if doing either,make a few value changes for the tubes they use.
I changed some 18watters from EL84s/6CA4 to run 6v6/SS recto.
Mostly because the 18w ran the EL84 hot, and had to use certian tubes in those amps. The voltages on an 18 watter are much more suited for 6v6s with an SS recto. Seems most people like the 6v6 change over the EL84s. or at least the ones i have changed they have all liked the 6v6 sound.

If doing the circuit with presence control, you can use a switch pot to take the feedback circuit in or out and still have the control.
Or some might like to use a cut control or combination control there.
But if doing the single straight forward amp, you can use the inputs for high and low gain to make that much more useable. Like one being more a simple more standard marshall, and the other a more higher gain 800 type channel.
Some may use the more standard circuit in the PI, some may like the more 18w marshall PI. But then there are differences there to being able to add the feedback circuit,and the effect it has on the amp.
You can also use cathode bias or non cathode bias setup.
Or also if you want to get elaborate, look up the amp that you could use either or tubes in the output. Mark D. Had an amp that had a control in an amp you could use either 84 or 6v6s.

Its just hard to please everyone. So whatever you decide on, try to think ahead, and make the amp have room for adding another feature if you need to later on. I think though one of the key parts in doing those amps are making some small changes in values that makes the amps much more useable and sound better. The CF, and PI, and tone caps.
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renshen1957
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Re: 18W Plexi or JCM800?

Post by renshen1957 »

Colossal wrote:Mark,

I'm pretty smitten with the EL84 for its magical midrange, sparkling clarity, and that softer pentode knee. You can get some remarkably tight low end out with EL84s and they do perform well in a high gain circuit. I think it's important to keep the grid leak values 220k or less to keep the fizz down.

Some of the guys on 18Watt built 2xEL84 plexi variants as well with great results. There is also the Brownnote Dirty 18 which has a cascaded preamp.

Hi,

When Dick Denney was designing the first AC30 in 1959, he initially used two EL34 as the power tube, but it lacked something the AC15 had, ergo the change to a quad of EL84 was the first major revision to the new amp.

The AC30 was an upgrade in power as The Shadows in England needed more amps to play larger venues. Vox couldn't have dreamed what would happen next, when the Beatles hit the scene with Please, Please Me.

The rest is AC30 history but short lived as the Beatles shrieking fans necessitated more powerful EL34 fueled AC50 and very quickly up graded to the AC100 to play stadiums. (And as they upgraded the Beatles recorded with each newer model and later used SS amps, and after their manager's death, started using Fender Amps toward the end of their recording career).

The EL84 was also employed in Fisher and other brands of Hi Fi Tube amps for their sterling qualities.

Best regards,

Steve
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dartanion
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Re: 18W Plexi or JCM800?

Post by dartanion »

A 2203 type preamp with either 6V6s or EL84s rips!
Eardrums!!! We don't need no stinkin' eardrums!
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martin manning
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Re: 18W Plexi or JCM800?

Post by martin manning »

What are you after here, Mark? Small wattage? Small size? EL84 tones?
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ToneMerc
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Re: 18W Plexi or JCM800?

Post by ToneMerc »

I'll throw another option out there for a power tube off the beaten path the 6CM6, which is a small bottle 6V6.

TM
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Reeltarded
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Re: 18W Plexi or JCM800?

Post by Reeltarded »

Make it with 34s and a PT with more like TW voltages and maybe a tap for even less. No reason to make a li'l boy amp that can't do bigboy stuff! It's a bigboy amp until you get to it's legs anyhow.

Use a big chassis too, and a big headbox. People will think it's louder when it ain't. My idea works if you get trapped on an island with Tom Hanks and all you have is a soccer ball and el34s... or 6v6s, and 120 wall voltage, granted...

TM stop that being different! Use 807s if you want to make a statement. haha
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M Fowler
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Re: 18W Plexi or JCM800?

Post by M Fowler »

Like Darin said 2203 preamp with EL84's :lol:

I haven't seen much on that kind of build.
ampgeek
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Re: 18W Plexi or JCM800?

Post by ampgeek »

Check out Dreamtone for a JCM into EL-84 plan.

http://www.dreamtone.org/Mini_JCM800_2204.htm#12

Looks to be a 2204 preamp but that is very similar, if not the same, as the 2203 preamp IIRC.

You will need to sign up at their forum to get the password to open the pdf of the layout. I don't recall ever seeing an actual schematic per se but will need to go back through my files to confirm.

Looks like a great little project to me!

Cheers,
Dave O.
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M Fowler
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Re: 18W Plexi or JCM800?

Post by M Fowler »

Dave,

Yes I have seen that before thanks.

No layout that's just plain wrong, join to view :lol:

:arrow: POST LAYOUT HERE :!:
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M Fowler
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Re: 18W Plexi or JCM800?

Post by M Fowler »

Looks like he is using gain, gain master and drive is PPIMV with single input that can get tricky with the JCM800 preamp.

Or maybe I just can't think anymore :lol:

Mark
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