Guts - 1971 Marshall JMP Lead

antichef

pornk rock
I've been talking smack about having this amp for a couple of years on here - finally got around to taking it apart and snapping some pics. Here's the front:

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Here's the back:

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Here's the backplate off (all the tubes are new, but the originals were there when I bought it):

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Here's the QC label thing that I can't read:

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and here's the guts:

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I don't know the whole story, and I'm sure I'm at least the third owner. Looks like someone did a mod of some sort (probably master volume), but then backed it out -- hence the open hole in the back. I had to get some work done on it, but both techs who worked on it assured me that it was pretty much original -- even the filter caps, which they thought were fine.

I had the output impedance selector replaced. The old (original one) was chintzy and it fell out while I was playing - there was a small fire and I lost a pair of output tubes (new ones) - thankfully that's all. But I figure I like playing the amp with the original transformers more than I like blowing it up because I refuse to change the selector :)

Sounds great, by the way -- and must be played very loud to be appreciated.

edit: another thing I had done was to get the power cord replaced with a 3 prong grounded one. I'm pretty sure doing that rendered the polarity switch inoperable. I kept the original power cord, and the job is reversible -- this is just a safety related mod - doesn't affect the sound.
 
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Cool man, that is a bad-ass looking amp...To me, that's the holy grail of tone right there...That's where it all started, with those old Marshalls...

While I'd love to have one of those, & I kinda do, I'm pretty happy with my Ceriatone clone because it's got a master volume & extra gain stages to help get the cranked up sound without blowing the windows out...But yours is the real deal, mine's just a clone with a Marshall badge on it...

Cool amp dude, post some clips of it if you get a chance!!!
 
thanks guys! Yeah minerman, there's something to be said for a well built reproduction with everything being new and strong and stable - and it seems like they kinda *do* build them like they used to at least recently. I've heard Gerg's and yours on here, and I think they're both more stable sounding when dimed than this one is. The sweet spot for this one is to start with both channels (jumpered, of course) at around 6 and then adjust between I and II for tone based on the sound of the guitar - I usually prefer II to be the one that's up higher with my SG Supreme, which sounds a little brighter than most SGs. After a few minutes of that, I'm usually playing along with the police sirens (so to speak - the angry neighbors haven't actually called the cops on me yet) -- I still need to sound proof the floor in my studio.
 
My Ceriatone is about 5 years old now man, I bought it used (obviously), & I think I'm the 2nd owner, but not 100% sure....I don't really care though to be honest, it seems to be in great condition...Other than the indicator light/lamp/led, I was playing this evening & noticed it wasn't lit up, but that should be an easy fix....I hope...lol....


What's not stable about your amp man??? Maybe you could do a little work to it & get it fixed??? Just sayin'....An amp like that needs to be heard dude, like I mentioned, I'd love to have one, but the clone I've got is enough for me, even with it's master vol, it's still loud as fuck, & I can only imagine how loud your amp is when you get it to the sweet spot....

Killer amp you've got there man!!!
 
It looks like maybe your bright cap is missing on the Vol 1 pot? If so, that has a big effect on how the amp behaves overall.
 
It looks like maybe your bright cap is missing on the Vol 1 pot? If so, that has a big effect on how the amp behaves overall.
hmm - maybe so - you know the circuit much better than I do. On my 2204, I pulled the bright cap myself about 10 years ago - much prefer it that way.
 
hmm - maybe so - you know the circuit much better than I do. On my 2204, I pulled the bright cap myself about 10 years ago - much prefer it that way.

I got my 2204 without the bright cap and it was dark to me. When I put it back in, the amp woke up and I got the grinding bite and cutting mids it was lacking at lower gain levels. But it's all personal taste. Tons of people snip the bright cap out or change the value. If you're already fighting brightness, just leave it out.
 
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