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PostPosted: Tue, Aug 27, 2013 9:34pm 
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I've been looking for an unmolested JMP 100w locally now for a few years. A guy locally has a 1977 JMP 100w for sale but he lives about an hour away and I would like to know if its worth the trip. I think the price sounds good but the downside is it is seems to have a few mods. Any heads up on what to look/listen for, as well as any insight on this particular year would be greatly appreciated.

Here is what the guy emailed back with:

"The amp was modified about 20 years ago by a previous owner. It has a direct out and an effects loop. It has not been serviced, mostly just been sitting around.
The amp does work, just played through it last Saturday to make sure."

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PostPosted: Tue, Aug 27, 2013 9:38pm 
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1977 is beyond time for a recap on that old bird. Normally you do not recap an amplifier just to recap an amplifier but at that age it is well beyond time to have new new electrolytics installed being as though it has been sitting around in storage.


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PostPosted: Tue, Aug 27, 2013 9:41pm 
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If it's truly just a line out and an FX loop, the mods would be the least of your worries. However, we don't even know exactly what has been modded without seeing gut shots.

I'd be more worried about a '77 JMP that "has not been serviced, mostly just been sitting around." There's a strong likelihood you'll need a cap job, new tubes and likely some additional minor required maintenance. I'd budget an additional $300 with a tech, just to get it up and running at full steam. If you can do the work yourself, even better (i.e., cheaper).

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PostPosted: Tue, Aug 27, 2013 9:54pm 
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Thanks for the input! I forgot to mention that he was asking $500. So if I could get away with about $300 to get it back up to speed (recap, tubes, etc) it doesn't sound like too bad a deal. That's if the guts are original.

What would I look for if it had bad caps, leaking/corrosion? What type of audible symptoms are caused by bad caps?

I'm going to ask him to try and send me some gut shots.

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PostPosted: Tue, Aug 27, 2013 9:57pm 
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nevusofota wrote:
Thanks for the input! I forgot to mention that he was asking $500. So if I could get away with about $300 to get it back up to speed (recap, tubes, etc) it doesn't sound like too bad a deal. That's if the guts are original.

What would I look for if it had bad caps, leaking/corrosion? What type of audible symptoms are caused by bad caps?

I'm going to ask him to try and send me some gut shots.


If it works and sounds good, I'd def do that 500$. This way you know with a cap job and some new glass, it is def worth any extra you put into it.


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PostPosted: Tue, Aug 27, 2013 10:25pm 
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I'd buy it for sure.


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PostPosted: Tue, Aug 27, 2013 10:58pm 
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I don't think that is a '77. If the chassis is, it's in an older box. In '76 they went to the different cosmetics and they have the plastic corners. The rocker switches make me think '76 or later, but the box is older than that.

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PostPosted: Wed, Aug 28, 2013 5:36am 
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Chubtone wrote:
I don't think that is a '77. If the chassis is, it's in an older box. In '76 they went to the different cosmetics and they have the plastic corners. The rocker switches make me think '76 or later, but the box is older than that.


It could be a 76, I have owned Marshall's from 76 and they transitioned out of the headshell seen in the OP during the year. Either way, if it works it is a good deal for $500. I'll buy it the OP does not want it. ;)

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PostPosted: Wed, Aug 28, 2013 6:23am 
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Jump on that, you don't find them everyday and that one looks to be in fairly good cosmetic shape. Get it serviced like everyone else mentioned and you will have a killer amp for years to come. You can have the tech put it back to spec and remove the mods too. I find that those rubber plugs they sell at auto parts places fill holes drilled in chassis really well and don't look terrible. Good luck with it. I have a '76 and '77 JMP and they are really killer amps for what they do.

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PostPosted: Wed, Aug 28, 2013 6:49am 
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I'd buy it in a second for 5 bills, even if the headshell isint original :yes:
But yeah, a cap job and retube/bias would be in order at that age

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PostPosted: Wed, Aug 28, 2013 6:51am 
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Buy it, post haste ... :thumbsup:

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PostPosted: Wed, Aug 28, 2013 7:59am 
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guitarmike wrote:
Chubtone wrote:
I don't think that is a '77. If the chassis is, it's in an older box. In '76 they went to the different cosmetics and they have the plastic corners. The rocker switches make me think '76 or later, but the box is older than that.


It could be a 76, I have owned Marshall's from 76 and they transitioned out of the headshell seen in the OP during the year. Either way, if it works it is a good deal for $500. I'll buy it the OP does not want it. ;)
This... 500 is a very good deal even if it needs some work..but if you play it and it sounds great, you may not need to do much other than a bias check. A local guy here in Wi has a great collection of plexis and JMPs and every one except one (according to him) has the original can caps..one way to check is if the top is bulging they are dried out and need to be replaced. Snap that one up!

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PostPosted: Wed, Aug 28, 2013 8:39am 
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If it is a '77 or '76 it could also be the odd transition model before the true cascaded Master volumes. Read:

http://home.comcast.net/~mamp17/Unsorted%20Pics.html

SDM has a great step by step to convert from this model ( a 1987 with a master volume ) to a true Master Volume setup...the easy way to know is that it wont have a ton of JCM 800 type gain and be pretty bassy sounding...BUT for $500.00 it is a deal...


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PostPosted: Wed, Aug 28, 2013 8:48am 
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mixn4him wrote:
If it is a '77 or '76 it could also be the odd transition model before the true cascaded Master volumes. Read:

http://home.comcast.net/~mamp17/Unsorted%20Pics.html

SDM has a great step by step to convert from this model ( a 1987 with a master volume ) to a true Master Volume setup...the easy way to know is that it wont have a ton of JCM 800 type gain and be pretty bassy sounding...BUT for $500.00 it is a deal...
From my memory just the 50 watters had the un-cascaded preamp in 76-77..but the 2203s were all cascaded from the start. OP says it's a 100 watter.. :thumbsup:

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PostPosted: Wed, Aug 28, 2013 9:16am 
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This is all great info. Thanks a ton!! I'm going to try to pick it up this evening.

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PostPosted: Wed, Aug 28, 2013 10:05am 
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Look the caps over, if they're not bulging or leaking, Plug it in and play it, Sometime in the near future you can get those changed, but they should be OK to play for a while if there's no bulge or leakage. Great deal!!

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PostPosted: Wed, Aug 28, 2013 10:06am 
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Racerxrated wrote:
guitarmike wrote:
Chubtone wrote:
I don't think that is a '77. If the chassis is, it's in an older box. In '76 they went to the different cosmetics and they have the plastic corners. The rocker switches make me think '76 or later, but the box is older than that.


It could be a 76, I have owned Marshall's from 76 and they transitioned out of the headshell seen in the OP during the year. Either way, if it works it is a good deal for $500. I'll buy it the OP does not want it. ;)
This... 500 is a very good deal even if it needs some work..but if you play it and it sounds great, you may not need to do much other than a bias check. A local guy here in Wi has a great collection of plexis and JMPs and every one except one (according to him) has the original can caps..one way to check is if the top is bulging they are dried out and need to be replaced. Snap that one up!

Image

Image

Image

Image


Cap cans dont have to be bulging or leaking to be replaced. 15+ years old is a good candidate. I replaced bias filters & cap cans in two 1978' JMP's it tightened up the low end, took away alot of buzziness and gave the amps alot more MoJo in general. :thumbsup:
Make sure u replace bias filters too they're electrolytic as well and failure of one could take a Tranny.

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PostPosted: Wed, Aug 28, 2013 10:31am 
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Yeah it's all a matter of opinion on the caps..I guess I've been lucky with all the vintage Marshalls I've had, modded or stock in that I've never had to change filter caps on any of them. And they've all sounded good to my ears. Never had a transformer go with the exception of a Ceriatone Cali mod I had..and that was after one gig..the amp was only 3-4 years old so that was just a bad PT..

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PostPosted: Wed, Aug 28, 2013 10:40am 
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I'm not meaning to say that the caps are always good if they're not bulging or leaking, but after buying it, if he's wanting some time to save a few $$$ before having it worked on, if the caps aren't bulging or leaking, it *Should* be fine. I've had amps 5-7 years older with no problems and their original caps. They need changed, but should be fine for a while to play with, and get used to the amp. IMHO. I definitely wouldn't start taking it to 3-4 hour shows 2 nights a week until they'd been changed though...

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PostPosted: Wed, Aug 28, 2013 9:43pm 
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One of my favorite amps ever!
Let me know if you want a cap job done or a loop than doesnt suck tone!


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PostPosted: Thu, Aug 29, 2013 3:26am 
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Cabinet might be original... In that 75-76 transition period, Marshall made some strange combinations.


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