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Marshall JMP Questions

Discussion in 'Amps and Cabs' started by cancelthesound, Jan 19, 2008.

  1. cancelthesound

    cancelthesound Member

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    I got to try a 50-watt Marshall JMP model today. I believe it's a 50-watt big box model. It sounded amazing. The guy wasn't sure how much he wanted to get for it. I'm not sure what year it was but it is a 4-input non-master volume model. 6550 tubes w/ a circuit board. it's definitely not point to point.

    The amp is a sorts hacked up. Apparently way back in the day, someone installed a fan and a male-to-male power chord so it couldn't be played with a standard removable chord. The back plate on the actual amp (not the chasis) is completely missing so there's no serial number or markings on the back at all. The impendenace selector is definitely not original. It's looks like some home made job. The pots are pretty dirty and the second input channel doesn't work all to well and the channel volume is really touchy. The first input sounds great.

    Other than those mods, i think it's all original. I have no idea if the amp has ever been serviced.

    Does anyone know when marshall made the switch from ptp to circuit board? What's a the going rate for this in mint condition? or with all these mods?
     
  2. mxr2000

    mxr2000 Member

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    Damn If you like it just pay like $400 because of the conditions of the amp and take it to a good Amp tech for service..
     
  3. cancelthesound

    cancelthesound Member

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    I would easily buy it for $400 but the guy was looking around on ebay and saw some that "looked" the same for $2500-3000. He also said he took it by a dealer who said it was worth $2000-2500. I don't think the guy is looking to get a lot of money out of me but he may think it's worth more than it is.
     
  4. bonchie123

    bonchie123 Supporting Member

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    If the guy can't even prove to you what model it is because it is so beat to hell tell him to keep it unless he wants to get rid of it for cheap.

    Its worth about 500 dollars in the condition you described. If it was mint, around 1500-1800. If it were all original PTP he might have a case to get 2000 out of you, but not a circuit based late 70's (I'm guessing) JMP in terrible condition thats been modded to death.
     
  5. cancelthesound

    cancelthesound Member

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    I think the only mods are the fan and the power chord. Otherwise i think the amps is stock. The back plate is missing so there is no serial number to pull. The sticker on the amp that usually has the inspection date is ripped off.

    I really think the guy just doesn't know what it's worth. I don't think he's trying to pull one over on me and I definitely don't think it's worth $2000 by any means. If he wants $2000, i'll definitely pass. I could get a roccaforte for that kind of $$. i've been jonesing for one for a while now. Either a HG 100 or a custom 80.

    I think the amps an early to mid 70s large box jmp. definitely a circuit board cause i asked him to pull the amp out so I could see it.
     
  6. Roccaforte Amps

    Roccaforte Amps Member

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    They went to PCB between 73-74
     
  7. cancelthesound

    cancelthesound Member

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    Hey Doug. Thanks for the info. Your amps rock man!
     
  8. SatelliteAmps

    SatelliteAmps Member

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    $500 might even be high. Mint ones are realistically around $1000-$1500 tops.
     
  9. John Phillips

    John Phillips Member

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    If both transformers are original and the chassis has not been drilled, it might be worth $500 in that state. You really shouldn't pay any more than this because you have no idea what else might have been done to it or what needs replacing, and don't ever trust a description of "all original" on an amp that has clearly been worked on by someone incompetent.

    At the very least, it will need a some work to make it safe, from your description of the power cable "mod", and more to make it reliable if the impedance selector has been bodged. It will also almost certainly need a full filter cap job (I wouldn't consider not doing on an amp that age, if it needs other major work) and at least some other repairs if one channel is not working. This work could easily cost you another $500 or more. If either of the transformers has been replaced (suspect the OT especially if the impedance selector has been damaged), that will significantly devalue it unless you re-replace it with the correct one, which will also cost a few hundred dollars. The missing back panel could be replaced if you're very lucky - basically you need someone with another dead/hacked amp with an intact one to 'donate' - and also seriously devalues the amp as it is.

    Marshall changed to PCB on the standard Lead and Bass models in mid-1973. Some other models (PA heads, 20Ws) remained turret-board until they were discontinued in 1974.
     
  10. cancelthesound

    cancelthesound Member

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    Thanks John!

    The transformers both look to be original. At least they look to be from the same era.

    I told the guy that the back plate would have all the information he needed to date the amp but he said it was gone when he bought the amp back in '80.

    I didn't know that not having the panel at all would signifcantly devalue the amp, but that makes sense since it's a pain to date/identify the amp without it. It's usually the back panel of the chasis that's missing...not the plate. But the back panel is still there. It's actually kind of funny because it looks like there's an electrical outlet on the back of the amp because of the power chord modification.

    The only hole that's been drilled in the chasis is in the front of the amp where an on/off switch for the fan was installed.

    The impendance selector looks fine, it's the plug for it that looks to be non-original or homemade. It's removable so replacing it wouldn't be a big problem.

    I hear you on getting the amp serviced. I know for a fact the guy hasn't had it serviced since he bought it. The only tubes he replaced were the pre-amp tubes.

    Do those old JMPs have trim pots to adjust the bias or is it hard-wired?

    I really should have taken my camera with me. I could have posted some pics for you guys to judge.

    Sounds like I should offer between $400-600 for the amp. If I have to get the amp serviced the puts me closer to $1000. Not sure I want to sign on for that if I can't ever sell the thing for much more than what I'll pay.
     
  11. riker4208

    riker4208 Member

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    Don't pay too much....my buddy got an excellent condition JMP 2/12 combo with blackbacks for $850

    they are out there
     
  12. John Phillips

    John Phillips Member

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    Why the HELL can't people not do stupid things like this?!!! :mad:

    That has very seriously damaged the value - any holes in the front are bad news. If you must fit unnecessary crap like this, do it round the back... :rolleyes:

    The whole impedance selector needs to be replaced. They are unreliable and a major hazard to the OT even if the original plug is there.

    Trim-pot, but there's a good chance you will also have to replace the bias filter caps to bring it into the right range - even if you don't want or think you need to replace the main filters. Leakage on the bias caps (which reduces the available voltage) is getting very common, even more than main cap failure, and you often see bodges like resistors changed or extra ones fitted to try to 'crowbar' the voltage back into the right range.

    Exactly. I wouldn't pay a cent over $500 and possibly not even that much given the drilled front panel.
     
  13. cancelthesound

    cancelthesound Member

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    Thanks for all the advice guys. I'm going to give the guy a call and tell him what I found it. If he doesn't bite at 400-500 then I'll just pass. Otherwise for an amp that will probably need $500 worth of work, I'd rather pay a grand up front that something that's in better shape and would have a good chance at retaining that value.
     
  14. gldtp99

    gldtp99 Member

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    My '76 JMP 1987 has a PCB loaded with mustard caps--- i've replaced the bias caps and converted it to run EL34's (was a USA model orig ran 6550's).
    Orig transformers and no holes drilled but it's beat-up looking and has no back panel.
    Amazing tone with channels jumpered and cranked--- it had a tendancy to squeal at hi vol when i got it (probably why the prev owner sold it) but i tweaked the oscillation out.
    i think you should get that amp if it can be had for cheap enough and get it serviced properly.
    then people will tell you: "Hey, that old beat-up amp sounds great!!!--- I don't believe it".
    And you won't have to worry about it getting scratched, etc when taking it out---- as long as you can get it cheap enough because it will always be a "player" amp, not some big $$$ collectors' item............gldtp99
     
  15. cancelthesound

    cancelthesound Member

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    I hear you man. I'm not looking to get a collectors amp. I just don't want to pay too much for it or more than it's worth, especially if I have to drop some $$$ to get it to where i can gig with it.
     
  16. hbar

    hbar Member

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    I had a '78 JMP, and it had 78 written all over the place. several places on the inner walls of the case, on the transformers, on the chassis, all in addition to the date code in the serial #. Sorry if you've already seen the innards and still don't know what year it is.
     
  17. thorny64

    thorny64 Supporting Member

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    Your buddy got a screamin' deal then. That amp goes for about $1200 or more in the condition like you describe. I paid more than that for mine than your buddy and that was 7 years ago! Combos used to go about the same as the heads (because heads used to be more popular) but now they go for more as you would expect. Mine is exactly the same, a JMP 2x12 combo, blackbacks, mine is a master lead, stock (except modded to run EL34s instead of 6550s). It is a KILLER amp! I love the thing. Don't be afraid of the PTP JMPs, they are still excellent amps because they did a pretty good job with the construction of the PCB and overall build. They are very solid. Different regions might vary, but old marshalls are still pretty popular (and a whole lot better than the new stuff that has poor build quality - from a guy that repairs these all the time).

    One hacked up would be worth quite a bit less. Figure out what it would cost to bring it back up to shape, and subtract that from the price you would offer as well as subtract for the cosmetic issues that you can't fix - and that is around where you should offer. I don't think the prices mentioned are too bad. If you can find a nice combo for $850 - Yeah, definitely buy it! It is a good deal.

    A few years ago my buddy picked up a tweed deluxe for $50 at an auction becuase it didn't work when they plugged into it. I put a 12AY7 into it and it sounded GREAT. I never get those kind of deals!
     
  18. 908SSP

    908SSP Supporting Member

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    Many metal panel amps have the original serial numbers stamped in the top surface of the chassis near the little transformer, the choke or around the corner where the paper tag was. The letter at the end of the number tells you the year. If you want real advice you need picture
     
  19. themusicboxstudios

    themusicboxstudios Member

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    I just got a JMP 2x12 combo w/ Original G-1265's for 880 shipped :BEER.

    Best buy I've made in a while!
     
  20. SvenHock

    SvenHock Member

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    Great amp and price. I have the same one that I paid 600.00 about 3 years ago.
     

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