Thinking of selling my ol' Marshall JMP 50 1987 head (from 1968) .....

What's Hot
2»

Comments

  • lukedlblukedlb Frets: 488
    Then again, looking at the crazy prices over here, you could ask for a lot more. 
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • ICBMICBM Frets: 71955
    lukedlb said:
    From my understanding, a black switch indicates a replaced part, common since they were often broken in transport.
    Other way round - the black plastic switch is stock. They were used for most of the JMP period, and since they did often break they were replaced by the more easily available metal ones. The hex nut on the metal switch is another clue - they weren't used on the outside, it was always a round one even when the switch was originally a metal toggle.

    lukedlb said:

    The presence pot was probably changed unnecessarily: presence is rarely moved and so develops noise.
    Is it the pot that's been changed or just the knob? Although in fact, all the knobs are replacements, it's just that the presence one is newer and the colour doesn't match.

    The reason the presence pot produces noise is because in the original circuit it has DC on the pot track - that was changed in the mid 70s - and replacing it doesn't fix the problem.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

    0reaction image LOL 0reaction image Wow! 1reaction image Wisdom
  • Hi everyone.

    Well, well... very interesting to hear all the opinions.

    The knobs were poss changed by me in the 80s and for some reason I I didn't change the presence knob. Nor was Martin able to find a replacement, hence the mismatch.

    An amp 'tech' in London replaced the presence pot with something fiddly which Martin rectified, hence what you see now. 

    I still have the invoice from Gartone for all his work done and a bag containing the old parts, inc Bulgin plug.

    I wouldn't want to sell if the price wasn't high enough. I'd keep it and sell my 18/20 combo n custom extension (as advertised here).

    I wish I could work out how to post pics as I now have a load of the amp post-Martin :-)
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • SpankThePlankSpankThePlank Frets: 15
    edited July 2020
    http://imgur.com/a/vaAH0ps

    Please let that work..... :-)
    0reaction image LOL 1reaction image Wow! 0reaction image Wisdom
  • Knurled ring moved back to outside, presence vs bass pot, inner detail, etc
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • ICBMICBM Frets: 71955
    Yes, presence pot changed. The knob is now original :).

    Is the impedance selector fused inside or has it been bypassed? A fuse would be a very bad idea...

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

    0reaction image LOL 0reaction image Wow! 1reaction image Wisdom
  • @ICBM ;That knob is one I prob had before I changed the others.

    I would very much doubt Martin at Gartone would do anything unnecessary or dangerous, if that is what you mean. I have no idea about the impedance selector. I just play em. :-)
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • ICBMICBM Frets: 71955
    edited July 2020

    I have no idea about the impedance selector. I just play em. :-)
    That type of red plug-in for the impedance selector normally contains a fuse. Unless the fuseholder clips inside have had a wire soldered across them, there's a very real risk of the fuse failing - or even just making a bad contact with the clips - and leaving the amp with no load, which would be very dangerous to the output transformer.

    The selectors are one of the major hazards for all old Marshalls, and one of the reasons so many suffered blown transformers - personally I would always hardwire the mains one for safety reasons, but if you have any doubts at all as to whether the fuse has been bypassed, it's better to use the red cap on the voltage selector and the black one on the impedance. If the amp suddenly stops working then the fuse has blown!

    I should have some spares of the correct 'bean' inserts, I'll send you one if you want.

    Having seen the power transformer I can confirm that it's one of the early ones intended for a valve rectifier by the way - the two terminals for the rectifier filament winding are the unused ones at the top left in the pic.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

    0reaction image LOL 0reaction image Wow! 1reaction image Wisdom
  • Wow. 
    Thanks for that info. I'm amazed at your knowledge :-)
    I had no idea about those red selectors, of course. I may investigate but certainly swap them for now. 
    I'll happily buy the insert. I'll PM you.  
    Cheers!
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • More pics above @Modulus_Amps ;
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • Modulus_AmpsModulus_Amps Frets: 2569
    tFB Trader
    More pics above @Modulus_Amps ;
    Looks in good nick really, Did Martin change the choke transformer? your top picture was original, the link you sent showed a Hammond unit.

    The head case effect on price will really depend on the the buyer, sell it like it as and it will attract buyers looking for a better price and willing to put soem effort in to get it back to spec. but buyers who want it perfect will probably avoid it.


    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • @Modulus_Amps ;
    Yes, the first pic  was before Gartone.
    I note you don't have a head box in your site for a JMP these days. Will you be making any?
    0reaction image LOL 0reaction image Wow! 0reaction image Wisdom
  • Modulus_AmpsModulus_Amps Frets: 2569
    tFB Trader
    @Modulus_Amps ;
    Yes, the first pic  was before Gartone.
    I note you don't have a head box in your site for a JMP these days. Will you be making any?
    There were a number of variations on head shells so I don't have them all up in my shop as it is confusing, PM me if you want to to talk about price/options etc Cheers

    Michael
    0reaction image LOL 1reaction image Wow! 0reaction image Wisdom
Sign In or Register to comment.