Marshall Jmp 50 (1971) - Advice

Discussion in 'Let's Talk Vintage' started by LesPaulLover, Jan 14, 2017.

  1. LesPaulLover

    LesPaulLover New Member

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    Dear all,

    I am in the market for a vintage Marshall amp and came across this super lead that's for sale nearby. It's a Marshall JMP50 (1987) from 1971 and supposed to be all original. I am not however a vintage Marshall expert and was wondering if any of you true experts could have a quick look at the pictures below and tell me if you see anything strange or questionable pop up.

    Thanks !

    Screen Shot 2017-01-14 at 10.20.13.png Screen Shot 2017-01-14 at 10.08.56.png Screen Shot 2017-01-14 at 10.08.48.png
     
  2. neikeel

    neikeel Well-Known Member

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    Hi, welcome to the forum
    Yes it looks typical for a 71/72 Model 1987 Lead spec amp. 71 the number would end with C and 72 D.
    You will have to bear in mind the pics are ok but not the best so I will tell you what I see. Overall looks fine, what I point out may not be wrong but worthy bargaining chips if you want to buy.
    For me these are typically very good useable NMV Marshalls, loud, aggressive but clean up well with the guitar if you play that way!
    The on/off switch has been replaced (standby looks correct flat black bat) NOS on ebay $15.
    Does front panel have a ripple (cool if you are not bothered but hard to replace)
    The power transformer has been replaced as have the snubber caps that clean the diode switching noise (the big yellow caps, not necessary with modern high spec diodes)
    Diode block replaced (looks like flying diodes in heat shrink) new blocks/diodes available.
    Presence knob missing (ebay for correct old type, modern ones look trashy to me:2c:)
    Replaced pilot lamp - v common, looks correct no biggie on players amp.
    Replaced bias caps - look correct, quite important IMO.
    The big 0.68uF mustard on V1b has been stolen and replaced with Mallory or similar (they never fail but are now fetching big $).
    Someone has piggybacked another cap (phillips mustard) across V1b coupler to 'fatten' the sound (also looses some 'cut' on a lead amp, again IMO)
    The bypass cap on vol 1 pot looks like a smaller that normal to make that channel less aggressive (normally 5nF Lemco).
    Added silver mica on channel 2 pot.
    The impedence selector looks like a replacement but I know that some 69/70 era amps had turn switches rather than the usual window tip plugs.
    Also don't know what that red disc is mounted on the output jacks.
    Modder was probably a strat player.
    A stock 71/72 Lead amp sounds best with hot humbuckers to me.
    If the price is right (or can be negotiated right) I would jump on it and gently return it to stock but the beauty of these things s that you can tweak them to your taste.
    Please let us know how you get on.:)
     
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  3. LesPaulLover

    LesPaulLover New Member

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    Woah thank you Neikeel! Incredible you can tell all of that from 1 picture, I'm impressed.

    The seller is currently asking 1500eur which seems reasonable if you look at the market and the condition the amp is in? I am not a collecter but just looking for nice amps to play with so it might be something for me. I think I'll pay him a visit and test the amp out myself and see if I like it.

    Anyways thanks alot for taking the time to go over it. I'll keep you posted!
     
  4. Trapland

    Trapland Well-Known Member

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    If you pass on this, please let me know where to find it.

    Edit; please disregard my comment. I didn't know you were over the pond. Hope you love it.
     
    Last edited: Jan 14, 2017
  5. stickyfinger

    stickyfinger Active Member

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    Funny you should mention the NOS black bats on Ebay. I bought a pair for a restoration and they are used form what I can tell. Pre tinned and some of the solder terminals were bent out of place with solder between the two tabs was a give away they were pulls. Are these the ones you are talking about??

    http://www.ebay.com/itm/Marshall-Bl...JCM-plexi-EVH-Fender-Gibson-Boss/291993677015

    Hears the drama part-

    I left the seller negative feedback to warn potential customers they were 100% used pulls and not "New/Other/ Excellent condition. The seller used 'Feedback Extortion' to try and get me to revise the feedback to positive in exchange for a refund. The messed up part was she thinks she deserves 100% feedback. I wanted the feedback to stay for potential customers but we came to terms that if she revises the listing to "used" and remove excellent condition and to send me replacements (because I don't know the life expectancy of the switches I just bought especially if they were once used to switch B+) for exchange of feedback removal. She files with Ebay 'feedback Extortion' to get the feedback removed even after she used 'Feedback Extortion' first!

    Neileel- am I wrong and these are NOS? The seller never said they were in our conversations rather " they are in excellent condition" even though she doesn't know the mechanical life.
     
  6. neikeel

    neikeel Well-Known Member

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    Sorry I don't know about the seller but the price as in the back of my mind as I gave one away recently. I would expect NOS to be solder free too. I don't think these fail electrically - more because they break.
     
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  7. stickyfinger

    stickyfinger Active Member

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    Cant tell 100% because of the blurry pic but Dogbones (500p?) did make it to the Vol pot on a few of these amps.
     
  8. neikeel

    neikeel Well-Known Member

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    Odd that they would use one on the volume pot but not on the mixer or tone stack but I guess so (I've never seen it but then there is quite a lot that I have not seen first hand).
    500pF makes the control very spiky, oddly I quite like the 5000pF.
     
  9. stickyfinger

    stickyfinger Active Member

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    I have a few photos with these (FEC?) dogbones on the Vol pot with RS ceramic disks from 71' in mixer and Lemco dogbones in the Tone Stack.

    And a hand full of other 71', 72' Lead spec with Lemco dogbones on the Vol pot, with a mix of short (500p?)and long Lemco dogbones in mixers and TS positions
     
  10. LesPaulLover

    LesPaulLover New Member

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    Hey all,

    Thanks for all the reactions and help. After a quick test run I decided to purchase the amp :) :) :) It's an awesome players amp in relatively good condition and it seems difficult to find 50-watters from that era.

    I'll be bringing the amp to a good tech I know for a retube and see if we can bring it back to full original specs.
    I kinda like the sound at the moment so I'm thinking about just keeping it like this (dilemma).

    Also reached out to friend to a friend for a custom cab. 4x12 are a bit too big and sluggish so I was thinking about getting a Sumback M75 loaded 2x12, any suggestions are welcome but I'll have a look through the forum I'm sure there must be a tread somewhere.

    Anyways thanks again, I'll try to upload some nice close-ups once I have the time, I'm off playing now :hbang:
     
  11. neikeel

    neikeel Well-Known Member

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    Let us know how you get on
    That speaker should work well but I would get a M75 and H55 in the same cab and spec the 65w versions.
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    A. I can't see from the picture if the screen grid resistors are installed. If not you must install them. If these are were never updated, it can cause the amp to blow fuses.
    USA import may have had the resistors from the factory....maybe not.
    (resistor installed between pins 4 and 6 on the output tube socket)

    B. Check to see if over-sized fuses are installed.
    Always un-plug the power, before checking the fuses.

    C. Recommend a professional bench check, w/ test equipment.
     
  13. LesPaulLover

    LesPaulLover New Member

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    Thanks for the tips. There is a specialist close to where I live who has worked on dozens of vintage marshalls so I'll pay him a visit very soon
     
  14. chilipeppermaniac

    chilipeppermaniac Member

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    I am dealing with learning the status of my 1972 50 watt head, myself.

    Regarding your Letter A.

    What are screen grid resistors? And explain why it makes amps blow fuses.
    My amp is originally a British amp used in Europe. It has Bulgin socket and plug for the power cord,
    plug in and out adjusters for the voltage and the impedence.
    I am running EL34's and all the big Electrolytic caps Tubes and Transformers and choke have been replaced. I already know a White wire is wired wrong off the bridge rectifier and a few other things with a pair of resistors. Also, not sure why I see caps wired in to the Power valve sockets on some people's amps but mine does not have any.
     

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  15. chilipeppermaniac

    chilipeppermaniac Member

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    Also, if anyone can recommend 2 good caps to replace the .22UF Brown ones I need to remove, let me know what to look for and where, please.
     
  16. LesPaulLover

    LesPaulLover New Member

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    Hi everyone,

    Sorry it's been a while since my last post, things been crazy at work and haven't had a lot of time to enjoy my latest purchase.

    I've had the amp around a month now and man do I love it. It's been the tone I've been chasing for years. I'm a huge pedal addict and the amp just loves every pedal, must have something to do with all the headroom it has. Every fuzz I use just sounds 10x more epic then before (EQD hoof, fuzz face, etc). I just can't express enough how good I think this amp sounds, highly recommend it.

    I was surprised by the volume though. I had tons of friends warning me about the loudness of this amp but I never believed it until I tried it. It's crazy loud even on 0.5 of the volume it already shakes my room, incredible.

    Currently playing it through an V30 loaded Orange cab but might change to something like creambacks. I haven't had the amp checked out by a tech but I'm planning on it. Everything works splendid though. I did spend over 4 hours cleaning it, I don't think it has been dusted off since 1971 ...

    I attached some pics for the ones who are interested

    Cheers,

    PJ
     

    Attached Files:

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  17. Kris Ford

    Kris Ford Well-Known Member

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    Looks great!

    The Pres knob is a spot on match!
     
  18. LesPaulLover

    LesPaulLover New Member

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    Yeah got lucky, the owner still had it ;)
     
  19. chilipeppermaniac

    chilipeppermaniac Member

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    Great to hear you are getting along nicely with your new JMP, LPlover.

    With the help of Nekeil and a few other fellas on another forum I go to, I was able to get my '72 back to functioning nicely again. I still have a few fixes to accomplish at Nekeil's suggestion ( installing screen grid resistors) not "caps" as I mistook them for in pics of other amps. These go on the EL34 pins to essentially help tube life as the older Mullard EL34's were told to me as being more robust and able to handle the loads over the newer EL34's
     
  20. chilipeppermaniac

    chilipeppermaniac Member

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    Well, I got my Yellow wires swapped over from pins 4 to pins 6 on my 2 Power tube sockets, then got my 2 Ohmite 1k5w screen resistors installed tonight. Next order of business if to bias the amp and then give it a good test.
     

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