Why Did He Mod My ‘73 Jmp 50w Like This? Your Expertise Is Required!

Discussion in 'Let's Talk Vintage' started by Nick56, Feb 18, 2019.

  1. Nick56

    Nick56 New Member

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    Hi guys, 25 years ago when I was 15 my dad gave me 2 vintage amps which he found buried away in his pub. A black 1973 50W JMP and a 1976 MKII 100W Super Lead in fawn colour.
    stacked Marshalls crop.jpg
    I immediately used the 50W blackie for a few years and loved it because it was loud (I was 15!) but the 100W blondie was in a state of dispair and strangely modded so I didn’t touch it to this day.
    Both amps have been in storage for over 20 Years and I recently dug them out for servicing and repair so that I can get them both singing again.
    My question regarding ‘blackie’ is that I don’t understand why the previous owner took out the channel II lead sockets? Why would you want to remove them? I understand that he removed the polarity switch which is fine, i get that, but why the inputs? Is this a common mod that improves something? I’ve included photos of the wiring so that you can see what he did and possibly why he wanted to do it. Is it an improvement or a botch job? I can see wires wrapped in bits of tape which looks pretty shabby and i'm wondering how far off from the original wiring this is?
    small pic.jpg
    Plus what valves are these? I don’t see any writing on them and I’m no expert.
    tubes 1.jpg
    Your input on this is greatly appreciated.
     
  2. neikeel

    neikeel Well-Known Member

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    Without seeing the serial i would say the 50w is a 71 or 72 (a C or D suffix). The removal of the normal channel jacks is because it has been modded to a cascaded V1 (like a 2204). So the channel 2 volume pot is now a gain pot and channel 1 volume pot is a master. I actually think that the removed switch was the standby (maybe removed during a different master volume mod.) and the switches nudged along. The chassis has 3 holes but uk amps had the cover panel undrilled as they did not have a polarity switch and yours is (am pretty sure) a UK/Home model.
    Of course the PT has been replaced as has one of the fuse holders.
    Restoration would involve a pair of jacks, a couple of resistors and caps and ideally a new laydown PT, general service (almost certainly new filter caps and bias caps). If you are going to sell it leave it as is and put on ebay with lots of pics (road dogs often get more bids and higher price than not very well restored amps, so if you restore it - it will have to be done properly to get a good price (probably about £250 with a decent clone PT).
    The output tubes look like crimped plate EL34s - could be anything from those pics.

    C'mon, show is pics of the 'really' modded amp (are you sure it is not faded Orange rather than dirty fawn?).
     
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  3. wakjob

    wakjob Well-Known Member

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    Looks like someone wanted to make a clean microphone P.A. head out of the blonde for vocals or something?
     
  4. ampmadscientist

    ampmadscientist Well-Known Member

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    Somebody modified it into a 2203 preamp.
    This gives better distortion at low volumes + it has a master volume now.
    But they used crappy parts and did a really sloppy job.
    So, it could be cleaned up by a pro...
    does it sound OK?
     
  5. Nick56

    Nick56 New Member

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    It’s a ‘73, the serial number ends in E and it’s written ‘Test - Feb 1973’ on a slip of paper inside. And I’m not selling it, this is for me. But thanks for answering my question. So it’s an improvement of sorts, just done shabbily. Right. I like the fact that it has this mod then, I won’t be putting it back to factory specs. Just perhaps finding a tech who can keep it as is but do it properly and then throw in some dummy inputs and a dummy switch for aesthetics (I don’t like the holes). I don't suppose you know a tech in the London area that's good at this stuff?
    And from what I can remember this thing sounded great! Though I wasn’t much of a tonal expert in my teens. This thing came with a sound city 4 x 12 cab and it was LOUD!!!! That’s all I cared about back then so I’m really curious to hear her again but with a more refined ear and much more guitar playing talent.
    Please excuse my ignorance but what is a PT? Just curious.
    And the blondie is definitely fawn, at least I think it is, it’s just dirty as hell. It's a '76 as it has the H suffix. The mod that threw me was the microphone input. The insides are different too from pics of other amps that I’ve seen, though again i'm no expert. I’ll get around to posting about it in another thread later as I want to refurb it also. It has 2 KT88’s inside, that’s all I know. I’m going to need people like yourself to give me a heads up with what to do with it, what needs changing etc...
    The amp isn’t with me right now and I haven’t removed it from the chassis yet either. The back panel is missing and I only have pic of it like this. Not sure how much you can tell from that pic but I’ll post it here.
    resized stack.jpg
    Once I open it up properly i'll post the pics here in a new thread.
     
  6. Nick56

    Nick56 New Member

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    Yeah, that's what I figure too.
     
  7. Nick56

    Nick56 New Member

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    From what I remember (it has been over 20 years since I last plugged it in) it sounded great.
     
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  8. Ufoscorpion

    Ufoscorpion Well-Known Member

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    Take them to someone who knows what they are doing ! I'm guessing that you are in the uk , if you're near MK take them to Marshall they will sort them , they are reasonable price wise .
     
  9. Nick56

    Nick56 New Member

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    Any suggestions? I’m based in London.
     
  10. Ufoscorpion

    Ufoscorpion Well-Known Member

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    Lol, I just edited my post probably as you were typing your last message . Basically I suggest you take to Marshall MK , not far if you're in London .
     
  11. Nick56

    Nick56 New Member

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    Marshall MK? Is that a shop? Do they have a website? A contact number? I typed Marshall MK into google and got a whole bunch of stuff I don’t want!
     
  12. Ufoscorpion

    Ufoscorpion Well-Known Member

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    The Marshall factory in Milton Keynes ( well Blechtley actually ) is where I'm refering to . They have a service department that also does repairs , unsurprisingly they know their shit .
     
  13. Ufoscorpion

    Ufoscorpion Well-Known Member

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    Marshall amplification tel :- 01908375411
     
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  14. neikeel

    neikeel Well-Known Member

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    Controversial suggestion for a vintage Marshall:)
     
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  15. johnfv

    johnfv Well-Known Member

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    That XLR connector on the fawn amp looks to be a 5 pin (not 3 pin like a mic input). My guess is that it was intended for use with an Alembic bass or guitar (or similar)? If so, it would have some power connected to it for the active electronics in the guitar (and there appears to be a small switch next to the 5 pin, perhaps an on/off for that power?). Just a guess but not sure why else someone would hack a 5 pin connector on there...
    [​IMG]

    [​IMG]
     
    Last edited: Feb 19, 2019
  16. charveldan

    charveldan Well-Known Member

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  17. Nick56

    Nick56 New Member

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    Hmm, that’s interesting. I always thought it was a mic input. Well, when I finally open her up we’ll see more of what she’s about.
     
    Last edited: Feb 19, 2019
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  18. Nick56

    Nick56 New Member

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    Wow, that dude makes some killer sounding Marshalls. My only concern is that he seems to gut the amps and completely replace them with new innards which is not what I’m looking for with this amp. Perhaps with the blondie.
     
  19. johnfv

    johnfv Well-Known Member

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    It will be interesting to see what you find inside. A standard 3 pin mic cable will not connect to that 5 pin socket. It also looks like someone wrote + next to one of the pins (on the right) which further suggests to me there is power being supplied there. It could be for connecting something completely custom like a pedal board, etc. but who knows? Let us know what you find :yesway:
     
  20. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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