'72 Jmp 50 (canadian)

Discussion in 'Let's Talk Vintage' started by Metalone72, Jan 22, 2017.

  1. Metalone72

    Metalone72 New Member

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    Just picked up this Canadian '72 JMP 50 1987 and it looks pretty original for the most part. The bypass cap on V2b looks to be replaced. Current owner said there was once a Master Volume mod but it was removed. Supposedly it was gone over by a tech (Skip Simmons?) a few months back. Tell me what you see.

    Thanks,
    Scott
    [​IMG]
    [​IMG]
     
    Last edited: Jan 22, 2017
  2. stickyfinger

    stickyfinger Active Member

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    Nice score! I saw that one, forget where:hmm:, and wish I had the cash.

    How's it sound? Those chicklets look awesome and never heard them in person.

    The V2 bypass cap has been added, not replaced. 72's typically didn't have them like the plexis. They changed the feedback in the poweramp to 4ohm/100k to compensate.

    Pic isn't the best.. looks like a few joints touched up, a few pots, possibly the 220k iskras ect. Extremely clean example. Hope it stays that way!

    The valve labels on the chassis are stock Canadian. Should have white painted on the inside headshell too?

    What did you score it for?
     
  3. neikeel

    neikeel Well-Known Member

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    Looks very good from the poor quality pic I can see. The wiring has been fiddled with (lead dress is messed in places) but apart from that cap on V2a you guys refer to I see little to worry. Good to see those Plessey filter caps still in working order.
     
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  4. Metalone72

    Metalone72 New Member

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    Thanks for the comments. The pictures I was able to snag from ebay. That is where I bought and I talked to the guy for a good hour before purchasing. Once I get it later in the week or early next week, I get some better pictures of it.

    I couldn't remember if the V2b bypass cap was already removed in the early '70's metal faces. Adding the cap gives more gain, no? And I was thinking that some of the wiring was redone as it looks thinner that the stock wiring.
     
  5. stickyfinger

    stickyfinger Active Member

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    Yes the V2 cap gives more gain. A Marshall value would be .68uf that gives more mids and highs. Who knows what in there now. 71' is when we start to see the removal of this cap and even a few examples into 72 have two from Marshall inconsistency's. There seems to be a few examples with thinner wire as well. It must be stock because replacing the wire would have messed with the die on the joints.
     
  6. neikeel

    neikeel Well-Known Member

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    If you have the 0.68 on v2a check the nfb setting. I prefer 8ohm tap and 47k (i.e. Stock) with the cap. Your own preference may be different.
     
  7. Metalone72

    Metalone72 New Member

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    I'll check once I get it. Can't wait!!
     
  8. Metalone72

    Metalone72 New Member

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    I presume that I should run this amp on a Variac?
     
  9. Kris Ford

    Kris Ford Well-Known Member

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    Only if you want to kill it dead.

    PLEASE don't.


    I think the two common answers you'll hear are Post Phase Inverter Master Volume or attuenator..
    Or both..

    Or cascaded preamp with a PPIMV..my '74 JMP is this way, and it wlll rip you a new asshole. SOOO much gain.

    What style of music are you wanting this thing to do for you?

    That's a start..and a question you don't hear enoygh of..can't assume that everyone wants a saggy plexi when they want a tight nasty metal panel tone...it's better to tailor the answer when the desired result is known I think.
     
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  10. stickyfinger

    stickyfinger Active Member

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    Don't mod it. Leave it as is or remove the added V2 bypass cap. It was placed in a good spot that its unintrusive IMO. If you want a 68' plexi tone on the cheap get a 70' metal panel instead. These handwired Marshalls in clean, let alone unmolested condition are getting harder and harder to come by. I would personally play the circuit first to see what you like.

    However its your amp and can do what you please. My .02

    As far as the Variac. I think the OP wants to get the original tone the amps had back when the wall volts were lower. The components in the amp are all rated well enough that you don't need to run a variac is the other concern I hear. The only thing that will happen is there will be a hair more AC on the heaters and from a textbook stand point the tubes wont last as long.
     
  11. Metalone72

    Metalone72 New Member

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    I don't plan on modding it. If anything I might remove the 0.68uf on V2b to see if I like it and/or replace it with a mustard or chicklet cap.

    As far as the variac goes, my question was more since the amp was designed (?) to run at 110V. So it is safe to run it todays wall voltages?
     
  12. stickyfinger

    stickyfinger Active Member

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    Id say 95% + players don't variac their handwired JMPs. I don't.
     
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  13. brets9

    brets9 New Member

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    I have a '72 1986. It's my favorite amp for sure! My board is loaded with mustards though.. I put a .68 on the presence pot and power it through a variac set exactly at 110v. There isn't much headroom with a '72 50W but if you are like most guitar players you aren't going to care! With the right tubes and speakers it should start to break up with the volume at 3 or 4. Mine likes short plate preamp tubes best. Especially the old RCA's with orange ink. I also have XF2's in it..You are in for a real treat! Congrats!!!
     
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  14. soundboy57

    soundboy57 Well-Known Member

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    I have a 1971 Canadian small box Lead 50, and I love it.
    I run it, and a 1967 50 watt, with a variac setup that is set to 115 volts, where they both
    seem to sound best.
    My house voltage is 122 volts.

    [​IMG]
     
    Last edited: Feb 7, 2017
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  15. Kris Ford

    Kris Ford Well-Known Member

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    AHHH..thought you were gonna go Eddie Van Halen on it..which is surely bad for the amp.

    Pretty much what I've heard my whole life...they can take it!
    Though what SB57 has set up is more of a "tone tailoring" setup, as in finding the AC sweet spot, ..(VERY interested on the power conditioner...please tell me more about that, been considering one!)
    You can run it through wall voltage NO problem.
     
  16. Metalone72

    Metalone72 New Member

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    What is better for the amp, a PPIMV or an attenuator? I have a Fryette Power Station which is a reactive load.
     
  17. stickyfinger

    stickyfinger Active Member

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    Powestation by far. Havent tried it yet but its reactive and those are killer from my experience.
     
  18. coldengray

    coldengray Active Member VIP Member

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    YES to run a variac at 110v. Measure the heaters while trying 108-112v with the variac, and when you get 3.15 exactly on each side that is the voltage your amp wants to see.
     
  19. chilipeppermaniac

    chilipeppermaniac Member

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    Kris, My 72 JMP European market 1987 Lead is similar in some ways to this Canadian one. A few differences which could be because mine was Eurpean and fiddled with some over the years. I am diagnosing some runnability issues with it lately. Thiking a couple caps are bulging and need replaced. Plus a couple other resistor and wire issues I need to tidy up.
     
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  20. Kris Ford

    Kris Ford Well-Known Member

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    SO worth it to take it to a tech!

    Just got back my '74 JMP Super Bass, and it is AMAZING!!
     

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