How does the 1970 JMP50 look

Discussion in 'Let's Talk Vintage' started by Pageburst, Jun 19, 2019.

  1. Pageburst

    Pageburst Member

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    I am interested in purchasing this 1970 JMP50 and would be grateful for insights from some of the knowledgable folks on this board. The seller was gracious enough to allow me to post these pictures

    I do understand that the PT is a replacement but I'm not sure what that huge blue sprague cap is doing at the end of the turret board. Thank you in advance

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  2. charveldan

    charveldan Well-Known Member

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    Those tube retainers may be asbestos. Might want to get rid of those.
    Amp looks mostly stock except for PT, SGR's & blue Sprauge.
     
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  3. fifteenohms

    fifteenohms Well-Known Member

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    Asbestos?
    Why do you think that.

    But hey it’s a steel-paneled Plexi so for the right price buy buy buy!

    Ah the stories from the old days when a 100w mk2 could be had around $450 and there were several listings... forget that stuff.

    These quieter days is not so much about power or distortion but pure guitar volume-Pot roll off tone.

    It’s called a “player piece” with different iron in it who cares it’s still a 1970
     
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  4. fifteenohms

    fifteenohms Well-Known Member

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    For me a different output transformer is more a decision factor than the PT.
     
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  5. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    In so many cases like this, is not the price worth a thousand words?
     
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  6. jstich

    jstich Active Member

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    Asbestos was used in a lot of heat resistant products back in the day. And yes unless the amp is free, there should be a selling price listed for context.
     
  7. Antoon

    Antoon New Member

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    Is it just me or do those Erie filter caps look like they are badly bulging in the fourth picture?
     
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  8. fifteenohms

    fifteenohms Well-Known Member

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    The droolworthiness of how metal it is, is measured in the diameter of spit on the table
     
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  9. charveldan

    charveldan Well-Known Member

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    Leaking & bulging. they're bad.

    Can't wait for the "nothing wrong with original caps" crowd.

    Me personally i would not buy an amp thats not in working order unless i knew the seller & history of the amp.
     
  10. GIBSON67

    GIBSON67 Well-Known Member

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    Blue Sprague is a dual cap 120uf at 400v...I can't tell how it hooked up but it might be bypassing those bulging Erie caps. Better pics would help.
     
  11. neikeel

    neikeel Well-Known Member

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    No guys they are not bulging. On some of these caps the cap is live so there is a bit of tape on top of the exposed aluminium ( sorry - aluminum!). Sure the caps may well be past their best but a lot of conclusions being jumped too.
    The tube holders are asbestos and look like they are past their peak performance too.
    I agree the amp looks like a stock JMP50 Bass ( Model 1986)-apart from that Sprague cap.
    The pics are a bit limited but the cap is sitting where the rectifier block and snubbers (0.22uF 1000v) once sat. Hard to tell if it was a stand up or lay down PT originally.
    If originally stand up you can call it a sloppy install as they junked the reinforcing brackets.
    Price is important point negotiating point as it may well be a nice players amp with a little TLC.
     
    Last edited: Jun 21, 2019
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  12. stickyfinger

    stickyfinger Active Member

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    The tube retainers Rich M Sparky has been selling on Ebay has had his tested and came back negative for asbestos. Are they all equal??
     
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  13. neikeel

    neikeel Well-Known Member

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    :hmm:
     
  14. 67Mopar

    67Mopar Well-Known Member

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    The caps aren't bulging.
     
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  15. charveldan

    charveldan Well-Known Member

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    [​IMG]

    those caps have an easy 80 more years of life, ..... easy.

    When they are leaking it lets more tone out.
     
  16. neikeel

    neikeel Well-Known Member

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    You will note I did not say that. What I did say was that they are not bulging it is just the sticky lifting off.
    They should be tested and if duff replaced - simple. If we do not state things accurately we create the false impression that replacing tubes and the filter caps is a panacea for all tube amp problems which it is not.

    I buy amps that need fixing or have been f@+cked up by hacks and get them working properly, usually to as original correct working spec. preserving what is working well and replacing the junk, not ripping things out unnecessarily.

    YMMV.
     
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  17. charveldan

    charveldan Well-Known Member

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    50 year old electrolytics are way past due for replacement.

    Why do we even have to have this dialog over & over.

    Average electrolytic cap is spec'd for a lifespan of about 15 years.
     
  18. Pageburst

    Pageburst Member

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    My sincere thanks to all those forum members who were kind enough to offer insights with regards to that amp.
     
  19. neikeel

    neikeel Well-Known Member

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    Well.....did you?
     
  20. OatieO

    OatieO New Member

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    Hey Now,

    Beautiful 1970 JMP50 Bass.

    Looks like the Blue Sprague Mongo Capp is being used as a snubber cap, defiantly not the right type to use. I would change the Blue cap right away and install the dual .22/600 or .22/1000v. snubber caps. I use Sprague Vitamin Q .22/600v snubbers in my 1970 smallbox.

    The tube retainers are not asbestos, they are fiberglass and will put small glass splinters in your fingers if you handle them a lot.


    I would install all new F&T filter caps and bias caps for sure. Then install the square rectifier and snubbers like I did on this amp.


    [​IMG]
     
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