JCM900 100 watt 2100 - Charge the paddles to 300...

Discussion in 'Marshall Amps' started by coolidge56, Mar 28, 2020.

  1. coolidge56

    coolidge56 Well-Known Member

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    ZAP okay we have a pulse. Nurse prep the OR I'm going in.

    jcmrb4.jpg

    Choke incision completed lower left.

    jcmr01.jpg
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    What did you do to that poor little puppy? :shrug:
    Do you want to sell the circuit boards?
     
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  3. South Park

    South Park Well-Known Member

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    Are we installing a choke fear
     
  4. coolidge56

    coolidge56 Well-Known Member

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    Update:

    1. Placed 50+50uf filter caps with F&T's made in Germany.
    2. Replaced both the preamp and power tube sockets with Micalex. The old sockets were loose and beat up.
    3. Upgrade - stainless steel screws and lock nuts.
    4. Upgrade - added a Classic Tones 3H choke to replace the Marshall 100ohm resistor.
    5. Mod - added a mini turret board for the choke wiring.
    6. Mod - added a ground lug near the input jack for the Randall Aiken radio interference elimination mod.

    jcmr02.jpg


    jcmr03.jpg
     
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  5. coolidge56

    coolidge56 Well-Known Member

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    All the parts came in this week and I finished the rear board tonight. All new jacks, new effects loop level pot, replaced the cement resistors with wire wound, that black/white twisted pair on the right goes to the new choke replacing that cement resistor. Replaced all the wiring with Teflon insulated wire. Replaced the stiff as a board shielded wire left with Mogami.

    jcmr08.jpg

    I found and fixed one goober from a former tech or owner. Someone had soldered (I use that term loosely) a parallel resistor onto the R30 56k resistor to lower it to 47k. Since one end of the cold big ass globbed on solder job just popped off I removed it and the original which was a hot mess and replaced it with a new 56k.

    jcmr09.jpg
     
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  6. coolidge56

    coolidge56 Well-Known Member

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    Got a new toy in this week, made in USA I did my part to breath some life into the Covid-19 economy. Its a Pace ADS200 with the setback stand which automatically lowers the iron temp when its in the holder so it doesn't cook the tip. That's been an issue with my old Weller.

    jcmr05.jpg

    The Pace soldering iron is shorter which is great, and has a rubberized grip. Its all aluminum construction.

    jcmr06.jpg

    This unit is quite a bit heavier than the Weller, 120 watts, all metal construction. The ground jack was a nice touch.

    jcmr07.jpg
     
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  7. coolidge56

    coolidge56 Well-Known Member

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    The boards are finished, reassembly begins in 3...2...1

    jcmr12.jpg
     
  8. cozmacozmy

    cozmacozmy Member

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    tagged
     
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  9. anitoli

    anitoli Well-Known Member

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    Fuckin cool man.
     
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  10. coolidge56

    coolidge56 Well-Known Member

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    Nearly finished...

    jcmr15.jpg
     
  11. Lance Chambers

    Lance Chambers Well-Known Member

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  12. cozmacozmy

    cozmacozmy Member

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    Excuse my lack of intelligence here... Are these the original boards that you just replaced the wires with updated ones and added the choke? Or are these replacement boards?
     
  13. coolidge56

    coolidge56 Well-Known Member

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    Original boards with the following changes...

    1. Replaced the two main filter caps on the front board.
    2. Replaced all the pots front and back.
    3. Replaced all the cliff jacks front and back.
    4. Replaced the cement 4W resistors with wire wound 5W.
    5. Removed R37 the 100 ohm 4W resistor and replaced with a ClassicTone choke.
     
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  14. El Gringo

    El Gringo Well-Known Member

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    Pretty Impressive work . Is it fair to say that your JCM 900 has Point to Point Wiring ?
     
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  15. cozmacozmy

    cozmacozmy Member

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    I see, thanks.
     
  16. cozmacozmy

    cozmacozmy Member

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    Ps. you got all new updated tube sockets as well.
     
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  17. coolidge56

    coolidge56 Well-Known Member

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    Mostly no. The boards are PCB. The pots and jacks are PCB. Marshall's transition to PCB is almost complete with the exception of the tube sockets which on these are still bolted to the chassis. Later Marshalls move those to the PCB board as well.
     
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  18. El Gringo

    El Gringo Well-Known Member

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    Well, your work looked impressive to my eyes and I compliment you on a well done job !
     
  19. coolidge56

    coolidge56 Well-Known Member

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    Yes I replaced all the tube sockets. The original sockets were extremely loose e.g. tubes loose in the socket. I think the previous owner may have been rolling tubes I was kind of surprised how loose they were even the power tube sockets.
     
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  20. JCMDOUG

    JCMDOUG Well-Known Member

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    Very Very Nice.
     
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