PLASTIC JACKS

Discussion in 'Marshall Amps' started by dragonvalve, Nov 16, 2020.

  1. dragonvalve

    dragonvalve Well-Known Member

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    Amp gurus, is there an electrical reason for plastic circuit board speaker jacks and are they isolated from ground as they exit on the chassis?

    That said would replacing broken plastic jacks with metal ones wired to the board be any unseen problem ?

    [​IMG]

    The threaded parts with the nut separated from the rest of the speaker jacks, both on my JTM30. Just plastic turning back to petroleum I guess.
     
  2. william vogel

    william vogel Well-Known Member

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    I think the purpose of insulated jacks is to allow a specific chassis ground location.
     
  3. marshallmellowed

    marshallmellowed Well-Known Member

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    Not sure it would create any issues, but why not just replace any faulty jacks with the same design?
     
  4. dragonvalve

    dragonvalve Well-Known Member

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    Because they didn't last and the amp sat in a studio all this time from new. And finding the jacks might not be as easy as finding Switchcrafts.

    Are these board mount parts generic?
     
  5. South Park

    South Park Well-Known Member

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    Both metal and plastic jacks are isolated from chassis ground . The plastic cliffjack with the UK is good . If you get the metal ones don’t get the cheap ones . I think thar is a metal plating that good ones have . The Chinese crap don’t have the right plating to make a good contact. You can buy a old beat up fender amp with 50 year old jacks and it still works
     
  6. marshallmellowed

    marshallmellowed Well-Known Member

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    Not sure, it would depend on the pin spacing. I'd think replacements of some type should be available.

    Either of these could be made to work (wired if spacing is off)...

    https://www.musicalinstrumentshoppe...-wsdwkYosr14yvoyJHzEOegOkPfyumqwaAj6cEALw_wcB

    https://www.parts-express.com/neutr...K8jzQ_7AGUuU4ZwGql8nd7eExmO27ch4aAk7DEALw_wcB
     
    Last edited: Nov 16, 2020
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  7. dragonvalve

    dragonvalve Well-Known Member

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    Thanks marshmellowed. Was wondering if the branded makers made these types.

    Thanks South Park about the plating issues on some of these jacks. You're right about the conductivity. It is key.

    william vogel, that's what I was thinking but I'm not an amp tech.
     
  8. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

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    You need to measure the diameter of the hole in the chassis before ordering a replacement jack. Marshall style Cliff jacks require a .440 chassis hole and while you will see Switchcraft metal jacks advertised as .375 inch and the metal thread is .375 inch the Switchcraft isolation washers for them require a larger .440 hole.

    For the metal Switchcraft jack they make both a flat and shoulder isolation washer. The flat washers are worthless imo. The washer with the shoulder molded into it is best. The shoulder fits inside the chassis hole just put one on each side of the chassis panel.

    Also, with 3 pins the original jack looks like a stereo jack instead of a mono jack. Or the 3rd pin is a switch that grounds the tip when a guitar cord is not inserted. Best to confirm the operation of the original before ordering a replacement. The Cliff jacks are switched so removing the cord grounds the tip. Switchcraft makes a shunt tip jack that also grounds the tip when not in use.

    https://www.amplifiedparts.com/products/14-jack-switchcraft-mono-shunt-tip

    https://www.amplifiedparts.com/products/washer-switchcraft-s1029-shoulder-insulating-panels
     
    Last edited: Nov 17, 2020
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  9. dragonvalve

    dragonvalve Well-Known Member

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    Thanks coolidge56!
     
  10. CROWEMAG

    CROWEMAG Well-Known Member

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    Get Cliff UK jacks from a reputable dealer and be happy as a clam.
     
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  11. Flat5th

    Flat5th Active Member

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    Agreed. I don't care for cliff jacks. I tripped over the cord while it was plugged into my smalbox 50 and it immediately snapped the cliff jack in half. Luckily it did not break any connections,but it still needs to be replaced and the components are a really tight fit on that particular jack. The amp plays fine at home,but it won't be ready to go out and about with a broken cliff jack. Right now the jack is propped up on the circuit board with a wad of electrical tape. I don't trust my soldering skills when things are really tight so I am going to take it to a more confident tech.
    If you have your choice I would say go with switchcraft. They are metal and won't break as easily.
     
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  12. scozz

    scozz Well-Known Member Gold Supporting Member

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  13. dragonvalve

    dragonvalve Well-Known Member

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    Here's the patient. It had nothing to do with snapping a cord by trip. They both at the same time just came apart.



    JTM 30 SPEAKER JACK COLLARS DEFECTIVEgmp2.jpg JTM30 SPEAKER JACKS DEFECTIVE gmp1.JPG
     
  14. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

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    I did the exact same thing a couple months back. Got my size 12 foot snagged on a speaker cord and snapped the Cliff jack nearly in half.
     
  15. Flat5th

    Flat5th Active Member

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    Yep,I've seen that happen before with cliff jacks as well.
     
  16. Flat5th

    Flat5th Active Member

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    They will snap in a instant with a good pull from a careless foot. I found out the hard way and evidently you did as well. I make sure the cables are tucked under something or unplug when I am on standby.
     
  17. dragonvalve

    dragonvalve Well-Known Member

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    Ok the size of the chassis holes for the JTM30's speaker jacks is 0.5 a shade under 8/16ths or 12.3(?) mm.

    0.440 is 11.176mm

    Found this image online for a Fender blackface jack upgrade which needs a 1/2" hole.

    [​IMG]
    Shoulder washers for 0.5" chassis hole $0.16 a piece on a Switchcraft 1/4" jack.

    https://hoffmanamps.com/MyStore/per...plate&thispage=MiscHardware&ORDER_ID=!ORDERID!

    Inner hole size = .38"
    Chassis hole size/Shoulder = .5"
    Outer diameter = .63"

    Suggested is the long (0.375) shaft for use with shoulder washers instead of the standard (0.275) making it a Switchcraft L12A. "L" for long I surmise.

    JTM30 SPEAKER JACK hole  - Copy.JPG
    JTM30 chassis speaker jack hole is a 0.5" hole or 12.3mm.
     
    Last edited: Nov 17, 2020
  18. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

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    That's a sloppy chassis hole but you will be fine with this switchcraft jack and shoulder washers.
     
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  19. coolidge56

    coolidge56 Well-Known Member Double Platinum Supporting Member

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    Was it the 16 ohm speaker jack that broke or the 8 ohm/16 ohm extension speaker jack?
     
  20. dragonvalve

    dragonvalve Well-Known Member

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    It was BOTH at the same time. I noticed the nuts were loose on both. One collar fell off and the one with the speaker plug was broken but still attached by a sliver of the jack plastic.

    Ok that makes it simpler then. Thanks again!

    What I need to find out is what type of jack is on there whether shunting or not.
     

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