Vintage Super Lead 100 Problem, Please Help!!!

Discussion in 'The Workbench' started by Frank Plante, Dec 23, 2018.

  1. Frank Plante

    Frank Plante New Member

    Joined:
    Dec 23, 2018
    Messages:
    18
    Likes Received:
    1
    Hey everyone,

    I have a vintage JMP Super Lead 100 and it started making a sort of loud static-like sound when I play. It doesn’t have any problem if I don’t play, and the problem seems to increase as I increase the treble/presence. I have tried the head with another cab, it has the same problem. I took it to two different techs, they couldn’t fix it. I changed the preamp and power amp tubes, I cleaned the tubes sockets, nothing seems to work and I’m getting pretty desperate because it really is a killer amp and I don’t have any ideas anymore. Can somebody help me?

    By the way, is it possible to send a video or an audio file so that you can see or at least listen to the sound it makes? I'm don't seem to be able to.
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    15,419
    Likes Received:
    9,290
    Location:
    Start the reactor... Free Mars!
    (Bump this to Workbench?)

    Yes we will help you.
    You need to make several posts before you can attach files...but yes you can attach a sound cloud or you tube file.

    We will probably ask you to measure inside the amp with a volt meter, can you do that?

    Can you take pictures of the inside of the amp?
     
  3. Frank Plante

    Frank Plante New Member

    Joined:
    Dec 23, 2018
    Messages:
    18
    Likes Received:
    1
    Thank you so much!
    I can't even post google drive links to the videos... hmm and yes I can take a couple pictures! How would I take this thread to the workbench section? Sorry I'm new here haha
     
  4. neikeel

    neikeel Well-Known Member

    Joined:
    Feb 12, 2014
    Messages:
    3,764
    Likes Received:
    2,160
    Pics and voltages and sound clips are all good:agreed:
    One or two things spring to mind:
    1) Failing preamp filter cap (on V2)
    2) Failing plate resistor
    3) Had similar thing with a JMP - turned out to be a corroded HT fuseholder internals caused intermittent connection with the amp being cranked sitting on the cab, weirdly a similar intermittent static sound that was not apparrent with all my other debugging tests................?
     
    Last edited: Dec 23, 2018
    mAx___ likes this.
  5. Frank Plante

    Frank Plante New Member

    Joined:
    Dec 23, 2018
    Messages:
    18
    Likes Received:
    1
    Here are a few pictures, tell me if you need more! Although I still can't post any link so I can't send you the soundclips
     

    Attached Files:

  6. Chris-in-LA

    Chris-in-LA Well-Known Member

    Joined:
    Jul 19, 2018
    Messages:
    755
    Likes Received:
    430
    Location:
    Los Angeles
    I've had a problem similar to this that was caused by a cold solder joint. It can't hurt to check the connections with a magnifying glass.
     
  7. Frank Plante

    Frank Plante New Member

    Joined:
    Dec 23, 2018
    Messages:
    18
    Likes Received:
    1
    I already tried that, thanks though. Another thing to note is that I can play. the sound doesn't cut or anything like that. There's juste a weird static noise behind the sound of the amp, if that makes sense.
     
  8. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    15,419
    Likes Received:
    9,290
    Location:
    Start the reactor... Free Mars!
    Have you measured the bias current with a meter?
    Do you have a bias probe?
    What output tubes are installed?

    Cold bias will cause static noise, almost like the sound of a blown speaker.
     
  9. Frank Plante

    Frank Plante New Member

    Joined:
    Dec 23, 2018
    Messages:
    18
    Likes Received:
    1
    I
    I was planning to order a bias probe in like 5 minutes haha, will the Eurotube one do the job?
     
  10. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    15,419
    Likes Received:
    9,290
    Location:
    Start the reactor... Free Mars!
    Let's get more close up pictures of this area, output tube sockets.
    Looks like a burned screen resistor but can't see really clearly.

    SLP100.png

    SLP100.png
     
  11. anitoli

    anitoli Well-Known Member

    Joined:
    Jul 9, 2011
    Messages:
    7,002
    Likes Received:
    8,011
    Location:
    Lewiston, Maine U.S.A.
    All you need to bias that amp is 4 1ohm 2w precision resistors placed across the cathode connection and a multimeter.
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    15,419
    Likes Received:
    9,290
    Location:
    Start the reactor... Free Mars!
    What meter do you have?
     
  13. Frank Plante

    Frank Plante New Member

    Joined:
    Dec 23, 2018
    Messages:
    18
    Likes Received:
    1
    Is that better?

    By the way, can I inbox you the links so that you can post them in the thread? I think a sound sample would be really good thing to have here haha
     

    Attached Files:

  14. Frank Plante

    Frank Plante New Member

    Joined:
    Dec 23, 2018
    Messages:
    18
    Likes Received:
    1
    My brother is an electronic tech, he has a bunch of multimeters
     
  15. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    15,419
    Likes Received:
    9,290
    Location:
    Start the reactor... Free Mars!
    Looks like screen grid resistor is toast.

    slpscreenresistor.png
     
  16. Frank Plante

    Frank Plante New Member

    Joined:
    Dec 23, 2018
    Messages:
    18
    Likes Received:
    1
    Thanks! That would be the green one right? It is hard to see on the resistor itself, is there a way to know what the value of the resistor is?
     
  17. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    15,419
    Likes Received:
    9,290
    Location:
    Start the reactor... Free Mars!
    Turn amp off
    Unplug power
    Remove the 2 output tubes.
    Set meter on ohms
    Measure between pin 4 and pin 6 of output tube socket(s).
    Both sockets should read 1000 ohms.

    If you don't get the 1000 ohms, the screen resistor should be replaced.
    1000 ohm, 5 watt, wire wound resistor.
    Usually these are replaced on both sockets so that the 2 resistors match.
     
    Last edited: Dec 23, 2018
  18. Frank Plante

    Frank Plante New Member

    Joined:
    Dec 23, 2018
    Messages:
    18
    Likes Received:
    1
    Thank you very much! I actually have 4 tubes, so I should replace the 4 resistors?
     
  19. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    15,419
    Likes Received:
    9,290
    Location:
    Start the reactor... Free Mars!
    Take out all 4 tubes and test all 4 sockets.
    1000 ohms between pin 4 and pin 6 on each socket.
    But I think at least 1 is bad.
    Yes if you want you can make all 4 the same type.

    If you don't know how to solder find somebody to help you.
     
  20. ampmadscientist

    ampmadscientist Well-Known Member

    Joined:
    Jun 26, 2014
    Messages:
    15,419
    Likes Received:
    9,290
    Location:
    Start the reactor... Free Mars!
    It's good your bro is a tech, he can help you replace the 4 sockets and the screen grid resistors.

    SLPSOCKET.png
     
    mAx___ likes this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice