Announcement

Collapse
No announcement yet.

Excessive Hum for Marshall JTM100

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Excessive Hum for Marshall JTM100

    Hello all, I have a hum issue which I am trying to track down. Recently, at my studio someone accidentally knocked over my JTM100 head on to the carpet. It fell off it's half stack. It took out a couple of power tubes which I replaced but now I get excessive hum at idle (nothing plugged into the jacks). Here are some observations:

    1) Hum is affected by all pots but especially the bass pot. Turning up the bass pot really accentuates the hum and makes it louder.

    however 2) if i turn both volume pots up full, the hum disappears (even if i turn the tone pots and presence). that is, with all pots on full (amp cranked on 11), the amp vanishes and it just sounds like a normal cracked plexi.

    I replaced all tubes and poked around with a chop-stick but no luck. Banged around on the transformers and knocked on the tubes as well with no luck. Can anyone give me a clue as to where I can look to so as to find where the hum might be coming from?? Input jacks? Leaky bias cap/diode? Any help is welcome.

    Thanks in advance...

  • #2
    My first thought would be a mechanical problem like a broken ground connection. That doesn't mean a big broken off wire, even though it could be that. More likely a oxidized jack ground or a loosened pc grounding screw that was made high resistance by the fall.

    Comment


    • #3
      Originally posted by 52 Bill View Post
      My first thought would be a mechanical problem like a broken ground connection. That doesn't mean a big broken off wire, even though it could be that. More likely a oxidized jack ground or a loosened pc grounding screw that was made high resistance by the fall.
      thanks bill. i'll go over the amp again tonight.

      Comment


      • #4
        went over the amp and finally found the problem. the power board stand-off had come loose which grounded the power caps. tightened it up and and the hum went away. Thanks again bill.

        joseph

        Comment

        antalya escort
        kartal escort
        sex vidio
        altyaz?l? porno
        antalya escort
        beylikduzu eskort bayan eskort bayan escort antalya sirinevler bayan escort
        Working...
        X