Plexi 911!!!!!!!!!!!!!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Mooncusser, Jan 5, 2008.


  1. Mooncusser

    Mooncusser Member

    Messages:
    2,216
    Joined:
    Jul 28, 2005
    Location:
    CC, MASS/SW, FL
    Hey y'all,

    Happy New Year......................

    Ok, I have a 2000 model 100 watt Marshall 1959 SLP RI (no fx), and I need some help.

    My "High treble" loudness1 channel isn't working properly. Loudness 2 "normal" channel is fine.

    The High treble channel is all of a sudden fizzy, and has a massive volume drop.

    For years, I have jumpered out low1 into high 2, and then plug into high 1 as alot of folks do. This just happened a couple of days ago and I am bummed out pretty bad.

    I took out the jumper and tested the "high treble" channel by itself and sure enough,.........almost inaudible volume and a harsh fizzy sound, even cranked.

    The "normal" channel on its own is perfect. Thats why I noticed something wrong because it was getting the normal operation from the normal channel, but the non functioninal blend of the two tipped me off instantly.
    What could this problem be?
    A HUGE thanks in advance,
    Mass
     
  2. bob-i

    bob-i Member

    Messages:
    6,876
    Joined:
    Oct 16, 2005
    Location:
    Central NJ
    I'd start by replacing V1. The normal channel uses one half, the bright uses the other half. All other tubes run with both channels.
     
  3. Mooncusser

    Mooncusser Member

    Messages:
    2,216
    Joined:
    Jul 28, 2005
    Location:
    CC, MASS/SW, FL
    Thanks bob-i!

    I'm running one of those GT Mullard copies in V1. I'll switch out asap and re-post on the results. I hope thats it.

    All the best,
    Mass
     
  4. jezzzz2003

    jezzzz2003 Member

    Messages:
    2,794
    Joined:
    Dec 6, 2005
    Location:
    aussie
    Does the amp jump and drop in volume if you tap the chassis?
    I had a very similar problem recently that was hard to trace, it turned out being a bad connection on the PCB which is hard to get at without pulling it out.
     
  5. Mooncusser

    Mooncusser Member

    Messages:
    2,216
    Joined:
    Jul 28, 2005
    Location:
    CC, MASS/SW, FL
    Hi jezzzz2003,

    No, it didn't drop in volume from a chassis tap........I would figure a PCB or grounding problem there. The tubes weren't microphonic either. In this case I got lucky because I was getting ready to field strip the head and go through it with a fine toothed comb. I popped that older GT-Gold series Mullard copy out and it failed on the 'ole Hickock.
    I popped a NOS GE 12AX7A in and voila~~~ she's alive and well again.

    Thanks for all your help!
    All the best,
    Mass
     

Share This Page