Tube Amp probelm...must fix by tomorrow!!! (video included)

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Trego, May 1, 2008.

  1. Trego

    Trego Member

    Messages:
    1,038
    Joined:
    Jun 10, 2002
    Location:
    Lancaster, PA
    So, I was hoping this was something that would figure itself out. The amp is a Mesa Boogie .50 Cal +

    When the amp is not doing anything, it makes no noise. If the amp is touched or tapped, or in my case, on a stage with people walking around and a drummer, the amp makes a crackle sound. I played a whole show with it doing it the other day, because it was a small little venue. Tomorrow's show is pretty big and I would love to fix this if it something simple.

    Link to video of problem:
    http://www.youtube.com/watch?v=O18__YG5qTw

    FYI:

    The amp makes noise if there is a guitar going through or none at all.

    The amp has two 6L6's and five 12AT7's

    All the tubes are lighting up.

    The plastic pin on one of the MESA 6L6's broke, I took the plastic pin out of the amp, and I replaced both 6L6's with brand new GT 6L6's rated at 6.

    If you have any idea to what this might be, please message me.

    Blessings, Matt Trego
     
  2. Dave C

    Dave C Gold Supporting Member

    Messages:
    1,360
    Joined:
    Jun 10, 2005
    Location:
    Waterford Ct
    If the amp worked ok with the old tubes...either put them back in (if you can get the correct pin in the correct hole in the socket) or try another pair. Sounds like connection is bouncing with vibration...it could be inside the tube...or elsewhere. Try tapping on the power tubes to see if you can induce the noise.
     
  3. Adwex

    Adwex Member

    Messages:
    520
    Joined:
    Jun 15, 2007
    Location:
    Long Island, NY
    Yeah, sounds like either a microphonic tube, or some loose connection external to the tube.
     
  4. IIIBOOMERIII

    IIIBOOMERIII Member

    Messages:
    1,392
    Joined:
    Nov 14, 2003
    Location:
    Texas 27.742857, -97.401927
    :agree


    Get a new 12ax7, it is probably V1. In Boogies V1 really take a pounding
    and it is a common problem. When I had a MkIII there was even a tube holder for an extra 12ax7 in case you needed one in a pinch. IIRC there is nothing in the signal path from the input to V1.
     
  5. Trego

    Trego Member

    Messages:
    1,038
    Joined:
    Jun 10, 2002
    Location:
    Lancaster, PA
    No, the same thing happened with the old 6L6's

    If I hold the 6L6's and tap them, they don't do anything but I can gently tap just about anywhere and it will make the noise.

    Could it be a problem with the spring reverb?

    Thanks for the help so far guys.
     
  6. Trego

    Trego Member

    Messages:
    1,038
    Joined:
    Jun 10, 2002
    Location:
    Lancaster, PA
    okay...I will borrow one of my friends test it out...

    does it matter that mine is a 12at7?
     
  7. Adwex

    Adwex Member

    Messages:
    520
    Joined:
    Jun 15, 2007
    Location:
    Long Island, NY
    Hmm, that sounds odd to me. A 12AT7 is lower gain than a 12AX7.
    A low gain V1 in a Boogie??
     
  8. Apprentice

    Apprentice Member

    Messages:
    33
    Joined:
    Sep 25, 2007
    check your plate resistors, their connections and those of the components around them.
     
  9. IIIBOOMERIII

    IIIBOOMERIII Member

    Messages:
    1,392
    Joined:
    Nov 14, 2003
    Location:
    Texas 27.742857, -97.401927
    Well if you like the tone of the 12at7 stay with it. You will get higher gain
    with a 12ax7. A 12ax7 is like a gain rating of 100% while and 12at7 is about 60%.....but I may be wrong. No matter how you slice it the 12ax7 will give you more gain.
     
  10. Trego

    Trego Member

    Messages:
    1,038
    Joined:
    Jun 10, 2002
    Location:
    Lancaster, PA
    what is that?
     
  11. Apprentice

    Apprentice Member

    Messages:
    33
    Joined:
    Sep 25, 2007
    they're the resistors that are part circuit that supply the voltage to the plates of each tube. your problem sounds a lot like one i came across while working on a 22+. in that amp, a plate resistor was failing and leaking voltage. it was a simple fix, but those amps can be somewhat of a pain to diagnose. sounds like you need to take the amp to a tech as it is not likely something that can be solved w/o opening up the amp and poking around.
     
  12. Trego

    Trego Member

    Messages:
    1,038
    Joined:
    Jun 10, 2002
    Location:
    Lancaster, PA
    Just now...

    I replaced the 12ax7 in the V1 and it is still making noise...maybe I am crazy, but I think it might be less than before...but it is still very sensitive to touch and movement.

    Any other ideas?
     
  13. soldersucker

    soldersucker Member

    Messages:
    2,397
    Joined:
    May 20, 2006
    Sound like every cold solder joint ive ever heard.Chop stick the board and i'm betting you will find a bad solder joint,remelt add a little fresh solder.
    If this sounds over your skill level don't do it:worried
     
  14. VikingAmps

    VikingAmps Member

    Messages:
    395
    Joined:
    Feb 21, 2007
    Location:
    VA
    It's something right up front since the volume control affects it. Could be a bad connection around V1 somewhere.
     
  15. Trego

    Trego Member

    Messages:
    1,038
    Joined:
    Jun 10, 2002
    Location:
    Lancaster, PA
    I do not now how to solder.

    Is there anything I can do or is this going to need to go to a tech?
     
  16. soldersucker

    soldersucker Member

    Messages:
    2,397
    Joined:
    May 20, 2006
    Get to a teck is my advise.
     
  17. pfrischmann

    pfrischmann Member

    Messages:
    2,989
    Joined:
    Jan 6, 2002
    Location:
    In the ATL.
    If you cannot find it by substituting tubes. Take it to a tech. Based on your responses, I believe this will save you time, money and frustration.
     
  18. pfrischmann

    pfrischmann Member

    Messages:
    2,989
    Joined:
    Jan 6, 2002
    Location:
    In the ATL.
    While we're at it, have your tech put in and old fashioned bias adjustment. Most Mesas do not have one. It can really help the tone of some amps.
     
  19. Rattle&Hum

    Rattle&Hum Supporting Member

    Messages:
    276
    Joined:
    Feb 28, 2007
    Location:
    Indianapolis, IN
    The sound was echoing in the reverb - so that would indicated that it is somehow in the signal path before the reverb circuit. It is possible that one of the preamp pots is going bad, and the slightest movements are causing connections.

    Try turning each knob and gently wiggling them to see if one of them is particularly symptomatic.
     

Share This Page