Dead tube socket

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Randy, May 13, 2008.

  1. Randy

    Randy Member

    Messages:
    3,885
    Joined:
    Sep 9, 2002
    Location:
    CT
    I've got a '71 Marshall Super trem which gives me a 0 reading on one tube socket with my Weber Bias Rite. I tried switching tubes and switching heads but the problem stays with the socket. :(

    I know how to solder and have a meter but have no real amp repair experience (although I want to learn). Where should I start?
     
  2. Nolatone Ampworks

    Nolatone Ampworks Silver Supporting Member

    Messages:
    2,736
    Joined:
    Jun 4, 2006
    Location:
    Flowery Branch, GA
    Before you do anything, make sure you fully understand the safety aspects of working on an amp as tube amps carry deadly voltages, and can store them in the filter caps and zap you even with the amp powered off and unplugged.

    Aside from that, I'm not familiar with the Bias Rite. What readings is it reading zero on? Basic intuition would lead me to look at the pin(s) that is/are showing zero and first visually inspect for loose/broken wires ,cold solder joints, etc. Make sure the socket contacts are not stretched out and someone not making contact.

    I'd check plate and grid voltage and if those are zero with amp not in standby, look for an open component (perhaps burned up?) that could effect the supply of those voltages.

    Beyond that, need more details to make any suggestions.
     
  3. Randy

    Randy Member

    Messages:
    3,885
    Joined:
    Sep 9, 2002
    Location:
    CT
    Hi Paul, thanks for the comments. The Bias Rite measures both plate voltage and cathode current. It does show a plate voltage of 496 V, but gives me a 0 ma reading of cathode current for this one socket only.

    I will look at the socket more closely tonight - it sure would be nice if it was simply a bent contact.
     
  4. Blue Strat

    Blue Strat Member

    Messages:
    30,036
    Joined:
    Aug 2, 2002
    Location:
    Sterling, VA (not far from Washington DC)
    Could be an open screen resistor, the 1.5K to pin 4.
     
  5. sickboy79

    sickboy79 Member

    Messages:
    10,417
    Joined:
    Aug 17, 2006
    Location:
    Chicago
    I was thinking the same thing. I had that happen to me a few years back. Turned out to be that resistor.
     

Share This Page