Power tube rattle in combos - no cure?

Discussion in 'Shock Brother's DIY Amps' started by Little Ricky, Feb 16, 2009.

  1. Little Ricky

    Little Ricky Tele-Holic

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    I have an Ampeg Jet (15 watts 112) combo, and attempted to fix some rattling, but it seems that power tube rattle is just here to stay. I used 2mm rubber tape with glue on one side (normally used to insulate pipes) to insulate most of the chassis, ruling that out as a possible source. Then I added some to the metal bar that holds the power tubes, then I made a 3-sided cardboard cage for the tubes and insulated that, and wrapped it around the tubes with rubberbands (leaving room for air to move). The power tube rattle refuses to go away :confused:
    It's a shame because I love to crank this thing. Of course, this probably wouldn't show up on a recording if you mic it from the front, or in live situations with a drummer, but it's annoying when jamming alone.

    So, FYI, rubber tape insulation doesn't dampen power tube shimmy.
     
  2. marshman

    marshman Friend of Leo's

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    Just to be sure, have you tried to physically seperate the tubes from the vibration source, see if they still rattle, make sure they're the problem?

    Try driving a separate cab from the amp, OR remove the chassis from the cabinet and set it on a table, hook up an extension of some sort, then play the amp as normal and see if the vibration persists. Be careful, though, there are little, inoffensive bits inside a live tube amp that can kill you right quick.

    Next step for me if the rattle persists would be to try and get a different set of power tubes, see if it's just that one set that does it or some sort of design hitch...
     
  3. shadowfan

    shadowfan Tele-Meister

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    Could the glass envelope be loose from the bakelite base on the power tube? If so you might be able to glue it back. I imagine JD weld would stand up to the heat. Did you try another tube?

    Could also be a tube that has become microphonic. With the amp on tap each tube with a pencil and listen. When you hear noise, you have found the faulty tube; replace it as one of the elements has become loose inside the tube from metal fatigue or even a shock.
     
  4. SimpleOne

    SimpleOne Friend of Leo's

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    "Tube Tamers" avail. on ebay, maybe "Tom's Tube Tamers" I think. Google that on this forum. Comes up rather frequently. Adieu.
     
  5. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    It could be a microphonic tube or a physical sound from the cab itself.

    As mentioned, try plugging the amp (it's brain) into another speaker cab (of the same impedance). This will eliminate cab rattle from the equation.

    Try new tubes. This will eliminate a bad/microphonic tube from the equation. You can gently tap the smaller preamp tubes with the amp on to see if they're bad/microphonic - if they are bad, the gentle tapping will actually come out through the speakers.

    If both of these things still don't work, you may need to get tube retainers for the power tubes. They mount to the tube socket itself and use springs to hold the tube against the socket better. Replace all preamp sockets with ones that have sleeves for the twist-on sping loaded preamp tube retainers.
     
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