Tubes Going Bad?

Discussion in 'Amps and Cabs' started by musical123, Feb 27, 2009.

  1. musical123

    musical123 Member

    Oct 20, 2008

    I have a Mesa SOB 1x12 combo and I think the pre-amp tubes are going bad. My tubes are from Mesa and are around 1 year old.

    When I hit a harmonic, even at low volume, sometimes I get a sound like someone is lightly hitting a wine glass at a rapid rate. I assume that this is a pre-amp tube since this happened in the past and was corrected when I swapped one of them out.

    My questions are:

    Why do I keep needing to replace tubes?

    Is there a way to secure the tubes better so they do not vibrate as much (right now they are held in place by a metal cover which uses a spring to hold the tube in place)?

    Do you think this is a pre-amp tube?

  2. surfdawg99

    surfdawg99 Member

    Feb 20, 2009
    I just had a 12ay7 go bad in my amp. Every time I played a B, for some reason it would start this horrible sound. Try plugging the amp in with the volume on about 3, pull the tube covers off before you turn it on! Now with the amp on, tap the tube with your finger, if they sound strong through the speakers they may be going "microphonic", when I did this V1 sounded terrible, V2 was quiet. I replaced the bad 12ay7, and it sounds like a million bucks again.

    It is most likely that you just got a bad tube, and there is nothing wrong with the amp. Try and get the best quality tubes you can that have been tested.

  3. Blue Strat

    Blue Strat Member

    Aug 2, 2002
    Sterling, VA (not far from Washington DC)
    Probably a microphonic preamp tube. The only way to know for sure is to replace it.

    Some amps are very picky about preamp tubes...especially "high gain" amps with built in overdrive.
  4. majorledhead

    majorledhead Supporting Member

    Mar 5, 2006
    Slippery Rock
    What make of tube have you been using ? There is some low quality tubes out there that go bad very quickly. You can try tapping the tubes with the eraser end of a pencil ( with the amp on ) and listen for that vibrating sound. You can "sometimes" figure out what tube is bad. But some quality tubes from a reputable dealer. ( there is some on this board )
  5. RussB

    RussB low rent hobbyist Silver Supporting Member

    Jul 3, 2004
    Try NOS 5751's in that Mesa. I ran them in a MKIII and a 50Cal with much success. They sound geart and are very durable. You will only need two.

    MikeK can hook you up with some for a fair price
  6. Timbre Wolf

    Timbre Wolf GoldMember Supporter Gold Supporting Member

    Oct 14, 2005
    Berkeley, CA
    Because you keep buying Mesa tubes.

    Try KCA (Blue Strat; a few posts back), or another reputable tube dealer, and buy some better quality tubes. It may seem expensive at first, but you'll be happier in the long run.

    - Thom

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