Microphonic Tubes in Fuzz Box

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by stratovarius, Dec 14, 2005.


  1. stratovarius

    stratovarius Supporting Member

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    Every tube I try goes microphonic if some settings are too high. Should I try mechanical remedies such as rubber grommets? Could it be a component problem?
     
  2. bob-i

    bob-i Member

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    Are you sure it's a microphonic tube and not high frequency oscillation? I'd find it hard to believe that every tube was at fault, the issue may be somewhere else.
     
  3. stratovarius

    stratovarius Supporting Member

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    No, I'm not sure of anything! I did notice that with some tubes it's a little worse, so maybe I jumped to conclusions. I guess I need to take it to someone who knows what they're doing. It's almost not worth it to get a $150 item repaired but it is a rare effect with a really nice tone:

    http://www.thegearpage.net/board/showthread.php?t=116993
     
  4. Guinness Lad

    Guinness Lad Silver Supporting Member

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    Try a lower gain tube like a 12ay7, if it still goes ballistic on you there is probably something else wrong with it.
     
  5. bob-i

    bob-i Member

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    I'd say that it's most likely oscillation. Get a wooden stick, like a chopstick, and while it's making the oscillation try moving some of the wires around. If the sound changes, you've got lead dress issues. See if you can find a position on the wires that doesn't oscillate.

    Also, try tapping on the tubes using this chopstick. If it is a microphonic tube you should be able to set it off, or start some ringing with the settings lower.
     
  6. stratovarius

    stratovarius Supporting Member

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    Thanks for the suggestions, everyone. I'll order Chinese tonight so as to have the correct diagnostic tools. :AOK
     
  7. bob-i

    bob-i Member

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    :cool:
     
  8. stratovarius

    stratovarius Supporting Member

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    Good call, bob-i! The very first wire I touched made a huge difference. Thank you.
     
  9. bob-i

    bob-i Member

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    The pictures show lots of loose wires around in there. That's bad news, lead dress is critical, moving a single wire a 1/2" can make or break a ckt.
     
  10. stratovarius

    stratovarius Supporting Member

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    It's not easy to get past the metaphor of little ping pong balls flowing through a pipe, is it? It's not easy to appreciate that it's all about magnetic fields!
     
  11. bob-i

    bob-i Member

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    Yes, not to mention that a capacitor is nothing but 2 conductors close together.

    Often the difference between a good amp and a great amp is just the lead dress. HiWatt for example is excellent in this where Fender, especally the CBS Fenders can be really sloppy. Sometimes just rerouting wires is all that's needed.
     

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