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5f11 Troubleshooting

Discussion in 'Shock Brother's DIY Amps' started by Mark the Moose, Dec 1, 2020.

  1. Mark the Moose

    Mark the Moose Tele-Afflicted

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    I have a very quiet, high pitched sound in my 5f11 amp which I would like to try and chase down. It will "pulse" with the tremolo or even out if I zero the depth control. It does not go away with the instrument unplugged and it is not affected by the volume or tone control. I'm looking for some trouble-shooting advice if there are some steps beyond the following:

    1. Change preamp tubes
    2. Change power tubes
    3. Chopstick around, especially heater wires
    4. Check voltage levels and come back for more advice
     
    EmWeAh likes this.
  2. SnidelyWhiplash

    SnidelyWhiplash Friend of Leo's

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    All of the above wouldn't hurt.
     
  3. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    #4 is always a good idea.

    Can you post a sound clip/video? :)
     
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  4. Mark the Moose

    Mark the Moose Tele-Afflicted

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  5. JuneauMike

    JuneauMike Poster Extraordinaire

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    Verify all of your ground connections as well.
     
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  6. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Some spitballing to try:
    • pull V1 and see what happens. If it goes away you've shortened your list.
    • swap V1 & V2.
    • If you have switch or grounded rca plug, plug it in and see if it changes
    • the high pitch kinda sounds like a microphonic tube to me, like it's vibrating
    • gently tap the tubes
    • I want to say that if Vol/Tone don't affect the noise, it will probably be past V1, but don't hold me to that.
     
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  7. dan40

    dan40 Friend of Leo's

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    Is this a brand new build or an amp that has been working properly before this noise started?
     
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  8. Mark the Moose

    Mark the Moose Tele-Afflicted

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    Two year old build. Original JJ tubes.
     
  9. Mark the Moose

    Mark the Moose Tele-Afflicted

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    I found that the sound gets louder as I tap on the tubes. Also, it goes away if I tip the amp forward. I'm suspicious of the preamp tubes.
     
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  10. Mark the Moose

    Mark the Moose Tele-Afflicted

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    Thanks all. Couple 12ax7 tubes on order, I’ll be back if the problem persists.
     
  11. JuneauMike

    JuneauMike Poster Extraordinaire

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    Hmm. Have you considered re-tensioning the tube sockets? Its weird that changing the axis of the amp causes a difference. Also, those are not old tubes, and JJs have a good reputation as far as I know. This assumes all your pin readings are as expected. Is that true?
     
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  12. Mark the Moose

    Mark the Moose Tele-Afflicted

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    I need to open it up and take some voltage measurements. I thought it was odd that tipping the amp made a difference.
     
  13. Mark the Moose

    Mark the Moose Tele-Afflicted

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    Update: I bumped a power tube and the noise stopped. Bumped again and it started up again. Pulled and swapped the power tubes and it hasn't come back. I'll have to open it up over winter break and check voltages.

    If I did half the stuff I said I need to do over winter break I'd be a super hero...said every teacher ever.
     
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  14. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Good fix based on good testing. You're a teacher? Sure, voltages when able; we can hope the tube just got tired. You have bigger issues right now, I'm sure. Stay safe.
     
  15. Mark the Moose

    Mark the Moose Tele-Afflicted

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    Thanks KF. Yes, I'm a music teacher. Everything is online for me, so I have more risk of being electrocuted by my amp than from anything related to teaching!
     
    King Fan likes this.
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