Peavey Mace VT Blown Screen Resistor Question

Discussion in 'Amp Tech Center' started by joshote, May 16, 2021.

  1. joshote

    joshote Tele-Meister

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    A band mate dropped by his Peavey Mace VT for me to look at. He said it starting smoking and the power died. He noticed one of the tubes not lit.
    This is what I found after opening it up:
    upload_2021-5-16_15-34-13.png
    That hole is very suspicious! But I don't see any under board connections and I think that a bad tube killed the resistor, or that is what I am hoping.
    I only have a 250 ohm 5 watt resistor, not the 100 ohm like the blown one. Would it be ok to use that value? Fender uses 470 ohm in the same location. The replacement tube I have is going to be slightly unmatched to the original tubes anyways.
    I'm good with amp safety and have done multiple cap jobs and a few scratch builds. I'd like to see if a new resistor and tube fixes it, otherwise it'll go in to a amp tech. The caps likely need replacing anyways and I've gotten spoiled by how easy it is to work on my old Fender amps..this thing is a monster.
    Thanks!
    upload_2021-5-16_15-33-54.png
     
  2. dan40

    dan40 Friend of Leo's

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    The 250 ohm will be fine.
     
  3. joshote

    joshote Tele-Meister

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    Thanks dan40
     
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  4. J. Bonkosky

    J. Bonkosky Tele-Holic Silver Supporter

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    I would shotgun all of those sand filled resistors. I find a lot of bad ones in the solid state Peavey amps. Most I’ve seen have been drifted out of spec or have been physically falling apart. If nothing else check them. Good luck.
     
  5. joshote

    joshote Tele-Meister

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    Thanks, will do.
     
  6. Jon Snell

    Jon Snell Tele-Holic

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    The screen grid internal sparking from a faulty valve will cause the screen grid resistor to fail.
    Replace the faulty pair of valves or it will happen again.
    Wire wound cement resistors cannnot drift out of specification. They are not carbon composition but wire. Wire Wound resistors are either OK or broken/burnt and open circuit.
    They can even survive glowing for a while in some cases and are very forgiving.
     
  7. J. Bonkosky

    J. Bonkosky Tele-Holic Silver Supporter

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    The ones I have encountered look as though they have absorbed moisture the values were out of spec, almost zero resistance. I have found this issue in a few Peavey power amps and several guitar amps I have had for repair in the last 5 years. I know cement resistors are pretty tough. All I know is I have been finding bad ones in Peavey amps from around the same vintage as the OPs amp. Just trying to help.
     
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  8. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Same on the Peavey thing - had a XXX head just last week and *three* out of 4 screen resistors failed open. Put in all 4 and new tubes and the amp was fine.
     
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