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Peavey 5150 Woes

Discussion in 'Backline' started by Melodeath, May 2, 2016.

  1. Melodeath

    Melodeath Moonbow

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    Long story/question ahead: I recently had some issues with my Peavey 5150 where the volume would sometimes severely drop out. It was an intermittent problem -- sometimes it wouldn't happen at all and the amp would be normal. Other times, the amp's volume would drop significantly after just 5 minutes of playing. I decided to swap the power tubes to see if that was the issue, but doing so had no affect on the problem. I was able to replicate the issue despite switching to new power tubes. So, I decided to take the amp to an amp tech here in town.

    The guy looked at the amp, did some cleaning/"preventative care/maintenance," and then told me that my issue was caused by my power tubes (which I knew wasn't accurate). I told him that couldn't be the problem, but he insisted and said my old chinese tubes are bad, and probably overheating, causing them to drop in volume. He said the 5150 "prefers cold tubes," and that he tried some Mesa 6L6 power tubes, and had no problems with the amp. His explanation didn't make sense to me, since I had swapped the old chinese power tubes with new Sovteks, and still had the issue. Anyway, I figured either his cleaning fixed the amp, or he simply got lucky and didn't hear the intermittent issue just by chance once he swapped to the Mesas. Either way, he wouldn't "warranty" his repair unless I bought new power tubes from him or brought in my Sovteks and TADs for him to check in my amp and make sure they were suitably biased.

    So, I gave him my power tubes, and he tells me that both sets bias "too cold" for my amp (17ma for the TADs, and even less for the Sovteks), and now he claims the 5150 likes/needs 30ma bias to work correctly (even though it's a fixed bias amp and I liked how it sounded before). Plus, all of a sudden he is now agreeing with me that it was probably the cleaning he did that fixed my amp. Anyway, he told me I should do some research and see if I can find some tubes that will naturally bias around 30ma in a 5150. He then added a resistor to my amp so that the TADs would bias closer to 30ma (a mod I didn't authorize, and I will ask him to remove that resistor and leave my amp stock).

    Does the stuff this guy is saying even make sense? Everything I've ever read/heard is that 5150s are fixed bias very cold.
     
  2. waav studios

    waav studios Member

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    its the ribbon cable the connects the power amp board to the preamp board. look for burns on it, it might be small, it might not burn at all, but they are definitely making intermittent contact. those ribbon cables are junk and they fail all the time. try cleaning them out or buy a new one and i bet you your problem goes away.
     
  3. waav studios

    waav studios Member

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    here's the trick. when it cuts in volume, if you can pick it up off the cab and let it fall back down kinda hard and the volume cuts back in, my guess is those ribbon cables. they go bad all the time. terrible design.
     
  4. JeffTD

    JeffTD Senhor Testiculo

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    This guy sounds like a hack, or at least like he's not quite sure what he's doing with a 5150. I would get him to undo his mod and get another opinion from a different tech..
     
  5. waav studios

    waav studios Member

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    5150s do bias very cold when they are stock. that resistor he changed is the bias resistor and he modded it to run the tubes hotter, it sounds like. 30ma and around there is usually where you put it when you do a bias mod to a 5150. if you like the amp how it is stock then tell him to change it back. it does sound like he was slightly feeding you a line of bullshit though. tubes being too cold for an amp that takes 6l6's.......yea, no. especially an amp thats already fixed biased cold.


    most times, when volume is going in and out, its usually the tubes, but it can also be that ribbon cable i mentioned.
     
  6. Leevious

    Leevious Member

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    Hey now
    Are you using your effects loop? I had a very similar issue a few years ago with mine, long story short, the input/output jacks for the loop had to be replaced. Google "5150 effects loop issues" and see if there's anything that can help you there. Hope this helps...
     

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