Mosquito overdrive

Discussion in 'Amp Central Station' started by Tele295, Mar 22, 2004.

  1. Tele295

    Tele295 Poster Extraordinaire

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    My SF Vibrolux Reverb has a beautiful, rich, robust clean sound, especially with the Weber 10A150s. So why does it sound like an angry mosquito when it starts to break up?
     
  2. jmiles

    jmiles Friend of Leo's

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    T295, have you tried

    just plugging it into another speaker to see if it's the speaker or the amp?
    jmiles
     
  3. fezz parka

    fezz parka ---------------------------

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    Hey Miles...

    It's nice and full when clean, but when it's cranked it gets buggy? Like a nasty unmusical distortion? Does it noticably thin out as well? Sounds like you're getting some crossover distortion. Have the bias checked.
     
  4. jmiles

    jmiles Friend of Leo's

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    T295, do you have a scope?

    That'd tell you fer sure. I just thought it might be good to be sure it wasn't the speaker before rippin' into the amp.
     
  5. fezz parka

    fezz parka ---------------------------

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    Always good to check them speakers! Find someone with a bias probe to check it out, Miles. The plate voltage is higher on the SFVR than my BFVR. Are you using the 5U4 or a 5AR4 rectifier? If it's the 5AR4, your plate voltage will be around 460. I'd bias 6L6GC's around 60% (18w). Somewhere in between 35 and 39 ma should do the trick.
     
  6. Tele295

    Tele295 Poster Extraordinaire

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    It does thin out, but doesn't sound like that funky square-wave distortion I normally associate with crossover distortion. I'm not good with a scope, so I haven't checked the bias - wouldn't know what I'm looking at anyway.

    I'll check it with some other speakers this weekend.

    Chris - do you have a tech that you like to use down there? There's nobody up here anymore that I'd trust to do proper Fender amp work. I've even thought of shipping it out to Len to have a once-over. I just got the amp last summer and haven't have the hood popped and the oil checked.
     
  7. fezz parka

    fezz parka ---------------------------

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    The bias is pretty easy to check with a DVM. I could check it over for you...
     
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