Crate Palomino V-32 bias?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by rockon1, Aug 19, 2006.

  1. rockon1

    rockon1 Member

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    Just wondering if being a "class A" amp the bias needs to be adjusted when swapping power tubes or not. Thanks Bob
     
  2. Fretts

    Fretts Member

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  3. hasserl

    hasserl Member

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    Well, that isn't true. First off, I doubt the amp is truly Class A. It's probably cathode biased, which isn't the same thing. Operating class of an amp has no bearing on what type of bias method is used. Second off, just because an amp is cathode biased doesn't mean the bias should not be checked when changing tubes. It does mean that it will probably be fine. But it might not be and how are you going to know unless you check it?
     
  4. Fretts

    Fretts Member

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    OK you could say we are both right. You can't know unless you check it, but self-bias almost always works out pretty well, especially on a newish amp where the parts haven't drifted dramatically in value. The Palomino isn't true class A, of course, almost nothing outside of audiophile triode listening amps are true Class A. But there's no arguing that they are biased "hot". It's a 20 ohm resistor for the four power tubes.
    If the tubes are glowing red, then I can say the bias better be checked and probably replace the resistor. Otherwise, it almost always is fine to just replace the tubes on a cathode-bias amp, check for red plates, then button it up and play.
    As always, YMMV, but in my personal experience, so far so good.
    Except for a Sano I worked on that had EL34's in a cathode bias arrangement that were glowing. I did replace the resistor on that one, and it calmed down and stopped glowing red.
     
  5. hasserl

    hasserl Member

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    By the time they're glowing they are way hot. Not the best approach IMO. But as I've said before, these things are very forgiving of the abuse we put them thru.

    You pays your money and you takes your chances.
     

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