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Ultralead repair

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  • Ultralead repair

    Hi all,

    Anybody know of someone who could help me source and replace the KT-88s on a Fryette Ultralead? The good folks at Fryette customer service are less-than-responsive regarding service and getting replacements. I had e-mailed them after replacing all fuses, checking impedances, using other cabs, etc. They replied 3 weeks ago asking to confirm the serial number. Then nothing, despite my weekly queries.

  • #2
    Hi Erik. I buy my tubes from Mojo Music Supply. http://www.mojotone.com.

    You'll want to get a matched quartet. I usually go for JJ's. http://www.mojotone.com/amp-parts/va...e#.VYLc02Bn1Ys

    But you'll need to bias the amp. It's easy with one of these: http://www.mojotone.com/amp-parts/Tu...r#.VYLdJGBn1Ys

    You'll just need to find the bias adjustment in the amp. Hope that helps.

    -D

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    • #3
      PS - what's wrong with the amp? i.e. how do you know the PT need to be replaced?

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      • #4
        Hi Dave -- the amp kept taking longer and longer to "clean" up, so to speak. The best way to describe the sound is foggy. So I checked the aforementioned items, and then e-mailed them. It started blowing the mains fuse too, which probably means I have a short somewhere. I don't have a Gm tester to know for sure, though.

        So I hope it's just the tubes.

        As for biasing, KT88s should be ~65% of max plate dissipation? So 40W (PD(max)) / 450V (approximate plate voltage) = 0.08A == 80mA. That would be ~58mA per tube, or 231mA for all of them.

        Thanks for the links.

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        • #5
          Update -- that's what it was. Back in business.

          Ended up borrowing a Bias Rite which made it trivial. I remember my EE classes, but not well enough to go at it with just a multimeter. Dave (and others), what do you like for your bias settings? I ended up at ~55mA. The plate voltage measured higher than I was anticipating, but I didn't want to push the current too high.

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