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Laney AOR series 2 100 watt/Laney pro-tube 50 watt

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  • #1

    Laney AOR series 2 100 watt/Laney pro-tube 50 watt

    Hey guys. I have these two amps that both keep blowing fuses at maximum volume. They tend to be okay when not driven so hard. All the voltages in the amp are okay.
    I have noticed a crackling sound, momentarily before the fuse goes.
    I'm wondering if this is a documented problem with these amps? I have seen articles about similar problems with the AOR.
    Any help would be great,
    Thanks.
    Tags: None
  • #2
    Is this a bench test into the correct load?

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    • #3
      I didn't look it up, but if you have, and seen others with the problem then let's assume it's not uncommon. So why would the amp do this? I dunno? I don't have a schematic to look at (It's always good to post a schematic here when asking about a particular amp). I do know that many Laney's run high-ish plate volts. I know that people like to crank them up. I know that new tubes aren't always up to the same abuse as "back in the day" tubes. And I know that there are circuit changes that may help improve the pushed stability of a cranked amp in the event that newer tubes don't hold up like older tubes. But I can't say which ones apply because I don't know the Laney AOR circuit off the top of my head. With a schematic I could probably make some suggestions.
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "If you're not interested in opinions and the experience of others, why even start a thread?
      You can't just expect consent." Helmholtz

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      • #4
        Do they have those green plastic impedance selectors?
        I've seen those go bad.
        Can you jumper a load directly to the output transformer wire(s) to bypass that switch?

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        • #5
          High volume then fuse blows always makes me suspicious of power tube issues.
          Originally posted by Enzo
          I have a sign in my shop that says, "Never think up reasons not to check something."


          ​

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          • #6
            Originally posted by g1 View Post
            High volume then fuse blows always makes me suspicious of power tube issues.
            Well that was sort of my point above. Sort of. There may be circuit values in those amps that aren't as compatible with current production tubes as the tubes available in the 80's. It;s possible that 'as seen by that amp' all new tubes are bad power tubes.?.
            "Take two placebos, works twice as well." Enzo

            "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

            "If you're not interested in opinions and the experience of others, why even start a thread?
            You can't just expect consent." Helmholtz

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            • #7
              I would start with checking bias current of each output tube. Maybe we're running on "the edge of safe" and pushing just a bit harder sends you over the edge. Do the tubes red plate? Do you have a bias probe? Are there cathode resistors for measuring current? Do you have a schematic?
              "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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              • #8
                Thanks for the help guys. I'm going to look at a few of your ideas. Fyi, I have used a 16 ohm dummy load @ 400 watts. And I've been using this schematic
                https://www.google.com.au/search?q=l...CfK9BikfJcY%3D

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