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I think the 'H' in my H324 stands for "Huey"

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  • I think the 'H' in my H324 stands for "Huey"

    So, I've been going through this H324 I picked up and have a problem I've not encountered before. There is this thumping coming from the speakers. It is perfectly timed and never varies and sounds like a Huey (helicopter) about a mile out. At first, because of the timing (about 120 beats per minute) I figured it was emanating from the vibrato system, but stopping either drum has no effect. Neither do any of the tabs, other than the Volume Soft tab. And it's coming from all 3 speakers--channel A, B and the bass speaker--and I can put my hand on the cones and feel them shifting in and out. With this in mind I'm thinking power supply, but am open to other ideas....?
    Over the years: Hammond M3, BC, M102, B3, four X77s and three PR-40s, a Thomas Electra and a Celebrity, three Fender Rhodes, Roland HS-10, HP-2000, HP-600, RD-600, JV-880, a thing made by Korg (?), two Leslie 910s, 122, 257, 258, 247, two 142s, and three custom-built Leslies. Wow, way too much money spent!

  • #2
    120Hz, so twice mains frequency. Something in the power supply line is where I'd be as well.
    It's not what you play. It's not how you play. It's the fact that you're playing that counts.

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    Current instruments: Roland Atelier AT900 Platinum Edition, Yamaha Genos, Yamaha PSR-S970, Kawai K1m
    Retired Organs: Lots! Kawai SR6 x 2, Hammond L122, T402, T500 x 2, X5. Conn Martinique and 652. Gulbransen 2102 Pacemaker. Kimball Temptation.
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    Retired synths: Korg 700, Roland SH1000, Jen Superstringer, Kawai S100F, Kawai S100P, Kawai K1

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    • #3
      It's probably what is technically called "motorboating," which thanks to the masses we can't say in public anymore. It's oscillation in an amplifier. It's not in the power supply, but in one of the amplifier stages. It's caused by out-of-tolerance components. It could be a resistor that has drifted, or a capacitor that has developed high ESR.

      120BPM is not 120Hz. (It's easy to make this mistake; I have many times.)

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      • #4
        Originally posted by KC9UDX View Post
        It's oscillation in an amplifier. It's not in the power supply, but in one of the amplifier stages. It's caused by out-of-tolerance components. It could be a resistor that has drifted, or a capacitor that has developed high ESR.
        Except that he said this was occurring on all three channels, so it's likely the problem is something common to all three, like the power supply, or a pre-amp stage that feeds all three channels. Flakey grounds can cause motorboating as well.
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        • #5
          I considered Motorboating and have encountered that before, usually in -3s and PR40s. But as I mentioned all 3 channels are affected and I don't believe a problem in one could infect the others, although, there are large filter caps (100uf @350v) within each amp on its supply line and I'll certainly check those. I would like to find a service manual for a 324--I've been referring to a 100 manual which I know is largely similar, but it's be nice to have more accurate info. But they seem unavailable everywhere I've looked. Anyway, I sure appreciate everyone 's input.
          Over the years: Hammond M3, BC, M102, B3, four X77s and three PR-40s, a Thomas Electra and a Celebrity, three Fender Rhodes, Roland HS-10, HP-2000, HP-600, RD-600, JV-880, a thing made by Korg (?), two Leslie 910s, 122, 257, 258, 247, two 142s, and three custom-built Leslies. Wow, way too much money spent!

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          • #6
            As long as you only play "Goodnight Saigon", you should be good to go 8)
            Tom in Tulsa

            Fooling with: 1969 E100, 1955 M3, 1963 M100, Leslie 720

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            • #7
              Originally posted by bnelson218 View Post
              I considered Motorboating and have encountered that before, usually in -3s and PR40s. But as I mentioned all 3 channels are affected and I don't believe a problem in one could infect the others, although, there are large filter caps (100uf @350v) within each amp on its supply line and I'll certainly check those. I would like to find a service manual for a 324--I've been referring to a 100 manual which I know is largely similar, but it's be nice to have more accurate info. But they seem unavailable everywhere I've looked. Anyway, I sure appreciate everyone 's input.
              I have 2) 122 Leslies hooked up to my A105 and incured the exact same issue. Thought it out the same way as you. It was, in fact, one of my 122 amp with a bad cap in it. Somehow, someway effecting the other Leslie which are interconnected via a relay box.

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              • #8
                Originally posted by Hamman View Post
                I have 2) 122 Leslies hooked up to my A105 and incured the exact same issue. Thought it out the same way as you. It was, in fact, one of my 122 amp with a bad cap in it. Somehow, someway effecting the other Leslie which are interconnected via a relay box.
                That must be an awesome sounding rig. Once you add that 2nd Leslie it's a whole new sound, especially combined with the straight A100's channels.
                Over the years: Hammond M3, BC, M102, B3, four X77s and three PR-40s, a Thomas Electra and a Celebrity, three Fender Rhodes, Roland HS-10, HP-2000, HP-600, RD-600, JV-880, a thing made by Korg (?), two Leslie 910s, 122, 257, 258, 247, two 142s, and three custom-built Leslies. Wow, way too much money spent!

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                • #9
                  After I recapped the amp chassis the thumping is now gone. I didn't take the time to check after each cap was replaced (17 in all,) so I'm uncertain which one was the culprit, but it definitely resided in the amp chassis, and since several of the caps are tied to several B+ supply lines, it's no wonder the thumping occurred in all three channels.
                  Over the years: Hammond M3, BC, M102, B3, four X77s and three PR-40s, a Thomas Electra and a Celebrity, three Fender Rhodes, Roland HS-10, HP-2000, HP-600, RD-600, JV-880, a thing made by Korg (?), two Leslie 910s, 122, 257, 258, 247, two 142s, and three custom-built Leslies. Wow, way too much money spent!

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