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Calling Techs: 1959slp woes...

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  • Calling Techs: 1959slp woes...

    This amps pissing me off so much, I haven't had it working properly for weeks/months now. It emits sound ok, I don't have any master volume or power scaling yet though so I'm playing clean. The worst thing about this situation is when something goes wrong with this amp I usually know what it is, but I'm having a hard time figuring this one out.

    Problem 1:

    When Channel I is on 0, there's still sound coming out, it's like when you turn up the volume slightly. It's thin/weak but it's very audible. It works pretty much normally besides that, the sound comes on properly about 1-2. I've removed Channel II and that hasn't helped at all. I think the volume pot might be broken, but on 0 the two sides seem to measure correct resistance. However, when it's on 10, one side is 0K and the other is 470k? (It's a 1M pot).

    Problem 2:

    Theres more hum than there should be, it's like the sound single coils have when you turn on the TV. However, turning the volumes off doesn't get rid of the hum. Messing with the tone controls doesn't get rid of the hum.

    Problem 3:

    Every minute or so there's this rustling sound, and whenever I turn on the fan in my room theres a very loud pop. There's also a loud pop when turning off the standby switch.


    I just fired the amp up without the headbox, and turned off the lights. I can't see any arcing at all when it makes the popping/rustling sounds (which can be provoked by hitting the amp). Not surprisingly, the hum gets worse the brighter I turn the dimmer switch in my room.


    Any ideas as to what the causes might be? I replaced the two can caps with lumps in with F&T caps a few weeks ago when the amp first started having problems (horrible blocking distortion), but I've still got some of the old Ruby caps there. I can't see anything wrong with those. Now that my PPIMV pot isn't working anymore (values have drifted, pot's probably fried so I removed it and rebiased), I can only play the amp clean but even then there's still these problems. :dammit:
    Richard

    Free Shred Guitar Lessons
    Marshall Mods

  • #2
    Re: Calling Techs: 1959slp woes...

    Some ideas:

    I think your filtering network may be on the fritz. You should probably do all new filter caps and reform the caps using a variac over a period of several hours. A little cross talk between channels is pretty common, but you might want to check the mix resistors. Also check the cathode resistors and caps for V1 at least. It wouldn't hurt to just try a different tube in V1, although I'm sure you tryed that. Electromagnetic interferance can find it's way into tubes. Are you using the metal shields over them?

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    • #3
      Re: Calling Techs: 1959slp woes...

      I'd take a close look at the ppimv reversal thing you did. It sounds kinda obvious you have a ground issue somewhere. I know that's not a lot of help. How old is this amp? If it's more than 10 years old, check the rest of the caps like LPB suggested.

      Have you tried the chop stick, poke around until you find the noise, trick?

      Move some wires around and see if the hum goes away. You might have rerouted some wires in an unintentional, yet noisy, way.

      That dimmer switch needs to go. Those things are notorious as hell for causing hum in all sorts of equipment.


      www.CelticAmplifiers.com

      "You can't save everybody, everybody don't wanna be saved."

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      • #4
        Re: Calling Techs: 1959slp woes...

        My 1987x had a presence pot go bad. Had horrible Buzz, no signal, volumes issues, ect. Easy enough to swap one in and see if it the prob.
        ]
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