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Thread: Amp trouble...

  1. #1
    Eruption
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    12.31.69 @ 04:00 PM
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    Sounds like you've done just about all you can do. You might need to have it taken apart to find that elusive "loose wire". I don't mess with internal diagnostics on an amp either. I know a guy here in the upstate that travels to all the music stores that works on amps. Getting in contact with him is a bitch but I'll try. He's got a name similar to Jose Arredondo too. Ain't that a kick!
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    03.30.13 @ 09:28 AM
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    Abe, I'll talk to my tech this afternoon. He's ripped 5150's apart. Couple of questions first.
    Does it hum any louder or quieter when the guitar's plugged in, and is the guitar's volume affected at all? Also is the gain stage affected, does it break up more or drop to less gain, or is everything about the same, other than the hum?
    The steel wool doesn't work huh? Boy I don't understand that. [img]smilies/biggrin.gif[/img]
    I'll get back to you as soon as I talk to my tech.

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    12.31.69 @ 04:00 PM
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    The hum is unaffected by having a guitar plugged in, EXCEPT that, if I use my regular Strats, the guitars pick up the noise and feed it back into the system. (if that makes sense)

    Sound-wise, it is the same as usual, except that it hums. Turning up the gain DOES increase the noise, as does turning up the volume. Using a gate in the loop does cut it back SOME, but not nearly enough. Overall, the signal remains intact; I haven't had occasion to turn it up to 'ear-piercingly loud' to find out what happens, but other than that, the performance of the amp hasn't changed.
    Don't bark at me...<b>I</b> didn't name ya.

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    XTC man! homeunit's Avatar
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    09.05.15 @ 12:20 PM
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    I've heard of this exact problem before!

    Unfortunatly, I've forgotten the solution, sorry.
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    12.31.69 @ 04:00 PM
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    <BLOCKQUOTE>quote:</font><HR>Originally posted by homeunit:
    I've heard of this exact problem before!

    Unfortunatly, I've forgotten the solution, sorry.
    <HR></BLOCKQUOTE>


    I think I'll let you slide...this time. [img]smilies/wink.gif[/img] [img]smilies/biggrin.gif[/img]
    Don't bark at me...<b>I</b> didn't name ya.

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    12.31.69 @ 04:00 PM
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    Although I am pretty decent with guitar electronics, I am quite the novice when dealing with amps. Anyhoo, here's the problem:

    My 5150 has suddenly acquired a nasty hum problem. It occurs all the time, even without a guitar plugged into it. I took everything out of the loop, I switched ground positions, tried another wall to plug it into, etc. I ran all the tubes through a tube tester, and they're ok. I tapped on 'em, and no microphonics or anything of that sort. I even use a filtered surge protector, but it sure a hell isn't doing me any good at this point.

    My GUESS is that it's the filter caps for the power supply itself. The sound of the amp is unaltered except for the hum of course. Does the filter cap theory seem right to those of you with more knowledge/experience in the field? And if so, any idea what the repair would run? (there ain't NO way in hell I would go near those things myself, even though I know how to bleed them. Plus, I don't wanna open the thing up myself to look, coz high voltage makes me a TAD edgy. Nor do I wanna look like this---&gt; [img]smilies/scared.gif[/img]

    Even after a thorough scrubbing with steel wool, the noise is still there. And when steel wool fails, I am at a loss. [img]smilies/biggrin.gif[/img] [img]smilies/biggrin.gif[/img]

    Thanks guys!
    Don't bark at me...<b>I</b> didn't name ya.

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    03.30.13 @ 09:28 AM
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    Abe, I talked to my tech and I'm afraid you're not gonna be happy with the answer he gave me.
    He doubts it's a filter cap from what you say, but it could easily be a faulty ground, and the bad ground could be anywhere in the system. That means removing the chasis and some components and checking ground points. Because it's such a high gain amp, and it's feeding back with single coils, his assumption is that it's in the preamp stage. Only problem is that it uses a no. of gain stages, each amplifying the next.
    His advice was to take it to a qualified "peavey" service tech. experienced with 5150's. Do not even attempt to service it yourself. If you know how to discharge caps you might be able to open it and see if something has physically come loose, but the chances of that are slim.
    If you've switched the preamp tubes around(tube 1 in no. 5 socket, etc..)(they could be bad without being microphonic)
    and it still hums then it should go in for a checkup.
    There is a chance, assuming it hasn't been dropped or mishandled, and I doubt that's happened after talking to you, that a preamp tube somewhere in line is bad. It could be a problem in the power grid as well, or something very simple.
    Sorry bud, I wish I could have been more help but when you're dealing with a peice of equipment as electrically powerful as that he said the smartest thing to do is take it in. It's not worth blowing off the family jewels for an amp. [img]smilies/scared.gif[/img]
    I can tell you that I had a similar problem with one of my marshall heads and he found a faulty ground in the power amp section, but since you're not losing power the consensus is the preamp section.
    I also mentioned that you gave it a good rub down with steel wool, and if that didn't help it could be anything.

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    12.31.69 @ 04:00 PM
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    Thanks much for your time and effort Tribb! [img]smilies/smile.gif[/img]

    It certainly hadn't been dropped at all. In fact, it hasn't really been moved other than a little bit of rolling around. Add to that it hasn't been played loud in quite a while, it's been well-taken care of. I baby ALL my stuff as much as I can; as a result, everything usually looks/works like new.

    For further clarification, the humming WAS present in the send jack of the loop, so I figured it kinda had to be either in the preamp or the power supply. I know some amp designs take advantage of some form of feedback from power amp back to preamp, but that's WAY beyond anything I would understand. So I assumed it was somewhere early in the chain. It's been my experience that fried transformers (and their aftermath) are generally the most expensive repairs, so I'm hoping this won't be too bad to deal with. After the initial inspection cost, any components shouldn't be too much, and I know from experience what labor goes for. I just want to be as prepared as possible when I take it in, since I don't know who I can trust in this town yet.

    Thanks again!
    Don't bark at me...<b>I</b> didn't name ya.

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    XTC man! homeunit's Avatar
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    09.05.15 @ 12:20 PM
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    Did you ever get it figured out abe?
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  10. #10
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    12.31.69 @ 04:00 PM
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    <BLOCKQUOTE>quote:</font><HR>Originally posted by homeunit:
    Did you ever get it figured out abe?<HR></BLOCKQUOTE>

    Well, the list of possible problems has been made pretty clear to me by about 100 sources, and none of them seem to be serious or costly. But, I haven't taken it in yet to have it taken care of.

    I'm not in any big hurry-it's not like I really NEED the thing right now anyway. I don't see any gigs coming up any time soon. [img]smilies/biggrin.gif[/img]

    So, when I have the $$ to burn I'll deal with it.
    Don't bark at me...<b>I</b> didn't name ya.

 

 

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