What could this be?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by squeally dan, Sep 12, 2006.

  1. squeally dan

    squeally dan Member

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    After about 15 minutes of playing my twin will start making a loud sorta buzzing noise. It won't stop until I put it on stadby. When I put it on standby it goes away. Then I can start playing for another 15 minutes or so before it comes back. What is this? Also when I hit some low notes on the E string there is a little bit of a rumbling kinda buzzing noise.

    I think the twin is a silverface '72. It has apparently been "blackfaced". I got it shipped to me a week ago. I changed out the Ax7's but all the other tubes are what the previous owner had in there. I had a tech. look over and he said he "went over it with a fine tooth comb", but now its making this noise. He said he fixed some speaker wire. He "checked the caps" and did some cleaning of the sockets. He I will say from past experiences I'm not 100% with this tech. Also I changed the speakers that were in there to to California Webers last week. Would that have anything to do with it? If I hooked the wrong speaker wires, what would that do (negative to postive, etc.)? I played a gig with it Friday and Saturday night with no trouble.

    I have a gig in a couple weeks at a festival opening for Boyz II Men & Kool & The Gang. I am hoping to use this amp but I am scared it won't be reliable.
     
  2. donnyjaguar

    donnyjaguar Member

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    Are the output tubes overheating?
     
  3. squeally dan

    squeally dan Member

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    How would I know that. It gets fairly warm back there but isn't that normal.
     
  4. Blue Strat

    Blue Strat Member

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    There are many things that could be happening. I highly recommend taking it to a qualified tube amp tech.

    I wouldn't use this amp for ANY gig until you figure out what's wrong.
     
  5. squeally dan

    squeally dan Member

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    My problem is finding a guy that I trust. The guy here in town isn't cutting it.

    I do know a guy about 1 1/2 hours away that I trust.
     
  6. Blue Strat

    Blue Strat Member

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    Then you know what you have to do.
     
  7. squeally dan

    squeally dan Member

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    THis might sound like a weird question, but is there a way to determine if the guy I'm using really knows what he is doing. I don't mind going back to him if he can actually fix it.
     
  8. Blue Strat

    Blue Strat Member

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    That's a really good question. It's always amusing to me when people say that "Joe Blow" or "Tom Blow" is a great tech! How could anyone possibly know this without being a GOOD tech himself? It's like any one of us critiquing a surgeon. Just because the patient survived doesn't mean that the doctor didn't leave 3 sponges and a scalpel inside ;)

    Reputation is about all you have to go on.
     
  9. donnyjaguar

    donnyjaguar Member

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    Mike's right, you'd better get that thing looked at by someone with a good reputation or your next gig might be unplugged. :) ;)

    When I was referring to overheating, I was thinking that one of the output tubes may be running red hot (you can't miss this when looking at it). When this happens it will draw too much current and the amp will hum very loudly. Often it will just blow the fuse - unless you turn it off quickly. If all the tubes are gowing red it'll usually blow the fuse immediately and this indicates a bias circuit problem. The only other way for hum to get in is via the filament circuit so one of the small signal tubes you swapped may be whipped.

    There is one other way, and that is through a defective guitar cable. But I'm guessing we're all familiar with this problem and you've ruled it out.

    DJ
     
  10. brad347

    brad347 Member

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    I'd try a new set of power tubes before anything else. When you say he "checked" the caps, I take it to mean he didn't replace them. So I would also be curious to see what the filter caps in that amp looked like.
     
  11. squeally dan

    squeally dan Member

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    The hum is actually more tham a hum to my ears. Its a loud noise. Hard to describe, but its more than just a little buzz. Once the noise starts you can hear it with the volume down all the way and the guitar unplugged.:mad:

     
  12. brad347

    brad347 Member

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    maybe a ground is intermittent somewhere?
     
  13. Blue Strat

    Blue Strat Member

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    That kinda sounds like one or more of the power tubes is losing bias. Possible cause? Loose socket(s), problem with bias circuit.

    Note that this is just a guess based on my interpretation of what you're describing as a hum.

    It's really futile to do this over the internet. If the guy with the problem was qualified to do anything with the information we're giving him, he would have already tried these things.
     
  14. squeally dan

    squeally dan Member

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    Your right I'm not really qualified. I can change out tubes thats about it.
     
  15. Antero

    Antero Member

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    This is very similar to my own problem. Overheating sounds like it's possible in my case, since the thing is running at GAAAAH degrees... what is there I could do about that?
     
  16. teleamp

    teleamp Senior Member

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    I've had rectifier and power tubes make those kind of noises before.

    MikeY
     
  17. bluesmann

    bluesmann Guest

    I've had a bad preamp tube in V1 do this same thing, even new tubes.
     
  18. squeally dan

    squeally dan Member

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    It's funny. I dodn't do anything to the amp, but the last couple days I can't get it to make that noise anymore. It won't do it. But now it makes a kinda crackling noise when I first turn it on, but it goes away after about 15 seconds. It's fine after that 1st 15 seconds.
     

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