Amp smoking. Help!

Discussion in 'The Workbench' started by Filipe Rolim, Mar 25, 2021.

  1. JP2036

    JP2036 Well-Known Member

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    oh please.
    Only thing i know is the guy should get a good amp.
    Go troll yourself and stop being annoying.
    After all just because his amp was on fire doesn't mean its not bad.
     
  2. _Steve

    _Steve Well-Known Member

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    With you on this. I just don't understand what motivates people to act like that. I think there's a function on the forum somewhere to ignore/hide a user. Hope you get your amp fixed!
     
  3. guitronics

    guitronics New Member

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    I read once that Angus Young of AC/DC was playing in the studio, and his Amp Head began to smoke, then caught fire. He briefly quit playing, and then his brother Malcolm burst in, and excitedly told him to keep playing!
     
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  4. Pete Farrington

    Pete Farrington Active Member

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    A couple of points -
    1/ old ecaps that haven’t charged up for a long time will tend to deform, ie lose their insulative property. Which is bad news when putting a lot of VDC across them. The caps pictured look to have vented, note the lump in their end cap, between their terminals.
    A suitable procedure to reform them is described on the geofex site, but for the caps pictured, it’s too late for that, they will almost certainly be ruined.
    2/ a light bulb limiter limiter is extremely beneficial when powering up an amp whose condition is unknown, and also if a fault is known or suspected. As it will act to limit fault current, hopefully to a non damaging level.
     
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  5. jazzdj

    jazzdj Active Member

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    Amp head smoking, not good, sure sign to a very short life.

    Be its friend, grab it by the handles, shake it and sincerely say, please don't smoke!!

    ..... and then go get it a pack of these, sure thing for curing a Smoking Habit.

    BTW - most frequent cause of smoke from a tube amp is a bad Cap, overheated resistor or a wiring short.

    [​IMG]
     
    Last edited: Mar 31, 2021
  6. neikeel

    neikeel Well-Known Member

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    Yes commonest cause of smoke in an amp like this would be a cooking screen resistor, but the venting caps shorting internally could have been part of the reason for failure with the PT drawing far too much current (ideally fuse should blow but heaters and bias are not fused) - unless the infamous tin foil fuse was in use!!
     
    Last edited: Mar 31, 2021
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  7. Pete Farrington

    Pete Farrington Active Member

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    The ecaps I was referring to are shown in the 2nd photo of post #47, the 4 large chassis mounted can caps, typically blue Dalys.
    As they seem to have blown their pressure vents, all the ecaps should be assumed to be bad, and so be replaced.
     
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  8. neikeel

    neikeel Well-Known Member

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    I agree with the sentiment - just can't see the bubbling electrolyte!?
     
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  9. Filipe Rolim

    Filipe Rolim New Member

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    Hey Peter, thanks for the reply.
    I've the same doubt as neikeel... can't see where them seem to be blown
    Cheers
     
  10. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Out of curiosity, what is that big smear of brown goo next to the board?
     
  11. Pete Farrington

    Pete Farrington Active Member

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    My experience is that just the fact that the pressure vents are visually apparent is sufficient evidence that seals have blown. ie they wouldn’t have looked like that prior to the venting incident.
    Crust around then would make it obvious and unarguable, but I don’t think that its absence should be taken as an assurance that those caps have not vented.
     
    Last edited: Apr 1, 2021
  12. JM5010

    JM5010 Active Member

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    Jesus christ that would scare the **** outta me if it was my amp. I'd throw in a new PT if rewinding the current one is too pricy.
     
  13. Filipe Rolim

    Filipe Rolim New Member

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    Thats glue residue from the QC label
     
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  14. BatmansMarshall

    BatmansMarshall Well-Known Member

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    The power transformer is near failure but hasn't completely blown. It is your safety box with a fuse for electrical complications that can send a zap up your guitar cable if things go wrong, such as the amp wiring being compromised or another part going. When PTs blow that is usually it. Yours still has brain activity. It shouldn't. Time to turn that head into a professional repair service to do an inspection and replace. You will probably get a new PT and some tubes and be ready to go. This time without the vape.
     
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  15. southbound suarez

    southbound suarez Active Member

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    No Doubt ,,,, you are killing the worthwhile of the center of this amp. If ya don't have the orig Iron, ya junked this amp.... Better just do it right and pay alot of money to have that orig trans rewound... Send it to Mercury in Chatsworth.
     
  16. Pete Farrington

    Pete Farrington Active Member

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    In the absence of having the transformer from Filipe’s amp dissected on your workbench, how are you able to determine that?

    That seems to be scaremongering somewhat to me. The only way I can see that a dangerous voltage could appear at the amp’s input and hence anything plugged into it is if there was a coincidence of 2 significant failures, namely -
    1/ the amp chassis’ safety grounding was lost somehow,
    2/ the insulation of the mains / PT primary circuit broke down after the chassis safety grounding failed, such that the amp chassis became connected to the mains circuit.

    As responsible adults, it is beholden on us all to ensure that the mains electrical equipment that we use, especially if we’re electrically connected to it, doesn’t have any of its safety features compromised.

    Note that a PT has various failure modes, only one of which would result in ‘2’ above. Transformer designers and manufacturers recognise the high potential consequence of such a failure, and several separate layers of high temperature insulation would have to break for it to occur.
     
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  17. BatmansMarshall

    BatmansMarshall Well-Known Member

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    It's most probable because the transformer is smoking and because his amp still works. Might not be but it sure seems like it.

    It's not a widowmaker amp but obviously opened up and smoking while playing reduces safety and increases the risk of shock. He probably won't be but the vintage old amp has at least a semi-damaged PT. That will probably blow.
     
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  18. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Pete, your name is familiar and you seem quite knowledgeable. Are you an amplifier designer and builder?
     
  19. neikeel

    neikeel Well-Known Member

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    The amp is a PA mid 70s. It needs a decent clone PT.
    It would be very hard to justify shipping a blown PT from Portugal to USA to MM for a rewind. Do they even do paper bobbin rewinds? If so how much?
     
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  20. Wildeman

    Wildeman Well-Known Member

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    I thought this was another Hot Rod Deluxe thread for sure.
     

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