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Another amp blowing fuses... but why?

Discussion in 'Amp Tech Center' started by MrCoolGuy, Jul 10, 2020.

  1. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    They connect here. You think this orange cap could have failed?
     

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  2. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Holy ****. That was it!
     
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  3. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Dude... this amp has been killing me!
    I should have known to check that cap.... you led me right to it (several people probably did and I just didn't realise). Honestly, had it been an electrolytic cap, I would have caught it day one. But these sprague orange drops... I thought it would be fine.
    Thank you, Asmith, Jhundt, Tubegeek, etc.
     
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  4. tubegeek

    tubegeek Friend of Leo's

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    I love the smell of victory!
     
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  5. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    The culprit. Failed open. (Correction: short)
    1.1 ohm resistance...
    OL capacitance...
    Thanks again, everyone.
    Learned a thing or two on this one.
     

    Attached Files:

    Last edited: Jul 19, 2020
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  6. tubegeek

    tubegeek Friend of Leo's

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    Failed SHORT. Open wouldn't have caused a problem. I think it's only there to quell the 'pop' of the standby switch? I think?
     
  7. D'tar

    D'tar Friend of Leo's

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    Assume nothing! Suspect everything!

    Next time you will find it in 10 minutes!!!

    Good job
     
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  8. tubelectron

    tubelectron Tele-Afflicted

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    Fine @MrCoolGuy ! :cool::)

    It was a short, indeed. The problem was to locate where it occured... Without having the amp on my bench for vision and testing, it's always more difficult to direct at distance... ;)

    But as @D'tar mentions :
    -tbln
     
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  9. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Indeed, short. Thanks again everyone!
     
  10. tubelectron

    tubelectron Tele-Afflicted

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    I personally place that anti-click capacitor directly accross the 2 terminals of the SBY SW, not vs. GND. I choose a 630VDC 0.1µF and it's fine to make the switching competely silent.

    But it's me, OK ? :D

    -tbln
     
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  11. tubegeek

    tubegeek Friend of Leo's

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    But if it failed short YOUR way the standby switch wouldn't work! Instead, with the stock setup you might take out the power transformer and the amp is totally dead.

    What kind of tradeoff is THAT? ;)
     
  12. Asmith

    Asmith Friend of Leo's

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    I would have said Eureka personally but that does the job just fine. :D I'm glad I guided you to the source, now make some noise!

    Follow up question: The cap isn't on the posted schematic, correct?
     
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  13. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Not on the one I was using. I kept going over that schematic and pulling things in that line... I looked at it a hundred times, I don't know what I was thinking.
    But thanks again.
     
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  14. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Question... how is what this cap did "open"...

    A short circuit implies that the two terminals are externally connected with resistance R=0 , the same as an ideal wire. This means there is zero voltage difference for any current value. ... An open circuit implies that the two terminals are points are externally disconnected, which is equivalent to a resistance R=∞
     
  15. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Oh I'm retarded sorry. I thought I wrote it ther other way. Nevermind! Lol
    I need rest.
     
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  16. tubelectron

    tubelectron Tele-Afflicted

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    Well, I do this on all the amps that I built on which I have a SBY switch or any HV switching. I never had any issue with that switch shunt capacitor solution and indeed the treated switches by this method are absolutely quiet and klik-free...

    Here's an example on my last one - The Serial Tone Killer :

    [​IMG]

    [​IMG]

    That said, I really invented nothing here : it was (and still is) extensively used on tramways, trolleybuses, circuit-breakers, any electric motor or contact prone to generate arcing and RF noises... ;)

    -tbln
     
    Last edited: Jul 20, 2020
  17. tubegeek

    tubegeek Friend of Leo's

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    I dunno, I'm still leaning towards the potential-PT-damage method, @tubelectron .
     
  18. MrCoolGuy

    MrCoolGuy Tele-Meister Silver Supporter

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    Yeah... who needs a PT?
     
  19. tubegeek

    tubegeek Friend of Leo's

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    Exactly! They're heavy, expensive....
     
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  20. King Fan

    King Fan Poster Extraordinaire

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    Yes, and that would end the constant stream of "which PT?" threads and "wrong PT" comments...
     
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