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Help Blown cathode bypass cap 5f1

Discussion in 'Shock Brother's DIY Amps' started by IITTII, Sep 18, 2020.

  1. IITTII

    IITTII TDPRI Member

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    Hi, im a newbie when it comes to tube amp's but have a lot of exp. in electronics.

    Anyway today i was playing on my joyo jta05 (5f1 champ clone) i was driving it really loud with pedals. And all of a sudden it started losing volume then i heard a loud bang then dead silence and the amp started smoking.

    I opened it up and noticed a cap was blown anyway i took the time to take it apart and replace the blown 6v6 cathode bypass capacitor (50v 22uf with 450v 22uf) and while i was in there i tought about doing a few mods to make it better.

    So i added a tone control, removed the low input and make it so that i only have 1 high input. In the place od the low input hole i placed the tone control. And i added a 350v 22uf capacitor to the C7 position as the 12ax7 cathode bypass cap.

    All looked good and promising i put it all back together and turned it on. And all i get is hum and some low noise crackeling here and there. When i plug in my guitar there is no volume.

    Now my question is why the amp failed, is the power tube (6v6gt) dead? , is the 12ax7 dead? , or maybe some other component is dead too? , why did the cap blow (cheap chinese caps)?

    P.s.
    I checked all the resistors and other caps everything looks ok. All conections are ok so i dont know what else.

    Did the power tube fail? Is it possible that it failed when the cap blowed or the cap blowed becouse the tube blowed?

    All the tubes look ok and filaments glowing so i dont know what else to check.

    Please help i bought the amp new 2 days ago and now i dont have anything to play on.

    IMG-20200918-WA0017.jpeg
    IMG-20200918-WA0024.jpeg 20200918_201528.jpg
     
  2. IITTII

    IITTII TDPRI Member

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    Oh yes and not a single fuse was blown. It has like 4 internal and 1 external fuse.
     
  3. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Any of those options are a possibility.

    I'd start by undoing the mods and just get the amp working in its stock form. See if that works, then go from there.
     
    Linkjr and Dan_Pomykalski like this.
  4. EmWeAh

    EmWeAh Tele-Meister

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    You should also clean up the remains of that bypass cap. Electrolyte is mildly hazardous to health (no worries, you will survive this incident ;)) and highly corrosive which might lead to other problems with your amp in the future. I would recommend examination gloves for that job.
     
  5. IITTII

    IITTII TDPRI Member

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    Just replaced the 6v6gt and SOUND!!!! Everything works even the mods. Yeeeeeepeeeee thanks guys.
     
    tubegeek likes this.
  6. Squawker

    Squawker Tele-Meister

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    Hazarding I guess, I'd say that the 6V6 failed and took the capacitor with it, rather than the other way round :)
    If the anode shorted then you probably had 350VDC across a 50V eletrolytic - that will boil the electrolyte and go pop!
     
  7. Squawker

    Squawker Tele-Meister

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    Was the 6V6GT Ruby branded - that's what I see on the Joyo site. Was just wondering who actually made it.

    I believe it was our honoured member, Mr. Jon Snell, who said that JJ power valves sound great until they fail, which they will(*). By implication, anything the New Sensor brands (Electro-Harmonix, Tung-Sol) lack in sound, they make up in ruggedness. If yours was Ruby it could be any of JJ, EH, Tung-Sol or maybe Chinese (Sina/Shuguang) depending where they sourced it - a suffix/code after 6V6GT would give a clue.

    (*) I only have good experience with JJ EL84s but YMMV
     
  8. IITTII

    IITTII TDPRI Member

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    It was a made in china 6v6gt i think a brand named electron.

    The 12ax7 i got with it is sovtek brand. The 5y3 is ruby.
     
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