Dripping power transformer

Discussion in 'Shock Brother's DIY Amps' started by MrDouglasN, Feb 21, 2020.

  1. MrDouglasN

    MrDouglasN TDPRI Member

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    Yesterday I received a 60's Harmony H410-A amp and after testing it out I noticed some tan wax-like substance dripping from the smaller power transformer.

    Other posts I found about "dripping" PTs ended up being either potting wax or varnish that was actually hardened and not soft, however this is definitely soft and dripping. In the photos you can see where it dripped onto the speaker, and the imprint from where I touched the PT itself with a screwdriver.

    Does this look like a problem? Is the PT about to go? The amp is crackling more than I was hoping for and I'm not looking for a basket case.

    Thanks
     
  2. Engine Swap

    Engine Swap Tele-Meister

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    Check for leaking or shorted filter caps. Either of these issues will cause the tx to heat up and melt the potting.
     
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  3. MrDouglasN

    MrDouglasN TDPRI Member

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    IMG_20200221_072230.jpg IMG_20200221_072206.jpg
     
  4. Cruisin Home

    Cruisin Home Tele-Meister

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    I think that is your output transformer? And dripping is not good (like any good urologist or guitar-ologist will tell you, haha).

    if it is the output transformer (or even the PT) check your B+ voltages, particularly the main voltage off your rectifier. Your rectifier tube could be bad.
    you'll want to make sure that the transformer is ok as well.
     
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  5. Engine Swap

    Engine Swap Tele-Meister

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    That's an output transformer, not power. Given the proximity to the tube, I guess it would be from the tube heat. Is the tube "red-plating"?
     
  6. MrDouglasN

    MrDouglasN TDPRI Member

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    Sorry, I'm just getting into tube amps and how they work. It's the smaller one. Sounds like it's the output transformer
     
  7. MrDouglasN

    MrDouglasN TDPRI Member

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    No, all of the tubes were visibly normal after about 15 minutes of playing. One did seem a bit loose though.
     
  8. schmee

    schmee Doctor of Teleocity Silver Supporter

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    Well, being that it's been in there 60 years, it's likely ok. Are you sure it's dripping NOW? or is that just past evidence? Does it feel like wax?
    An amp that old definitely needs filter caps if they haven't been done, and that can be an issue maybe I suppose.
    Those old Harmony, Valco, Dano amps had small output tranny's in them, so it may not be too unusual for an OT to get warm and release some wax that was in there from the beginning.
    But if it's recent, then something must be going on, likely capacitors.
     
  9. MrDouglasN

    MrDouglasN TDPRI Member

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    Thanks to both of you for the feedback. Sounds like there's definitely a problem causing the OT to overheat. I guess I'll have to decide if I'm going to keep it and take it in for work, or return it to the seller.
     
  10. MrDouglasN

    MrDouglasN TDPRI Member

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    It's new to me, just received it yesterday, so I'm not sure how long it's been dripping. I think I'll reach out to the seller and ask about it. Looking now I see the wax (feels like wax) on the speaker in the amp listing.
    But it definitely heated up and was dripping after 15 mins of play yesterday
     
  11. ArcticWhite

    ArcticWhite Tele-Holic

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    That is your OT (output transformer), it is not normal, and you should NOT turn the amp on again until it is repaired.

    My first suspicion is that one of the electrolytic capacitors is going bad (shorting internally) and passing a lot of current through the transformer. You will destroy it very soon if you power it up again.

    Transformers are expensive and a PITA to replace. Caps are cheap and easy.

    Your choice.
     
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  12. schmee

    schmee Doctor of Teleocity Silver Supporter

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    If it's dripping now, then you need to fix it before you blow the transformer. The transformer must be hot, it shoudlnt be anything more than luke warm at the most.
     
  13. MrDouglasN

    MrDouglasN TDPRI Member

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    Yikes, understood. Thank you for stressing this point.
     
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  14. Commodore 64

    Commodore 64 Friend of Leo's

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    Trafos do get hot, rule of thumb, if you can't leave your hand on it for a few secs, it's too hot.
     
  15. ArcticWhite

    ArcticWhite Tele-Holic

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    An additional warning.

    If you decide to open it up to take a look, or to take some pictures for the forum, please understand that the big capacitors can hold 500 volt charges, after the amp is unplugged, for many days.

    It is a simple matter to discharge them, if you know how, and you have some simple tools.
     
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  16. MrDouglasN

    MrDouglasN TDPRI Member

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    Since I can see from the Reverb listing that it was dripping before I got it (I see the wax on the speaker in the photo now that I know to look for it) and therefore being run as-is, is there a chance that the output transformer has been damaged to the extent that it should be replaced? Any other damage I should look for? For example would whatever is causing it to overheat also damage to tubes?

    Now that I think about it, the tone was getting muddier as I tested it last night, I kept checking the tone knob thinking I'd turned it down, and it was breaking up at lower volumes than when I first plugged it. Related?
     
  17. ArcticWhite

    ArcticWhite Tele-Holic

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    Tubes are designed to get hot. They're okay. The OT is probably okay too.


    You can get the amp recapped for less than a hundred bucks. Probably maybe fifty. I haven't had to pay anyone to do mine since I started doing it myself about ten years ago.
     
  18. MrDouglasN

    MrDouglasN TDPRI Member

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    Okay cool. And thanks for the cost estimate. That helps with my decision making.
     
  19. schmee

    schmee Doctor of Teleocity Silver Supporter

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    That's a bit worrisome to me. The OT is dripping, must be hot. Whether it will recover after the amp is fixed is a big question. But small OT's aren't very expensive either...
     
  20. ArcticWhite

    ArcticWhite Tele-Holic

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    I've read that OT's are generally quite robust.
    If the amp works, I think it's likely to be okay.
    This reminds me of when I bought my 73 Princeton Reverb. It was barely running with no volume. I put in the new caps, and BAM like a new amp.
     
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