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Thread: Vintage cap voltage rating question

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    Stray Cap DrGonz78's Avatar
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    Vintage cap voltage rating question

    So I ordered a 25uf 50v cap as that's what I read on it before pulling it out. Pulled it out and it actually reads 25uf 50/60v. So my guess is that it's a 50v rated working voltage cap with a 60v peak rating. Does that seem correct? Not too worried about really, just curious for educational reasons. The cap was found in an old Fender Taurus solid state amp.
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    Last edited by DrGonz78; 09-10-2019 at 12:46 PM.
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    Bent Member Chuck H's Avatar
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    That seems like an odd way to indicate voltage rating.?. AC/DC maybe?

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    So my guess is that it's a 50v rated working voltage cap with a 60v peak rating. Does that seem correct?
    That is correct.

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    Old Timer J M Fahey's Avatar
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    Yes.
    The higher value is called "surge" voltage, whatever it can stand for a few minutes.

    Significative in Tube amps, since until filaments heat up supply voltages peak/surge significantly higher, irrelevant in SS amps, so it was dropped.

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    Also helpful for those times you are testing an amp without tubes installed, no?

    Justin

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    Old Timer J M Fahey's Avatar
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    Yes, same thing.

    But in general mopern caps do not even show it, although I guess it´s still in the datasheets.

    Now WHO reads a capacitor datasheet is another problem

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Now WHO reads a capacitor datasheet is another problem
    Well "I" do because I don't just build, I design. So things like surge voltage matter to me. Guys that build often use caps that some reputable source has already determined the suitability of for tube amps in general. The number of amps getting built with over 550V of unloaded voltage is pretty small I think. It comes up here with certain models that are sort of known by this community to have special needs. Otherwise, not so much. But I think you might be heartened by the number of members here that actually DO check out spec sheets when it seems appropriate.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Chuck H View Post
    Well "I" do because I don't just build, I design. So things like surge voltage matter to me. Guys that build often use caps that some reputable source has already determined the suitability of for tube amps in general. The number of amps getting built with over 550V of unloaded voltage is pretty small I think. It comes up here with certain models that are sort of known by this community to have special needs. Otherwise, not so much. But I think you might be heartened by the number of members here that actually DO check out spec sheets when it seems appropriate.
    I bet chuck reads datasheets while eating his Rice Crispies
    nosaj

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    Stray Cap DrGonz78's Avatar
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    Thanks for the responses!! All of the small eletros had spewed their guts out all over the place.

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by DrGonz78 View Post
    Thanks for the responses!! All of the small eletros had spewed their guts out all over the place.
    Can you spell m-e-s-s-y ?
    Well "I" do because I don't just build, I design.
    I know, I know

    I think you might be heartened by the number of members here that actually DO check out spec sheets when it seems appropriate.
    Here? sure!!!!

    But this is an above average Forum ... and that is an understatement

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by J M Fahey View Post
    But this is an above average Forum ... and that is an understatement
    I do have horse blinders on, I suppose, because I'm not an active member of any other forums. In my head this place represents "the rest" of the demographic in this amp genre that isn't me. I'm familiar enough with the gear forums that I have perused. Specialized forums for Marshall owners or Les Paul owners. I always take those forums to be more "gear head" rather than gear build places. So I don't expect much going in. And I've read enough good tech at places like the Amp Garage and the old AX87 site that I just figured it was all like it is here, though I knew this was the best of them. Still... It's hard to imagine the number of shade tree techs that are still operating low tech on mojo based lore while this forum exists. But I do know it's still happening.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by DrGonz78 View Post
    Thanks for the responses!! All of the small eletros had spewed their guts out all over the place.
    Eewww! I've only had to clean up after that sort of thing twice. Such a smelly mess. And you will never think you got it clean enough Still beats having them go off like little fire crackers or dead shorting and taking out more expensive components I suppose.

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    "Never bet your life on somebody else doing their job." SoulFetish's good friend

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    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

    "Back to the amp. It makes horrible sounds when I play my guitar thru it... because I suck at playing guitar." Mike6158

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    Supporting Member The Dude's Avatar
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    Smell is actually a good troubleshooting tool. If you've done this for long enough, you can distinguish between leaky caps, burnt transformers, carbon resistors, solid state devices, etc.

    It's still never a good sign when a bad smell is emanating from an electronic device.

    Edit: I forgot selenium rectifier on my list of smells.

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    Lifetime Member Enzo's Avatar
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    Oh, AMEN.

    NOTHING smells like burnt selenium rectifier. And even after 50 years, I would recognize it instantly.

    Burnt resistors smell different from burnt plastic transistors. Caps smell different. Transformers have their own smell. Burnt circuit board smells different too. Yes, by experience, you usually know what burnt up by the aroma.

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    Stray Cap DrGonz78's Avatar
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    You know what the amp didn't actually smell bad. The amp had that 60's Fender tube amp smell to it, even though it is a solid state amp. I think they could package that scent and a bunch of vintage amp loving techs would buy it off the shelves.

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by DrGonz78 View Post
    You know what the amp didn't actually smell bad. The amp had that 60's Fender tube amp smell to it, even though it is a solid state amp. I think they could package that scent and a bunch of vintage amp loving techs would buy it off the shelves.
    I know that smell very well, and here it means "US made amp" whenever you go to a rehearsal room.

    After some time, I found it´s some kind of evil chemical added to animal/hide glue used by Fender (and many others) in their Potdevin gluing machines to Tolex amps.

    Otherwise such organic stuff rots or grows mold easily.

    The product is actually a milder version of Morgue approved Formaline or embalming fluid.

    There´s a similar smell coming from old Russian Cameras, which had thin leather covered parts using a similar glue.

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