50w Plexi - Voltage Rating on Can Caps, 500v vs 600v

Discussion in 'Shock Brother's DIY Amps' started by itsGiusto, Aug 5, 2020.

  1. itsGiusto

    itsGiusto Tele-Meister

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    My Ceriatone 50 watt plexi kit came with 600v can caps (32+32uf and 32+16uf), but I'm replacing them with 50+50 uf ones to try to get rid of this damn buzzy horrible sounding distortion that I haven't been able to track down for 9 months (see https://www.tdpri.com/threads/how-t...-down-weird-overtones-in-plexi-build.1025094/ and https://www.tdpri.com/threads/not-sure-if-my-plexi-build-has-problems.984480/ )

    However, all the can caps I'm finding (mostly F&T) are only rated for 500v, and they all say that they're good for Marshall-style circuits. Is 500v suitable, or is 600v necessary for these circuits?

    FWIW, the normal voltage I usually see on the plates is 410v. But I think that it's supposed to be higher when you immediately switch on the amp, right?
    Also, if I switch in the tube rectifier, then the voltage on the plate is usually higher, more like 430 to 440v (because I use a special power transformer that has a dedicated tube rectifier tap with higher voltage).
     
    Last edited: Aug 5, 2020
  2. tubegeek

    tubegeek Friend of Leo's

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    600V would be more of a nice-to-have than a necessity in that case, I'd say. Closer than you'd prefer, but still room for safety. What's the temperature rating on the 500V caps? Hoping for 105°, that's another indicator of good construction & longevity.
     
  3. itsGiusto

    itsGiusto Tele-Meister

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    Thanks! They're the 50+50 of these: https://www.tubesandmore.com/products/capacitor-ft-multi-section-electrolytic
    Looks like they're rated for 85°C.

    Do you have a recommendation for other cap cans with better ratings?
     
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  4. tubegeek

    tubegeek Friend of Leo's

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    I haven't used these, but there are several high rated 105° can caps on their site - I would definitely ask them if they sell anything to replace yours. Their site is annoying to navigate. Others on here have liked this vendor.

    https://hayseedhamfest.com/products/fisher-500-c-re-cap-kit?_pos=7&_sid=ffa0b282b&_ss=r

    The F&T you linked to has a 550V surge rating, 5 x 1 minute surges per hour, which is reassuring, too. That's buried in the data sheet. 85° is correct.

    One good thing about can caps - they are always on the outside, so if you can keep them away ftom the tubes you can keep them a little cooler.
     
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  5. itsGiusto

    itsGiusto Tele-Meister

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    Actually, since I did the switchable rectifier tube-thing, one of the cap cans is mounted on the inside, as is done sometimes with JTM 45/50 builds. I could put it in place of the recto tube on the outside, though, if that makes a difference, since for the time being I'm taking out the rectifier anyway, as to try to debug this nightmare of an amp.
     
  6. tubegeek

    tubegeek Friend of Leo's

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    Again a nice-to-have not a necessity. Inside, try and keep some space from the big power filter resistors as best you can, that's where you'll have heat.
     
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