1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

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-Holic

    Posts:
    523
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    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

    Age:
    60
    Posts:
    3,879
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    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-Holic

    Posts:
    523
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    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?
     
    tubegeek likes this.
  4. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,879
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    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.
     
    itsGiusto likes this.
  5. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    523
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    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

    Age:
    60
    Posts:
    3,879
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    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.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.