Coupling Capacitor Voltage...400V okay??

Discussion in 'Tube Audio' started by HiFi-Stereo, Aug 12, 2017 at 2:30 PM.

  1. HiFi-Stereo

    HiFi-Stereo Active Member

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    Working on a Magnavox 8601 amp;
    It has .01 ceramic coupling capacitors, I am assuming are rated at 500 Volts?
    I have .01 PIO caps I was going to use in place of the ceramics IMG_0308.JPG IMG_0309.JPG IMG_0308.JPG IMG_0308.JPG IMG_0308.JPG IMG_0309.JPG , but they are 400V...anyone know if these would work?
     
  2. HiFi-Stereo

    HiFi-Stereo Active Member

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    Looks like I chopped up my post a bit!
    There are some new features for posting since I was last on Audiokarma...
     
  3. gadget73

    gadget73 junk junkie Subscriber

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    In that amp I'm reasonably sure you'll be OK. If you want to be absolutely sure, remove all the tubes except the rectifier and measure the voltage at the first power supply cap. If its not over 400, you're good. The caps do see the DC + AC, but considering the plate voltage at the driver tube should be well below max B+ there should be ample wiggle room.

    Personally I don't buy anything but 630v caps just because they work everywhere.
     
  4. arts

    arts Super Member

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    Seeing as the unit uses a cathodic tube rectifier (6CA4) and all of the tubes will begin conducting at almost the same time,you won't experience the voltage surge normally experienced with a filamentary or solid state rectifier.Also,the maximum circuit voltage appears to be 245V. So,to answer your actual question,yes,your 400 volt capacitors will work without issue in this application.
     
  5. HiFi-Stereo

    HiFi-Stereo Active Member

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    Thanks, I will measure the voltage at the first power supply cap...
     
  6. HiFi-Stereo

    HiFi-Stereo Active Member

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    Thanks, good to know! I really enjoy tube audio, and have learned how to easily change caps and resistors, but I should learn more of the science behind the hobby...
     
  7. arts

    arts Super Member

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    For folks just getting started,the internet is great for finding literature,especially texts from that period.No more trudging to libraries or book stores.
    There are some real treasure troves of info out there:

    http://www.americanradiohistory.com/
    http://www.tubebooks.org/technical_books_online.htm
     
    rollcentre likes this.
  8. jdsalinger

    jdsalinger AK Subscriber Subscriber

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    If the cap is rated higher than the plate voltage...it should be fine. That's just my reasoning. I assume there is some safety factor engineered into that rating. They aren't going to blow at 401VDC
     
  9. primosounds

    primosounds AK Subscriber Subscriber

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    Capacitors from reputable manufacturers will usually specify the overvoltage specs as well as temperature specs. Sometimes depending on the specifications other requirements will be built in.
     
  10. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    I presume your talking about the output coupling caps (C-9 & C10). If you look at the B+ for that stage it's only 200V or so. So a 400v cap would work fine.
     

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