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Is 450 volts close enough to 550 volts for a capacitor?

Discussion in 'General Electronics Discussion' started by dietermoreno, Sep 21, 2015.

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  1. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    Is 450 volts close enough to 550 volts for a capacitor? And is it okay to buy capacitors from China or are they bad?

    I desoldered electrolytic power capacitors from my guitar amp, and they say 550 volt 100 uF. I am replacing them.

    The closest I could find on Ebay is 450 volt 100 uF, and they ship from Hong Kong.
     
  2. Martaine2005

    Martaine2005

    3,489
    944
    May 12, 2015
    Hi,
    I would go the other way. Get a higher voltage cap.
    100 volts less for a cap is quite significant.

    Martin
     
  3. davenn

    davenn Moderator

    13,833
    1,950
    Sep 5, 2009
    and what is the actual voltage across the capacitor ?)
    where in the circuit is it ?


    Dave
     
  4. rickselectricalprojects

    rickselectricalprojects

    118
    12
    Feb 1, 2015
    definitely go for a 550v cap and i would get a Chinese ebay special. here is a mouser link to a united chemicon 550v 100uf cap- a high quality cap: http://au.mouser.com/ProductDetail/...EpiMZZMukHu%2bjC5l7Yd1USvXUBa9Cck%2bWrLVVvvM=
    but they are out of stock so it would take a very long time to arrive. if you have the space then i would get two 450v 200uf caps (make sure to get a high quality brand for high voltage uses) and put them in series.
     
  5. dietermoreno

    dietermoreno

    238
    0
    Dec 30, 2012
    I didn't look up a schematic. I would assume that capacitors to filter the power would be connected to diodes connected to the mains power (at least this is what we learned in physics class). The capacitor PCB traces appear to be connected to a large black diode about 2 inches long that is raised about an inch off the circuit board, appearing to be for rectifying high voltages. The high voltage diode is connected to thick red wires that run to the power switch. Thick black wires connected to the power switch connect to the edge of the circuit board.

    This is a 100 watt Peavey Windsor guitar amp with three 12AX7 preamp tubes and four EL34 power amp tubes I am aware that tube amps have two transformers, one for setting the voltage for the tubes and one for setting the voltage for the output, and I'm not sure if the transformer for setting the voltage of the tubes is before or after the power filtering capacitors. This link says that the operating voltage of an EL-34 tube is commonly anywhere from 425 volts to 500 volts. In physics class I think we discussed that the transformer is usually before the diode...wait...oh that's right, it has to be because transformers don't work with direct current.

    So the voltage across the capacitor is 425 volts to 500 volts.

    So 450 volt capacitor is a very bad idea and I should deal with the 14 week order window and get the 550 volt capacitor.
     
  6. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    Why are you replacing the capacitors?
     
  7. Martaine2005

    Martaine2005

    3,489
    944
    May 12, 2015
    I would put in a higher voltage cap.
    600v 100uf . This site in USA has 4,207 in stock.

    Martin
     
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