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Thread: Question about capacitor power rating

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    Question about capacitor power rating

    I have heard it argued both ways that if capacitors are in series the voltage rating is doubled, some say it isn't.
    In the bassman AA864 in the power supply there are two capacitors in series with a rating of 350V and right next to that point the voltage is shown as 422V.

    Do the resistors in parallel have anything to do with increasing the voltage rating here?

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    Quote Originally Posted by E biddy View Post
    I have heard it argued both ways that if capacitors are in series the voltage rating is doubled, some say it isn't.
    In the bassman AA864 in the power supply there are two capacitors in series with a rating of 350V and right next to that point the voltage is shown as 422V.

    Do the resistors in parallel have anything to do with increasing the voltage rating here?

    Click image for larger version. 

Name:	bassman power supply capacitors.JPG 
Views:	16 
Size:	20.8 KB 
ID:	48647
    The two resistors form a voltage divider that splits the voltage across the two capacitors evenly, otherwise there would be different voltages on each of the caps.

    As an added benefit, the two resistors act as a bleeder, to drain off the stored voltage on the caps when the amp is turned off.

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    Yes Voltage rating for two series caps is x2 and the cap values are /2, in other words half the value of.
    so two 70uf 350vdc in series would be 35uf at 700 VDC.

    Edit: second question answer is no. Its what bill said.

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    If two perfectly matched capacitors were used then the balancing resistors wold not be required and each capacitor would share the voltage equally. Matched electrolytic capacitors would not be an economical proposition, plus the matching would need to be maintained for the life of the capacitor. Now if two random caps are placed in series then it's likely that their capacitance, ESR, and leakage characteristics would differ. This means that one cap may charge to a higher voltage than the other by an indeterminate level. This could exceed one capacitor's voltage rating. The easiest way is to make sure that each capacitor sees equal voltage is to force them to share by using the balancing resistors. There are calculations for the resistors, but tube amps stick to standardized values - usually between 180k and 220k.

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