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Peter Wieck Peter Wieck is offline
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Default Dynakit 70 filter cap question


west wrote:

I don't like using 525v replacements especially since the AC input has
increased from days gone by. Chris, why don't you provide us with real
values for your stacking caps and balancing resistors? I think this would
be more of a practical help for many.


Agreed. However, the balancing resistors are a nicety that is
unnecessary in this particular application. It is simple enough to use
450V caps, two-each in series of the appropriate capacitance to make up
a considerable safety margin. 2 x 60 @ 450V = 30 @ 900V. If one does
not want to spring for the (fairly) expensive 60s, go to 330V caps at
about half the price and have your rating at 660V. It is not as if you
are taking anything off the junction, and modern capacitors are far
more consistent than vintage types. If the balancing resistor makes you
feel better... sure. But the amp (and the caps) won't notice. However,
it is the 'right' thing to do so:

If you want to be elegant, it can be calculated:

For 2 capacitors in series: R = (2Vr - Vb) / (0.0015 C Vb)
For n 2 capacitors: R = (Vr - Vb/n) / (0.00075 C Vb)
where R = resistance in Megohms

Vr = max rated surge voltage
Vb = max voltage across entire bank of caps
n = number of caps in series
C = capacitance in uF

With thanks to Cornell-Dublier for the formula.

DO NOT, repeat, DO NOT Mix voltages if installing caps in series. And
it is nearly infinitely better to use only identical caps to replace
any one section.

Peter Wieck
Wyncote, PA