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In Reply to: RE: First filter stage question in amp's PSU posted by Gingertube on August 18, 2014 at 18:40:56
would it be ok to replace a 220mfd/100VDC rated cap with a 220mfd/500VDC one? Keeping the 47/500 intact. With same leveling resistors?
Much thanks!
Follow Ups:
The two caps in series, 220uF and 47uF, add up to 38.73uF. What I'd think you would want is a cap within the rating of the rectifier tube and rated above the no load voltage on the transformer. You could measure what the voltage is and add a safety factor.
In other words, why pay for a 220uF/500VDC cap when a single 40uF cap might do better. Given you would be replacing two caps with one perhaps a film cap would fit. Likely it would perform better and last much longer.
Thanks! I've redone 5 or 6 of these DRRI main filter caps. The last two I used two 80mfd/450VDC F&T (for C31 and C32) and replaced R65 & R66 with 220k-ohm, 1-watt resistors. The first few DRRI's got Sprague ATOM 100mfd/350VDC caps, with 220k-ohm resistors.I asked about the 220mfd/500VDC cap replacing the 220mfd/100VDC because someone on the Fender Amp Board is redoing his amp's caps and wanted to use this higher voltage rated cap. I'm not sure what effect the voltage rating has on the GZ34, which sits next to it.
Thanks!
Edits: 08/19/14
Using a higher voltage cap (than needed) results in longer life. No problems at all other than increased size and cost.
I like to avoid series caps when I can. Not long ago it was hard to find high voltage caps. Today, because of variable speed drives, good high voltage caps are easy to come by.
Thanks! There are few oddball things with these reissued amps. If you get a chance, look at the new '68 Custom Deluxe Reverb schematic. More head scratching circuitry mods.
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