Recapping a Fender DRRI

[ajeffcote]

I plan on replacing all the Illinois brand electrolytic caps in my DRRI with Sprague Atoms or another high quality brand if one is suggested.The question that I have concerns the main filter or first stage caps.The amp has two caps in series.A 220uf 100V and a 47uf 500.What is the actual capacitance value of that combination?The way I understand it,if you have two caps of the same value in series,then the actual capacitance is only 1/2 of the value of one of those caps.
I haven't found those particular values available in the Sprague cap,so now I am wondering how much capacitance do I need for my situation.How much is enough and how much is too much?
I would also like to keep them enclosed under the protective cover if possible,so that means size becomes an issue.
Any and all suggestions will be appreciated.Thanks,Aubrey

[Enzo]

Series caps are figured the same way as parallel resistors. If two SAME value caps are in series, the resultant will be half what one is. But this combination comes out to about 38uf. 40 would be close enough, or 47.

220 and 47 are not in their catalog? How about 200 and 50? Anything close will work fine, they are not critical values.

Note the voltage divider formed by the bleeder resistors. The voltage across the pair will not split 50/50. If the B+ is 396v like the schematic says, then the upper cap will settle to about 70v across itself. And 330v across the lower.

I don't know what the rationale behind this arrangement was, but the result is essentially a 500v 40uf cap.

I can't imagine there are not suitable value caps in a premium brand. Personally I'd stick pretty close to what's in there to keep them all under the box and not looking like some kid's science fair project.

[ajeffcote]

That's about what I was thinking,only my thinking was more guessing on the actual capacitance.Two 100uf 350V caps is what I will use.What value for the bleeder resistors?
And what about F+T caps?I read somewhere that they are on a quality par with Sprague Atoms,but are a little more compact?

[Enzo]

I'd change the bleeders then to 220k each.

[Rick1114]

ajeffcote,

If you pass back through this way I'd be interested in what caps you used to stay as close to stock in terms of values & size. I'd like to do this to my DRRI but haven't started any research yet.

Thanks,

Rick