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Post subject: Re: Deluxe Reverb Reissue Filter Cap Replacements
Posted: Sun Aug 17, 2014 1:14 pm
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Shimmy, this is what I was told by some techs on another board. Anyhow, why would Fender use a 100VDC rated cap in a position that sees several hundred volts? If the 220mfd/100VDC + 47mfd/500VDC worked well, why did Fender not use this combination with all their earlier SF and BF? Which used two 70mfd/350VDC caps, in series, in the first stage?


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Post subject: Re: Deluxe Reverb Reissue Filter Cap Replacements
Posted: Sun Aug 17, 2014 1:25 pm
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socal323 wrote:
[


No problem, I did the math using capacitors ratings and specifications. Illinois capacitors are rated for 2000 hrs @ 85C. een years. . :D


85 C is 185 F . Do you think temperature where cap is in the amp is at 185 F ?

It is your money and it is your amp .


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Post subject: Re: Deluxe Reverb Reissue Filter Cap Replacements
Posted: Sun Aug 17, 2014 4:21 pm
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BMW2002Ti wrote:
Shimmy, this is what I was told by some techs on another board. Anyhow, why would Fender use a 100VDC rated cap in a position that sees several hundred volts? ...


I am not sure what you were told, maybe you misunderstood? It is always OK to use a higher voltage rating for a cap, and never use a lower voltage rated cap.

In a series circuit, the voltage divides accordingly, so possibly 100 volt rating was enough in that case, I don't know the thinking in their choice of cap.

Again, the voltage rating of a cap is how much voltage that the cap can handle, not how much it needs to see. Think of the cases where Fender used 450 volt rated caps, and the available replacements are rated 500 volts, that is perfectly fine. It would be just as fine to use any voltage rating above the original's rating, but at some point you would be wasting money paying for too much, but never causing any harm.

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Post subject: Re: Deluxe Reverb Reissue Filter Cap Replacements
Posted: Sun Aug 17, 2014 4:50 pm
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Thanks, for the answer. So, in essence, what Fender is doing is making the first stage's filtering = 38mfd/600VDC. Odd, as the second cap in this stage is a 47mfd/500VDC cap. Which could be ok, by itself?

Would five 220mfd/100VDC tied in series = 44mfd/500VDC work fine in the first stage? If each cap had a parallel 220k-ohm resistor?

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Post subject: Re: Deluxe Reverb Reissue Filter Cap Replacements
Posted: Sun Aug 17, 2014 5:07 pm
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BMW2002Ti wrote:
...Would five 220mfd/100VDC tied in series = 44mfd/500VDC ...


Yes. All caps being equal and in series, the capacitance divides, and the voltage applied would divide equally. So, in that case, the max total voltage that could be applied across the series of caps would be 500 volts, each cap would see 100 volts. At the same time, applying 500 volts, the math would be exactly the same if you used five caps that were each rated 250 volts. Each cap would still see 100 volts each, but the higher rated caps would hold up better/longer.

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Post subject: Re: Deluxe Reverb Reissue Filter Cap Replacements
Posted: Mon Aug 18, 2014 11:33 am
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So maybe the reason for using different values is to filter out a broader range of frequencies?

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Post subject: Re: Deluxe Reverb Reissue Filter Cap Replacements
Posted: Mon Aug 18, 2014 1:33 pm
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Abe,

Prolly not to filter out frequencies. Perhaps, the 47/500 cap was not quite enough voltage rating for this amp. So, Fender added the 220mfd/100VDC (maybe most readily available cap in this mfd range, at the time) --- to increase the first stage to 600VDC rating. Figure out the appropriate leveling resistors and went with it.


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