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Old 2nd May 2009, 05:00 PM   #1
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Default Capacitor Question...

I have a Bell Sound 2420 amp and I need to replace two multi section can caps, and I really don't know much about them.

one is a 40uF/450v,40uF/450v,20uF/450v

I have found a three section cap that is 40uF/525v,40uF/525v,40uF/525v

would this be a suitable replacement even though the last section is 40uF versus 20?

the other is a 20uF/350v, 20uF/350v, 500uF/25v

I found a 2 section cap: 20uF/450v, 20uF/450v and then would have to put a third cap separate from it as I couldn't find one that had all three.

Does this make sense or am I coming to wrong conclusions?

I had considered wiring separate caps and leaving the cans unconnected, but there just isn't room in the spaghetti nightmare that is the underside of this chassis.
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Old 2nd May 2009, 06:00 PM   #2
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The replacement capacitors that you have listed are perfectly good to use. A higher voltage rating is ok. A lower voltage would probably not be as good unless the actual applied voltage was even lower. Also the added capacity of 40 verses 20 is perectly ok too because it's not excessively larger. The only other thing to keep in mind is the physical size and height of the new can. This is only important if you are confined inside a cramped cabinet of come kind where headroom is close.
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Old 2nd May 2009, 06:28 PM   #3
tomchr is offline tomchr  United States
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As the previous poster said: Higher rated voltage is fine (might even lengthen capacitor life) as long as the can fits in your application.

As for the capacitance. It depends a bit on where the cap is used. It sounds like a power supply cap in which case more capacitance is usually better. If it's a coupling cap (who would use a 3-section cap for that anyway), you might end up affecting the frequency response of the amp by a factor of 2.

In many cases with the old capacitors the tolerances are really W-I-D-E. As in +100/-50 % or the like. So your 40 uF would put you at the upper end (perhaps slightly outside) the original specifications. Modern caps are usually +/- 10 % or so.

Conclusion: Using the 40 uF cap instead of the 20 uF is likely to be OK. So if the can fits, I'd say go for it.

~Tom
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Old 2nd May 2009, 06:36 PM   #4
tomchr is offline tomchr  United States
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Oh... For the other (20+20+500 uF) cap: You'll probably end up with 470 uF/25 V as it's a standard value.

Replacing the 3-section caps with individual caps would work as well. But finding exactly the values you need will be a challenge. You could use the standard values of 22 uF, 47 uF, 470 uF to replace 20 uF, 40 uF, and 500 uF respectively.

www.digikey.com will have the individual caps if you decide to go that route.

~Tom
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Old 2nd May 2009, 06:43 PM   #5
SY is offline SY  United States
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Be careful that the caps are not too old. Check the date code. If they're more than 10 years old or so, it's not worth the risk of using them.
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Old 2nd May 2009, 08:25 PM   #6
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I have to agree with pretty much everything said here. Given the tolerances 50 volts less wouldn't likely be a problem. Your amp uses 6V6s I believe??? 450 volt caps should be fine. The only thing I would be concerned with is putting the 40uf in place of the 20uf depending on where it is. I almost always beef up the plates and screens in the output section as they're usually skimpy from the manufacturer. The 20uf may be in the PI, so that would be ok, but I am cautious about filters in the preamp...could change the tone if you bump them too much.

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Old 3rd May 2009, 02:15 AM   #7
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bereanbill-
Yes, it uses 6V6GT's, and these caps are replacing the old electrolytic FP type cans

I was just looking on AES's site and saw they have two FP cans that might be better than the 40/40/40 I was looking at. Provided they fit they have either:

a 4 section 40/20/20/20 @ 525v - so I would parallel two 20's to make the 40 (right?)

or

a 4 section 40/40/20/20 @ 525v - and I would just not use one of the sections.

these are all new production, so don't have to worry about them being old.
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Old 3rd May 2009, 12:38 PM   #8
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I'd go with the 40/40/20/20...I can't remember which way it is with caps, series or parellel, but one way halves the capacitence while doubling the voltage ...I know that parelleling resistors halves their value. I haven't done it in so long I honestly can't remember. Let's appeal to the uber-gurus of this forum for an answer to that. Hey SY...got your ears on???
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Old 3rd May 2009, 12:40 PM   #9
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they're the same price, so I imagine you are correct, the 40/40/20/20 would be easier
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Old 3rd May 2009, 01:52 PM   #10
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Parallel adds. Series adds reciprocally, i.e. 1/C = 1/C1 + 1/C2 +... With these twistlocks, the negative terminals are all connected together, so series becomes a bit of a challenge.

Can I take my ears off now, please?
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