Capacitor Questions Please

Sk8Ter

Member
2011-08-09 12:12 am
I have several speakers that have old.... 2 section with common ...common for both sections can type capacitors ....

can you still buy these as new production just like they used to make them?

2nd question

this capacitor is wired in series in my speakers.... in to the one of terminals out the other terminal not using the common! how can this be possible or why would you wire these this way..In my thinking you would wire in on one of the terminal and exit out the common. this has me scratching my head...

Thanks

Lawrence
 

rayma

Member
2011-04-29 8:37 pm
this capacitor is wired in series in my speakers....
in to the one of terminals out the other terminal not using the common! /QUOTE]

That's being used as a non-polarized electrolytic capacitor (2 is series, back to back).
You'd be better off just replacing it with a fresh, single non-polarized type.
If each section is say 40uF, replace the dual cap with a single 20uF.
An example: https://www.madisoundspeakerstore.com/electrolytic-cap-100vdc/bennic-22-mfd-electrolytic-caps/
 
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Sk8Ter

Member
2011-08-09 12:12 am
Thanks

my first thoughts were the same... some how using them as a Bipolar but then again im still confused 2 separate sections that share a common neg terminal should be total separate but they are not!

for example if these were used in a power supply how would you use them with differing voltages if they are some how connected together?

Thank you for your response

Lawrence
 

rayma

Member
2011-04-29 8:37 pm
these were used in a power supply how would you use them with differing voltages
if they are some how connected together?

In older equipment (and even in some current tube amps), multiple section capacitors were often used.
They are smaller and cheaper. That terminal common to both capacitor sections is grounded in most circuits.
A typical example: https://www.tubesandmore.com/products/C-EC40X4-350
 
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Sk8Ter

Member
2011-08-09 12:12 am
In older equipment (and even in some current tube amps), multiple section capacitors were often used.
They are smaller and cheaper. That terminal common to both capacitor sections is grounded.
A typical example: https://www.tubesandmore.com/products/C-EC40X4-350
40 bucks is not cheap for 4-40mf caps!


anyways still didn't explain it to me why they would be tied together somehow?

Lawrence
 
rayma… if you think it thru, I don't believe the advice of “replace 2 ea 40 μF with 1 ea 20 μF” is correct.

YES - we've all come to learn that capacitors in series divide the capacitance, rather much like resistors in parallel lower resistance. Same basic equation

CA+B = CA • CB / (CA + CB)

But… since in a back-to-back string of polarized capacitors the one in the wrong direction acts like a diode … during each reversed cycle the capacitance is only that of the capacitor which is working in the 'right' direction.

So, I'd say one would need to use (in your example) a 40 μF non-polar capacitor as the single-part replacement. And last I checked, they can be pretty pricey. Well, not that bad, only $10 to $20 at Mouser for good ones.

GoatGuy
 

rayma

Member
2011-04-29 8:37 pm
since in a back-to-back string of polarized capacitors the one in the wrong direction acts like a diode …
during each reversed cycle the capacitance is only that of the capacitor which is working in the 'right' direction.

I know this works for smaller signal levels on electrolytics, you can try it and see on your cap meter.
Maybe if someone wants to test for a capacitance change with large AC voltages, we'll see if there's a difference.
That might be dangerous, though.
 
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The fact they are inside a can doesn't change the fact they are two electrolytic caps connected together at their negative ends. If you used one in a 400v circuit and another in a 300v circuit, as long as the cap was sufficiently rated, then grounding the can makes it two caps to ground, No further internal connection that that, so the separate circuits is no challenge.
 
common?

But… since in a back-to-back string of polarized capacitors the one in the wrong direction acts like a diode … during each reversed cycle the capacitance is only that of the capacitor which is working in the 'right' direction.

Yes, I guess :eek:

And that is not to be confused with speaker's phase, which is marked red (positive ) and black ( negative) and it is related to the movement of the membrane if goind forward or reward :rolleyes:

I have several speakers that have old.... 2 section with common ...common for both sections

this capacitor is wired in series in my speakers.... in to the one of terminals out the other terminal not using the common! how can this be possible or why would you wire these this way..In my thinking you would wire in on one of the terminal and exit out the common. this has me scratching my head...

Thanks

Lawrence
 
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