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Old 14th December 2004, 12:57 AM   #1
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Question coupling caps

greetings-
how does one test for leaking coupling caps?
i have a good fluke DMM, but it does not measure capacitance.
the caps are 600v .047, waxed paper in oil, and are at least 44 years old.
thanks
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Old 14th December 2004, 01:46 AM   #2
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Measure the voltage on the "cold" side. If you apply a couple hundred volts to one end and connect the other end to ground via 100K, you can measure and calculate the leakage current. Take into accout the impedance of your meter.
-Chris
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Old 14th December 2004, 02:12 AM   #3
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these are "pyramid" brand, made in usa caps.
i was a bit worried about unsoldering/resoldering them as the leads are quite short, and i read about beeswax caps being vulnerable to heat.

i realise that i can always replace these with the "jupiter" beeswax caps, but i am trying (who isnt) to do this on a budget.
worst case scenario: i wreck the caps by trying to test them. what type should i replace them with?
paper in oil
beeswax
solen
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Old 14th December 2004, 04:10 AM   #4
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Orange drop caps will be fine or Solens if you want "audiophile" parts Solens are priced pretty decent.
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Old 14th December 2004, 05:38 AM   #5
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Hi,

Quote:
i was a bit worried about unsoldering/resoldering them as the leads are quite short, and i read about beeswax caps being vulnerable to heat.
Pyramid Caps are beeswax insulated? Didn't know that.........

Anyway, soldering and unsoldering them shouldn't cause any damage provided you do it the same way as you would with any other cap.

Quote:
Orange drop caps will be fine or Solens if you want "audiophile" parts Solens are priced pretty decent.
I'd rather use Orange drop than Solen Craps any day of the week but YEMV.

Cheers,
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Old 14th December 2004, 07:20 AM   #6
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Simple way to test:

Hook up a 100 to 500V supply (more volts to test to a higher rating on the cap) and connect the capacitor in series with a 1k current-limiting resistor (just in case...) and with a neon lamp.

Operation: after the initial turn-on spike which charges the cap (put up a sheet of paper in case the neon lamp blows, large caps may hold more energy than a neon can handle), any leakage will discharge the cap, putting more voltage across the neon. After a while it drops to the firing voltage and the neon fires, charging the capacitor up to the turn-off voltage. A good cap will fire once or twice in a minute, and that includes the first (hookup) pulse. A leaky one will just blink on and on.

To find the exact leakage current, I = C * dV/dt, where I is the leakage, C is capacitance, dV is the difference in voltage (measure on a scope; it varies with the neon, its age, how much light or radiation is around, etc.) and dt is the time period of the oscillation ( = 1/f).

Tim
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Old 14th December 2004, 08:42 PM   #7
anatech is offline anatech  Canada
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Hi Tim,
That sounds like an evening of fun! It's the right season for it too.

-Chris
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Old 17th December 2004, 12:51 PM   #8
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@Frank
I havenít tried orange drop. Are they better than Solen? What about Audyn (standard series) caps? Or Audyn KP-SN?
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Old 17th December 2004, 03:42 PM   #9
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Hi,

Quote:
I havenít tried orange drop. Are they better than Solen?
Intrinsically, yes.
The major advantages of the Solens used to be that they were about the only ones availble in large values at 200V + voltages.
Unfortunately, the suffer from a QC problem that detoriates the sound considerably.

Quote:
What about Audyn (standard series) caps? Or Audyn KP-SN?
Not the ultimate cap but they are excellent value for money. The SN range is audibly better but more expensive.

Cheers,
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Old 17th December 2004, 04:42 PM   #10
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which orange drop is preferred, 715 or 716 series? or does it depend upon the application?
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