Electrolytics and Old Caps

[digital-conjurers at ADELPHIA.NET]

Mike,

This is the preferred approach at this shack.

The "traditional wisdom" has always been to replace wax-and-paper, electrolytic, and paper-and-foil caps, as well as any resistor 20% or more out of spec in vintage gear.

You're dealing with components that are 40, 50+  years old. Piecemeal part replacement usually results in the remaining weaker, old parts being put under higher B+ voltage, and that means a failure not too far down the road; sometimes a catastrophic one that can damage very hard-to-get and expensive components, like transformers, filter chokes, field coils in dynamic speakers, etc, etc.

Think of a concrete dam analogy: the thing has many leaks (old, leaky caps), and the water level and dam pressure is low as a result...plug one and the level/pressure rises...and the rest of the leaks start running faster.  Worst case, there's a blowout.

In the radio with old, leaky caps, say the B+ is limping along at 40% under spec.  Oh, the set will still work, but not as good as it could.  Replace one or two caps, the B+ rises, and something weak in the same line may not like the additional strain; it's been limping along with 40% under voltage for a long time.  POW!  And when it goes, it may go shorted, not open, the B+ goes right to ground, and the rest of your power supply components (and some other things) may take the hike with it.  Fuses may or may not prevent a catastrophe.

Now, having said this, there are SOME cases where it may make sense to keep the older electrolytics...like a transmitter where the things are $40 a crack, you use several of them, you're on a tight budget and they all test out good at rated specs on a good cap checker.

But if price is no problem, replace 'em, and sleep well at night.

-Lin/KJ6EF


At 07:49 AM 08/02/2004, Mike wrote:
>Check out the specs for electrolytics - as rated in
>hours...  read them in the specs printed in Digikey
>and Mouser electronics catalogs, easy to obtain.  5000
>hours running continuously is less than a year!  and
>typical is 3000 hours...  and caps age (although
>differently) with power off.
>
>I met a guy years ago that refurbished old high-end
>home audio equipment.  BEFORE ANYTHING, even power up
>and test, he clipped out ALL the caps and replaced
>them.  not just electrolytics either.
>
>Older electrolytics were probably rated much LESS than
>our new caps.  So I doubt equipment with 30 year old
>electrolytics is running perfectly.  I suspect you
>would actually experience improved performance if old
>caps are replaced.  (power supply levels and
>regulation especially would improve.)
>
>Mike
>W2MK

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