reforming caps

[George Maier]

Ken:
Your'e on the right track with the Sprague. I have used a TO-6 here for the last ten
years, and have developed some proceedures that work for me.  If you are going to check an
old electrolytic, it's really wise to re-form it first.  I usually start with a very low
voltage; if it's a 450V cap, I'll start at 50V, and wathc the leakage current.  Most of
the time it settles down to microamps.  Every time this happens, I raise the voltage by
30V or so, until I get to the full value, or at least to the voltage that it will be
operated at. Each time, you have to wait until the leakge current drops.  It works in
about 80% of the cases.  Some are just beyond reforming.
Once it's reformed, wait until the cap has completelty discharged, then do the value and
power factor check.
Vy 73
George Maier - K1GXT

Ken Ketner wrote:

> Bruce and others:
>
> Thanks for info about reforming caps. I have been able to find axial
> caps of new manufacture of any voltage up to 450 wvdc through antique
> electronic supply (I have no interest in the company) in Tempe AZ for a
> buck or 2.
>         I have a Sprague cap analyzer in my shop which has an eye tube and a
> bridge for determining value, a voltmeter and an ammeter built in, as
> well a provision for putting up to 600 volts (variable) onto a cap. One
> can watch the meter and see what the leakage current is. When I clip a
> lead on an el cap and slap the Sprague on it, I find that no matter how
> long I keep the voltage on most old caps, they still will come down to
> leak around 3-10 milliamps, which is too much it seems to me. A cap will
> settle down after 3 or 4 minutes on voltage, but almost never at an
> acceptable leakage value. SO I have always thought that clipping in a
> recently manufactured one from Antique el sp is the way to go. That
> means I won’t have top be back in that particular chassis for some time.
> I also routinely clip in interstage caps for the same reason. Am I
> missing some part of the forming procedure? Does one have to leave them
> on voltage for a week or a day or something?
>         On can caps, Antique offeres new manufacture on those too, but they are
> 20-30 dollars. So I get a tie strip, fix it to a bare spot on the
> chassis, and using new axial lead caps, rewire the can leads. Same
> effect for half or third of the money. And if one wants the can to stay
> there for esthetic reasons, that is fine.
>         We inquiring minds want to know
>
> Many thanks
> --
> Ken Ketner, KA5ELD
>         Postal Address:
>
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