Electrolytic Cap Reforming

[Charles W. Morehouse]

Hi Russ,
Excellent comments. If the variac ploy doesn't work go on to the cap checker. Then
replacement. My rule is to replace. I too rebuild FT type cans with new caps
inside. You can hardly tell. The new caps are smaller and easier to work with.
Same for mylar caps and resistors. Bottom line is to buy NEW. Mouser has an
excellent supply. 73's.
Wayne;
W4GBW

Russ WQ3X wrote:

> I seem to hear it every time I express an opinion but here goes.
>
> I do use a variac to bring up old unknown radios. I like to see if a radio
> still works at all before doing anything to it. The variac may save the
> transformer if the capacitors are a dead short. Some of the oldest and
> nastiest radios work great - for awhile.
>
> To replace or not to replace the caps? If an electrolytic cap is
> mechanically and electrically sound then reforming it would be beneficial.
> But there is no way to know this. I think usually these old caps have either
> corroded internally or dried out and nothing is going to bring them back.
> One school of thought is that old electrolytics are either bad or going bad.
> I really enjoy rebuilding caps so would rather do this than clean up a bunch
> of melted wax from a radio chassis! I have seen some of them blow up while I
> was right there and it is pretty spectacular. With the electrolytic cans and
> multisection cardboard tubes you can replace the guts and make it so it is
> barely perceptible. I don't think it detracts from value if it is nicely
> done. I would rather have a working radio with new caps (done right) than an
> original radio waiting to burn my house down. (Overly dramatic)
>
> Another way out. There is a good way to check the condition of electrolytics
> and that is with an ESR (Equivalent Series Resistance) meter. This is an AC
> Ohmmeter. I built the one described in Nuts and Volts magazine last year
> which is based on an old circuit from Creative Electronics (no longer in
> existence). The info on this meter including schematic and notes was
> available on the Internet but I was not able to bring up the page today. A
> company in Australia (Dick Smith Electronics) makes a digital ESR meter kit
> for $50 or less. A lot of good links are available by doing a Google search
> on "ESR meter" or "Creative Electronics ESR Meter".
>
> The ESR meter works amazingly well and tests in-circuit so you don't have to
> disconnect leads. I never even made a proper scale for the meter but after
> some experience with it you don't really need it. (The closer to full scale
> the better but it depends on cap value.)
>
> This subject really gets into the "restoration philosophy" area and everyone
> has their own views. Non-electrical things that may influence the decision
> to replace caps are: How hard is it to work on? Are you keeping it or
> selling it? Sentimental attachment. Is it made of metal or wood? (Remember
> the fire thing.)
>
> 73,
> Russ WQ3X
>
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