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old electronic devices electrolytic capacitors

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Wallace Gasiewicz:
About caps exploding;
I only had that ONE cap go POP in a regular Ham Radio. It was in DC to AC converter. Dont remember if it was a RIFA, but caps in this application have a very stressful life.
Must not have liked me at all.

Caps in old RF amps are another story and are used in voltage doublers and triplers and are a bigger problem and can go off sounding more like a firecracker.  This happens more often. Voltage is something like 1 KV in old tube RF amps so caps can have 500 V on them. I have worked on these things and have decided it is best just to avoid them.
I have seen 100's of old radios start up without a hitch after many years in garages and basements. Most likely problem is not a POP but a 60 cycle HUM from bad electrolytes. Sometimes this is not loud enough for me to hear but drives audiophooles nuts.
Some people say that starting old radios with the variac can reform the electrolyte caps so you do not have hum and don't have to replace them. I don't know how true this belief is. Variac is just being careful and possibly saving some  PS caps that would fail and make noise. I kinda agree with the 90 to 95% analogy.
Most of failures on caps in more modern equipment is easily fixable when the caps go. They are of course much lower voltage. If you get an old piece of equipment, just find a group that uses it and they will tell you what problem caps to look after or replace. RIFA caps are a known problem as pointed out by another poster.
I sometimes have trouble starting myself up once a month, hard to remember to plug all this stuff in.

james_s:

--- Quote from: Siwastaja on November 27, 2020, 04:35:24 pm ---IMHO, there's nothing weird about this.

People expect old electrolytic caps to explode, but this isn't typical, I think it's more about hearing the stories than actually experiencing problems. I have never seen it happen, personally. I always just plug in the old stuff.

Reforming increase the chances of success, maybe from 90% to 95%, but old devices Just Working despite no reforming at all is still the expected result.

In audio equipment, the problem with bad electrolytics may be increased hum due to increased ESR and decreased capacitance, and reforming may not help significantly, replacement is often necessary.

--- End quote ---

I've never had one explode, but I have encountered a lot of electrolytics in old radios that were completely dried out and open circuit. A much bigger problem is wax paper coupling capacitors, they absorb moisture and become electrically leaky. They probably won't explode either, but you might find that a precious tube fails is degraded by overloading or an unobtanium IF coil burns out.

bob91343:
The problem here is in the original question.  What we are trying to do is to make a scientific assessment of something that was not considered too important in manufacture.  By that, I mean the capacitor maker has no interest in how the products are used and is just trying to make a living building components.  You are asking questions that are simply answered by tallying the experiences of others rather than something that can be answered scientifically.

Variations in manufacturing processes and variations in applications are too wide to allow a solid answer to the question.  If you are worried about it, check operation now and then.  If you want to know how often, good luck.  A part can fail immediately after test and it can even recover without outside stimulation.

If you want to be more certain of operation, use a better part, preferably one with a different failure mechanism.

Otherwise we are just accumulating anectodes.

GlennSprigg:
This is an interesting question for "Mr. Carlson's Lab" on YouTube.
Interestingly, on a few of his videos, he even talks about the importance of 'Mounting Polarity' of NON-Electrolytic caps.
This being for the reduction of Noise by mounting them the wrong way. Basically, caps that are wound as a circular Foil,
should have the 'outer' part of the coils lead to ground. (If applicable). They often (old caps) have a black mark indicating
the outer coil end, but he has proven that numerous times, they are labeled incorrectly! (He shows how to check this).
Basically, if 'Electrolytics' are old, then just replace them!

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