I replace caps that need to be replaced. I have found that every
electrolytic that has a small voltage rating is bad and they get changed
out without even thinking. I have found a lot of electrolytic that are
higher voltage units to be higher in value but then after they get
reformed end up reading within tolerance. I have only started looking
at leakage and so far after a good reforming they seem to be what I call
good enough to use. Of course some will not reform and they get trashed.
I have found just as many silver mica and ceramic disk caps bad as I
have found black beauty caps and the other paper caps. . Unless a cap
is in a part of the circuit where a failure would cause a major failure
like in the 75A4 where it will take out a filter I don't even think of
swapping them out unless my testing shows a problem with that part of
the circuit or the part is literally falling apart. My feeling about
the caps of old was that quality control was there major problem. I
expect that assemble of these caps was a big factor and that depending
on who did the assemble some ended up never being a problem and some
got contamination during manufact and ended up failing early in there
life.

My two cents worth,
Ron WA0KDS


geojunkie wrote:

I have several postings here about an SX-101a I am restoring. Up to
now I have done consumer radios, TVs, and an SX-71. I found the
majority of the paper caps (wax or molded) to be bad in them. By bad,
I found them to be out of tolerance (usually reading high on my old
60hz reactance bridge meter) and showing significant leakage at rated
voltage. So now I start on the SX-101a and wouldn't you know it the
first 4 paper caps I pulled check perfectly in all respects. These do
appear to be a much higher quality cap than those I have seen to date,
but paper they are. So if 4 out of 4 are good, do I need to replace
all the paper caps in this unit? Perhaps this radio never saw much
humidity, and coupling that with higher quality parts they might still
be just fine. I am tempted to reinstall the ones I just pulled to keep
the vintage look. I really don't know how to test the caps in circuit
individually unless I pull one lead, and then you are half way to
replaced anyway, so if there is high likelyhood of some bad ones out
there, I might as well replace them all. Are there certain circuit
locations more prone to fail? I have stopped further work until I get
some feedback on this.

Dan