I'll concur with the other comments. I (personally) wholesale change out
caps when one or more go out and/or when I first check out a radio before
powering up (and find bad ones). Having said that, I have found both
extremes in older radios. For example, my HQ-120 was dead, blew fuses,
and had about 500 ohms plate resistance presented to the PS. All caps
were changed and the radio in now fine. In my National receivers, the
Black-Beauties split, leak oil, short, and are generally very disagreeable
components. My BC-669 transceiver (circa 1944) required all the mica caps
to be replaced, something I would not have expected, until now.
Sangamo's, included! There aren't any caps that are bullet-proof after 50
years. My SX-28 still has most of the wax/paper caps working just fine.
One of these days, though............ Finally, the sage advice to change
those parts which will precipitate other, perhaps worse, failures is
mandatory. Its just not worth the risk and to try and find some old IF
can, etc. if one smokes, after the fact. My take on the issue... 73 de
K3HVG

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