Quote:
Originally Posted by geojunkie
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
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Dan: Having been in radio for over 50 years I have had numerous experiences with capacitors in both consumer electronics and industrial applications.
It has been my experience that micas and ceramics give less trouble from a statistical standpoint. However, they can certainly fail. The older "paper" dielectric tubular capacitors were not top notch performers from an electrical standpoint when they were newly manufactured. The commonly known capacitor parameters such as insulation resistance, Q, series R, etc. have certainly improved when applied to the modern dielectrics of today's capacitors. Having stated this I recommend replacing "paper" capacitors whenever they are encountered just to take advantage of the improved performance of a modern unit. One of the other respondents also gave good advice when he related to future troubles and "callbacks" that might well
occur when old units are left in place. Good luck with your restorations.
Dr. T