[Heathkit] sb-200 capacitors (again)

[Michael Tortorella]

I have been following the recent thread regarding 85C vs. 105C electrolytics
in the SB-200 supply.  I spent a good deal of my career at Bell Labs in
reliability engineering and I want to add that the voltage- and heat-related
failure mechanisms in electrolytic capacitors are quite well understood
(wish I could say that about other classes of components, but that's a
discussion for another day).  It is true that derating (i. e. using the
device at a lower power/temperature/voltage/current/whatever than it is
rated for) will, other things being equal, lengthen the comnponent's life.
In the SB-200 case, we should also consider the issue of duty cycle.  Most
of us don't have the amp on (i. e. transmitting) for 100% of the time and
even when it's transmitting, SSB and CW duty cycles are less than 100%.  So,
harking back to my days in undersea systems, to be conservative I'd go with
the 105C rated capacitors (and if I could get some with a higher voltage
rating I would use those too) but this is PROBABLY overly conservative for
typical amateur use (unless you use the amp on AM for hours every day <g>).
In any case, the cost difference is probably minimal, particularly when
compared with the annoyance of having to replace them yet again, so I guess
the bottom line is that the proverbial amateur frugality should be judged in
complete context (not just first cost!).

That said, can anyone point to a source for the 105C rated caps?

Again, no disrespect intended to Glen who has offered more help to more
people on this list than I can possibly remember.

73 and happy T-day to everyone
Mike, W2IY