CJT wrote:
Ian Malcolm wrote:

James Sweet wrote:

I don't understand why you think it necessary to replace the paper/wax
ones without testing. In my experience those can last a _long_ time.




It's standard procedure. They already *have* lasted a LONG time. Ask
any of the experienced guys on rec.antiques.radio+phono and they'll
tell you the same thing. Skimping out on replacing a 10 cent
capacitor can easily burn up an expensive output tube or
irreplaceable transformer. 70+ year old paper/wax capacitors are
simply not reliable and can't be depended on. Do the job right and do
it once, and the radio may well be playing for another 70 years.

Tin foil + waxed paper insulator, wrapped construction. I thought it
was overkill to replace them all at first, but then I remembered tin
whisker growth has taken out *many* far more recent AF117 transistors
and that is *TIN* foil in the caps. If they aren't shorted now, they
soon will be . . .

They'd have to be some pretty darn big whiskers. Transistors are on
a different scale.

Have you read NASA's tin whisker and their impact on satellite
reliability pages? http://nepp.nasa.gov/whisker/

Of specific interest is
http://nepp.nasa.gov/whisker/background/index.htm#q5
I quote:
"Whisker Length: Whiskers as long as a few millimeters are not uncommon
with some experimenters observing whiskers as long as 10 mm (400 mils)
in length."

And:
"tin whiskers can grow through conformal coating and once exposed can
then short to other tin whiskers or other exposed surfaces."

So it looks like they can be pretty darn long *and* grow through soft
plastics. Wax isn't going to stop them . . .
--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
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