Meat Plow wrote in message
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On Sat, 14 May 2011 15:47:18 +0100, N_Cook wrote:

At least these amps have separate LV DC supplies and the biasing part
can be probed out of casing , powered from +/-15V bench ps without
+/-92V around

TO92 60V, 0.6A , 9V on one end of the 47K base resistor and 8mV on the
other. Checks out DVM diode test and no obvious DVM resistance between
pins. Now removed can see ,under x30, slight build up of corrossion crud
where the legs enter the plastic, marginally more than the layer of
corrossion over the rest of the legs.
I will let the owner see the result under pocket magnifier , that and
bill might change his storage arrangements.

Some people just don't realize that electronics of this type really need
to be stored in a climate controlled storage unit.



--
Live Fast Die Young, Leave A Pretty Corpse


The other owner , with the Crest audio amps thought covering with a plastic
sheet , include a bag of silical gel, and leave in a Dutch barn was
sufficient. He never even recharged the silica gel - having no knowledge of
that process.

I wonder why TO92 and not TO220 or TO3 fail in these circumstances. I
suppose the leads corrode and swell and then like concrete spalling due to
rusting of rebar, the plastic splits enough for capilliary water condensate
to migrate up into the die. Something to do with small diameter leads for
TO92?
I will try to remember to split open this TO92 and see if it cleaves along
the corrossion plane.
Different maker to the Crest TO92 so not a batch problem.