"Engineer" wrote in message
...
Hi, Vacuumlanders (boat division :-) )
I don't spend much of my time on boatanchors but this may
be of
interest.
While restoring a Bendix RA 10DB receiver as part of a
CASM, Toronto,
Lancaster bomber restoration project, see:
http://casmuseum.org/avro_683_lancaster_x.shtml
one of the decoupling caps failed spectacularly. It was
C54. First
there was a smell as plate decoupling resistor R15 (1000
ohms)
overheated, then smoke (I think from from R15 paint), then
C54 got
very hot and oozed a white bubbling substance... B+ had
dropped from
221 VDC to 183 VDC... hit the off-switch fast!
Fortunately, no
dynamotor damage. This unissued, NOS Bendix radio had
earlier been
powered for about a hour or so in several check-out
sessions without
any trouble.
The cap is one of several marked "Solar TYPE [blank] MADE
IN USA .1
MFD 400 VOLTS DC GRD (at one end)" It has a rectangular
brown
plastic case (bakelite?), about 1 3/8 x 5/8 x 5/16 inches
in size.
There are several of these in the set, some but not all
are under B+.
I'll be watching them. I presume this is a mica cap but
others may
know better.
Just one small event in a myriad of restoration
experiences, but
factual data... not just an anecdote!
Cheers,
Roger

The value is somewhat high for a mica cap but its
possible and the shape is right. If it is mica its probably
a stacked cap rather than silvered mica. I suspect that any
modern plastic cap would replace it. GRD probably indicates
the outside foil. Grounding that gives some shielding to the
cap. It was common for tubular paper caps to indicate the
outside foil by a line at one end and this may be the same
sort of thing.
I don't know the mechanism of its shorting but that is
evidently what happened.


--
Richard Knoppow
Los Angeles
WB6KBL