[Boatanchors] micamold caps

[Rob Atkinson]

thanks everyone for all the help.  the cap was 330 pF 500 v. and was
in the grid input network to the 6L6 buffer (driver) stage in a
hallicrafters HT-20 rig I own.  The rig crapped out because the bias
on the grid of the 6L6 got messed up.  Something seemed to have
started to leak or short and the driver quit conducting and I fixed
the rig and it is back on the air now but when I saw "micamold" I
yanked the cap and replaced it with class 2 dielectric RF ceramics to
be on the safe side.  It wasn't the problem but I thought "paper cap
out it goes"  because I was into the rig and figured while I have it
on the bench a stitch in time saves 9.   The leaker was one of those
red postage stamp caps which was the dc blocking cap between the 6AG7
oscillator and the grid of the 6L6.

The final plate  dc blocking cap is a 2000 pF 2.5 KV brown micamold
and the plate choke bypass is a 4700 pF 2.5 KV brown micamold.  I
replaced them with new ceramics because even though they may be okay,
they are 64 year old caps and I have had 50 50 luck with old micas.
The loaded B+ on the final is 800 v.

73

Rob
K5UJ

On Mon, Mar 21, 2016 at 9:07 PM,  <w5jo at brightok.net> wrote:
>
> Mistake, I should have said the first dot on the top left.
>
> Jim
> W5JO
>
> -----Original Message-----
>
> Rob you are talking about the "postage stamp" type of caps with the dots on
> them.  If so, with the arrow(s) pointing to your right, the first dot on the
> left should be either black or silver.  The black indicates mica and the
> silver indicates paper.   That holds true for caps purchased under JAN or
> AWS that will be found in military equipment.  The bad thing is the in many
> cases the silver paint would come off leaving a blank dot.  If that is the
> case assume they are paper.
>
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