[R-390] Lightning crashes in audio

[Barry]

In the radios where they put the unprotected silvered micas inside the IF cans, those would cause the same phenonema when the silver starts to migrate.  I'd guess it's a silvered mica.

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "Stan Gammons" <sg063015 at gmail.com>
> To: n4buq at knology.net
> Cc: "Collins R-390 HF Receiver List" <r-390 at mailman.qth.net>
> Sent: Saturday, August 15, 2020 9:11:38 PM
> Subject: [R-390] Lightning crashes in audio
> 
> Hi All,
> 
> I have an R-390A that I recently put back on the bench and noticed it
> has developed a lightning crash sound in the audio. It's much more
> noticeable with no signal.   It appears the problem is around the 1st IF
> amp.  With a scope on the plate of the 1st IF amp I can see the signal
> change when I hear the lightning crash sound.  Some time ago I replaced
> all of the black beauty caps with orange drops. The cap that goes bad
> and takes out the mechanical filters has been replaced too.  I didn't
> replace the disc, which I assume are ceramic disc caps or the green
> rectangle shape caps which I assume are mica caps.  I'm guessing one of
> the ceramics or mica caps is bad and causing the lightning crash sound
> in the audio?
> 
> Thanks for any help.
> 
> 73
> 
> Stan
> KM4HQE
> 
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