[R-390] capacitor analysis

[John Saeger]

JAMES T BRANNIGAN wrote:

> More 2 cents..........
> Except for electrolytics, black beauties and C-553, I see no reason to
> replace good parts in a functioning radio.
> That said, after all the work to identify and remove a component, it is a
> false economy to replace it with a cheap substitute.
> I have also learned, the hard way, not to re-engineer Collins radios.
> Jim

Yeah, if it ain't broke don't fix it.  I agree.  But there's still something
flaky about my radio.  So today I finally pulled it out of it's case and had
a look at things.  The bottom where the audio deck is was spectacular.
Pristine.  The gear work on the band switch stuff looked clean and things
turn pretty smoothly.  Maybe some lubrication would be nice, but I'm not in
a hurry.  Sometimes too much lubrication is worse than too little.  I took
out the audio deck and it looked great.  It's a 1956 Motorola, and it's
amazingly clean and I could find no traces of repairs.  The rectifier tubes
had been replaced with solid state plugins that were nicely potted.  They
looked commercial.  So I don't think I can bring myself to spoil it since
everything looks so nice.  And I don't think the problem is here anyway.

The IF deck is another story.  It's pretty ugly, and to tell the truth I
suspect the problem is here.  When the radio flakes out, the carrier level
drops.  But it doesn't happen very often.  And it doesn't last very long.  I
hate these intermittant kind of problems, they're almost impossible to find.
It just feels like a capacitor somewhere to me.  I could be wrong of course.
The IF deck is an old Collins.  There are no adjustable tuning capacitors
near the mechanical filters, and one of the filters had been replaced with a
Dittmore Freimuth filter.  When I looked at C553, and also at Chuck Rippel's
page showing how to change it, I see that although it was an original
looking Vitamin-Q, it was not dressed against the chassis like he shows in
his picture.  So I'm thinking maybe it has already been replaced before.
But I went ahead and put in a 1KV ceramic, because it's what I had, and it
didn't seem to make any difference.  I don't know.  Maybe later I'll put in
something better after I order capacitors.  Or maybe I won't.  I don't know
why I like ceramics so much.  Maybe because *ceramic* sounds heavy-duty.
;-)  But I have a hard time paying twice as much for an orange drop than a
Cornell Dublier polyester, which is what I'm leaning toward right now.  You
can get them in a 1KV rating.  But I'm still thinking about it...

Thanks,  John