[R-390] IF deck caps

Sat, 4 Jan 2003 22:54:20 -0800

----- Original Message -----
From: "blw" <[email protected]>
To: <[email protected]>
Sent: Saturday, January 04, 2003 7:09 PM
Subject: Re: [R-390] IF deck caps

>
> Jerry,
>
> Are you talking about wax covered paper caps?
>
> If so, these have to go. They leak badly. These are good candidates for
> reforming as you bring a variac up slowly, but you will probably find a
high
> number of them out of tolerance. These get pinhole leaks in the foil
> innards. You reform them by bring up the voltage slowly and the holes get
> filled again. But, you can guess the probability of failures soon with
that
> many of them in there.

This is true of electrolytics, but not of paper caps.  The latter may
initially operate ok in a set that has been on the shelf for a long time,
but will begin to leak badly in only a few hours of operation.  You can hear
a set "tighten up" if you place a set with bad caps in operation.  Whistles
will appear, audio becomes distorted, AVC doesn't work, and the AF gain
control has to be turned up well beyond the first 20 or so degrees where it
usually operates.

I have found a simple test with a VOM works well.  Disconnect on end of a
suspect cap, and measure the resistance with the highest ohms scale.  If any
residual resistance shows on the scale, the cap is leaky.  Disconnect the
probe, then reattach.  If the cap shows a "kick" on the meter each time the
probe is attached, it can't hold the charge of the vom battery, and is
leaky.

Many, but not all, electrolytics will self-heal, if allowed to reform as
described above.  Not so with papers, they will just get worse.  They also
have a tendency to open or exhibit a poor power-factor over time.

73 de Bill, AB6MT
[email protected]

>
> Pull those wax covered paper caps out carefully and put them up for sale
on
> ebay. Advertise them as excellent dummy caps for the *L@@K* crowd who
cover
> modern caps with the shells of old ones to make it look *ORIGINAL*. Don't
> laugh, a lot of people do this. I was just reading an old article about a
> guy who forms his own square molds for the old type resistor look.
>
>
> Barry
>
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