[R-390] Leaking C103?

[n4buq at knology.net]

Yes, I happened to check it with an ohmmeter.  I was checking the RF gain 
via the back panel with the jumper disconnected.  I happened to connect the 
meter to the C103 side and observed the meter climb to 500k and stop.  I 
expected it to go nearly to infinity.

Now knowing the function of C103 and how it doesn't really matter since the 
RF gain control is approaching its low end at fully CW, then I'm not going 
to worry about it.  If I'm unable to reduce the gain, then I'll know it 
could be the cap.

Thanks for the info!

Barry - N4BUQ

On Mon, 18 Sep 2006 13:39:34 -0700, "David Wise" <David_Wise at Phoenix.com> 
wrote :

> You are measuring it wrong, Barry.  The leakage current of
> electrolytic caps like C103 is not proportional to applied
> voltage - you can't express it as a resistance.  The fact
> that you did suggests that you used an ohmmeter, which
> probably did not apply more than a volt or two.  The cap
> would have to leak at least a few mA to give the behavior
> you observed*.  Suitable replacement caps (47uF/100V)
> caps are abundant and cheap.  The easiest way to check the
> original is to temporarily remove it.  This is feasible
> because its only role is to keep the scratchiness of the
> pot from blowing your ears out as you turn it.
> 
> 73,
> Dave
> 
> * I hope I'm not confusing threads.  Someone reported
> unexpectedly high gain when RF GAIN was set to minimum,
> and I replied that a possible cause was a leaky C103.
> 
> > -----Original Message-----
> > From: r-390-bounces at mailman.qth.net
> > [mailto:r-390-bounces at mailman.qth.net]On Behalf Of Barry
> > Sent: Sunday, September 17, 2006 11:46 AM
> > To: R-390-List
> > Subject: [R-390] Leaking C103?
> > 
> > 
> > Was checking the RF gain control last night and discovered 
> > C103 (the 50uF
> > bathtub cap) appears to be leaking (was reading about 500k 
> > without the RF
> > gain control connected.  I wonder if this is hindering the 
> > operation of
> > things?  I don't find what it's purpose is so not sure how 
> > that would affect
> > the operation.
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