[NJARC] Capacitors

[antqradio at juno.com]

Seasons Greetings
Capacitors are not perfect devices so depending on the application one
type will give better performance then another.  So what you have to do
is figure out the function of the capacitor in the circuit you are
repairing.  Frequency determining circuits require accurate and
temperature stable capacitances.  Coupling and bypass capacitors are less
critical with regard to value and stability but leakage may be a concern.
 Power supply filtering requires large values of capacitance in small
packages but exact values are not critical and neither is some leakage
current.  Again, what to use and where it is used all depends on
application.

Some prefer one type, for instance "orange drops" for coupling and by
pass.  Ceramics with high dielectric constants work just as well and are
cheaper.  Just be aware that they will change in value with temperature. 
The same is also true of electrolytics but in power supply filtering, it
is not much of an issue.  Electrolytic capacitor leakage can be a problem
because it leads to self destruction.  High leakage causes power to be
dissipated in the capacitor which causes higher temperature which then
causes more leakage.  Even is the capacitor doesn't end with a bang, the
capacitance value will decrease, allowing more hum in the high power
audio circuits.

Finally, remember that the coupling or bypass capacitor you are replacing
will most likely have a pretty high tolerance.  Plus and minus values of
20% are not uncommon for paper capacitors.  With electrolytics,
tolerances can be +80%, -20%!  What you get today is vastly superior to
what was available 30-40 years ago.

As for web sites. Try: www.uoguelph.ca/~antoon/gadgets/caps/caps.html  . 
I am sure there are others that may better explain the differences
between types.

Hope this helps and happy repairing, it keeps you off the street!
Jim

On Fri, 17 Dec 2004 15:25:14 +0000 "Eugene Hertz" <ehertz at tcaf.org>
writes:
> Win a new Icom IC-756PROIII and help QSL/QTH.net
> Details at: http://mailman.qth.net/index.html
> _______________________________________________
> yes, good question. I recently read an article in nuts and volts 
> that said one must know the difference between applications of mica, 
> polyester, electrolytic, ceramics and other types of capacitors. 
> Does anyone know a good resource (on the web or elsewhere) that 
> succinctly explains when to use what type of capacitor?n  I always 
> here about orange drops, ceramics, etc., etc.,
> 
> thanks
> Eugene
> 
> 
> >-----Original Message-----
> >From: StephenTetorka at cs.com [mailto:StephenTetorka at cs.com]
> >Sent: Friday, December 17, 2004 09:19 AM
> >To: njarc at mailman.qth.net
> >Subject: [NJARC] Capacitors
> >
> >Win a new Icom IC-756PROIII and help QSL/QTH.net 
> >Details at: http://mailman.qth.net/index.html 
> >_______________________________________________ 
> >Hi Guys: 
> > 
> >I'm in the process of bringing my circa 1937-39 National NC 81X 
> back to life. 
> >They did a really smart job painting the chassis...it looks like 
> new with none of the usual pitting etc to be seen. 
> > 
> >The bugger has a cast metal oscillator coil tray? - about the size 
> of cigar box under the chassis - that slides the whole width on two 
> 1/2" round tracks...powered by a small chain from the panel control. 
> 
> > 
> >One capacitor lead is undone. 
> >Might as well change the group. 
> > 
> >My fundamental question is: given a value of say, 0.1 mfd @ 
> 200v...why can't I use any TYPE of capacitor of this value?..even an 
> electrolytic 
> >( if I knew my + from my - ). 
> > 
> >Why isn't a rose a rose? 
> > 
> >PS: need an output xmfr for the 25L6..2,000 ohms primary...4 watts. 
> 
> > 
> >And those guys put around 200vdc between their ears with the 
> headphones! 
> >I may attempt that tonight with mine since I don't have the speaker. 
> 
> > 
> >Thanks, 
> >Steve 
> > 
> >_______________________________________________ 
> >NJARC mailing list 
> >NJARC at mailman.qth.net 
> >http://mailman.qth.net/mailman/listinfo/njarc 
> >
> 
> 
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