Sun May 13 10:46:53 EDT 2007
ATC was talking about ceramics. I don't think this effect happens with other dielectrics like mica, mylar, polystyrene, etc. Of course, aluminum electrolytics drop in value when they dry out, but that's a different effect.
Tony Golda wrote:
> This may sound like a dumb question, but will the value of the caps change
> just "sitting there," or do they have to be in their application?
> >From: Bob Bruhns <bbruhns at erols.com>
> >Reply-To: amradio at mailman.qth.net
> >To: amradio at mailman.qth.net
> >Subject: Re: [AMRadio] Johnson Ranger Capacitor Question
> >Date: Sat, 19 Jan 2002 10:10:41 -0500
> >Hi Bob,
> >GMV means Guaranteed Minimum Value. In your case, this spec must be for RF
> >bypass purposes, to make sure the bypass is effective under all conditions.
> >Most common ceramic capacitor dielectic materials cause capacitors to fall
> >in value over time, especially the higher-dielectric materials normally
> >used for ceramic capacitor values over 500 to 1000 pF. Also, you will
> >often see tolerance specs of +80 / -20%, which is also basically about
> >staying above some minimum value over temperature.
> >Check out www.atceramics.com/pdf/technotes
> >- a nice collection of informative tech notes about ceramic capacitors. In
> >particular, look at dielectric_aging.pdf. The ATC chart included in this
> >document shows Z5U (the most common capacitor material used in such disk
> >ceramic capacitors, in my experience) losing 20% of its capacitance in
> >10,000 hours (about 14 months). Interestingly, the document states that
> >the industry standard process to restore a degraded capacitor to its
> >original value is to heat the capacitor to 150 C (302 F) for one hour.
> > Bacon, WA3WDR
> >Bob Sova wrote:
> > >
> > > Hi folks,
> > >
> > > There are 32 capacitors listed in the Ranger's Parts List as:
> > > .005 mfd GMV, 600VW, disc ceramic condenser
> > > My question is what is the difference between a "GMV" ceramic disc and a
> > > standard ceramic disc.
> > >
> > > Thanks, Bob
> > >
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