I doubt that its strictly a voltage rating problem, though that is the most
conspicuous rating on capacitors. More important is probably the current
rating, though that isn't always available for capacitors. Where possible I
chose rf rated capacitors, take a look at two 270pf 1000v rated mica
capacitors that come up in digikey's search:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=338-3104-ND
And
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=338-3143-ND
If you look down under 'Features' in the bottom table you can see that the
first one is an RF rated one and the other one is General Purpose.
Otherwise they look almost identical except for price... Why the rf rated
one is cheaper is a good question, maybe volume of sales helps?? If you dig
deaper and look at the detailed spec sheets you will see:
http://www.cde.com/catalogs/CD-CDV16.pdf
Vs
http://www.cde.com/catalogs/STD-DIPPED.pdf
Obviously the data sheet for the std-dipped version is short on detail, the
one matching spec besides voltage and capacitance is the dv/dt capability,
which is related to current handling ability. For the standard one is it
quoted as 100kv/us but for the rf rated one it is 275kv/us... Its more
interesting to look at the detail in the rf rated one, they have obviously
been tested with rf applications in mind.
While those dv/dt values may seem to be more than adequate consider this...
At 100vACp-p, not out of the question at 100w, especially in a filter or
with a mismatched antenna, at 1mhz the peak to peak transition occurs in
.5us giving 200v/us on the back of an envelope (actually a digikey order
receipt)... Up that to 10mhz and it goes up to 2kv/us, at 30mhz that becomes
6kv/us, up the mismatch and add circulating currents in the filter and I
could easily see 60kv/us at 1000vACp-p.. Someone can probably plug in a
simple filter like the 419 series uses into spice and see what the currents
really come out to in a worst case.... I wonder what happens if you
accidentaly put 100w into one with no antenna connected?
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: James C. Hall, MD [mailto:nwtcc@earthlink.net]
> Sent: Monday, July 18, 2011 23:00
> To: 'K1TTT'; towertalk@contesting.com
> Subject: RE: [TowerTalk] ICE 419B schematic
>
>
> Hi David:
>
> Thanks for the reply. I could deconstruct one set of them and
> basically
> 'reverse engineer' the thing. I can get the capacitor values,
> of course, off
> the component itself. I wonder if a pair of half value capacitors in
> parallel with high voltage ratings would improve the
> 'survivability' of
> these capacitors ? Recently I had to deal with a blown 8.215
> MHz trap on my
> K3 after Field Day. Both the inductor and capacitor were
> fried from loading
> into a not-too-matched load on RTTY. I heavier duty toroid
> and a pair of
> capacitors in parallel were supplied to replace these
> components. The fried
> capacitor had a 1.6 kV rating.
>
> It appears I need a decent LC meter as well.
>
> 73, Jamie
> WB4YDL
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of K1TTT
> Sent: Monday, July 18, 2011 5:27 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] ICE 419B schematic
>
> I just had to repair the 10m and 20m sections on my 419b.
> The capacitors
> had apparently changed value enough that those sections were
> really bad. I
> just bought replacements for all the values on those 2 from
> digikey and
> replaced them all... Now its working fine again. There isn't
> much else that
> could go wrong except for bad relay contacts.
>
>
> David Robbins K1TTT
> e-mail: mailto:k1ttt@arrl.net
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>
>
> > -----Original Message-----
> > From: James C. Hall, MD [mailto:heartdoc@nwtcc.com]
> > Sent: Monday, July 18, 2011 21:29
> > To: towertalk@contesting.com
> > Cc: tcg1@googlegroups.com
> > Subject: [TowerTalk] ICE 419B schematic
> >
> >
> > Hello:
> >
> >
> >
> > I sent an email to ICE inquiring about their ability to
> > repair my ICE 419B's
> > which have a couple blown filters. I got a response that
> > since Mike died,
> > they can't repair anything right now.
> >
> >
> >
> > I asked about a schematic of these 2-stage filters and they
> > came back with
> > 'they don't have them either', which I found rather strange.
> > At any rate,
> > does anyone have a schematic or parts list of the 419B so
> > that I may attempt
> > to fix them myself ?
> >
> >
> >
> > This may or may not be the correct forum to send this, so if
> > not, please
> > advise and I'll redirect this.
> >
> >
> >
> > Thanks.
> >
> >
> >
> > 73, Jamie
> >
> > WB4YDL
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
>
>
> _______________________________________________
>
>
>
> _______________________________________________
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> TowerTalk@contesting.com
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>
>
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