On Sun, 24 Oct 1999 22:11:24 -0400 "Phil T. (VA3UX)" <phil@vaxxine.com>
writes:
>
>Without knowing what manufacturer and their designation, I can't answer
the
>questions specifcally. But, I do have a recent CDE catalog and the RF
>current ratings for some of the small radial leaded micas is
surprisingly
>high....but not in all cases. Here's some info for comparison :
>
>The RF current rating changes with the Series of product, and the
different
>Series appears to denote different physical sizes and voltage ratings.
>Current rating goes up with size, voltage rating and frequency.
>
>For example, a 220 pf cap in the CD15 Series (500VDC or 300 VAC) will
>handle 0.6 amps continuously at 5 Mhz. These measure 0.46" L x 0.38"
>high.
>
>A 220 pf cap in the CDV19 Series (1000 VDC or 350 VAC) will handle 1.4
amps
>continuously @ 5 Mhz. These are 0.64"L x 0.50"H.
>
>A 220 pf cap in the CDV30 Series (1500 VDC or 400 VAC) will handle 2.8
amps
>cont. @ 5 Mhz. A 2200 pf cap in this same series will handle 5.5 amps.
>This series of caps measure 0.77"L x 0.88"H, and are 0.25" thick.
>
>The quarter inch caps Vic mentioned compare (size wise) to the UHF caps
in
>the CDE catalog. No RF current rating is given for these, which implies
>that caps this size weren't intended to handle much current on a
continuous
>basis. But they may survive anyway since the intended duty cycle is
>considerably less than "continuous", and they will probably be in moving
>air to keep the temp down.
>
Vic, Phil & Phil
I too have the CDE catalog but, I also have an ARCO catalog which
shows a table of capacitance and frequency versus current capability but,
additionally discloses a maximum current constraint based on size (and
construction).
Designator Arco / Mil current package length & lead spacing
for field I.D.
DM05 .15A .27" long -- .12 lead spacing
DM10 / CM04 .2A .360 long -- .14 lead spacing
DM15 / CM05 .3A .450 long -- .230 lead
spacing
DM19 / CM06 3.0A .640 long -- .340 lead spacing
DM20 3.0A .750 long -- .430 lead
spacing
DM30 / CM07 4.5A .770 long -- .430 lead spacing
Note: the lengths of these parts grow a bit at the top end of the
supplied values
I think that the bottom line here is to use CM06's or better for
"real" input networks though, If only CM05's (the "standard" small mica)
are handy, paralleling a two or more smaller values to increase the
overall current capability is a valid strategy.
As always, should radio amateurs (and/or defunct kit companies)
disregard the manufacturers specifications, we will disavow any knowledge
of your actions... :-)
73,
Marv WC6W
*
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