[Amps] HT 57 blocking cap ratings?

[R.Measures]

Colin --  The RF current carrying ability of mica dielectric caps 
typically decreases as  freq increases.  Ceramic-dielectric caps are 
typically able to carry more current as freq increases.

On Dec 4, 2004, at 5:44 AM, k7fm wrote:

> Wishing to complicate the discussions of the current capacity of
> transmitting capacitors vs. frequency, I am looking at the Cornell 
> Dubilier
> advertisement for Type 86 Transmitting Capacitors.  This ad appears in 
> the
> 1938 Radio Handbook.  Most of you will know what the type 86 is, as it 
> is
> the large WW II mica cap with screw terminals on the top.
>
> What complicates things is that they have a chart showing the 
> frequency vs.
> max. current in amps.  Each value has a separate chart, indicating 
> life is
> not so simple.  For example, Cat No. 31A-86 has a capacity of .0001 at 
> 12.5
> kv.  At 30 MHz, it is rated at 5 A, while at 1.8 MHz it is rated at 2 
> A.
> Contrast that with Cat No. 21A-86 which has a capacity of .001 at 12.5 
> kv.
> At 30 MHz, it is rated at 5 amps, while at 1.8 MHz it is rated at 12 
> amps.
>
> Even more peculiar is that the 35A-86 .0005 cap is rated as follows:
> 30 MHz     5 amps
> 15 MHz     8 amps
> 7,5 MHz    9 amps
> 4   MHz    8 amps
> 1.8 MHz   7 amps
>
> I suspect the unique problem is that each value is constucted quite
> differently and the internal lead length causes the variation.
> Nevertheless, it blows the simple formulas away.  And, some of us 
> still like
> to use the WW II micas since they like as old as our 304-TL finals.
>
> K7FM, Colin
>
>
>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org