Rod Elliott wrote:
> At 19:14 11/13/2007, you wrote:
>> [snip]
>> I used some Caddock power resistors in the grid circuit of the
>> "Sunnyvale/Saint Petersburg Kilowatt Plus" that appears in the 1999-
>> 2004 ARRL handbooks. They are mounted on a pretty big heat sink, and
>> have their own fan. This setup has been very satisfactory, and
>> capacitance hasn't been a problem.
>
> I did a ballpark calculation of the capacitance of one Caddock MP9100
> unit, and came up with 5pf. Using that value with their specified
> inductance of 20nH gives a self-resonant frequency in the order of 500 MHz.
>
> Wiring four of these units in series/parallel would produce a 400
> watt power rating. If mounted taking great care to minimize lead
> lengths, the self resonant frequency of that array would not be much
> lower than that of a single unit. Should be able to use these at HF
> without compensation.
>
> Interesting! Anybody know what these units cost? ... couldn't find
> them in my DigiKey catalog
Farnell/Newark list them at £6.25/$13 each. As an alternative
Anaren 250W flange mount stripline resistors and terminations were
around £10/$20 ea. when I last bought them some months ago. The
product range is in flux because of the RoHS lead free nonsense,
and stock at Richardson is variable. The new lead and BeO free
lines were predicted to be cheaper.
Steve
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