Thanks! Yours, and a private reply, both said the same thing
and the last bit about the "small 1KV air variables may be
paralleled with the micas. The ARCO 500V mica padders will
also survive in this application with low SWR" is really
good news!
73, doc
wc6w@juno.com wrote:
-- doc <kd4e@verizon.net> wrote:
I need to access the gathered wisdom here ...
I am building a switched low pass filter for my full legal
160-10M solid state amp (1500W).
I have access to a number of free (from a friend) older surplus
Mica caps rated at 2,500V (a few are 3KV and 5KV).
I also stumbled across unionel.com where they have 1KV
Ceramic Disk caps for $0.32 each.
Questions:
Hi Doc,
1. Are the Micas likely to have drifted significantly in
value over time?
Nope, but, I'd verify the original markings before using them.
2. Is 2,500V a sufficient rating for this application?
Yes. Plenty of headroom for a KW at 50 ohms.
3. Are series-stacked Ceramic Disk caps of the same value
(e.g. four 100pF caps for a 4KV rating) a good alternative
to achieve high power handling capacity?
No. Ceramics are not the best in this application.
4. Are Micas and Ceramics of the same capacitance, voltage
rating, and tolerance % equivalent components in this app?
I think I just answered that... :-) Any Ceramics, save NPO'S, will drift with temperature and likely most that you will find of any moderate value will have both large temperature coefficients and loss factors that will exacerbate the effect.
Bottom line, use the mica parts.
Incidently, if you need to adjust some values small 1KV air variables may be paralleled with the micas. The ARCO 500V mica padders will also survive in this application with low SWR.
--
Thanks! & 73, doc kd4e
A blessed and joy-filled New Year to all!
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