On Fri, 11 Dec 1998 07:07:04 +0000 "Ian White, G3SEK"
>>Silver micas are still readily available in the US.
>>Mouser carries a reasonable collection of 500V and ARCO still
>>Amp Supply used a Teflon insulated disc cap but I never did find out
>>source; they ran up to about 12KV or so.
>>Ameritron uses a pair of 1000pf 7.5KV discs in parallel and they
>>work just fine at 1KW out of an AL-80B, no overheating noted.
>It seems to be a case of choosing a high DC voltage rating, and
>that the RF voltage and current ratings (two different things) will
>be OK. Just wear earplugs for the first six months?
I suspect they are quite reliable, I have not heard of any failures and
they have been used for many years, going back to the SB-1000/AL-80 and
LK-450 at least . i just mentioned the AL-80B since I have one on the
>>Apparently there are sources but the manufacturers seem to protect
>>from the mere mortals that would dare to build instead of buy.
>More likely they protect their cost-cutting sources from one another.
>So... let's try to gather some data points of our own. For example,
>what power levels do SEMCO silver micas start to go bang in lowpass
>filters for various bands? And was it voltage or current that caused
I dont have any info on LP filters per se but the generic 500V variety
work just fine up to the 200-240W level ( a typical FT-1000D) as input
networks for amps.
There are also different current handling capacities within a voltage
rating. The CD-15/CM-05 is used up to approximately 500pf and the larger
CD-19/CM-06 above that.
I would not use the smaller CD-10/CM-04 size for much above 30-50W.
Heath used a 500pf/2KV silver mica in all their amp series as an 80M
loading cap. The older postage stamp case does fail but the dipped and
sealed units are reliable.
The voltages that are possible in a conventional LP filter would seem to
preclude micas at much over the 100W rating.
73 Carl KM1H
>73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
> 'In Practice' columnist for RadCom (RSGB)
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