[Amps] ratings for caps for filters, for SSPA

[John Lyles]

Another source of high Q low ESR ceramic RF power chip capacitors 
besides American Technical Ceramics:

http://www.passiveplus.com/index.php

I haven't priced them, though, they look expensive but very strong..


73
John
K5PRO

> Sent: Samstag, 19. August 2017 18:54
> To: amps at contesting.com
> Subject: Re: [Amps] peak voltage rating for load cap
>
> Conrad, and all,
>
> keep in mind that the voltage rating of the capacitor is just one part
> of the whole thing. The other is its current rating. Once you have found
> out what's the highest RF voltage the capacitor will ever see, simply
> use that value in Ohm's Law, along with the reactance your capacitor has
> at the operating frequency, to get the current flowing to it. Then look
> for a capacitor that can handle both the voltage and the current, with
> some safety headroom.
>
> You will quickly find that for most capacitors no current rating is
> given. Usually these are ABSOLUTELY unsuitable for RF applications at
> anything close to their rated voltage! In these applications you need
> "transmit-type" capacitors, which are designed to handle high current.
>
> I have the same problem right now, only that I have it at least 18
> times. I'm looking for capacitors suitable for a set of legal-limit low
> pass filters. That requires capacitors of roughly 100 to 2000pF, each of
> them able to withstand AT LEAST 500V and 10A. Preferably some more, to
> have a better safety factor for high SWR situations. Can anybody point
> me to good sources of such capacitors? Everything I have found is either
> unsuitable, or unspecified and thus risky to use, or extremely expensive.
>
> There are lots of hams out there trying their luck and using capacitors
> that lack a current rating. And also there are lots of reports out there
> of these capacitors blowing up in use... Not all do blow up, but I think
> it's a good idea to use capacitors rated to handle the job, rather than
> run risks. Specially with solid state, a blown capacitor can blow up a
> $200 LDMOSFET.
>
> Manfred