[TowerTalk] Need Capacitors for Matching Network

[Art Greenberg]

I want to build a matching network for a 53-foot vertical for 80/75 and
40. I should be able to cover 80/75 with three LC pairs and 40 with a
single pair. So a set of fixed inductors and capacitors with a few
relays would work.

The design calls for capacitor values in the range 100pF to 300pF. 
Assuming an unloaded Q of 1000, TLW says at legal limit the capacitor
will see worst-case peak voltage around 1500V and RMS current around
5.5A.

RF capacitors (doorknobs and plate mica) are built for this application
but they are way too expensive new, and not a whole lot more affordable
used. If they're the only real fixed-value choice, it would be less
expensive to use rotary components and motors, since I have a vacuum
variable and rotary inductor on hand. But I don't think the application
merits that complexity. I'd rather save those parts for a more deserving
application.

The MFJ legal limit tuner uses a bunch of 62pF high voltage disc ceramic
capacitors in series-parallel combinations to make up the values it
switches in. They are apparently sourced overseas and I haven't found a
local source for the small quantity I need. I can get some very
reasonably priced 1.5kV C0G disc ceramics. But I cannot find current or
dissipation specs for those parts.

Would silver mica capacitors in series-parallel be OK? I haven't found
current or dissipation specs for those either.

What should I expect the unloaded Q of a disk ceramic or a silver mica
capacitor made up that way to be?

Thanks.

-- 
Art Greenberg
WA2LLN
art at artg.tv