Real Centralab and other US RF doorknobs are mostly 5, 7.5, and 15KV in the
most common 2 sizes. The caps in Heath SB amps are cheap non RF rated that
will often do bad things on 10M.
Check out High Energy Corp for what is currently in production.
There are also Teflon disc caps being used but I dont have any
manufactrurers names handy.
Carl
KM1H
----- Original Message -----
From: "Rob Atkinson" <ranchorobbo@gmail.com>
To: <amps@contesting.com>
Sent: Tuesday, March 01, 2011 12:32 PM
Subject: Re: [Amps] door knob capacitors
> Yeah but how do you tell a fleamarket doorknob is okay for RF. If you
> have a lot of do re mi and can get them new I guess it's easy, but
> your typical $2 doorknob in a box sitting on the pavement in a parking
> lot is a different situation. The markings are often cryptic and vary
> by mfr., -- It's better to be safe than sorry. OTOH, I did not know
> micas, eg. the big brown jobs with the binding posts on top ever
> leaked. I test mine with my el cheapo Eico 950 cap tester, one of
> those things with the magic eye tube but it only puts up to 500 v. on
> one. If it says a cap is good, I'm not sure it is really good or not
> except the eye opens up at or near the spec'd value.
>
> So I'm not sure what to reccomend for 160. I thought the 1 MHz tx
> micas were a safe bet. the trick is getting them to fit inside.
> Some amps are cramped for space.
>
> The Centralab doorknob I used was about 3/4 inch diameter coated with
> blue green glaze and 250 pF at 20 KV.
>
> Rob
> K5UJ
>
> <<<
> Rob,
>
> It depends on the capacitor. The ones intended for high RF
> currents are marked to show the maximum reactive current
> they can handle. Some time ago I had the same experience
> as you, with a cap literary exploding. Now I use only caps
> that are spec'd for high RF current. I have had no trouble
> wiht those.
>
> 73,
>
> George, AA7JV
>>>>
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