Hi Guys,
All this talk about door knob capacitors only serves to remind me of all of
the many travails & troubles that I've had over the years, using them as
padders in both the plate loading and plate tuning side of my kilowatt input
pi-network set-ups...
The solution in each and every case here...? Direct replacements with
properly pre-set air variable capacitors.
Lucky for me, both of my homebrew designs had room to spare inside them that
I could make the switch...NO REGRETS---and no more problems---either!
~73~ de Eddy VE3CUI - VE3XZ
*****************************************
----- 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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