[Amps] door knob capacitors

[Rob Atkinson]

Thanks Carl; mine were probably 15 KV then.  I looked at the High
Energy website.  Those caps look great but they also look kind of
pricey.  Well you get what you pay for.

I'm gg to give some micas I have a try for loading on 160.  A guy had
a half dozen for sale at the Ft.Wayne hamfest last November for around
$2 or $3 each.   Sangamos and Cornel Dubliers--3 or 4 A 200 to 500 pF,
the kind in a plastic body 2" x 1" x 1.5" with the lugs on top.

Glenn, I don't intend to steal the thread away from you so go ahead.

73

Rob
K5UJ

On Wed, Mar 2, 2011 at 2:32 PM, Carl <km1h at jeremy.mv.com> wrote:
> 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 at gmail.com>
> To: <amps at 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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>