[Boatanchors] Capacitor Information?

[Richard Knoppow]

----- Original Message ----- 
From: "Michael D. Harmon" <mharmon at att.net>
To: <boatanchors at mailman.qth.net>
Sent: Monday, March 31, 2014 9:49 AM
Subject: [Boatanchors] Capacitor Information?


> Hi Folks,
>
> I bought a big Rubbermaid bin of components from a 
> Craigslist seller across town yesterday,
> and have been going through the goodies trying to identify 
> just exactly what I have.
>
> One of the 'finds' in this box of junque is a pair of 
> brand-new in-the-box Cardwell Condenser
> Model 9801 capacitors.  These caps look like variable 
> caps, but they are not.  They are air
> dielectric fixed capacitors.
>
> The caps have ceramic end-plates 2-1/4" X 2-1/4".  There 
> are steel support posts at the four
> corners, comprised of 6-32 threaded rod with 1/4" spacers. 
> There are 19 plates spaced on
> 1/8" centers, separated by the spacers on the threaded 
> rod.  Half of the plates are connected
> to the upper-left and lower-right rods, and half are 
> connected to the upper-right and lower-left
> rods.  The end plates are secured with lockwashers and 
> nuts at both ends of the capacitor,
> with 1/4" of threads extending at one end of the cap and 
> 1/2" at the other end.
>
> I have never seen a fixed air-dielectric capacitor like 
> this before.  I assume that they were
> designed for use in a transmitter circuit, based upon the 
> plate spacing.  According to my Tektronix
> 130 L-C meter, the value is approximately 155 pF.
>
> Has anyone ever seen anything like this before?
>
> Mike, WB0LDJ
> mharmon at att dot net

     Fixed air dielectric caps were pretty common and I 
think all the larger manufacturers of air caps made them. 
They were used mostly in transmitters and antenna tuners. 
Air dielectric caps have the advantages of extremely low 
loss and good stability, only vacuum capacitors have are 
superior.  I do not know if there is any Cardwell literature 
on line. They were a very old and well respected capacitor 
manufacturer who advertised in QST and the ARRL handbook for 
decades.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com