[Amps] PTFE dielectricum variable cap

[la7sl Nils Petter]

I tried to make a fixed padding (parallell) cap for 160 plate circuit ( PI )
using a stack of brass/ptfe/brass etc connecting together
every second layer. It was finally pressed together by means
of 3mm ptfe sheet.
The dielectric layers were 0,5 mm
It was supposed to be used in a 2x 4CX250A  amp.
It tested just fine at highpot to 4 kV
The amp was run at 1800V.
The "smoke test" ended as just that...
fine up to 50% drive ...then smoke...then BANG !
Inspection showed a lot of very fine holes burned through the
PTFE-dielectricum all across sutfaces. May be I did not pay enough attention 
to
polishing the brass sheet, and so created "hot spots"---
or maybe it was just a bad idea ??

----- Original Message ----- 
From: "pc5m, Carel" <pc5m at xs4all.nl>
To: <amps at contesting.com>
Sent: Monday, March 15, 2010 9:36 PM
Subject: [Amps] PTFE dielectricum variable cap


> Hi, I would like to get the opinion of this group on constructing a 
> homemade
> variable 500 pF/1nF capacitor for my new 160mtrs amp. To get sizes down I 
> am
> considering using 1mm (40 mill) thick teflon sheet material as dielectric
> (10 times or so capacitance increase when comparing with air 
> construction).
> So a sandwich of several stator-PTFE-rotor-PTFE-stator-etc, etc. Capacitor
> stress will be around 5KV and 20 Amps of RF current.
>
>
>
> Did google a bit,but no hits.should this be attainable ? I think losses of
> PTFE are well enough at 2 MHz to cause any heating or change in Eps
> R/capacitance and 40 mill will provide enough rigidness and stability ?
>
>
>
> Thanks, Carel
>
>
>
> p.s. Yes, of course I do know that vacuum capacitors do exists ...
>
>
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> 
-------------- next part --------------

No virus found in this outgoing message.
Checked by AVG - www.avg.com 
Version: 9.0.790 / Virus Database: 271.1.1/2748 - Release Date: 03/15/10 08:33:00