Re: Capacitor construction

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Original poster: "John Philip Sanderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <John.Sanderson-at-eng.monash.edu.au>

>    Hi all!
>    I'm new to the list and currently building my first coil. From 
> What I have
> seen, MMC's are the capacitor of choice, but I was wondering if 
> anyone has
> experimented with glass plates with aluminum foil or brass sheets 
> for the
> electrodes. Both of these are in abundant supply in my shop and 
> I'm trying to
> save a buck :)
> Has anyone had any luck with this? is the dielectric constant of glass
> sufficient to get a good Q in the primary?
> TIA,
> db
> <mailto:dbarrett-at-clearcube-dot-com>dbarrett-at-clearcube-dot-com
> 
>
Dear Daniel, 

Others may have different views and stories on this, but my experience 
with tank capacitor construction goes as follows:

*Acrylic (Perspex) sheeting + alfoil - bulky for its rating, but never 
let me down on small scale work.
*Beer-bottle/salt-water caps.  As above, plus wet.
*Window glass/galvanised steel sheets under oil - blew up repeatedly, a 
tale of woe and misery generally speaking.
*Polythene sheeting/alfoil roly-polies - worked well "dry" with 
occasional blow-ups if over-stressed.  But easy to make and there were 
always "spares" handy.  
*Same deal under oil was electrically robust, but I was always fighting 
the oil leaks.
*Second-hand commercial pulse cap - great performance until one day blew 
its guts out all over the place.  
*MMC - no problems yet.  Seems like the go if you can afford it.

 
I was attracted to glass because of the higher relative permittivity (ie 
more capacitance per square metre in simplified practical terms) but  
never had a good time with the glass-metal sheet arrangement.  I don't 
know about primary Q, I just found that the dielectric strength of the 
glass was immensely variable and nowhere near what the books "said" it 
should be.  Maybe others had more success...

Cheers, 

John.

John Sanderson
Fluidization Group
Department of Chemical Engineering
P.O. Box 36
Monash University
Victoria 3800
Australia