Re: .062uf 20,000 volts cap on Ebay

• To: tesla-at-pupman-dot-com
• Subject: Re: .062uf 20,000 volts cap on Ebay
• From: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Mon, 13 Mar 2000 16:25:59 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi all,
         I had to jump in on this one:

> Original Poster: "Adam" <adamsmith-at-mediaone-dot-net> 
> 
> > Original Poster: "Skip Malley" <skipm-at-bellatlantic-dot-net>
> > 
> > Hi guys,
> > I ran across what looks like a very HAPPY capacitor.  It is rated at 39
> > AMPS at 10MHz.  Sounds like a Tesla capacitor to me.
> > 
> > http://cgi.ebay-dot-com/aw-cgi/eBayISAPI.dll?ViewItem&item=278201331
> 
> That's a mica radio transmitting cap.  It is not the best choice for coil
> use, but it can survive if you respect the voltage rating.  In the case of
> this cap (rated 20kV), I would not expect it to survive more than a few
> minutes if used alone.  In series with another one of it's kind, it should
> be safe.  Mica's also lossy, and these caps will run hot (too hot to touch).

Which is why it's used on hi Q radio tuned circuits -- right?  ;)  
Having personally used mica transmitting caps (Sangamos) in 
various coils I can attest to their excellence for this application. It is 
most wise to respect the voltage ratings but a coil I sold is still going 
strong a year and a half later despite having its caps run *at or 
above* the voltage rating. Prior to that it was tested for a year by a 
friend.

> PE and PP are less lossy, and much more forgiving of overvolting than the
> mica, and that's why they're prefered for coiling.

I'm not sure I can even agree with the more forgiving bit except in 
the case of metallized caps (typically used for MMCs) that PP caps 
are far cheaper than micas.

Regards,
Malcolm

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