RE: Capacitor needed

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

Hi Jack:

The cap you bought is unlike any I have seen before, so I can't at all
be sure.  Since you're using a relatively low powered NST, you may in
fact get by, even if the dielectric is ceramic or Mylar.  Good luck, and
let us know how you fare!

Regards, Gary Lau
MA, USA

> Original poster: "Jack" <Jack@xxxxxxxxxxxxxxx>
>
> Hi Gary and all,
>
> The Russian cap is listed as
>
>
>
> Soviet capacitors PKGT-I 15KV
>
>
>
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=007&sspagename=STRK%3A
> MEWA%3AIT&viewitem=&item=170055836253&rd=1&rd=1
>
> and my friend Frank Jones ( you may know him ) located them for me.
>
> Not much description on this eBay listing but Frank feels they will
> work for the Model T-Tesla coil when substituting the 3/30 NST for the
T-coil.
>
> I would be interested in your thoughts.
>
> Again, thanks for the helpful notes on capacitance. I am learning,
> albeit slowly!
>
> Best,
>
> Jack
> Hilo
> ----- Original Message -----
> From: Tesla list
> To: tesla@xxxxxxxxxx
> Sent: Wednesday, December 06, 2006 8:58 AM
> Subject: RE: Capacitor needed
>
> Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
>
> Hi Jack,
>
> Beware that there is much more to choosing a capacitor than voltage
and
> uf ratings.  The dielectric material is critical in Tesla coil
> capacitors.  Polypropylene (PP) is the state of the art and first
choice
> for TC caps.  Mica was widely used, but as I had mentioned, is bulky
and
> expensive when compared to PP.  Mylar, a.k.a. polyester, is NOT
suitable
> for TC caps, as it is lossy at RF frequencies and will get hot and the
> cap will die.  There are many types of ceramic dielectrics, and almost
> all of them are also not suitable for TC caps.  The losses are high
and
> the capacitance changes significantly with temperature.
>
> Even among polypropylene caps, there are good caps and there are bad
> caps, the difference being the interconnect between the foil plates
and
> the leads.  The high pulse currents we use require a very robust
> construction!  It's very difficult and no doubt frustrating to
beginners
> to get this, ignoring what appear to be dream-deals on eBay for much
> more expensive parts that a bunch of strangers on the list suggest.
>
> If it's not already too late, you may want to float your Russian jobs
> past the List to see what we think.  While it's remotely possible that
> they're suitable, I think it's more likely that they are small, Mylar
> units that will die in a coil without so much as a whimper.
>
> Regards, Gary Lau
> MA, USA
>
>
>
>   > Original poster: "Jack" <Jack@xxxxxxxxxxxxxxx>
>   >
>   > Thanks for your offer, but today we found a couple of Russian jobs
at
>   > 15kv and .01 uF that will work perfectly.
>   > You and Gary are kind to respond!
>   > JT
>
> Have a great day!
>
>