Re: Capacitor needed

["Tesla list" <tesla@xxxxxxxxxx>]

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%3AMEWA%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!