Re: HV capacitors
J. Aaron Holmes, Tue Mar 13 2007, 03:28PM

Welcome aboard!

Terry Fritz had good luck with his MMC made from the Panasonic 1600V metalized polypropylene caps, even pushing them to 3000V! http://www.hot-streamer.com/TeslaCoils/MMCInfo/mmcinfo.htm DigiKey sells them for ~$2.30 (USD) each in quantities of 10 or more, or ~$1.80 for 100 or more (see link for part number). I think Terry made this MMC before the days of the Geek Group caps, though. The so-called "Geek Group caps" are generally regarded as the very best (the CDE 942C series, specifically), but you're going to be forced to buy at *least* 50 from a place like Richardson, and unfortunately they don't come cheap. You'll probably pay at least $3.50 each no matter where you go. Geek Group used to sell for less, I think, but I haven't seen them advertise them for a long time. You can get them in small quantities from "Dr. Resonance" (a.k.a. D.C. Cox of Resonance Research Corp.) on the TCML sometimes. If you decide to go with the 942C's, check with him first and see if he has any. You can also use the much-cheaper CDE 940 series if you're nice to them (use longer strings and more in parallel to accomodate the lower voltages and/or current ratings).

Another route for you, if you're really only after 3.3nF, might be to try the Strontium Titanate doorknob caps sold by 'yishdz' on eBay. Currently, he's selling 400pF 50kV doorknobs for $9 each. Eight of these in parallel would give you 3.2nF at 50kV for $72, and would probably handle crazy peak currents. You might look at the other doorknobs he's selling to see if there's a better combination for price/performance. Not everybody has had good luck with doorknobs in spark gap coils, though, and I cannot claim to have used them myself. Some people swear by them, though.

Good luck!

Regards,
Aaron, N7OE

Re: HV capacitors
Dr. Drone, Tue Mar 13 2007, 03:52PM

Re: HV capacitors
J. Aaron Holmes, Tue Mar 13 2007, 05:37PM

Might be worth adding that 3.3nF for an OBIT is probably too small. What are the specs of your OBIT? Usually they're something like 10kV at 23mA. And for that, the recommended LTR cap value for a static spark gap is 9.2nF (for 60Hz mains). If you've got 50Hz mains or are using a synchronous rotary gap, you probably want even more. Check out http://www.classictesla.com/download/MMC_Cap_Chart.pdf for the proper values. The "resonant" values are for reference only. Use those with your NST or OBIT and it will be probably be destroyed in short order.

EDIT: Ack! Ignore this post. I'd somehow read "ignition coil" as "ignition transformer" So you are not using an OBIT. Sorry...

Regards,
Aaron, N7OE

Re: HV capacitors
Terry Fritz, Tue Mar 13 2007, 11:26PM

Hi,

Chip A. replaced his exploded commercial caps with these ) Chip's caps blowing up on the roof of his house on Halloween sort of got the whole MMC thing started... The Panasonic caps are super fine.

Cheers,

Terry

Re: HV capacitors
JamesH, Wed Mar 14 2007, 08:49AM

Thank you ALL for your responses
I should have mentioned
I AM IN ENGLAND .......... Even I do not know where UK starts and Ends and hate the term GB

By Ign Coil I meant motor car ignition coils ( Auto ignition) not ORBITS

In the words of Mr Winston Churchill :- Two nations divided by a single Language .

THANKS very much for your advise and recommendations... I will take a few days to digest

Re: HV capacitors
Proud Mary, Thu Mar 29 2007, 09:40PM

Hi James,

Anthony Welsh is based in England and always has doorknobs and HV ceramic plate types for sale,
which are mil-spec parts imported from the former Soviet Union.



cheers,
Harry