Maxwell VS. MMC capacitors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: dgoodfellow-at-highstream-dot-net 

Capacitor fans,
Seen here is an experiment to compare the cornell dubilier 942 series
capacitors against the famed Maxwell capacitor. The test coil is on a 4" x
18"  tube with about 1100 turns of 28ga or so wire. The spark gap is a
single gap inside of the plastic hosing of a squirrel cage fan. 14 cde caps
in series gave us .00714 uf.
The CDE cap coil run can be seen here:

http://hot-streamer-dot-com/temp/16pflex.jpg

4 Maxwell capacitors gave us a capacitance of .0075uf. I did not fiddle with
the tune point because both capacitors were so closely rated.
Since a Tesla coil never does exactly the same thing twice, it is hard to
make assessments from two photos as to which issues a better spark. Both
capacitor banks produced 24 to 28 inch sparks. The image of the Maxwells
does not look as full as the image of the cornell caps, but that's just the
way it photographed.
Maxwell cap coil run can be seen here:

http://hot-streamer-dot-com/temp/maxwellcapsa.jpg

I realize that there are 2 transformers in the picture
with the Maxwells in it, but I can assure you that only one of the
transformers was powered at the time of the photos. I think that 4 Maxwells
could handle the 15/30 for some time since they are rated at 35,000 volts
each, so 4 in series puts them at 140,000 volts, a factor of nearly 10 times
the operating voltage.
Cost of the cornell dubilier capacitor bank.......under $50.00
Cost of the Maxwell
bank..............................................$240.00 (for 4) used off ebay
Thank the electron gods that we have a cheap alternative to paying full
price for a world class capacitor!!
Before the advent of the MMC it was the occasional lucky Hamfest find, or
stacks of old mica's or doorknobs. I too have a half built rolled poly
capacitor. The first one I did make did not last long. The cost  of the cde
caps is about the same as a rolled poly capacitor. I have not yet lost a cde
cap. Given the advantages of the mmc, I can't imagine why anyone using a
single 30 or 60 ma. nst (as many of us are) would even consider a Maxwell,
or bank of Maxwells. Pay the price if you want, but in my opinion, you will
be ahead of the game with an mmc!

Dave Goodfellow