help me put my coil on a diet; its capacitor appetite is expensive!

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Original poster: "seanick" <edgarsbat@xxxxxxxxxxx>

I have now toasted one of my two maxwell's, as well as one of my four 
strands of CDE 940C's. In the interest of not blowing up too many 
more capacitors, I am trying to do my research this time before 
ordering their replacements (and not using any of the remaining caps, 
for this coil anyway).

unfortunately finding a few roadblocks to that end:
1. I have a possible source of doorknob caps, in the form of another 
pacific northwest coiler who I recently bought a pole pig from, who 
is going to try to acquire some soon. However, I have heard doorknob 
caps might not be as effective, not to mention they are going to be 
HEAVY to get enough of them for a 25KVA pig powered coil, which is 
using a 120BPS synch rotary.
2. Have a rell.com shopping cart, containing 90x CDE 942C's (the -F 
version, which they have in stock, not the non -F which has a lead 
time of weeks). however, that is a $300 order that will still only 
have the same voltage rating as the 940C's which failed QUICKLY when 
I used them last week. A safer voltage rating would require more 
caps, and would still be less than the resonant cap voltage by about 
1/2. .06 uF is what the 2 37667's I was using added up to, with great 
results, so that is what I was aiming for this time. LTR according to 
JavaTC is something closer to .48 uF (hmm... $2400 worth of 942C's, 
even if I only use strands of 15! I think I am going to pass on that option).
3. Maxwells- I would love to find out more about Dr. Resonance's 
better Maxwell caps, than the 37667's which are known to fail easily 
in a 25kva pig powered coil. (Between Aaron and I we have fried 2 of 
the 3 maxwells that I have ever seen in my life, both within the last 
month or two. ) Unfortunately all I can find is part numbers and 
ratings, nobody selling anything other than the 35 kv .03 uF 37667's, 
and even those are $225 where I have seen them. Does anyone know of a 
current source for better maxwell's, and/or have other 
recommendations in this area?
4. Any other options? I haven't found any that don't involve a custom 
order from CSI (which doesn't seem to take me seriously, judging from 
their lack of a response to my recent request for quote). I didn't 
even mention that I would be using it for a hobby!

So, in lieu of having many other options, I am starting to lean in 
the direction of building my own. I have tried this in the past but 
didn't know what I was doing, at all, last time. This time I am a bit 
more educated, prepared, and have a more impending need now that 
everything else in my coil seems stable including for the first time 
ever a synchronous rotary.
For building this cap, I have a vacuum pump that will pull 29+ inches 
of mercury, and a t-shirt press which may help between the two of 
them to remove air bubbles. I was thinking that if I ordered a roll 
each of these two, I might be able to make enough caps that are both 
fairly efficient, and high capacitance/ voltage, that I could replace 
the maxwell/ MMC with something not too much larger, in the overall 
scheme of things.
<http://www.papermart.com/Templates/47-0-40.htm>http://www.papermart.com/Templates/47-0-40.htm 
(a 100' roll of 30" wide metallic .8 mil polypropylene sheet)
<http://www.papermart.com/templates/47-0-15.htm>http://www.papermart.com/templates/47-0-15.htm 
(a 500' roll of 30" wide clear polypropylene 1.2 mil sheet) (multiple 
layers of, between each layer of the above.)

I figure if I do a careful job in the overlapping, and use some 
mineral oil or something to pot it once the whole thing is rolled up 
in a tube and wires attached, I would be able to make it fairly 
robust. I even thought about making it in a sandblasting chamber that 
was completely cleaned out, and had an argon tank hooked up to it or 
something to purge the air (and corresponding particulate) out of the 
chamber after putting the parts in it, then sealing it before working 
on assembly. but that is way overkill considering it wouldn't even 
fully do the job- better just to use multiple layers of clear 
polyprop between each metallized layer, and leave large areas of 
clear overlapping all 3 edges of the metallized, and most of all 
removing every single air bubble by pulling a full vacuum for a few 
days after filling the tube with oil. then maybe a little more oil, 
an over-pressure safety valve for when the oil gets hot enough to 
raise the pressure inside it, and it should be decent enough for a 
run or two of the coil, right?

Definitely has to be better and smaller than a fishtank with 2 
half-racks of saltwater filled/ motor oil covered corona beer bottles in it.

please give me feedback if you think I am nuts or could do this 
better another way or using something off the shelf. Regardless of 
what option I choose, I only budgeted myself about $400 to spend on 
replacement caps and I am hoping to use them more than once. I also 
don't feel like waiting more than a couple weeks for something which 
is on backorder so that rules out at least one option.

thanks in advance,
NICK