[Amps] Maxwell oil filled capacitors?

[R.Measures]

>Hi group,
>
>     Does anyone have any info on these units, or rather any preference as 
>to which would be best used in an amp HV supply...
>
>Maxwell Cat# 30580 54uF 4.2Kv
>
>Maxwell Cat#38697 35uF 5.1Kv
>
>These I just could not resist at a local electronics 'junque' shop. One 
>(30580) is labelled as being the NOS spare for a defibrilator, and is 
>slightly smaller than it's lower capacitance sibling. Now I don't fancy 
>making an Amateur Defibrilator, but it saves space on electrolytic strings 
>in the PS case.

Defibrillator (and flash service) capacitors save space by using 
thinner-foil.  They can do this because they are not subject to high 
average ripple current -- i.e.,  ESR is not a consideration in the 
design.  For contesting, derating to about 60% of the peak-V rating is 
probably a good idea.  Also, moving air around such caps might help to 
dissipate the heat caused by the increased ESR.  
> 
>Is it advanced technology (castor oil in the 54uf one, unspecified but 
>non-pcb containing in the other) that makes the size difference, or is 
>there some other issue?
>
>73
>
>Adam