The Keytek ECAT E501 surge network uses a CSI 7W513TN 10uF 7500V film capacitor.
In our system, this capacitor was shorted and needed replacement. Unfortunately,
this part is not easy to get and hideously exensive at $2000pcs at 5pcs MOQ!

First solution was to snatch a capacitor from a non-working ECAT E502 module, which 
contains two of these 7W513TN capacitors. Next we looked for an alternative solution
to fix the E502 and found a fix in the form of 4pcs of Kemet C4AQ 40uF 1500V in 
series (C4AQSEW5400A3BJ). Resulting nominal voltage is only 6kV. Luckily, the C4AQ 
have fairly relaxed overvoltage specifications; 1.15*Vndc for maximum 30 minutes 
once per day, 1.3*Vndc for maximum 1 minute once per day.

The 20uF capacitor in the E502 (10/700us) surge network has to deliver a peak current 
of almost 600A at maximum pulse voltage (6.6kV) and experiences a dV/dt of ~30V/us.
The C4AQSEW5400A3BJ is good for 562Apk and 14V/us, 4 in series is 56V/us. So that 
seems a good match.

Furthermore, 4pcs of this capacitor is quite close to the dimensions of the original 
capacitor. We used 1x20mm copper strips to create the connections and some M5 hardware
for the terminals. Then improvised an enclosure from 2pcs Hammond 1591XXGSBK boxes. 
The contraption cannot be mounted as securely as the original, but considering the 
application and the relative fragility of the rest of the parts of these test systems, 
a couple of tie-wraps will be more than adequate.

Note that this is probably not a good solution for the E501 caapcitor. That one has a
much tougher job at 3.75kApk and 375V/us!