Swan Mark II dual 3-500z amp question

[cncjerry]

I have the subject amp, replaced both of the 3-500Z tubes a while back with the ZG graphite after I popped one. I recently hooked it back up to my IC-7610 for the heck of it, don't know why as I hardly ever transmit except for rare DX.

For some reason I need more capacitance on the load cap to tune the high-end of my loop.  I was thinking of just adding some fixed capacitance right at variable cap.  See any drawbacks?  I guess I would need a high voltage cap, around 5KV? 

I could always just fix my antenna or use an external tuner, which I have, but get tired of tuning everything.  I am only using a short piece of coax between the amp and a remote balun that then feeds the antenna with ladder line so I'm not overly concerned about SWR either if the amp tunes it.

I also have an EL-80B bipolar amp I've been building for 15yrs, just need a power supply.

So what would I need, maybe 100pf at 5KV?

Thanks,

Jerry