Wanted: Big air dielectric capacitors (>2 nF)

[heliosh]

Variable or fixed capacity. >1.5 kV.

[woodchips]

Wow, have you worked out how large these will be?

>1.5kV means a plate spacing of >1mm, 2000pF means a very large plate.

[pamphonica]

Look for the capacitors used in high-power amateur radio antenna tuning units (ATUs).  These are often 1000pF+ and multi kV.
Multiple units can be ganged via the shaft extensions to get larger values.
This chap has been selling good-looking units:
https://www.ebay.co.uk/itm/Variable-air-capacitor-1000pF-2KV-transmitting-13-56MHz-HF-ham-radio/202706490824?hash=item2f323f95c8:g:ntUAAOSwZeRdAoUt

[dzseki]

The one on the picture of the e-bay ad looks like an "Oren Elliott" brand capacitor, they are good at this indeed. Otherwise if you don't need variable capacitance you may conside consider building your own as the construction is really simple. In fact you could have the plates made of 2 layer PCBs, connect and fix the corresponding plates step and repeat, there you go...

[heliosh]

Yeah I've tried to build one with PVC foil as dielectric and it has molten pretty quickly (not because of arcing)   

[T3sl4co1l]

Well yeah, PVC is shite.  Do it with PE or PP.

Tim