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General => Buy/Sell/Wanted => Topic started by: heliosh on June 14, 2019, 08:28:07 am

Title: Wanted: Big air dielectric capacitors (>2 nF)
Post by: heliosh on June 14, 2019, 08:28:07 am
Variable or fixed capacity. >1.5 kV.
Title: Re: Wanted: Big air dielectric capacitors (>2 nF)
Post by: woodchips on June 14, 2019, 11:16:35 am
Wow, have you worked out how large these will be?

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

Title: Re: Wanted: Big air dielectric capacitors (>2 nF)
Post by: pamphonica on June 17, 2019, 10:11:05 am
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 (https://www.ebay.co.uk/itm/Variable-air-capacitor-1000pF-2KV-transmitting-13-56MHz-HF-ham-radio/202706490824?hash=item2f323f95c8:g:ntUAAOSwZeRdAoUt)
Title: Re: Wanted: Big air dielectric capacitors (>2 nF)
Post by: dzseki on June 17, 2019, 10:56:15 am
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... :)
Title: Re: Wanted: Big air dielectric capacitors (>2 nF)
Post by: heliosh on June 17, 2019, 02:07:30 pm
Yeah I've tried to build one with PVC foil as dielectric and it has molten pretty quickly (not because of arcing)    ::)
Title: Re: Wanted: Big air dielectric capacitors (>2 nF)
Post by: T3sl4co1l on June 17, 2019, 03:00:03 pm
Well yeah, PVC is shite.  Do it with PE or PP.

Tim