Re: High voltage variable capacitor

by Andrew Sun Dec 19, 2021 6:14 pm

Ivan wrote:
Andrew wrote:
here's a video from the same author showing the capacitor connected to a tx loop
The capacitor in this video differs from the former one. It is even easier to make, it does not require the metal cap (although the author used it) and mainly it gets rid of the potentially bad contact to the inner metal plate. On the other hand, it is harder to tune it by sliding the outer plates instead of turning a knob.

VBR from Ivan

yes, you're right, the video I posted is about a "trombone" style one, time ago I was toying with the idea of building one of those but submerging it in mineral oil... Smile

by **Ivan** Sun Dec 19, 2021 6:03 pm

Andrew wrote:
here's a video from the same author showing the capacitor connected to a tx loop

The capacitor in this video differs from the former one. It is even easier to make, it does not require the metal cap (although the author used it) and mainly it gets rid of the potentially bad contact to the inner metal plate. On the other hand, it is harder to tune it by sliding the outer plates instead of turning a knob.

VBR from Ivan

by Andrew Sun Dec 19, 2021 9:16 am

here's a video from the same author showing the capacitor connected to a tx loop

https://youtu.be/7B4p3LJZPZk

by Andrew Sun Dec 19, 2021 9:07 am

Ivan wrote:Hi Harry,
no, it is another case. The main part is a glass jar from mixed pickles with a metal lid (but a similar jar from marmalade, fruit salad, mayonaise etc. will do as well ). Two pieces of sheet metal are the electrodes. One is glued with a tape on the outside, the other is attached to a piece of threaded rod and can rotate inside. A hole in the lid forms a bearing. The beauty is that no complicated equipment (like a 3D printer, a lathe or a nuclear reactor) is required for the manufacturing. IMHO the bearing could be improved by use of a short piece of metal tubing, so that the parasitic serial resistance is smaller and the rod does not wobble. But it is upon the fantasy of each maker. The material is cheap and easy to get, so it is possible to experiment.

VBR from Ivan

looking at the video, I believe that the metal cap of the glass jar is adding some residual capacitance, I think that the design may be improved by using a non conductive material cap, the latter may be realized with wood or even 3d printed Wink

the resulting variable could be used for a tx loop antenna, eventually adding switchable parallel/series capacitors to reach the desired values range

by **Ivan** Wed Nov 10, 2021 7:43 pm

Hi Harry,
no, it is another case. The main part is a glass jar from mixed pickles with a metal lid (but a similar jar from marmalade, fruit salad, mayonaise etc. will do as well Very Happy

). Two pieces of sheet metal are the electrodes. One is glued with a tape on the outside, the other is attached to a piece of threaded rod and can rotate inside. A hole in the lid forms a bearing. The beauty is that no complicated equipment (like a 3D printer, a lathe or a nuclear reactor) is required for the manufacturing. IMHO the bearing could be improved by use of a short piece of metal tubing, so that the parasitic serial resistance is smaller and the rod does not wobble. But it is upon the fantasy of each maker. The material is cheap and easy to get, so it is possible to experiment.

VBR from Ivan

by **admin** Wed Nov 10, 2021 9:37 am

Hi Ivan,
This video is blocked for my by an over-zealous security connection. I presume this is the PET plastic bottle and strips of foil glued to the side?

If this is the case then I have used one of these several years ago.
I found that the conductive liquid in the bottle tended to slosh around a bit, so I filled it with oil to dampen the movement. It worked great after that Very Happy

If this is not the case then I would be interested if you could just give a quick description.

BR Harry - SM0VPO

by **Ivan** Fri Nov 05, 2021 7:48 am

Hi,
I came across this video: how to build a high voltage variable capacitor from a glass jar easily. The capacitor should suit e.g. for MLA. Maybe someone will make use of it.

VBR from Ivan

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