DIY Vacuum tube capacitor

[thadman]

I've been dissatisfied with the inherent low voltage limits, non-linearity and variability of commercial capacitors. Electrons will drift between the dielectric medium between the plates of the capacitor. This effect will vary with frequency and will be VERY difficult to model since it will be highly dependent upon the material properties and manufacturing process.

In addition, a combination series / parallel circuit involving a number of capacitors to achieve the desired current / voltage might be unnecessarily complex.

Consider 2 hollow conducting cylinders (different diameters) placed within a cylindrical vacuum tube. The cylinder with the smaller diameter is placed within the cylinder with the larger diameter. They are separated by a distance. A distance separates the cylinder with the larger diameter from the inner surface of the vacuum tube. A +Q charge is deposited on the inner cylinder and a -Q charge is deposited on the outer cylinder.

Wouldn't this produce an extremely linear capacitor capable of EXTREMELY high voltages?

I'm not familiar with the cost of producing vacuum tubes, however considering light bulbs utilize vacuum tubes...the manufacturing process must be relatively mature.

Could anybody offer further insight on this?

Would it be possible to DIY a vacuum tube capacitor similar to what I described? What sort of manufacturing processes / equipment would be required? I do not expect it to be inexpensive, but could it be done for less than $5000?

[jackinnj]

uhhhh, I think Lindbergh landed.

[Andrew Eckhardt]

I'm trying to imagine a Leyden jar big enough for the HT filter in a 100W tube amp.

[woody]

First off vacuum caps are available in the small pf range. I seem to recall a 100pf
10kv being about 2" x 3" .

[thadman]

Originally Posted by woody

First off vacuum caps are available in the small pf range. I seem to recall a 100pf
10kv being about 2" x 3" .

Could you recommend any manufacturers?

[Spiny]

These are high voltage, high frequency RF transmitter caps. Several KV at upto 1000pf or so. Probably expensive There are currently some on Ebay!

jennings

[oshifis]

I have seen even a variable HT vacuum capacitor for HF transmitter use. Very special construction.

[runebivrin]

Originally Posted by thadman

I'm not familiar with the cost of producing vacuum tubes, however considering light bulbs utilize vacuum tubes...the manufacturing process must be relatively mature.

Could anybody offer further insight on this?

Last time I checked light bulbs were filled with inert gas, often mixed with halogen. I think the early Edison lamps were vacuum, but that's a mighty long time ago...

[jackinnj]

Originally Posted by runebivrin

Last time I checked light bulbs were filled with inert gas, often mixed with halogen. I think the early Edison lamps were vacuum, but that's a mighty long time ago...

Come over to NJ and see -- the Edison National Museum in West Orange is now open again.

[unclejed613]

the capacitance per volume ratio of a vacuum capacitor is extremely small, just about the same as for air dielectric caps (dielectric constant for a vacuum is 1, DC of air is 1.0059), actually it's worse for a vacuum because it has to be enclosed in a glass tube, and an air cap doesn't. many plastics have DC's of between 2 and 10, making them suitable for physically smaller devices. there are some exotic materials with DC's as high as 178 (titanium dioxide TiO2) and even up to 310 (strontium titanate SrTiO), and my guess would be that the TiO2 would also exhibit a high dielectric strength (maybe even as high as that of teflon) since it is a ceramic material.