```On 1/22/15 5:40 AM, Jim Lux wrote:
```
```On 1/22/15 5:26 AM, Tim Flood wrote:
```
```Yes, just be sure the total surface area of all your tubes is close to
the
surface area of the toroid.

Tim

On Thu, Jan 22, 2015 at 8:10 AM, Jim Lux <jimlux@xxxxxxxxxxxxx> wrote:

```
```On 1/22/15 12:30 AM, JoeBonanno wrote:

```
```this is an interesting thread!

i have to build my own in a few week! For calculating the final
capacitance
i can use the same formula of solid one? right?

```
```
That's what I would do. Short of using a finite element tool of some
sort.

```
```

Well.. I would think that the charge on the surface of the tubes that is
"inside" the toroid would be less than the charge on the outside, so on
a surface area basis, maybe 1/2 the sum of the tube circumferences might
be a better approximation.

Greg Leyh's Electrum had a tube topload in the shape of a sphere.  The C
of a solid sphere is easy to calculate, and if Greg ever measured the
tube top load C, we could calibrate with that.

```
```Having found some data at
http://www.lod.org/Projects/electrum/techdata/electrumspecs.html

```
Greg has his secondary L at 0.13 Henry, and two resonant frequencies, one with topload (7 foot sphere) and one without at 27.92 and 52.60 kHz respectively. Working backwards, that gives a total secondary C of 135.5 pF for "with topload" and 70.4 pF for "without", a difference of 65 pF
```
```
a 7 foot diameter sphere is 1.06 meters in diameter. I calculate a C for a sphere of that size as 119 pF. That's about twice what would be implied from the frequency shift calculation above.
```

```
I don't know that this is conclusive (there's a lot of interaction between the field of the topload and the field of the secondary, for instance)..
```

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