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Re: Please Help me design primary

Hi Brent,
(comments intersperced)

> Original Poster: Brent L Caldwell <stretchmonster-at-juno-dot-com>
>
> All coilers:
> My unfinished TC needs a new primary.  The old one was an inverted cone
> of copper tubing.  But I think I need more turns and the cone is almost
> half way up the secondary already.

Yes, based on your description below, you need more inductance and
therefore, more turns.
This coil can be a problem with helical or inv. cone primary's. I would
suggest to anyone
to use a flat spiral (archimedes spiral) simply based on the idea of
keeping the primary
as far away from the top terminal as possible. All three types will work
fine and the
advantage of keeping the primary out of harms way is a "real" advantage.

>         Here are my specs, first:
>
> Secondary:
>         4" diameter pvc pipe.  From 1st wrap to final wrap is about 24".
Used
> .01" diameter magnet wire (whatever gauge that is, I forgot).

Should be about 30 awg. If this was a close wound coil, then you've got a
bunch of turns
(~1800).

> And here's my plan for new primary:
>         A 6.5" diameter drum will have about 6 or 7 wraps with 22 gauge
> insulated stranded wire.  Then, the rest will be a flat spiral of copper
> tubing, with 7 more turns.
>
> Will the 6.5" diameter be too tight?  I think so, but I'm not sure.  I
> need it because I don't have that much copper tubing and I need some way
> to take up the extra length of primary.  Also, I don't have much money to
> spend on this.  And how much spacing between turns on both parts?

A flat spiral coil with 6.5" inner diameter will give you 1.25" spacing
between primary
and secondary. This is cutting it close to the minimum I personally would
use. However,
with spiral coils, as you adjust coupling, you will probably also increase
the distance
between the two coils, so there is another advantage of flat spirals (may
or may not
happen - depends on the need).

A flat primary will need about 19 turns if the secondary was close wound
(this number will
vary a bit depending on top terminal type/size). If you use 0.25" or 0.375"
spacing
between turns, it won't change the inductance much. I would use a distance
that allows
easy connection for the primary taps.

Bart