@ Chet:

Thanks for posting the link.  That is the topic started by LocalJoe.  A lot of good experiments and information there.

The topic I started is: http://www.overunity.com/index.php?topic=4455.0

Sorry I didn't hunt up the links in my earlier post.

As far as what to read and what to skip....very hard to say.  A lot of good information is buried in along with our learning curve and patent research.  A lot of good folks contributed to both of these topics.  I just think it's cool to wind a coil and be able to produce numbers like 1.8 vdc and 80+ milliamps for free.

Bill

Tinselkoala:

The coils are simple.  copper wire (solid, bare, not magnet wire) and iron wire. (also non-coated)  These are wound bifilar style around an iron core. (large mass, very high iron content)  Now for the hard part.  Nathan Stubblefield used cotton insulation between his core and the fe and cu wires and between the cu and fe wires themselves, and the layers too.
Back in his days, late 1800's, cotton insulation was just about all there was.  You can still find it today but very expensive. (It comes in tube form and you slip it over your wires as you wind)  Some of us cut cotton strips and wound that around the wires while winding but that makes the coil pretty bulky in my opinion.

What I did was to insulate the core with cotton cloth, wound my first layer of copper and iron together and then, took cotton cord and forced it in-between the wires by turning and winding the coil. (hard to explain)  This isolated the cu and fe wires.  Then wrapped cotton material around 1st layer, repeated everything for the following layers.

These types of coils put out power when totally dry.  When moist, the output really goes up.  When planted in the ground and left for a while, you get the best output by far.  One of our experimenters wound a Tesla type pancake coil but I don't think he got any decent results out of it, I am not sure.

Funny thing is, we found (Thanks Hans) photos of Stubblefield and Tesla together.  Stubblefield is honored here in KY (Murry) as the father of radio.  In actuality, he invented the cell phone and this was in about 1890.

Fun stuff.

Bill

Oc:

The Stubblefield coil is actually a self-energizing electro magnet in itself.  It is also a primary which, with the addition of a secondary, can produce ac.  We did many experiments using a compass and the results were both interesting and confusing. But, if this does not help in your research, I can understand that.  Stubblefield's coil is the only one I am familiar with.  I never tried Tesla's.

Bill

Now, now, let's not get snippy. I think maybe 0c isn't getting enough sleep. Neither am I, for that matter.
I didn't have time to break out the big guns today, but I did manage to test the two coils on the little GenRad RCLomometer.
The coils don't differ much at the two frequencies used, 120 Hz and 1 kHz. The Tesla bifilar reads 0.032 milliHenrys at 120 Hz and 0.0141 mH at 1 kHz. The pancake coil reads 0.033 mH at 120 Hz and 0.0151 mH at 1 kHz. I couldn't get a good capacitance reading on this instrument.
I'll try some active experimentation tomorrow if I have a chance. The local TC expert was watching and expressed an interest, and mentioned the patent, and we talked about the interturn capacitance for a while. It's been a long time, but I seem to remember this could be useful...

Now, now, let's not get snippy. I think maybe 0c isn't getting enough sleep.

Sorry 'bout that. You're right about the sleep. 

Bill, I for one am glad for your input. Please keep reading and commenting. I am truly interested in the Stubblefield bifilars, but they are different from what we are talking about here. I'm just trying to characterize these coils, and 0c has some specific things to look at with this configuration.
But I'll be winding some Stubblefield coils too. I have lots of strange wires, all different materials and insulations (enamel, silk, cotton single and double, rayon, gutta-percha, rubber, etc.) that might be interesting to examine in those configurations.
Please don't go away.

@TK,

Whenever you are ready, could you see what shape magnetic field is produced with a small DC current? Is it evenly distributed above the coil? Does it intensify towards the center? Does a ferromagnetic core (steel washer) concentrate the field towards the center? Is there a difference in field intensity or distribution between the two coils?

Thanks,
0c