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Welcome to spider coils page. As you might have noticed, this
is my favorite coil. They are easy to make, adjust and to use. I have always preferred them
to cylinder wound coils. Below I have the formulas for calculating your own coils, as
well as some examples.
Spider Coil Calculations
To calculate your own coils, here is some information
and a few tips.
cell name formula ____ ____ _______ C4 Wire diameter Input this value C5 Number Turns Input this value C6 Inside Diameter Input this values C7 Coil Depth (C4*C5) C8 Mean Radius (C7+(C6*0.5)+(C6*0.5))/2 C9 Outside Diameter (C7*2)+C6 C10 Inductance (((C8*C5)^2)/((8*C8)+(11*C7))) [The main formula] C11 Wire Length (C5*C8*2*3.14)/12 [Add a little more wire for connections] Length measurements are in inches, inductance in µH.
When winding spider coils with thin wire strand gauge size such
as the 660/46, there was a difference found between the calculated coil depth
(wire diameter times number of turns) and what the coil actually turned out
to be. This drove a couple of us nuts until it was discovered that when a spider
coil with litz is wound, the windings are compressed at the crossing points.
Long Wave Coil
A few weeks ago, while experimenting with the long wave
coil I made for my 1625 tube all wave set, I discovered that I was able to hear some
European broadcasters. Most of the time it was just hearing
a heterodyne whistle, but I did clearly heard a station too. That is what it took
to get me started on a dedicated long wave receiver.
How I Make My Coils
The first step is to cut a piece of HDPE (high density polyethylene) to the size
needed. You will need a protractor, ruler and a compass to lay out your form.
(hint: If you expect to make a lot of forms, make one as a master template
to trace others) The width of the form is determined by the diameter of your
proposed coil. The height the same as the width plus 3/4 to one inch additional
(18-24 mm) to accommodate the mounting area.
Spider Web Coil Links