On Sat, 20 Sep 2008, charrid wrote:

Would anybody who owns Eico model 710 GDO be willing to supply coil
data (diameter, length, No. of turns, wire diameter) so that I could
duplicate the coils? I bought the coil-less 710 at the fleamarket and
cannot find the coil set. I am mainly interested in the 2.9-7,5 and
7.5-18 MHz ranges. Or maybe a close-up photo with a ruler laying next
to the coils would be enough.
73, Rich OK8RF


The coils are bound to have so many turns that they will be hard to
count, unless someone actually unwound them.

Open it up, see if you can figure the capacitance of the variable
capacitor (or maybe there's a schematic somewhere that provides
that information?), and then use the equations to figure out the
needed inductance and then the number of turns to make that value
of inductance. Then you can use any size coil form, just so long
as you can rig it to fit whatever the GDO is using for the coils
to plug into. Wind some extra turns, and then remove them if
necessary (since it's easier to remove than add turns).

It won't be exact, but any GDO dial is fairly vague. The inherent
capacitance of the coil will come into play, so you can decide whether
it's best to have the GDO dial match at the high end or the low end.

Thirty years ago there was an article in "73" about revamping a GDO,
I think he solid-stated it but can't remember, but he didn't have a
coil set either and described the process he went through to give
it a set of coils. I think it was radical surgery though, I seem
to recall that he even changed the jacks used for the coils. He
took the easy way out, providing a jack to feed a frequency counter
so the original dial was relatively unimportant.

Michael VE2BVW