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

Michael Black wrote:

...
Michael VE2BVW

So then, start out with the highest frequency coil--this one you should
be able to count the turns on.

Then, look at then next, wind it, test it, and adjust turns so that in
conforms to the expected frequency coverage of the "next band."

Then, sit down with your calculator and "predict" the next ... adjust
your calculations and predict/compute the next ... etc.--repeat as
necessary ...

Logic ... it pays off in the long run, is usable across all disciplines ...

Regards,
JS

On Sep 21, 3:54*am, Michael Black wrote:

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

I think I have a pretty good idea from various pictures of Eico or
other GDO's what the coils should look like. I want mainly to get the
instrument operational on 80-20m ranges, so there won't be too many
turns. I have the manual but there is no variable cap value - looking
at it and comparing to standard BC band 365pF it can't be more than
50-80 pF per section. So as you say - calculate the inductance, wind a
coil... etc. adjust the winding until I hit the dial on one end.
Sounds like a lot of work for the old clunker, but I have the time and
enjoy this kind of stuff...

73 Rich OK8RF