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

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 Sat, 20 Sep 2008 16:14:21 -0700 (PDT), 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?

Yech, tubes. I have several Heathkit grid dip meters, but no Eico.

This may help:
http://www.qsl.net/n4xy/GDO_EICO.html
The photo shows one coil, which should give you an idea as to the
general size and construction of the coil.

The photo of the Eico 710-A looks very much like one of my Heathkits
(buried somewhere). Do you have a 710 or a 710-A. There's a huge
difference.

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

Others have suggested cut-n-try which is probably good enough. As
long as the coil looks roughly like the original, it should work.

However, if you wanna do the math, look at the schematic and figure
out the minimum and maximum capacitance on the variable tuning
capacitor. Be sure to include any trimmers or padding capacitors in
the tuned circuit. You know the lowest and highest frequencies from
the dial. Drag out your abacus and plug the numbers into the usual LC
resonant frequency equation. Solve for a value of L that will be
roughly the same at both the high and low ends of the dial. You
probably won't hit the exact value, but it should be close. Lots of
online calculators for the inductance of solenoid wound coils. No
need for an LRC meter as you can just plug it into the grid dip meter
and count the frequency.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 20 Sep 2008 20:02:57 -0700, Jeff Liebermann
wrote:

This may help:
http://www.qsl.net/n4xy/GDO_EICO.html
The photo shows one coil, which should give you an idea as to the
general size and construction of the coil.

More photos.
http://reviews.ebay.com/Eico-710-Grid-Dip-Meter-Coil-Set-protection-packing_W0QQugidZ10000000001863194?ssPageName=BUYG D:CAT:-1:SEARCH:5
Oh-oh. My Heathkit coils do not have ferrite or iron slugs. The Eico
710 coils apparently do. The coil on the left is obviously broken.

Free manual for the Eico 710:
http://bama.edebris.com/manuals/eico/710/
I'm too lazy to find a DejaVu decompressor, but I expect there are
some instructions and diagrams of the coils in the manual.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:

...
Others have suggested cut-n-try which is probably good enough. As
long as the coil looks roughly like the original, it should work.
...


Yeah, working as a software engineer and finding I get the most money
from convincing those "with money" that I am worth "some of their money"
has made me aware of the value of reverse engineering--whether software
or hardware--it works!

But, if you have built enough "old box tube xmitters", you can almost
guess the dia./turns/and-caps wink Heck, bet I could come up with a
circuit using the same coils, using a fet, and saving the cost of the
filament power! Indeed, if the tube uses an octal socket, in his current
GDO, why not replace the tube with a fet(s)?

Regards,
JS

On Sat, 20 Sep 2008 21:27:20 -0700, John Smith
wrote:

Jeff Liebermann wrote:
...
Others have suggested cut-n-try which is probably good enough. As
long as the coil looks roughly like the original, it should work.
...

Yeah, working as a software engineer and finding I get the most money
from convincing those "with money" that I am worth "some of their money"
has made me aware of the value of reverse engineering--whether software
or hardware--it works!

The very first think I did when starting a new product, was to do a
"survey" of the competitions products. If possible, some were
purchased, dissected, reverse engineered, and on one occasion, cloned.
No need to reinvent the wheel when the competition has done it for
you.

But, if you have built enough "old box tube xmitters", you can almost
guess the dia./turns/and-caps wink Heck, bet I could come up with a
circuit using the same coils, using a fet, and saving the cost of the
filament power! Indeed, if the tube uses an octal socket, in his current
GDO, why not replace the tube with a fet(s)?

Because the typical FET as a much higher transconductance (typically
about 30 millisiemens versus 5 millisiemens) and a much wider
frequency response, that you'll probably spend considerable time
stabilizing the oscillator. It's not easy to build a tunable
oscillator that operates over such a wide frequency range. Also, the
grid and gate currents are quite different. It can be done because
there are FET grid dip oscillators available. However, if you compare
schematics, they are sufficiently different to require a rebuild.

It's also criminal sacrilege to despoil such a vintage boat anchor.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sep 21, 5:11*am, Jeff Liebermann wrote:
On Sat, 20 Sep 2008 20:02:57 -0700, Jeff Liebermann
wrote:

Free manual for the Eico 710:
http://bama.edebris.com/manuals/eico/710/
I'm too lazy to find a DejaVu decompressor, but I expect there are
some instructions and diagrams of the coils in the manual.
....
Jeff, thanks very much for your suggestions and links. I have actually
already downloaded BAMA manual (Dejavu plugin works great on IrfanView
4.20, saves as pdf) and I will get to work calculating the approximate
inductances. The variable C is the only component they don't show the
value for, but I'll take a guess, wind a coil and listen for the
signal. Then with some trial and error I can probably come up with a
couple of coils for the ranges I am interested in. I know the scale
won't be accurate, but in this day of digital readouts it's not
important.

I am fascinated with the number of GDO's shown on N4XY's site - I
remember seeing just Heath, Eico and an old Mullen.

Thanks agn
Rich OK8RF

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

On Sun, 21 Sep 2008 12:52:35 -0700 (PDT), charrid
wrote:

On Sep 21, 5:11*am, Jeff Liebermann wrote:
On Sat, 20 Sep 2008 20:02:57 -0700, Jeff Liebermann
wrote:

Free manual for the Eico 710:
http://bama.edebris.com/manuals/eico/710/
I'm too lazy to find a DejaVu decompressor, but I expect there are
some instructions and diagrams of the coils in the manual.

Jeff, thanks very much for your suggestions and links. I have actually
already downloaded BAMA manual (Dejavu plugin works great on IrfanView
4.20, saves as pdf)

Duh. I use Irfanview heavily, but have never bothered to download the
DejaVu plugin. Thanks.

and I will get to work calculating the approximate
inductances. The variable C is the only component they don't show the
value for, but I'll take a guess, wind a coil and listen for the
signal.

That will work as long as you don't accidentally land on a
sub-harmonic. Methinks a frequency counter might be more useful than
tuning around the bands looking for the signal.

If you have a capitance meter or bridge, it might be possible to
measure the value of the tuning capacitor.

Then with some trial and error I can probably come up with a
couple of coils for the ranges I am interested in. I know the scale
won't be accurate, but in this day of digital readouts it's not
important.

Chuckle. A few months ago, I won a used HP something universal
counter on eBay because I wanted the extra digits of resolution.
However, that was for period and event counting, not frequency.

I am fascinated with the number of GDO's shown on N4XY's site - I
remember seeing just Heath, Eico and an old Mullen.

Search Google for "base dip oscillator" and "gate dip oscillator".
There are a few designers that couldn't find the grid pin on the
semiconductor devices. My Heathkit HD-1250 calls it a "solid-state
dip meter".

I don't know if this will help, but the HD-1250 looks very much like
the Eico (other than the tube versus the xistor). Here's a table of
coil values for it assembled from various parts of the manual:

MHZ uH
L1 1.6 - 3.4 171 red
L2 3.2 - 6.6 41.1 orn
L3 6.3 - 13 10.2 yel
L4 12.5 - 26 2.62 grn
L5 25 - 51 0.72 blu
L6 48 - 100 0.196 vio
L7 100 - 250 ???? brn

As usual, no value on the tuning capacitor in the manual, but it can
be calculated from the above data.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558