# Coil Winding

Discussion in 'Electronic Basics' started by Dave.H, Mar 22, 2008.

1. ### Dave.HGuest

I'm winding a coil for a home built regen radio, and I need to know
how much wire I need. The coil form is a 2 inch mailing tube. Main
winding is meant to be litz wire, but I'm using 28 gauge magnet wire,
and is 66 turns. The second winding is meant to be 8 turns of 30 gauge
wire, but I'm using 28 gauge magnet wire again. Third winding is 20
turns of 30 gauge, but again I'm using 28 gauge.

Radio schematic (at bottom of page) http://www.schmarder.com/radios/tube/1-12af6.htm

2. ### BobGuest

Surely you where taught basic mathematics in school, such
as the circumference of a circle?

Pi times the diameter gives the circumference. Multiply by
the number of turns and add a few percent because it's not
in perfect circles.

Bob

3. ### Michael BlackGuest

Take a piece of string, surely you have some of that around, and make one
winding on the coil form. Then measure that, and multiply by the number of
turns. Add a bit extra for leads and "just in case".

Michael

4. ### John PopelishGuest

Every dimensional change you make to the design will require
a compensating turns change. The trick is to either make
one as directed, measure its inductive properties, and than
adjust the turns count on your modification to have about
the same measured properties, or make calculations or an
educated guess of how much you have to change the turns
count to compensate for the dimensional changes you have
made. At the very least, you should have an idea which way
the turns count much change to be a correction in the right
direction.

If your mailing tube has the same outside diameter as the
author's, that is one variable eliminated.
The author says his Litz wire is the same size as 28 AWG, so
this coil should have about the same length as his 66 turn
one. Its inductance will be just a little less, because the
solid wire repels the flux from inside some of the wire
cross section with eddy current, but this is a tiny part of
the total flux, so maybe a single additional turn will
compensate for that. The effect is proportional to
frequency, so there is no count that will work exactly like
the Litz coil would. Your coil will also have a lower Q
because it is absorbing a little of the RF energy into eddy
current losses.

The second winding is meant to be 8 turns of 30 gauge
Your winding will be quite a bit longer than the author's,
so will have lower inductance (less well coupled turns),
but, again, an extra turn might compensate, or put it just a
bit closer to the tuned winding so that the mid point of
this winding is about the same distance to the midpoint of
the tuned coil as is the case with the author's design. It
won't take much of a correction, and the author may not have
done it the best way possible, so your changes might even
make it better. Too many variables. You might have to make
more than one and compare them in experimental trials.
Again, your coil will have more axial length than the
author's, but it is not tuned, nor part of a feedback gain
ratio, so its inductance is not critical. I'm guessing this
one doesn't matter so much. It also might work better if
this coil were closer or further from the tuned one. I
doubt if the author optimized it in any way. It is probably
just something that worked.

5. ### Bob EldGuest

http://www.schmarder.com/radios/tube/1-12af6.htm

Fifty feet. Why don't you purchase a 1/4 lb spool of 36 gauge magnet wire.
Parallel seven strands to make the 28 gauge litz wire and parallel four
strands to make the 30 gauge litz wire. In litz wire, the strands are
insulated from each other and connected together only at the ends.

To make the 28 ga.stretch out the seven strands about forty feet. Use nails
in boards at each end to keep the strands from tangling. With an electric
drill twist up the strands from one end into the litz bundle. Keep the
bundle loose, do not twist too tightly. Use this forty foot length to wind
the 66 turn winding. Tin the ends together into a single group for
connection.

Repeat with about 18 feet of four strands to make the 30ga. Litz wire.

Note, you can use more strands of thinner wire to make the litz bundles, but
thinner wire is more expensive and harder to handle. For example, you could
use 17 strands of 40 gauge wire to make the 28 ga. bundle but that's a bit
harder and not necessary for your application.

6. ### Michael A. TerrellGuest

winding 1 = 2*3.1416*66/12 = ?feet
winding 2 = 2*3.1416*20/12 = ?feet

so you need to do this simple math. Add them together, then add a couple
feet for the fly leads and a little extra, just in case there is some
variation in the tube's diameter.

--
aioe.org is home to cowards and terrorists

Add this line to your news proxy nfilter.dat file
* drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.

http://improve-usenet.org/index.html

7. ### whit3rdGuest

The form size and turns count gives you a length; but magnet
wire is sold by the pound, so using 28 gauge wire you look
up... it's half a pound per thousand feet.

The minimum purchase quantity is about a thousand feet.
That should be enough.

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Continue to site