[Boatanchors] Making coils

[Arthur Shulman]

An addendum to the Litz wire vs. frequuency question:

I have several medium power ultrasonic cleaners running a single 811A
oscillator with a plate voltage of abt 1000VDC. Frequency estimated between
25-50khz.

Plate tank coil is wound with 2 strands (twisted pair) of what looks like 18
of 20 ga. cotton insulated wire, in an interesting basket-weave pattern in
which all the turns seem to fit within the layer they are wound over. Ron
comments he does the same.

Construction is 2 sections (pi's) in series for the plate, with a separate
single section for the grid. I recall this was a very common pattern for RF
chokes at MF/HF as well, so obviously the winding pattern is of great
importance, perhaps even more than the wire type!

Does anyone remember the old Morris Coil Winder, that was capable of a
variety of winding patterns? Or am I just showing my age?

Arthur Shulman
-----------------


Ron wrote:

> Hi Kees
>
> I use multistranded wire for the switching power supplies that we design
> here. Although it is only used to 100 Khz it does lower the series
> impedance due to skin effect and keeps the coil cooler.
> In your design , you will need to use wire no larger than twice the skin
> depth.
> ---
> Ron
>
> Sandy and Kees Talen wrote:
>
> > I'm playing around with some homebrew RF coils, RF
> > transformers, etc and will put together a coil winder in the
> > near future.
> >
> > My question is about wire. I have plenty of magnet wire up to
> > #38AWG (from good ol' swapmeets), however, the earlier
> > aplications used Litz wire but the "modern" (60's) JW Miller
> > coils seem to use magnet wire. What are the advantages ?
> >
> > Since the Litz wire is multistrand, the surface area is increased
> > which should improve it's capabilities at higher frequencies
> > due to "skin effect", the coil "Q" may be higher because of this,
> > and since it's not "round" it would lay in place better. Any other
> > reasons ? Is the main reason for the pattern winding to keep
> > the turns in place ? In other words, if you were winding on a
> > spool, you would be OK by just winding uniformly ? The
> > drawback would be finding the small stuff at a reasonable price.
> >
> > Magnet wire is cheap, might require the use of bobbins to get
> > it to stay in place (although JW miller solved this with enough
> > adhesive), and maybe multiple strands of #38 has the same
> > effect as Litz wire. Would it have to be twisted ? Is the only
> > reason for the winding pattern to keep turns in place ? Any
> > other comments ?
> >
> > 73s  Kees K5BCQ
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