Hi,
does anybody know if coating on Amidon toroidal cores has any dielectric
properties, such as a particular breakdown voltage rating, or it is not
meant for electrical insulation.

Thks

Why not email or visit amidon.com ??

tori

Ivan Makarov wrote:

Hi,
does anybody know if coating on Amidon toroidal cores has any dielectric
properties, such as a particular breakdown voltage rating, or it is not
meant for electrical insulation.

Thks

Amidon dust-iron cores are not uniformly coated.
It is just a colour-coding paint, sprayed on.
Otherwise the paint may just as well not be there.

From: "Ivan Makarov" on Thurs, Dec 1 2005 11:47 pm

Hi,
does anybody know if coating on Amidon toroidal cores has any dielectric
properties, such as a particular breakdown voltage rating, or it is not
meant for electrical insulation.

Since Bill Amidon sold his business to another company, the "new"
Amidon company has been reselling another company's toroidal core
forms.

The original Amidon company resold Micrometals toroidal forms.*
Micrometals still very much in business in Anaheim, CA; website:

http://www.micrometals.com

Micrometals also makes power-application toroid forms for 60 Hz
and those are described as coated with Parylene C with a given
insulation rating of 500 V RMS at 60 Hz. By casual observation of
some Micrometals powdered iron toroid forms I have on-hand, the
coating appears to be the same. Parylene is a relatively inert
polymer which is unaffected by typical hydrocarbon solvents found
in varnishes and lacquers. I use McCloskey "Gym Seal" varnish
(oil based) as an over-coating of finished toroid windings with
great success in withstanding humidity and general aging. That
is available at most do-it-yourself hardware chain stores. The
same could be applied to the "standard" toroid forms if more
insulation of the core is desired.

The coatings on most toroidal cores is applied mainly to protect
the core material from oxidation. One can get uncoated cores
on special order but those unused cores should be sealed away
from air movement to avoid oxidation. The second reason for a
coating is to make winding easier and reduce sharp edges that
could stress the wires (true even with special toroid winding
machines)...especially if winding by hand.

There's not much need to worry about core insulation with
powdered iron materials. The powder itself is in a binder
which adds some isolation from breakdown in addition to holding
it all together. On actual application, check out one of the
early Amidon kits available in electronics stores, a 1 KW
Balun kit with huge core (to handle the RF power) and rather
ordinary coated solid wire. The RMS voltage at 1 KW in a
600 Ohm open-wire feedline application is 775 Volts. Given that
real-world antennas can get mismatched, high VSWR situations
could have double that voltage fairly easily. I've never
heard of any such Amidon baluns that flashed-over in normal
use (disregarding lightning strikes).



* Micrometals has a minimum quantity requirement on orders, used
to be minimum of 100 of any type core...that might have changed.

Nice posting, Len, thank you.
Ivan

wrote in message
ups.com...
From: "Ivan Makarov" on Thurs, Dec 1 2005 11:47 pm

Hi,
does anybody know if coating on Amidon toroidal cores has any dielectric
properties, such as a particular breakdown voltage rating, or it is not
meant for electrical insulation.

Since Bill Amidon sold his business to another company, the "new"
Amidon company has been reselling another company's toroidal core
forms.
...

From: Roy Lewallen on Fri, Dec 2 2005 4:20 pm

wrote:

Since Bill Amidon sold his business to another company, the "new"
Amidon company has been reselling another company's toroidal core
forms.
. . .

I didn't know that anyone else but Micrometals made powdered iron cores
suitable for RF.

I have a few left-over Arnold Magnetics powdered-iron toroidal
cores that were used by RCA Corporation back in the 70s. For
the high end of HF for maximum Q.

Must have been a pot full of powdered iron core makers during
WW2. I still have some screw-in "slugs" which were sold under
"surplus" in 1948 at H & H Electronics in Rockford, IL. Their
Qs peak at around the bottom of HF. The old AN/PRC-6 Handy-
Talky of Korean War time had little powdered iron slugs for
preset tuning...and it covered low VHF. Collins Radio used
them quite a bit in the now-famous R-390 series of receivers
(besides as permeability-tuned master oscillator).

I'd say that the ham magazine editors didn't get around to
playing much with powdered-iron cores in the last half-century
so not much was stated about them. Few hams had Q Meters at
their disposal (way too expensive) and toroidal coil winding
is a picky thing done by hand. Folks in the RF industry knew
about them long ago.

Amidon never manufactured their own cores. They used to carry
Micrometals powdered iron and Fair-Rite ferrite cores, with a few other
ferrite cores from Magnetics and other manufacturers. Whose cores are
they selling now?

Bill Amidon set up a small packaging business as a sideline
to working at NBC Western Hq in Burbank, CA, many years ago.
He included data from Micrometals and Fair-Rite in those
packages as they applied to the kit. Good deal for the average
hobbyist. Micrometals turns out toroid cores almost like
Krispy Kreme makes donuts in each shop...and they don't make
real money selling in singles or very small quantities. A
reseller/packager like Amidon could make some profit. It
served the more serious home-builder very well, no minimum
quantities and rare Q curve info was included.

At www.amidoncorp.com you can find a line card on PDF as well as
in HTML at that page. The PDF didn't want to download this night
for me...:-) Amidon stocks/distributes Micrometals, Fair-Rite,
Philips/Ferroxcube, Arnold, Ferronics, Chang Sung, American Cores
& Electronics (located in China near Hong Kong), Associated
Components, Coiltronics/Cooper, NEC/Tokin, Coilcraft, Mag-Layers,
AEM, Magnetics Inc.

"Amidon Associates" (the old label for the plastic envelope kits)
is now described as a custom winder of coils under the Amidon
Corporation umbrella.

As to getting toroidal cores in small quantities, I found that
www.partsandkits.com was quite good. Dieter Gentzow, W8DIZ,
has that in Florida. Genuine Micrometals cores from what I
could tell were in my order. Good prices, quick service.

wrote:
From: Roy Lewallen on Fri, Dec 2 2005 4:20 pm


wrote:


Since Bill Amidon sold his business to another company, the "new"
Amidon company has been reselling another company's toroidal core
forms.
. . .

I didn't know that anyone else but Micrometals made powdered iron cores
suitable for RF.


I have a few left-over Arnold Magnetics powdered-iron toroidal
cores that were used by RCA Corporation back in the 70s. For
the high end of HF for maximum Q.
. . .

A look at Arnold Magnetics' current catalog doesn't show anything
suitable for HF or above(*). Do you know of any company other than
Micrometals that currently sells powdered iron cores suitable for HF?
I'd guess that while low frequency powdered irons are still pretty
widely used in power supplies, the market for RF powdered iron cores
must be relatively small.

(*) That is, materials having low loss at HF and therefore suitable for
use as cores for inductors in tuned or relatively high-Q circuits. Like
ferrites, powdered irons having high loss at HF can be very useful as
broadband transformer cores, chokes, and in EMI suppression.

Roy Lewallen, W7EL

From: Roy Lewallen on Sat, Dec 3 2005 1:48 am

wrote:
From: Roy Lewallen on Fri, Dec 2 2005 4:20 pm
wrote:


I didn't know that anyone else but Micrometals made powdered iron cores
suitable for RF.

I have a few left-over Arnold Magnetics powdered-iron toroidal
cores that were used by RCA Corporation back in the 70s. For
the high end of HF for maximum Q.
. . .

A look at Arnold Magnetics' current catalog doesn't show anything
suitable for HF or above(*). Do you know of any company other than
Micrometals that currently sells powdered iron cores suitable for HF?

At least a half dozen companies off-shore (to the USA). There's
probably three dozen (give or take) in the world that advertise
but their product lines vary according to which kind they are
able to sell.

I'd guess that while low frequency powdered irons are still pretty
widely used in power supplies, the market for RF powdered iron cores
must be relatively small.

It's just a specialized area of electronic components that has
been around for at least seven decades. "Small" is a sometimes
a subjective thing...depending on one's collection of catalog
data...:-)

In 1950 I had a chance to visit two companies, one in my home
town of Rockford, IL, (Greenlee Tool Co. division of Greenlee
Inc), one a small BC-SW radio factory in a suburb of Stockholm,
Sweden where my uncle-in-law was boss and only engineer. The
radios used Philips IF cans which had powdered-iron "pot" cores
and excellent voice bandwidth, sharp skirt response, etc. Those
Philips cans weren't advertised at all in the popular press but
they were relatively cheap in large quantities. Of course,
Greenlee chassis punches had been widely advertised and much
talked about by home-brewers back then. The actual production
area for the Greenlee chassis punches (sold all over the USA)
was about the size of my home office (13' x 13')...and they
also made files in that same cubicle. From the ads one would
have thought they had thousands of square feet of production
space! :-) Advertising can be deceptive. shrug

Powdered-iron and ferrite material production is done in huge
batches prior to molding (powdered) or sintering (ferrites).
It is relatively cheap per end item to produce. The QC needed
costs much more per unit item than many other components (such
as axial-lead resistors) so the manufacturers want to sell that
in large lots. The only ones buying large lots are the
manufacturers...who plan ahead for large-run (thousands of
units) production. [you know this, of course, Roy, I'm
mentioning it for others]

Most production lines shun making their own toroidal inductors
because they are time-consuming compared to axial or radial-
lead inductors. That's a specialized area and it is generally
cheaper for equipment makers to buy them from inductor-making
specialist companies. For home-brewers making as many as a
dozen toroidal inductors by hand for one project, it is quite
easy to do with normal dexterity. Doing it for hundreds of
equipment units in a factory run makes production costs go up
since the number of toroids needed may be ten times that. So,
despite the clear advantages of a toroid form and closeness of
magnetic field that is natural to it, many designers opt for
the cheaper solenoidal form inductors. Some get the idea that
solenoidal forms are "better" and toroidal forms should be
"avoided" which is contrary to what they do.

Getting into ferrites, the microwave area has long been a user
of specialized GHz-range ferrites for isolators, phase-shifters,
attenuators, dividers, etc., purchased in certain stock sizes
and ground to fit necessary physical shape. The makers of those
materials tended to keep advertising to the specialized micro-
wave side of "radio." Those parts just wouldn't work for the
HF spectrum.

(*) That is, materials having low loss at HF and therefore suitable for
use as cores for inductors in tuned or relatively high-Q circuits. Like
ferrites, powdered irons having high loss at HF can be very useful as
broadband transformer cores, chokes, and in EMI suppression.

Cable TV spread in North America has been a great boon to Asian
component making and aiding consumers with low, low prices. A
good example is the little balun in most TV receivers made for
decades allowing 75 Ohm or 300 Ohm "antenna" connection. Cheap
and works over nearly a decade of frequencies. The same with
"splitters" and "line amplifiers" (for several TV sets). It is
difficult to get ads from the component makers themselves but
those are starting to appear in the industry trade press. With
the explosion of PC-making came all kinds of relatively cheap
EMI-suppression material and gadgets around cables and the like.
Whatever their material is tends to be secondary if it works.

The search for the ultimate high-Q coils started around 1950,
popular in the amateur radio press with the SSB "revolution"
needing it for IF selectivity. Was a BIG thing then as I recall
but that wound down as mechanical and quartz filters became
available with their "textbook" filter responses. That led to
a general feeling of "high Q is always better" for nearly every
tuned circuit or low/high pass filter. Corners on bandpass
filters HAD to be sharp according to "CW" (Conventional Wisdom).
Not really so in practice. A few hours of experimentation
on computers with CAE analysis modeling actual Q losses will
show many misconceptions on the "necessity - always - of high Q."
The same with "chokes" and even sharp tuned circuits for tubes
(which need a high impedance tuned circuit for maximum gain).

To me, a toroidal form is superior for holding IN the magnetic
field, thus enabling a toroid to be snugged down to a substrate
with little effect on inductance or Q. That also allows toroids
to be placed closer together with much less mutual interference.
One just can't do that with solenoidal forms without individual
inductor shielding. Philips has a couple of great application
notes on broadband toroidal transformers and "how to do them"
written back in the early 70s...reissued on their big website
around Y2K. [links are buried in some archive CDs, not handy]

Please pardon a few "editorial comments" in here...it's a very
quiet Saturday and I'm trying to procrastinate away from hitting
the crowded stores for gifts. :-)

From: Tori Thurs, Dec 1 2005 9:23 pm


Why not email or visit amidon.com ??

www.amidoncorp.com to reach the correct site.