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Toroid Choke Cores

 * Carbons Sent to: scotty-at-wesnet-dot-com

 * Originally By: Oldradio-at-cheney-dot-net
 * Originally To: Richard Quick
 * Originally Re: Toroids


Greetings Richard,

   Got a message regarding large toroids at a very reasonable
price. Thought I would pass the important parts of it along,
because the price is so low.  I would be interested in your
opinion as to their usefulness in a protection circuit.

Anyway, I just received a catalog from Hosfelt Electronics.  They
only have one type available, but maybe it's what you're looking
for. On page 107 of the catalog, they show a ferrite toroid
manufactured by Arnold Engineering, Hosfelt stock number T-250B.
Following are the specs:

Mfg.# - FE-2500-1201
OD - 2.5", ID - 1.22", Width - 1"
Color - blue, 0.828 lb
Made from "Arnod HA" powdered ferrite
Initial Permeability: 60
Inductance per 100 turns: 2,032 uH
Mean path length: 14.96 cm
Cross section: 4.031 sq cm
Suitable for low freq choke or noise filter

PRICE:  $1.49 ea

Regarding the specifications for this item, Amidon rates their
ferrite cores in mH per 1,000 turns, not uH per 100 turns. 
However, I use a spreadsheet to calculate transformer/choke
inductance and have the most popular size Amidon cores entered in
the sheet.  This lets me do a pretty good comparison with most
brands.

In short, the closest Amidon core is the FT-240-61, which yields
1,730 uH for 100 turns, as compared to 2,023 uH for the Arnold. 
The initial permeability of the two cores differs quite a bit, in
fact, the Amidon core exhibits a permeability of 125, more than
twice the Arnold.  However, the inductance value of the two is
similar because the Arnold core is twice the thickness of the
Amidon, and nearly three times the cross-sectional area.  This
means the Arnold could be substituted for the FT-240-61 in say, a
balun, and would handle considerably more power.

At any rate, toroids this size are difficult to come by at a
price this low and I will probably order ten or fifteen for my
own use. If you want to place an order, Hosfelt's number is:
(800) 524-6464. They have no minimum order requirement for
customers in the continental U.S. paying by credit card or other
method of prepayment. 

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