There is no standard color code for toroids. Each manufacturer does it his
way. The color codes for iron powder cores shown in the ARRL handbook are
for cores made by Micrometals. These are readily available to hams through
Amidon and Palomar. The ferrite core numbers listed are for cores made by
Fair-Rite Corp, also sold by Amidon & Palomar. All Fair-Rite cores are
plain black, no coding. The numbers refer to the ferrite material. 73 has
been discontinued and replaced by 77. Over the years they improve some of
the materials and give the improved version a new number. This info does
not always get to writers of construction articles so you see call-outs of
obsolete materials. The new materials work as exact substitutes. -- Jack,
K6NY, Palomar Engineers
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