On Apr 29, 6:17 am, msg wrote:
K7ITM wrote:

snip

I wound three toroids, all 0.37 inch OD cores; one is on mix 2 powdered iron,
and the other two are on type 68 and type 67 ferrite.

snip

How do you determine the formulation of the cores that you use (I am
presuming they are taken from the junk box...)?

Michael

Well, I trust places like Amidon and Bytemark to supply what they
say... The ferrite toroids were delivered last week from Bytemark.
The powdered iron come mostly from old stock we have upstairs, some
from ones I've ordered in the past from Amidon. (I have a different
batch of cores in front of me right now that I'll try running the same
test on. These cover a wider range of formulations, but all in (F)T50
size -- 'cept I couldn't find a T50-6, so I may look for a T37-6 or
just run a T68-6A I do have.)

But you bring up a good topic. You can measure the dimensions of a
core and figure its relative permeability from the inductance of a
coil wound on it, and make a guess about the formulation from that,
but short of doing more complicated tests, I don't know that you can
really determine the formulation. Powdered iron toroids generally
come with a color code paint job, but the ferrite toroids I've always
gotten have nothing on them to tell you what they are. I've found
that an "extra fine" tipped paint pen is a good way to put a marking
on them. You could color-code them, but I just write what they are on
them, such as "FT50-67". That's not so important if I keep them
nicely sorted, but if I've wound a coil on one and then want to re-use
it, it's a big help.

Cheers,
Tom