Fair-Rite material type 43 is good for most baluns. It's available in a
large number of core sizes. With other manufacturers, look for material
with initial permeability of around 750. If you're not running more than
a couple of hundred watts or so, you can get more impedance for fewer
turns with one of the 70-series ferrites. This ferrite can get too hot,
though, if you run a lot of power. If type 43 overheats, one of the 60
series like 61 will have less loss. It also has considerably lower
impedance, though, so you might have trouble getting an adequate amount
for the balun to be effective.

Amidon Associates has long been a source for small quantities of ferrite
cores. I'm sure there are a number of others, which a web search should
reveal.

Roy Lewallen, W7EL

yea right wrote:
I'm trying to find a place (in the US) to purchase ferrite donuts so I can
wind my own balum. Any recommendations?

Also, when looking at manufacturer's websites, there seems to be a
selection of chemistry to their cores. Is there one formulation that I'm
looking for in particulate?