Larry Kayser wrote:

I have four large toroids that were bought some years ago

by a chap for use in amateur radio. I came into them after he passed on. They are labeled 144T500 - 3C5. I have seen somewhere on the many LF pages a reference to a material type "3C5", so I am asking if

anyone can tell me about the characteristics of these devices.

Sorry, as with Rik, I don't have any data on '3C5' material
either.  But, some time ago, Andre' N4ICK discovered the Philips
URL at:
http://www.acm.components.philips.com/pdf/

which includes data sheets for many materials, including 3C15 and
3C85
(but, I believe, not for 3C5).

[By the way, if I had such a core here which I wanted to check
out on LF,
I would wind a 10-turn primary, and a 10-turn secondary winding
on
the core.  I'd then fire up my LF TX (a robust pair of 572B
valves) and deliver power into the primary, with a 50 ohm load on
the secondary.  By checking the power loss through the
transformer (while monitoring, with some caution, its increase in
temperature!), I'd try and gauge its usefulness in LF transformer
applications.]

Regards to all,
Steve GW4ALG