"Michael A. Terrell" wrote in message
...

Jim Wilkins wrote:

"Michael A. Terrell" wrote in message
m...

A large, powdered iron toroid works even better. Like an old 3A
variac. I needed a modulation transformer for a AM mobile radio
back in the '70s. I wound a second winding on a surplus 88 mH
telco
toroid, and had excessive audio bandwidth.

However a coiled sheetmetal 3 Amp Variac core may not work at all.
The
response of one I measured fell to nothing above 600Hz.


Some are wound, some are powdered iron. The one I had may have
been
from a 400 Hz unit.

The type that was useless for audio was a General Electric Volt-Pac,
model 9T92A1, 50/60Hz.