Michael Black wrote:
And of course, one commonly written about trick in the old days was to
use a "useless" 400Hz transformer as an audio transformer, the operating
frequency being about where you'd want frequency response to start for
communication use. Since it moves the frequency up by six, the frequency
response is probably better at the higher frequencies.

That's only a useful trick, though, when 400Hz power transformers are
commonly available, and cheap because nobody can find a use for them.

I still see PLENTY of 400 Hz transformers coming out of the surplus
pipeline today, not to mention 400 Hz motors and brick power supplies.
You want some? I think I even have a box of 400 Hz fluorescent light
ballasts somewhere. Not even a little bit useful.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."