Michael Black wrote:

Of course, one solution in the old days was to use a 400Hz transformer,
which were cheap and available as surplus, and which didn't have much
use in the average ham shack at the time. The idea being that since
it's intended for 400Hz, the upper frequencies might get through
the transformer better, and the loss of lower frequenices didn't matter
since for voice you didn't care about much below 300Hz.

Nowadays it may no longer be a solution, given WWII is so far in the past
and the stores that might have them for next to nothing nearby are gone
too.

400 Hz transformers are still very popular for modern aircraft applications.
There are still lots of them on the surplus market.

They catch fire if you connect them to a 60 Hz source because the series
inductance is very low.

They actually aren't very good as audio transformers even.

Really, they aren't good for anything. If you want some, let me know.
I even have a bunch of sealed 120VAC-200VDC supply modules, 400 Hz only.
Not useful.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."