On Apr 22, 1:23*am, m II wrote:
Surely there should be enough broadcast power over the entire AM band,
that, if collected and rectified, would drive a 2 inch speaker at very
modest levels.
There was an article in Popular Electronics in the early 1960s about a
crystal radio that could directly drive a speaker. Two features that
I remember are dual tank circuits and using 1N54A diodes (selected for
high back resistance/low leakage) as a full-wave voltage doubler
instead of one of the more popular 1N34. I don't remember the speaker
being chosen for large magnet size, but the common 5" speakers were
pretty efficient.