‘Crystal’, piezo
earphones, actually went to 100kR, but thanks to
Brush Co. lack of type markings, good luck
separating these from 50kR ones.
There is no way just
looking at them. I find the Brush phones, about 50%
are now defective. I have a magazine article on how
to “grow” your own
crystal for headphone
use, but that’s something on the back burner for
forseeable future.
I noticed recently that
the little earpieces that came with ‘Rocket Radios’
and other Japanese import crystal radios 1960s –
1980s, have been
“improved” with brass
diaphrams. Whereas with the old ones, you look down
into them, and you see an aluminum colored diaphram.
The
“new improved” ones are
noticeably less effective, altho maybe more rugged.
Good crystal phones, you squeeze one lead in one
hand, hold the
other contact to a wall
AC switch screw, with the switch in ‘ON’ position,
you should hear a moderate strong hum.
Did you know ? A ‘crystal
radio’ with a piezo earphone, does NOT need a DC
circuit from diode to headphone. An AC circuit, with
a cap like
10nF, will do.
-Hue Miller