[ARC5] [Milsurplus] Audio Impedance Matching on USAAF aircraft

[Hubert Miller]

‘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
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