Some old detectors used a bilateral substance such as SiC.  A battery can shift the operating point away

from the center to a place where the material is nonlinear and able to rectify.

-----Original Message-----
From: 1oldlens1 <1oldlens1@ix.netcom.com>
Sent: Dec 31, 2025 1:09 AM
To: Hubert Miller <Kargo_cult@msn.com>, ARC5 <arc5@mailman.qth.net>, List Milsurplus <milsurplus@mailman.qth.net>
Subject: Re: [ARC5] [Milsurplus] Audio Impedance Matching on USAAF aircraft

 

Many very old diagrams for crystal detectors show a battery buying never used one on the crystal sets I built as a kid and don't fully understand  why they were used 
I've found exactly one Brusg headphone that worked,  the others just had mush inside. Brush held the patents for crystal microphones, headphones, phono pick ups and cutters. Licensed many other companies. But others seemed to have better sealing and protection. Unlike magnetic and dynamic phones, which are usually in series, crystal phones are in parallel. 
 
 
 
Sent from my Galaxy
Richard Knoppow 
Los Angeles
WB6KBL
 
 
-------- Original message --------
From: Hubert Miller <Kargo_cult@msn.com>
Date: 12/30/25 10:41 PM (GMT-08:00)
To: ARC5 <arc5@mailman.qth.net>, List Milsurplus <milsurplus@mailman.qth.net>
Subject: Re: [ARC5] [Milsurplus] Audio Impedance Matching on USAAF aircraft
 

‘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