[Boatanchors] Crystal Headphones

[J. Forster]

>
> To the best of my knowledge, xtal phones were introfuced by Brush
> Development Corporation, the same folks who brought you the tape recorder.
>  I am not sure when this occured, but they were used extensively in the
> broadcast field.

Could well be. At some point Brush and Clevite became Brush-Clevite.
Clevite made piezoelectric devices, including accelerometers.

> Dynamic headsets have been around forever. A company called Permoflux cam
> out with some dynamic headsets that had what looked like a miniature
> speaker inside. These really had great low end response. Many of them were
> found on the old HB-7 headset bands used during and after WW II, but I
> don't believe the Permoflux dynamic came out until well after that war.

I don't know about headphones like little speakers, but there were
ABSOLUTELY microphones made that way in 1941. They were used in the
Wireless Set No.19 Mk.II and Mk.III.

Five or six years ago I disassembled a dead one and documented the
process. You can see the pics here:

http://www.royalsignals.org.uk/mic.htm

What amazed me was the 'cone' was actually molded of very thin bakelite.
IMO, it's an exquisite piece of engineering. BTW, the microphone is not
very sensative...  you have to yell into it... because it's designed for
use inside a moving tank.

Best,
-John

=======================


> As far as which was best for copying CW, I think it is up to individual
> taste.
>
> 73,
>
> John,  W4AWM