[Elecraft] RE:whats a D104? Young whipper-snappers! :-)

[Ron D'Eau Claire]

According to Astatic, the D-104 dates all the way back to 1933.
(http://www.astatic.com/commercial/ASTATIC_Communication_History.html)=20

To put that in historical perspective, less than 10 years before =
virtually
every Ham was communicating by spark gap!=20

So for many of us "OTs", it's been an icon of the hobby for all of our
lives. It uses a Rochelle salts crystal that is deformed slightly when
sounds hit the diaphragm in the mic. Such crystals are "piezo electric";
they produce an electrical current when pressure is applied. So the =
output
of the crystal is an electrical signal of the sounds that hit the =
diaphragm.


Their advantage was that they were very sensitive and produced a lot of
signal. Back before solid state, it added significantly to the cost and
complexity of a rig to add another stage of audio amplification to use a =
mic
with lower output. So high-output mics were in high demand. Many hams =
used
"carbon" mics, which had great output but limited  audio quality =
(telephones
back then and up into the 1970's sometime all used carbon microphones in
them). The D-104 and other good 'crystal' mics were a whole leap forward =
in
audio quality.=20

The disadvantage of a crystal mic is that the crystal is very fragile. =
It
can be broken easily by striking the mic, or even by a very loud sound =
too
close to the mic diaphragm. Heat and cold can damage it. And, since it =
is a
salt crystal, it will dissolve in water. Even moisture in the air, given
enough time, would destroy the crystal. So they had to be 'sealed'.

Frankly, I'm amazed that so many ORIGINAL D-104's have survived and =
still
work!=20

Ron AC7AC=20

-----Original Message-----
I bought my first D104 in 1947 - they were a pre-WW2 item even then.

73, George W5YR
w5yr@att.net