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

[Stuart Rohre]

Crystal elements of the D104 can last indefinitely as long as it is not
exposed to water, or continuous too high relative humidity.   The type of
crystal element used is hydroscopic, (takes up water from air).
Too much heat is bad so be careful how crystal mikes are stored.  And do not
try to use them for mobile in hot sunny times.

Of course, if you do whack one, the replacements are available last I
checked last year.   But, you can also put a disc of cardboard in the mike
housing and glue an electret low impedance element onto that for modern
rigs.  If the sound does not suit your voice, you can experiment with some
cotton behind the cardboard to "tune" the mike housing.
73,
Stuart
K5KVH   Still using a D104 from late 50's picked out of trash in late 80's!