I've been having some success replacing the preamp in the base of 
amplified D104 mics with an FET buffer stage to ensure the crystal 
element is working into a very high load impedance.  See...

http://www.wd8das.net/D104-FETbuffer.gif

The 4.7k resistor in the drawing can be changed to match other rig 
input impedances.

Steve WD8DAS

sbjohns...@aol.com
http://www.wd8das.net/
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