[TenTec] Mic Help

[Bob McGraw - K4TAX]

The D-104 mike with out the preamp requires a very high impedance input to 
work correctly and sound good.  The preamp is basically an electronic 
transformer to provide the required high Z to the mike while at the same 
time being able to drive a somewhat low impedance load.  When I say high Z 
for the mike I'm saying something like 3 megohms or higher.  The Delta has a 
30 to 40 K ohm input which is much too low for the D-104 without the preamp.

Now, several versions of the TUG-9 stand offer PTT switching which has 
make-before-break contacts and also break-before-make contacts as well as 
contacts to turn the battery power off to the preamp.  These can be used to 
switch the audio after the PTT is activated thus eliminating the "clunk" 
when the stand bar is grasp.  In other cases one may not wish to switch the 
audio line so the mike stays connected or hot all the time for VOX operation 
and only use the other set of contacts for PTT operation.

Here is a link that explains it all with pictures and schematic.

http://www.qsl.net/wa2mzf/d104.html

Personally, I opt for using the preamp but be sure its gain is adjusted so 
as not to overdrive the input stage on the Delta 580.  Otherwise, no matter 
what you do, the audio will sound bad as the audio gain in the radio is 
after the input stage.

73
Bob, K4TAX