[ARC5] Hi-Z Microphones with the Navy ATD Transmitter

[David Stinson]

ATD
https://photos.app.goo.gl/859Q21luomqXxkN83

When the microphone circuit in the Navy ATD
transmitter is selected for "MAGNETIC," a 300 Ohm
resistor shunts the microphone audio line directly

to ground.  I suppose it's looking for a Low-Z
mike.
A simple, reversible change will allow Hi-Z, 
amplified microphones like the D-104 to be used 
with the Navy ATD Transmitter:

>Set the Channel to A, B or C.

>Remove the "D" tuning unit.

>Set the switch on the side wall near 
 the front to "Magnetic."

>Remove the shock mount under the Plate and
 Grid/Battery meters.

Locate the Microphone Resistor Board to the
rear of the 12SL7 Mic Amp tube, V107.
https://photos.app.goo.gl/BECccNq7YGlRTcly2

Locate the 300 Ohm resistor, R-145: it is most
in-board of the resistors and the smallest.

Cut the lead furthest from V107 and secure 
the resistor end.
https://photos.app.goo.gl/GIyBdfsuUbpzwEQ83

I used an amplified D-104 with the gain set low
to check into the Texoma AM Trader's Net this 
morning with good reports.  I have not yet tried
any other hi-Z mikes.

The full schematic and parts lists are online
thanks
to Mike Hanz at:

http://aafradio.org/docs/ATD_schematic.png

GL ES 73 OM DE Dave AB5S