Robyn SB-540D‏ Microphone

[cbdude1]

Radio Make and Model: Robyn SB-540D‏
PLL Number: LC7120

I have acquired one of these beautiful old radios, but it does not have the original "Clar-O-Mic". I wish to wire up an ordinary off-the-shelf dynamic type microphone. I was wondering if anyone would have a microphone pin-out/wiring guide for this classic. I don't want to try and short out pins in the normal manner to find tx/rx/audio/ground, as at least one of the pins has voltage on them. I'm really itching to get her up and running again, any help would be greatly appreciated.

[hackindave]

1 - Audio
2 - Shield
3 - Transmit
4 - Ground

Also add a .01 cap in series with the white lead