There is nothing mysterious about it. The military Dovetron only has polar outputs and I needed to key a neutral loop.

I grabbed the first polar relay my hand landed on, adjusted it by the instructions in "The New RTTY Handbook", tried it on the +- 12 volt output of the Dovetron and it worked.

I cut and filed a rectangular hole in the cover of a 4X4 inch electrical box and bolted the relay to it .I pulled wrap-around pins put of a broken octal tube socket, squeezed them a little tighter and used them to make my connections to the pins on the polar relay.

The Dovetron is connected to the external speaker jack on the Icom repeater receiver.  (The controller is connected to the DB-9 on the Icom adapter cable.)

The biggest problem is that the Dovetron Mark and Space settings drift. In my unheated radio building, they drift horribly. Even the one in the house drifts.

I have a dual function generator set for 2125 and 2295 sine waves in my den. I send the outputs to my radio building also. That makes it very easy to reset the tones on my Dovetrons.

This is the generator I bought: eBay item number: 112440163822