[DeleteMe]

I've read a couple helpful threads here about antenna couplers. In my case, I'm restoring a 42-390 console. According to a service bulletin, it calls for a 42-1361 antenna coupler, which I don't have. I live in the boonies, so I have to use my outside long wire antenna to pickup AM stations.  I know these couplers were used mainly to match the impedance of an outside antenna to the radio.

Anyway, my question is what impedance do these 1940 Philcos expect? 50 ohms? I know my long wire is much higher, but I do run it into a 9:1 unun, which feeds a RG-8x coax coming into my house. My radio does pickup AM ok if I connect the center wire of my coax to either pin 3 or 4 of the FM jack. That's with the cabinet FM antenna (pins 1 & 2) unplugged. It does sound a little distorted, but that may be a capacitor that needs to be replaced. 

I'm just trying to understand if my antenna hookup is working as well as it can, before I do more troubleshooting.