[Milsurplus] WR-1 DC input switch-over relay

[Hubert Miller]

Was looking at the schematic for the  German WR-1 troop broadcast receiver.
I see there's what I take to be the DC cut-in relay coil, across the mains input. 
This inductor simply has a resistor in series.
So how's this work?  I assume relay resistance and resistor are such that AC 
will not pull in the relay, but why doesn't the relay buzz on AC ? 
The set accepts 110 or 220 AC or DC but is not the basic AC-DC circuit. 
tnx-
Hue