Well, I fixed it. Whoever wired the cab used a TRS jack and miswired it. It looks like they wired the ring to the +. They did manage to solder the sleeve correctly....
I got a TS jack from the local electronics store, some 14 gauge speaker cable, spade plugs, soldered up the jack and...
I pulled two different speaker cables from the Marshall DSL in the room. Both work fine with the Marshall and its 4x12, but not at all with the RT2/50.
About damaging the amp, as far as I can tell, nothing is getting f'd up, but I'm not risking it anymore. It has been turned up pretty loud...
For some reason I can only use a balanced TRS cable going from the RT2/50 to the 2x12 cab. Is this normal operation?
I'd rather use my heavier gauge cable than the studio interconnects now being used.
Could it be a wiring issue? The 2x12 is wired as two 8 ohm speakers in Series for 16...
Is there a list of all the modules somewhere? Randall's site only show's 15, but I've read that there are at least 18.
So, how many modules and what are they?
Thanks!