Hi Will, I think Luke is right, I think it's only 8 Ohm bridged. I looked into this before I bought this amp but as my cab was 8 Ohm is was fine. Only really an issue if you only have one 4 Ohm cab as you can only use one channel.
Still a great power amp in fab condition & with HPF built in it meant I didn't need a Thumpinator I was planning on getting. Only selling as I've now got a powered cab so surplus ....