I have a first series ABM 300w and it is most definitely not a quiet amp.
First things first, you need to get the needle moving. If you're not getting the needle moving that means you're sending very little to the power amp, so this is where your problem is. Use the high input for passive basses - the one on the left. Even on my weakest output passive bass, I don't need to go any higher than about 3 O'Clock on the input gain to get the needle bouncing. If this isn't the case for you then you're never going to get any serious volume out of it. Try raising the pickups on your bass a little closer to the strings to see if that gives you more. If that doesn't work then try a different lead. Also, if you can, try a different bass with it too, just to compare outputs. In my experience, you need to get the needle going into the red with your loudest notes to really get the best out of that amp.
Another thing to consider, once you've got that sorted, is the ohm rating of your cab. The ABM will give you 300W into 4 ohms. If your cab is 8 ohms then you're not getting the full 300W of output.