My MA 50C has an internal speaker that is at 16 ohms and the amp is wired for 8 ohms max. I have a 2x12 cab that is at 8 ohms that I can plug in - BUT (and this is the question): Can I leave the Internal speaker plugged into the amp (again, at 16 ohms) and STILL plug in my 2x12 cab (8 ohms) without doing damage or do I have to unplug the internal speaker before I plug the 2x12 in? By my math (and this is always very questionable), it should be able to handle it because it will not make the amp go lower than the 8 minimum to get the full 50 watts. I need another set of eyes/brain to confirm/refute. Thank you in advance!!!
Regarding your MA50C, it is designed to take 1x16, 2x16 or 1x8 cabinet unfortunately the internal 16ohm connected to your 8ohm extension cabinet will give you an overall impedance of 5 ohms which would damage your amplifier. You can use your extension cabinet by itself using one of the 8ohm sockets.