It can power a 15" speaker or more, with the 9V battery (or 9V wall wart) it can offer around 750mA output. You can get more if increase the supply voltage to +12 (some versions of the LM386 can operate on up to +18V)
Actually it sounds good for such a small amp. I bet the original guts in that cabinet were a lot bigger. It's amazing how far electronics have come. I remember our English teacher telling us that someday all homes will have personal computers in them and we just laughed at him. Now we have the power of a mini-super computer in our hands called a cell phone.
