I have an Ampeg BA115 100W combo amp which is fitted with an internal 15" 150W 4 ohm speaker and a piezo tweeter. I am interested in adding a 4x10 extention cab to this amp in the future and have a few questions relating to this. 1) The amp doesn't have an external speaker jack, to add one myself would it just be a simple matter of adding a TS jack in paralell to the wires already connecting the internal speaker? I want the cab to run simultaniously with the 15" internal speaker, not to cut it out. 2) I understand that incorrect amount of ohms can damage the power amp, the internal speaker is 4 ohms so what impedence of cab would I need to buy to avoid damaging the power amp? What effect on the output power of the amp would this have, I assume that it will reduce my wattage, because it will be driving more speakers, but by how much? I am willing to sacrifice some power for a bit of articulation to my tone. Most gigs I play are with PA back up with the amp miced where possible so It only really gets used as a monitor anyway. 3) In the future I'd hope to upgrade and get myself a proper Ampeg SVT head, so I want the cab I choose to be able to accomodate this upgrade and not limit me. Any advice? I know thats a lot to ask, I hope someone will be able to help out in some way!