The AVT 150 combo has one internal speaker of 8 ohms. Unless there was a later edition with two speakers I dont know about. The AVT150 is capable of driving almost any impedance above 4 ohms. The lower the total impedance the amplifier is connected to, the closer you will be to its rated 150w RMS output.
So - yes you will be able to use that cab you're looking at, and no it wont cause any problems. As long as its a 'real' cab (ie a 1960 or similar) and not an MG or AVT series cab, you should end up with a much nicer sounding rig 
Unplug the internal speaker when using an external cab, except if its the official AVT112 extension cab. I dont recommend purchasing that though.
Steve.
Edited by Scrooge (07/08/10 09:56 AM)
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I've always prefered natural sounds to the synthetic...and valves grow on trees, dammit!
