Hi Never owned a tube amp but I see ampeg is offering a nice rebate on the portaflex series, so I'm willing to take the leap. Thinking about the PF-50t (50w tube head) My cab is an SWR big bertha (2x15) I'm thinking I'm really underpowering the cab, is this a dangerous thing to do?? The portaflex 115he is an 8 ohm 450w cab They pair it with?? The swr is a 4ohm 700w cab Any thoughts??