I got an Ampeg SVT II and was wondering if buying my own tube tester was worth it. If so, could you point me in the right direction? Also, the cage/screen on the back is missing and is that a big deal? If so... Thanks. AND...I see that most players with these amps seem to use the Ampeg 8x10 but that is too much in one. Is two 4X10's just as effective? Thanks again.