I just got an Ampeg B25B head and cabinet together for $400. It looks sweet and its in great shape and works fine. I was wondering if anyone knows what is the point of the 2 different channels on the amp? Which channel should i use or does it not matter? Also, would it be a good idea to change the tubes in the amp? What it make it any louder or sound better? which tubes would i get to replace them? Is there anything else i should know to use it right, I dont really know a lot about tube amps. Thanks!