Ditching my 5150 II for a 5150 block letter. Couldn't pass it up for $450 shipped and after reading all the 5150 praise around here I decided to give one a try. First question: I noticed that the mkI has 2 inputs, high gain and low gain. Whats up with this? Second question: I just had new tubes put in my mkII and I'm going to swap them into the mkI when I get it. As far as I know the mkI has no bias adjustment. Do I just pop the new tubes in and let 'er eat, or what?