I received an inquiry from a fellow TBer regarding taking a look inside the new WT-550's chassis; he also asked about swapping tubes. This new model packs a punch and seems to be more efficient than previous models. Here's a couple of photos. The tube socket is at the upper right of the first photo. The following photo is a close up of the Ruby 12ax7 in its socket. I was surprised to find a Ruby tube in there. I have to say that this amp sounds so good that I haven't even thought about swapping the tube to seek a better tone. I love the way she sounds just as it is. I understand others might be interested in seeking the Holy Grail of Tube Tone by swapping the tube with other brands. Please feel free to share the results of your experiments here!