The title is slightly misleading though. The real cost of most amps is in the transformers and all the remaining bits add up too. He just happened to have power and output transformers sitting around. That being said, I think someone even commented on the video about using torroidal power transformer helps reduce overall noise with single ended amps and ends up cheaper too. There are a few guys that built the Rob Robinette Micro Blackvibe with them. It would be cool if some of the Micro projects had PCBs here.