Oh man, there are so many reasons not to power on a pinball. You are right, there are not any tubes, but there are a million switches. Most of them connect through a common relay board full of barely adequate components. If any of these switches are stuck, or there is a short in the circuit, it can cause a board to burn, or at worst, the whole machine to catch. Solenoids that are stuck on will heat to several hundred degrees before blowing a fuse...trust me, thats not something you want happening in you spare bedroom during dinner