Hey Skitzo, my understanding of it (from this topic which also tells you how to fix it (ADA Microtube - "protect" problems http://adadepot.com/index.php?topic=138.0)) is that when the MT200 warms up, it stays in protect mode (no sound) until the tubes have warmed up. When the tubes are ready the neon light brings the PSU chip (power supply unit) out of protect mode, you can't switch it yourself.
(From one of Sparkers posts in that topic - "I think when the MT200 PSU startup thing was discussed some time ago, the neon inside the box, NE1 (a NE-2H type) was thought of as a suspect. This neon acts as an under-voltage protection for the PSU chip when the amp is switched on, when the neon strikes on the PSU chip is brought out of shutdown. The neons can degrade over time and the strike voltage can change, also they can show sensitivity to light")
Have a read of that topic (in the Power Amp Tech area), it's where I learnt about it. Cheers R