Here is a description of how mechanical TV works:
http://www.earlytelevision.org/mechanical_tv.html
The tube is neon, with the plate glowing in proportion to the current that flows through the tube.
It is easy to make a mechanical set like the ICA one with no synchronization. You have to manually adjust the motor speed control to keep the image still. Synchronized sets are a little harder to make, requiring either a synchronous motor in both the camera and receiver, or a so called "sonic coil" sync system.
Our site has a bunch of home made sets.