The Thermionic Fabricator is used to craft different items that need Liquid Glass, among others the different colors of stained glass.
The thermionic fabricator needs to maintain a certain heat level to operate. The amount of power you supply it determines how hot it will get. At least 2 MJ/t are required for the fabricator to warm up. If you do not supply enough power to maintain the current temperature, it will slowly drop.
Warning: If the Fabricator is at max. heat, it will continue to pull as much energy from the connected engines/tubes as possible, even if it doesn't need that much to maintain it's heat level. It is therefore not advised to directly connect your Thermionic Fabricator to your MJ power plant or storage, as it will waste every last bit of excess or stored MJ.
Glass or Sand or Glass Pane placed in the upper left slot of the fabricator will be melted into molten glass. The molten glass is stored in the slot below the solid glass. Molten glass is used in the construction of the electron tubes. The type of electron tube is determined by the materials loaded into the crafting grid. As long as the fabricator is at a higher temperature than the level indicated on the temperature bar and has enough molten glass and all of the required materials it can continue to produce items regardless of whether power is being supplied.
As of version 188.8.131.52, the fabricator can also be used to craft stained glass. To do so will require a Wax Cast to be placed in the upper-right plan slot and molten glass. Also required is Propolis (Or a variation) and any dye. The cast is not used up in this recipe, however it does take damage.
Note: the max heat level is 10,000 C.