The Amplifying Tube is a block added by Hearth Well. It is used as a component for several multiblock machines such as the Heat Furnace, or can be placed vertically to process blocks on its own.
When between 2 and 8 Amplifying Tubes are placed facing vertically on top of each other and a block is placed under the bottommost one, the block will slowly be melted. This process requires the topmost tube seeing the sky and only happens during the day. The more tubes are stacked, the faster the process is.