Please see title for exact description.

THD Hot Plate is a reactive power attenuator made for tube guitar amplifiers. It lets you run your amp wide open for natural power-tube distortion while controlling the volume to the speakers.

We have no accurate way to test these but it appears fully working with typical studio / pro sound wear. I can do any testing that could be needed and have listed below any issues I know.

All of this being said, you are buying used electronics.