Tube amplifiers need some time for the heater elements to warm-up before a tube starts conducting. If the high-voltage supply comes on before that, tube life is shortened. This small circuit is designed to delay the high-voltage supply section in a tube amp for 40 or 60 seconds (jumper-selectable). It uses a MOSFET as a switch, which is controlled by a simple microcontroller. After activation, the chip goes into sleep mode to ensure no digital nasties degrade your amp's sound.
The circuit is installed in series with the secondary winding of the power transformer and ground with a minimum of wiring – just two connections. It is powered from a separate dedicated heater winding.
This semi kit contains the PCB, the MOSFET and the controller chip. The other (common) parts come out of your junk box or from your preferred vendor.