Main cathode of SONY TRINITRON color picture tube is now Quick Start Cathode. Commercial name is Econoquick. Phenomena taking place toward the end of useful cathode life were discussed here. A summary of the results follows. (1) Long life Quick Start Cathode was obtained using newly developed Ni-Ba-Mg base metal. The best data of its life test indicated more than 90% emission to initial values at 29302 hrs and maintaining nearly complete emission still today. (2) Mechanism of these phenomena of Quick Start Cathode is Constructed of the growth of interface layer Ba_2SrWO_6 and the precipitation of high MgO at the boundaries near by surface bellow Ba_2SrWO_6 in traditional Ni-4%W-Mg base metal and of exhausting metal Mg and dispersed Ba in Ni-Ba-Mg base metal. (3) All oxide cathodes indicate the same mechanism of reaction of base metal with oxide layer each other at the end of useful cathode life in whether Quick Start Cathode or Preheat Cathode.