Thoriated tungsten filaments in rectifiers

THORIATED tungsten filaments have been in widespread use for low-voltage tubes for many years. By the addition of the carbonization process, they are used successfully at several thousand volts. The generally accepted view as expressed in textbooks and papers as recently as 1941 has been that 5,000 volts was the maximum voltage for a thoriated tungsten filament. Today, it is well known that during World War II the demands of radar and other electronic equipment raised the ceiling for thoriated carbonized tungsten filaments to 35,000 volts.