The manufacture of silicon carbide varistors

The introduction of variable resistors made from silicon carbide into the telephone set signaled the beginning of high volume low cost production of these devices by the Western Electric Company. Although these variable resistors, known as varistors in the Bell System, were introduced into telephone circuits in the early Thirties, their use in a volume regulating circuit of the new telephone set was the first high volume application in the Bell System. Today, two sizes of varistors used in this application account for more than 90 percent of our current annual production of 15 million silicon carbide varistors. It is the purpose of this talk to describe the manufacturing process and facilities used to produce these units at a low cost.