Fixed high-stability carbon resistors

High-stability fixed resistors of a wide range of values were developed during the war for special applications. Smooth ceramic rods were coated with carbon films, by pyrolitic decomposition of methane in a continuous furnace. The resistance value so obtained was increased by cutting a spiral track on the coated surface of the rod. A layer of graphite was applied to the ends of the rods, which were then fitted with metal caps and lead wires as contacts. Protection from atmospheric influences and mechanical damage was provided by specially developed lacquers, or alternatively, by hermetically sealing the resistors in glass envelopes. A description of the furnace used and its control characteristics are given. Typical stability characteristics of the resistors are quoted.