The C10 is a barretter, that is a series resistance to stabilise current flow. The barretter characteristic comes from the use of iron wire. The attached data sheet has a good explanation of the barretter and its function.
The C9 and C10 are quite similar with the main difference being the base connections. However, the filament connections are the same.
The coiled wire and the central glass support.
The wide glass tube envelope is 38 mm in diameter, and excluding the Ct8 base pins is 110 mm tall.
Reference: Datasheet Type C10 was first introduced in 1939.
Absolute Maximum Operating Conditions¶
Updated July 31, 2017. shape:wide.glass.tube construction:pinch type:barretter age:1930.1940 base:ct8 pins:8 pin:1.- pin:2.- pin:3.- pin:4.- pin:5.f pin:6.- pin:7.- pin:8.f