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The 165R4 is a ballast tube or baretter. The resistance wire runs from pin 1 to pin 4 with a tap connected to pin 3. The tube is designed to drop 49 Volts at 300 mA. The dissipation is 14.7 Watts.

The helical wound wire is mounted between notched mica supports.

A close-up of the winding.

The classic envelope is 38 mm in diameter, and excluding the base UX4 pins is 87 mm tall.

Reference: ³⁰⁰². Type 165R4 was first introduced in 1935. See also 1935 adverts.