Summary

Barretter, manufactured by Siemens, England, circa 1937. A paper label on the bulb indicates that the valve was installed in some equipment in February 1938. This is a current regulator designed to maintain a constant 100mA with a voltage drop from 15 to 40 volts.

A current regulator (ballast lamp or Barretter) uses an iron filament in a hydrogen atmosphere to produce a device through which the current is essentially constant over a range of voltages because of the large positive temperature coefficient of resistance of the filament. As the voltage goes up, the temperature rises, causing the resistance to rise, resulting in only a small rise in current.

Physical Description

Tubular bulb with a special 4 contact base with a threaded boss (incandescent lamp construction with mica spacer). Terminals apparently soldered on.

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