OSRAM GEC BARRETTER, 1930's

Barretters are temperature sensitive resistors used for stabilising voltages in wireless receivers, usually powering the heater circuits, of AC/DC receivers.
Acting like a resistor but with constant current characteristics, a current over a particular range can be held constant over a range of varying voltage. A Barretter usually consists of an Iron wire held in Hydrogen filled glass envelope. Also used for many other applications.

Your comments:

• The example shown is a Philips type 302 Barretter (current regulator) and was used extensively in Australian transformerless radios from around the mid 1930s. As already stated, it was used in conjunction with valves with 300mA heaters.
  .......... Ron Pond, Perth, Western Australia, 18th of October 2014
  
  
• I have one of these in a Philcophone 901 intercom set. The set dates from 1938. The heater string is series connected, with the barretter, across 115 volts and the current is well regulated at 300mA over quite a wide supply voltage range.
  .......... John Dodgshun, Christchurch, New Zealand, 30th of August 2012
  
  

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