The CV2734 (commercially the 4003A) is a current stabiliser or Barretter. The 4003A is designed to stabilise a current of 0.98 Amps for a voltage range of 3 to 9.5 Volts.
Domestic Barretters were used with series heater chains to stabilise the current for small fluctuations in mains voltages. This is clearly for a much higher current.
The CV433 has the same rating but is made as a double ended tube.
The helical iron wire has broken away from the lower support.
The STC logo and 4003A together with Made in England.
Microscope image of part of the active element.
The wide glass tube envelope is 28 mm in diameter, and including the ES base is 110 mm tall.
Reference: Data-sheet. Type CV2734 was first introduced in 1953. See also1953 adverts.
