The GTR150W is a voltage reference. It is too small to stabilise voltage directly for more than a few µA and so was probably used in a valve voltage stabiliser. In this application only a few µA of current would need to flow through the device.
The thin glass tube envelope is 9 mm in diameter, and excluding the flying leads is 31 mm tall.
Absolute Maximum Operating Conditions¶
Updated February 22, 2013.