The E122ER is presumed to be a valve but we have no information at all.
The top of the plastic outer showing the identification has been written by hand. This suggests an experimental device.
The miniature five pin base with pin numbers identified. The base is identical to that used on E122FC.
The envelope is 18 mm in diameter, and excluding the base pins is 19 mm tall.
Updated February 11, 2013.