The E1980 is an M-OV experimental valve. This carries the serial number 49. The base connections match the X78 from M-OV and visually they look very similar. The X78 has a 6.3 Volt heater and this exhibit has the correct heater colour at 0.1 Amp and 13 Volts.
Through the holes in the top mica it was possible to confirm that the triode grid was connected to grid three of the main hexode section.
The triode at the top.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 46 mm tall.
Updated February 03, 2017.