The E2047 is an experimental valve from M-OV and this one carries the serial number 43. On the envelope feintly etched is the identification W77. The W77 is a miniature variable μ pentode designed to operate at HF and with a 6.3 Volt heater.
This valve runs with 12.6 volts on the heater. Observation confirms that the pin connections match the W77. Our other E2047 had W107 written on the box as well as E2047 and the W107 has the same pin connections as the W77 and appears to be a 12.6 Volt version of the W77.
The W77 is just visible.
The bright anode with the three wire grids within.
The thin glass tube envelope is 18 mm in diameter and excluding the B7G base pins, is 45 mm long.