This is a mystery valve. One can read the the word 'type' but not the rest. The base is a nickel shell with a central groove. This base was used only by M-OV for its early Valves.
The internal construction is similar to the early 'R' Type valves with a horizontal cylindrical anode, single straight filament and wire helix grid.
The filament fixing is a folded and crimped support.
The balloon envelope is 40 mm in diameter, and excluding the B4 base pins is 79 mm tall.
Updated January 05, 2013. shape:balloon construction:pinch type:triode age:1920.1930 base:b4 pins:4 pin: