The M-OV DET12 is a VHF transmitting triode. The data-sheet is of the similar 834.
The graphite anode dissipation is 50 Watts.
The envelope has the CV1288 marked on it and there are vertical lines in the glass that look to be where the two halves of a mould came together.
The graphite anode is fixed by a metal support running the whole length and tightened by thin wire wrapped round the bulb end. The control grid is wound on two supports. The once helical filament is now just small pieces of wire in the envelope.
Minimising lead inductance is achieved by bring the control grid to a top cap as well as the anode.
The grid top cap is at the top of the image.
The standard notch and peen marks on the grid supports. The base of the filament is still in place.
The balloon envelope is 65 mm in diameter and, excluding the B4 base pins, is 150 mm tall.
