The T25D from Mullard is a directly heated triode. As yet we can not find operating details. One internet source suggests PX25 like. It was probably made as a transmitting valve for a special application.
The T25D has glass top supports and no mica supports. The filament voltage is 6.0 Volts and the maximum anode voltage is given as 500 Volts.
With the carbonised anode box seen in side elevation, the sturdy mounting supports are visible. These rod supports are attached to a band that clamps onto the pinch near the base.
The inverted 'V's of the oxide covered filament run inside the flattened control grid that runs parallel to the anode bod on the broad face.
The balloon envelope is 67 mm in diameter and, excluding the B4 base pins, is 143 mm tall.