The U27 is a directly heated high voltage high power half wave rectifier that can deliver 125 Watts. A pair producing 250 Watts could feed a high voltage low current transmitter output stage. A pulse modulator for a Radar transmitter needs high peak power but on average the power is quire modest. The U27 was rated at a maximum Peak Inverse Voltage (PIV) of 14 kV.
The anode is separated from the six vertical filament strands by a 5 mm gap, and is supported on substantial ceramic insulators.
The GEC brand label.
Two of the three oxide coated filament loops.
The lower mica and pinch end of the filament. The anode is supported on ceramic insulators for good voltage isolation.
The classic envelope is 50 mm in diameter and, excluding the B4 base pins stands 121 mm tall.
