The AU5 is directly equivalent to the type VU111 which is also known as a CV1111. The CV or Common Valve type numbers replaced the classifications of valves for the armed services in the early 1940s, prior to this each service had its own type numbers.
This high voltage high power half wave rectifier can deliver 125 watts. A pair producing 250 watts could feed a high voltage low current transmitter output stage. The alternative use is to feed a pulse modulator.
The anode is blackened for better radiation properties. The main heat is generated on the sides facing the filaments and here there are fixed the side flanges that provide extra cooling and fixings to the support rods.
The anode is separated from the six vertical filament strands by a 5 mm gap, and is supported on substantial ceramic insulators.
The pinch and lower ceramic insulator. The filament strands can be seen to be oxide coated.
The top of the anode contains a ceramic rod over which the filaments pass before connecting to the tensioning springs that are mounted off centre. In this way the filaments keep to the centre of the anode space.
The classic envelope is 54 mm in diameter and excluding the B4 base pins, is 123 mm tall.