The VU508 is high voltage rectifier designed for high power applications. The U19 (M-OV) and the CV187 are essentially the same valve. When looking at the different interpretations of this specification from different companies the variations in construction are interesting. Here the design uses a square ceramic plate top and bottom to hold the electrodes.
The maximum reservoir capacitor that can be fed is 4 µF and the valve needs a minimum effective series resistance of 600 Ohms.
The box anode is from front to back in the picture with the cooling fins seen left to right. Attached to the right side of the anode is the getter holder with the gettering on the glass.
The filament tension springs hold the three loops of wire. In fact the filament 'wire' is a length of coiled wire.
The classic envelope is 48 mm in diameter and, excluding the B4 base pins, is 160 mm tall.
