The SU25 is an EHT rectifier with the distinctive saddle of Cossor EHT rectifier design. The anode voltage is given as a maximum PIV of 25,000 Volts. The reservoir capacitor is limited to 0.1 μF maximum.
The Cossor design did not lend itself to the machine assembly of other manufacturers but the reliability of their design was much better.
The saddle anode seen end on. The cathode is the horizontal bar.
The anode is held in place by glass rods that are merged with the pinch.
The central oxide coated cathode.
The classic envelope is 49 mm in diameter, and excluding the base pins is 119 mm tall.