The CV4025 is the UK Government procurement specification and the commercial equivalent is the 6058 and the prototype was the CV140. This special quality double diode is based on the 6AL5. These diodes are for signal rectification at medium frequencies eg video.
One of the diode sections seen in face elevation.
The two sections and central screen end elevation.
The two diodes are separated by a full height metal plate screen. The anodes are made of two thin plates 10 mm long and 8 mm high, pressed to leave a vertical 2 mm diameter tubular cavity. Into this cavity is fitted the cathode assembly.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 48 mm tall.