The CV3891 is the service name for the commercial EZ40 full wave rectifier.
A respectable output current of 90 mA, sufficient for most apparatus can be drawn.
The maximum reservoir capacitor, a measure of the peak current rating, was 50 µF. The minimum effective series resistance is 300 Ω.
The two identical anodes are mounted at right angles. The top anode is inverted and the connecting rod can be seen together with the tape joining it to the anode plate.
The dirt on the glass testifies to a previous service life.
The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 60 mm tall.
References: Data-sheet & 1040. Type CV3891 was first introduced in 1954. See also1954 adverts.