The 3B28 is a half wave Xenon filled rectifier. The maximum Peak Inverse Voltage is rated at 5,000 Volts. Although the average rectified current is 500 mA the peak value can be as high as 2 Amps.
The pinch has three rods set into it but the central rod supports the ceramic insulator and has no electrical connection made to it.
The envelope carries the commercial Type designation and additionally the CV code, indicating the complete equivalence of the two names.
The screen around the filament and anode.
The top cap with the anode lead within a thick wall glass tube. The anode itself is a disc within the top of the screen.
The wide glass tube envelope is 52 mm in diameter and, excluding the UX4 base pins, is 134 mm tall.
Reference: Data-sheet. Type 3B28 was first introduced in 1952. See also1952 adverts.