old rectifier replacement options

I need to replace the rectifier in an interface circuit from a 1963 Janszen Z-600 electrostatic/hybrid speaker. (see schematic below...6S-1)

The oem rectifier is a Recticon Corp S6350 AB. It is a black cylinder about 3mm diameter and 30mm long with axial leads.

Can anyone suggest the specs for a modern replacement? Thanks!

janszen_jankit_41_z-600_electrostic_speaker_system_1963_sch.pdf_1.png