A quite simple old japanese compressor by Univox. For part substitutions (since stock parts is long gone obsolete...) the transistor were a low gain NPN silicon so PN2222 or 2N3903 should work. MD234 were silicon signal diodes so 1N4148s is a near enough sub. The spec of the original vactrol remains unknown so socketing a LED/LDR combo seems to be a wise decision.
Schematic, gutshots and info at FSB.
