The NZBC model 2839 was manufactured by New Zealand Broadcasting Service in 1955.
5-valve monitor amplifier for broadcast use
Two versions - 2839 and 2839/A (the /A model had a modification to reduce hum - see documentation below).
Chassis Notes(most schematics can be clicked to download a full size version)
Service information (2839.pdf) here
General Construction Notes for New Zealand Broadcasting Service: Exceptional quality equipment