SG2 Standard Signal Generator, manunfactured for servicing Radio Corp sets and most likely found in Columbus Radio Centre service departments. Note the photographed model has had its modulation AF choke removed (Z56 - probably failed in service) and an ECC33 fitted to replace the 6SN7.
RF or AF output, RF able to be modulated to provide tone for IF peaking and dial tracking adjustment.
Schematic has at least one error, showing 6A8 plate and screen joined, which they are not in the one examined example.
General Construction Notes for Radio Corporation of New Zealand Ltd: The first digit of the serial number typically indicates the year of manufacture of RCNZ chassis' (although not the decade - that requires a little knowledge of the valves, construction, etc). Sets from around 1934 onwards were often (but not always) constructed in a distinctive pressed 'baking pan' style chassis, seemingly unique to RCNZ.