The Columbus model 521 was manufactured for Columbus Radio Centre Ltd by Radio Corporation of New Zealand Ltd in 1956, production ran for about 4 years.

Columbus 5-valve radiogram.  Mono but able to be extended to stereo, possibly using the 'Stereo Pal' or some other second channel extender kit.  Apparently has a 2-gang volume control fitted.

Valves (5): 6BE6, 6BA6, 6AV6, 6AQ5, 6X4

Intermediate Frequency: 465kc/s

Frequency Bands: 1

Chassis Notes(most schematics can be clicked to download a full size version)

1956 Columbus model 521 schematic

1956 Columbus model 521 Oscillator Failure

1956 Columbus model 521 Chassis Notes

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.