The Columbus model 12 was manufactured for Columbus Radio Centre Ltd by Radio Corporation of New Zealand Ltd in about 1940.

The tiny broadcast-only Columbus Model 12

Valves (5): 6K8G, 6K7G, 6B8G, 6K6G, 84

Intermediate Frequency: 455kc/s

Frequency Bands: 1

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

A small 5-valve mantle-sized chassis used in Columbus and Courtenay sets - designed for AC or DC (transformerless) operation (with modifications). Notable for having a very shallow chassis necessitating a riser spot-welded to the back in order to mount the serial plate

RCNZ Model 12 Service Info

1940 Courtenay model 12 Schematic

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.

All documented models using this chassis (2 in total)

1940Columbus model 12 - this set
1940Courtenay model 12