5-valve dual-wave radio, referred to in Columbus literature as the "Radio for the Smaller Home". One of a pair of radios in that category release just post-WWII. This is dual-wave version of the model 53 Corvette.
Sighted variants include the 55A, 55R and 55S which appear to use different tuning capacitors and slightly different dial layouts (see photos). The 55R is also noted in service literature as having different tone control circuitry. The 55S appears to have newer and more compact coils.
Original sales booklet for the model 53 and 55 available for download here.
From the sales booklet:
The five-valve radio has held, and will always hold a prominent place in New Zealand homes for the reason that most of our larger centres have excellent coverage from nearby broadcasting stations which cater adequately for the entertainment needs of a large proportion of the listening public.
Therefore, in the knowledge that many people will choose five-valve radio in preference to higher-powered and more expensive models, Columbus has been concerned to provide in its range, two designs capable of superlative reproduction of local programmes but which will, if need be, reach further afield for distant broadcast and shortwave programmes.
In both Model 53 (broadcast only) and Model 55 (dualwave), emphasis is strongly upon quality of tonal reproduction tonal luxury, if you will, at the highest levels that modesty of cost will permit.
To reach this result, modern techniques of tonal control, which hitherto have been reserved for larger and more expensive radio, have been incorporated into these models and this inherent quality of design is further supplemented by the use of an 8-inch high fidelity loudspeaker and the acoustic advantages of substantial cabinet size. It is not usual to-day to find attributes such as these in five-valve radio, but it is precisely from such practice that Columbus is able to derive the undoubted superiority of performance of these models.
Intermediate Frequency: 455kc/s
Frequency Bands: 2
Chassis Notes(most schematics can be clicked to download a full size version)
Service information (RCNZ_-_model_55A_-_5V_DW_AC_-_1946.pdf) here
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.