The Planet was a 5-valve broadcast band Colt chassis in a solid oak (natural or dark coloured) cabinet.
Sales literature and sighted examples show that the Planet was a broadcast only model although in "More Golden Age of Radio", John Stokes refers to it as a dual-wave. It's probable that there were dual wave sets sold in these unusual cabinets as well, although all advertising indicates that these were 5-valve 'Australasian' reception (in other words, broadcast band - it was common to pick up NZ and Australian stations on AM in those days).
The solid oak cabinet was an oddity since most timber cabinets used by most manufacturers used veneer over plywood construction. Being solid timber, it is quite chunky and prone to warping and cracking. It would have been cheaper and easier to produce though.
There was an earlier version of solid-oak mantle design, with a square cutout speaker grill and a slope-back front panel which appears to have been produced between 1954 and 55.
Bell Colts ran from 1951 through until 1980 - the longest running model of NZ built domestic radio. It saw many different engineering changes over the years, and the last few models dropped valves in favour of new transistor technology.
Please note that not all radios shown in this series were known as Colt's - the Planet, the Mercury etc were models in their own right - but they have a Colt chassis in them and so are included here as part of the wider Bell Colt dynasty.