The cadet is a budget permeability-tuned 3-valve model - easy to spot because in place of the usual tuning gang are two metallic tubes.
Estimated introduction date - 1957
This appears to have been followed by the Champ, also a 3-valve but with a traditional tuning gang.
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. There is considerable information on the main Colt page about this Kiwi icon.
The radios in this series are: