The Bell Colt Original was manufactured by Bell Radio-Television Corporation Ltd in 1951, production ran for about 3 years.
This model is part of the Bell Colt series of radios.

The original 5-valve broadcast band Bell 'Colt'. 

Identifiable by having 5 rimlock valves and no chassis model marking.  Ther givaways that you have an original Colt are the round 'ETA' IF coil cans and the code on the rim of the speaker (the last digit of Rola codes was the year of production - 1953 in the case of the photographed model above).  Serial numbers of the original sets are likely to be up to around 1600 (confirmation required).

The next known model, the 5B4, does have its model code stamped on the chassis (most sighted examples, but not all). 

This set was one of the first to carry the Bell name, and the first in a line of Colts that would span almost 30 years and sell in the 10's of thousands.

The red dial is believed to be the first used on a Colt, and was also used on the Rolax Colt, with the Rolax brand replacing the Bell name on the glass (although interestingly it retained the bell logos).  A stylised version was also used on the Skymaster colt, although they were released in yellow and green - with the green retaining the bell logos while the yellow did not.

The Bell Colt Original is part of the Bell Colt series of radios.

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:
1951 Bell Colt Original
1954 Bell Colt 5B4
1955 Bell Colt 5B5
1957 Bell Explorer Colt
1957 Bell Planet Colt
circa 1957 Bell Colt 3B7 Champ Colt
circa 1957 Bell Colt Cadet
circa 1961 Bell Colt All Transistor
1967 Bell Colt 5B67
circa 1968 Bell Solid State Colt
circa 1975 Bell Solid State Colt Mk III

Technical Information

Valves (5): ECH41, EF41, EBC41, EL41, EZ40

Intermediate Frequency: 462kc/s

Frequency Bands: 1

Chassis Notes(most schematics can be clicked to download a full size version) David Clist noted an issue with the tone control circuit producing high harmonic distortion at the full bass position - although as most people never set the tone control here its unlikely anyone would have ever noticed. RJ Hatton notes in his 3-part series on the Colt (October 2004) that 100pF caps in this model could prove to be unreliable and cause a crackling sound (possibly a form of silver mica disease). I.F. transformers are ETA round-cans. These were on early 5B4 models as well.

1951 Bell Colt Original

1951 Bell Colt Original

Other documented models using this chassis (3 in total)

1953 Skymaster Colt
1953 Rolax Colt