The Bell Solid State Colt was manufactured by Bell Radio-Television Corporation Ltd in about 1967.
This was the second transistorised Bell Colt, although the first mains-powered model. The cabinets appear to have been 'tweaked' at this time as well - with the grill moved forward slightly and reinforced, as well as a slight change to the horizontal stripes where they meet the grill area. Also there are holes in the rear to attach a back panel. Later, speaker mounting holes would appear behind the grill as well.
Manufactured by Consolidated Audio Ltd - most likely a branch of Consolidated Industries Ltd - a joint venture between Bell and Dominion Rado and Electrical to gain better purchasing power and make better gains in a competitive market with the onset of colour TV.
Early examples had a plain back panel with a warning label, while later models got a nicer printed panel and the chassis got aerial and earth terminals as well. It's possible that this later version is the Mk II since the next (and final ever) model has Mk III on the back panel.
Chassis Notes (most schematics can be clicked to download a full size version): Appears to be a standard almost blank chassis, with the circuit board mounted to an upright bracket.