The Courtenay 5M was manufactured for Turnbull & Jones Ltd by Radio Corporation of New Zealand Ltd in about 1951.
This model is part of the RCNZ Model 5 series of radios.

The model 5M was an updated version of the model 5, using all miniature valves.  The tuning arrangement was also modified to give a better spread of the cluttered upper frequencies. The Courtenay 5M is part of the RCNZ Model 5 series of radios.

The first model 5's appeared in 1950, and the model lasted for around 4-5 years with various changes along the way.  The first model used a mix of miniature and octal valves, but subsequent models used all miniatures.  Externally they all looked much the same aside from the model 5B which had a slightly wider dial scale, and a slightly narrower speaker grill to make up for it. 

By the mid-50's Radio Corporation of NZ was producing new plastic-cabinet radios like the 504 and 565, and this new versatile and colourful material was rapidly replacing timber as the cabinet style of choice - the model 5 being one of the last wooden mantle radios from Radio Corp NZ.

The radios in this series are:
1950 Courtenay model 5 Talisman
1950 Columbus model 5 Bristol
circa 1951 Courtenay 5M
circa 1951 Columbus 5M
1951 Columbus 5A Bristol
circa 1953 Columbus 5B
circa 1954 Courtenay 5B Talisman

Valves (5): 6BE6, 6BA6, 6AV6, 6AQ5, 6X4

Intermediate Frequency: 455kc/s

Frequency Bands: 1

Chassis Notes(most schematics can be clicked to download a full size version) 5M used all miniature valves as opposed to a mix of miniature and GT valves used by the original model 5.  Also had a revised tuning arrangement which spread the broadcast band more linearly over the tuning range.  Used a RCNZ 5" EM speaker.  The dials are plastic and prone to fogging and cracking from UV damage.

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.