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 first model 5's appeared in 1949 (although the model is widely accepted as being released for the 1950 range), and 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 maintain the correct width for the model 5's cabinet.
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:
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.
Model codes beginning with a 0, for example the model 051, are Osram valve versions of the model without the leading 0. Technically the 0 should be an O (for Osram), however the digit 0 was used throughout the site before this fact was discovered.
The E suffix indicates a magic eye option is fitted (in models which were available with or without, such as the model 25).
A and B suffixes appear to be simply updates to the current model, R also appears to be simply an updated model ('R'edesign, perhaps?)
P indicates either a permanent magnet speaker version of a model which also came with an electromagnet speaker (the model 26 for example), or a portable model (like the model 694P).
N and M indicated miniature valve versions of a model which started with all (or a mix, ie: model 5) of larger valves. One of these two codes may indicate a transitional mixture of octal and miniature - clarification is required.
S often indicates a stereo model. It can also indicate 'self-biased' in the transition period between back-biased and self biased sets where there were models with both methods employed (53S for example)
Finally, other suffixes and prefixes make occasional appearances in the RCNZ lineup - like the 66W (a variant of the long-running model 66) and the 75XA (a 10-valve version of the model 75 with a separate amplifier chassis).
Model nicknames are often sourced from either newspaper advertising, company literature or the NZ Radio Traders Federation official trade-in price books (Particularly Courtenay models from this publication)