The Columbus model MC7 was manufactured for Columbus Radio Centre Ltd by Radio Corporation of New Zealand Ltd in 1947.

5-valve vibrator-powered broadcast-band car radio.

The MC7 was released for the 1947 season and advertised heavily.  At that time the fledgling Auckland-based 'Autocrat' was the only other company in New Zealand who were producing automobile radios in any quantity.  None of the major radio manufacturers had stepped into that market, and no doubt Radio Corp saw this as a great opportunity with profit to be made.  They were probably correct, but the MC7 would not be the success they had hoped for.

According to John Stokes in his 'Golden Age' books, the MC7 was not (even close to) the best of designs and it seems he was not a fan. 

If any manufacturer had tried to make every mistake possible in the design of a car radio, then Radio Corp did just that! The disastrous MC7 represented the company's only venture into the car radio field, a great blessing for all concerned.

John Stokes,The Golden Age of Radio (p.65)

Some units, designated MC8, have been sighted, although it is the authors understanding these were 1948 updates, but essentially still an MC7.  No reference information (service, advertising or otherwise) has been found for that later model code.  The MC7 model name continued to appear in advertising until at least 1950. 

Whatever the model code, this was apparently the first and last ever automobile radio they produced**, although it was still being actively advertised for sale nationally until the end of 1950 - so it was not short-lived for all its alleged faults.

1948 Columbus MC7 'Car Radio'
Upper Hutt Leader, 6 November 1947

** There was possibly a model 506 and 512 (6 and 12V respectively) auto radio in around 1955 - the author has never seen one although Ken Duncan, a Radio Corp trained serviceman who ran the K-road Columbus Radio Centre in Auckland, had made several notes in his service documentation including a hand-drawn layout of the chassis and an RCNZ memo on replacing a coil unit for better signal-to-noise and sensitivity.  Has anyone seen one of these?  Please get in contact if you have.

Technical Information

Valves (5): 6K7, 6K8, 6K7, 6Q7, 6V6

Intermediate Frequency: 455kc/s

Frequency Bands: 1

Chassis Notes(most schematics can be clicked to download a full size version)

Power supply in a separate cabinet to the radio, with a 4-wire harness running between.

1948 Columbus MC7 'Car Radio'

1948 Columbus MC7 'Car Radio'

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).  This suffix was used in the mid 50's when Radio Corp was changing over.

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)

In 1954, model numbering changed, to begin with the number of valves (ie: 501 - 5 valves, 1006 - 10 valves, etc) although the final 2 digits don't appear to have much significance.  Middle digits of 5 (portable) or 6 (mantle, including clock radio) are used on the AWA-designed plastic-cased sets.