The Columbus model 6 was manufactured for Columbus Radio Centre Ltd by Radio Corporation of New Zealand Ltd in 1946.

The model 6 is a miniature broadcast-band mantle set with an experimental cabinet design.  Available in red, cream, green and brown.

It had a Bakelite front panel, a formed sheet metal cabinet and it was remarkably compact for the time.  The connection between the Bakelite and the metal gave the engineers some trouble until machine screws were added to the front panel with matching welded brackets on the steel housing to allow both to be screwed firmly together.  There was also talk of glue being used (either instead of the studs, or as a supplement), with requests to military aviation companies in the US and UK being made for glue that would bond steel and Bakelite effectively.  It should be noted that it was considered that the glue would probably not be needed once the threaded inserts and associated brackets were implemented, but it shows the lengths RNZ went to in their design process to ensure a robust product. 

The authors own (broken) model 6 shows no sign of glue having been used on what remains of the front panel (although the evidence of spiders is clearly evident!).

And here is a conversation between Alex Marks (the son of the company founder, and a senior manager in the company by that time) in the factory and Fred Green who was the production manager, but on a buying trip in the UK - it gives a rare glimpse into the production process and figures at the time.

21st March 1946, Fred Green to Alex Marks (Fred was in England on a buying trip)

Columbus model 6 'Miniature'

5th April 1946, Reply from Alex Marks to Fred Green:

Columbus model 6 'Miniature'

15th April 1946, Reply from Fred Green to Alex Marks

Columbus model 6 'Miniature'

16th April 1946, Alex Marks to Fred Green:

Columbus model 6 'Miniature'

17 May 1946, Alex Marks to Fred Green on current production

Columbus model 6 'Miniature'

Excerpts from letters from Alex Marks (William Marks' Son) in the factory to Fred Green (who was in the UK at the time securing parts for the factory) about the upcoming first run of the model 6.  Note that in the space of 11 days they had gone from a threaded insert to a molded in screw - which is the final solution they went with.

Initially, 400 were planned, but only 200 were apparently made in that first run.  They were made on and off through 1946 and would not have been released until late that year as the company's production was slowed by staff shortages.  They were certainly released far behind other 1946 models such as the model 14's (Gainsborough and Raeburn).

Its also likely that the first dials were not etched and screen printed as was common, due to staff shortages in that department as well - there is a reference in company letters (see below) to the dials being 'painted' by a new lady (Miss Davies) in the department who reportedly did fantastic work (and based on sighted dials, the author can only agree).  These skilled staff shortages meant that only the higher-end sets were getting etched glass at this time.  The red set shown above (and probably the green) both look to have hand-painted dials, while the later model dial on the authors set (1YA is at the 1948-on frequency) appears to be at least screen printed, if not etched as well, as you can see below.

6th June 1946, Alex Marks to Fred Green:

Columbus model 6 'Miniature'

Authors dial above, red set below

Serial numbers noted:

Red : 61373
Brown : 61435 (Blenheim vintage radio museum)
Brown : 61612 (authors set)
Green : 61743

All sighted serial numbers are within 400 of each other, and this set is seldom seen - which means it is unlikely many were made, or sold.


1946 Columbus  model 6 'Miniature'

This set was also the subject of a YouTube series on re-creating the factory dial.  If you want to follow along in Inkscape to try and make your own version, the dial scan made in the first video is in the images above.

Technical Information

Valves (5): 6K8, 6K7, 6Q7, 6K6, 6X5

Intermediate Frequency: 455kc/s

Frequency Bands: 1

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

1946 Columbus model 6

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.