COLUMBUS MODEL 6 'MINIATURE' (1946)

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.

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 threaded inserts 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 a 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!).

The first 200 model 6's 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 Gainsborough and Raeburn.

Its also likely that the dials were not etched and screen printed as was common due to staff shortages in that department as well - there is reference in company letters to the dials being 'painted' by a new lady in the department who did fantastic work.  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 here:

Authors dial above, red set below

* Information from letters between Alex Marks at the factory and Fred Green who was in the UK handling the companies purchasing.

1946 Columbus  model 6 'Miniature'
OTAGO DAILY TIMES, 13 NOVEMBER 1946

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).

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).