The Columbus model 4 was manufactured for Columbus Radio Centre Ltd by Radio Corporation of New Zealand Ltd in 1952.

A 4-valve broadcast band alarm-clock radio.

1952 Columbus model 4

1952 Columbus  model 4 'Essex'
Dominion, 23rd October 1952

Technical Information

Valves (4): 6SA7, 6AR7GT, KT61, 6X4

Frequency Bands: 1

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

John Stokes wrote a 2-page article in one issue of the NZVRS magazine on the unusual design of this set and how it appears to have been a grafting of two circuits from the Radiotron Designers Handbook, 4th Edition (published 1952) to produce a reflexed superhet.  Its possibly the only commercial use of reflexing in a NZ-built set since the late 1930's when Radio Ltd produced a few el-cheapo 4-valve sets.  The article is available here.  Its possible that this set was the result of the RCNZ cadet program, where young men would be trained to be radio technicians?  Its hard to believe with the in-house skills that RCNZ had that it would produce a set based so closely on someone elses work.

1952 Columbus model 4 schematic

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.