The Columbus model 91 was manufactured for Columbus Radio Centre Ltd by Radio Corporation of New Zealand Ltd in 1950.

Other radios based on the same chassis:

Third of the 'Big Bandspread' models, in console form.

The Model 75 was the first in 1940, the model 90 was the next, in 1948 and this models big improvement was push-pull output, perfect for high output.

Some of the big console-model 91's came with a beefy Goodmans 12" speaker, but most had an electromagnetic 10" speaker (the 91P had a permanent magnet 10" speaker).

The Listener 8 May 1953

Technical Information

Valves (7 + magic eye): 6SK7, ECH35, 6B8, 6SL7, 6V6, 6V6, 5Y3 and 6U5 Magic Eye

Intermediate Frequency: 455kc/s (to be confirmed)

Frequency Bands: 5

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

Notes on service material suggest HT is too high and to insert a 250Ω 10W wirewound just prior to the reservoir cap / field coil junction to drop the 300V to around 260V.  Also use 5V4 as 5Y3 is possibly stretched in this role.  Other notes on the schematics in the service PDF - some are difficult to read.

Service information (RCNZ_-_model_91_-_7V_PP_AC_-_1950.pdf) here

This schematic may be an original draft - the initials on the torn corner suggest possibly Victor Marks (son of the company founder, Wiliam Marks) may have drawn or checked this one.

Columbus model 91 'Windsor'

And this one is the factory-released schematic

1950 Columbus model 91

1950 Columbus model 91

Columbus model 91 'Windsor'

1950 Columbus model 91

Columbus model 91 'Windsor'

Columbus model 91 'Windsor'

Tone control wiring notes (probably by Ken Duncan, K-Road Columbus Radio Centre, Auckland)

Columbus model 91 'Windsor'

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.

Other documented models using this chassis (4 in total)

1950 Columbus model 91 'Windsor'
1950 Courtenay model 91
1950 Columbus model 91 'Flotilla'