The Columbus model 90 was manufactured for Columbus Radio Centre Ltd by Radio Corporation of New Zealand Ltd in 1942, production ran for 9 years.

The model 90 followed the model 75 as the second high-end bandspread receiver from Radio Corp.  There was some overlap between the model 75 finishing and the model 90 starting - and they were quite similar in chassis appearance although quite different in circuitry. 

Unlike the model 75, the 90 had very few changes over its realtively long life.  Cabinet options were wide-ranging from table-top sets to large statement-piece consoles and radiograms.

Columbus model 90 'Caravel'

Tone Control

The 11-position tone control, the 'Columbus Electronic Ear' as is was known, was an advanced solution to try and help the listener get the best listening experience based on what they were listening to. 

Note: the following feature from The Listener on March 8th 1946 misnames the 'Convoy' cabinet style as the 'Conway'.

1942 Columbus model 90

Columbus model 90 cabinet options


Columbus model 90 details in The Listener, 1946

1942 Columbus model 90

Valves (6 + eye): 6K7G, 6J8G, 6B8G, 6J7G, 6F6G, 5Y3G, and 6U5 Magic Eye

Intermediate Frequency: 455kc/s

Frequency Bands: 5

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

1. Broadcast  (550 - 1600kc/s)
2. Shortwave (6 - 18mc/s)
3. Shortwave (14.85 - 15.73mc/s)
4. Shortwave (11.65 - 12.2mc/s)
5. Shortwave (9.45 - 9.75mc/s)

Note: the capacitors used in the tone cct are oil-filled and are often found to be leaky after all these years, making a mess under the chassis.  They are soldered into cups in the chassis and can be removed reasonably easily.

Sensitivity Tests

Volume control full on.  Tone control position 5.  Sensitivity based on x microvolts input to give 50mW standard output.

Frequency Input To: Microvolts
455kc/s Grid 6B8 5000
455kc/s Grid 6J8 80
1400kc/s Antenna lead through dummy antenna 2.5
1000kc/s Antenna lead through dummy antenna 3.0
600kc/s Antenna lead through dummy antenna 4.0
15Mc/s Antenna lead through dummy antenna 1.5
6Mc/s Antenna lead through dummy antenna 1.5
Bandspread Antenna lead through dummy antenna 1.5

1942 Columbus model 90 schematic

1942 Columbus model 90

1942 Columbus model 90

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.

All documented models using this chassis (2 in total)

1942Columbus model 90 - this set
1942Courtenay model 90