COLUMBUS 5A 'BRISTOL' (1951)

The Columbus 5A was manufactured for Columbus Radio Centre Ltd by Radio Corporation of New Zealand Ltd in 1951.
This model is part of the RCNZ Model 5 series of radios.

Miniature 5-valve mantle broadcast band radio.  Its likely that the 5A was the code for the switch to all miniature valves.

Photographed model has an extra knob (the middle one) which is not factory - possibly a home-brew tone control.

Valves (5): Model 5
6BE6, 6BA6, 6AV6, 6K6 or 6V6GT, 6X5GT

Subsequent models:
6BE6, 6BA6, 6AV6, 6AQ5, 6X4

Intermediate Frequency: 455kc/s

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

The model 5 lasted for a few years and was released in four different variants with two valve lineups.  The models were the 55A, 5B and 5M.

The model 5 was originally spec'd to use an octal 6K6** output valve, although its likely that most have a 6V6.  There is also a release note stating it would most likely change to be a 6AQ5 in time.  It also showed an octal 6X5GT rectifier.  All subsequent models have a full miniature valve lineup.  The early schematic showing octal output and rectifier valves has no date or drawing number and may be a lab drawing, or an unofficial release to meet requests from service departments around the country.  A subsequently released 'Model 5' drawing dated August 1951, almost a year after the release note, shows all miniature valves.  Its unclear if RCNZ was referring to the original model 5 or all available variants at that time (although not all variants had the shown loop antenna).

The later versions also had a better spread of the frequency band as can be seen in the comparison photo of the early model 5 dial and the later ones.

The model 5B has a wider dial, with a narrower speaker grill to compensate, and uses a standard aerial coil rather than the loop aerial the other models have.

**Of interest is the valve lineup provided by the release notice sent to Columbus Radio Centres (see below) - the output valve is listed as a 6K6, which may be updated later to a 6AQ5.  The 6K6 is a lesser known cousin of the venerable 6V6 and RCNZ must have had a few of these rarer output valves for them to spec it into the set - although the official RCNZ schematic shows a 6V6GT.  Of course, all subsequent variants of the model 5 used 6AQ5 miniature output pentode.

 

Release notes for the Columbus model 5

1950 Columbus model 5 Schematic

1950 Columbus model 5 later 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.

All documented models using this chassis (6 in total)

YEARMODEL NAME
1950Courtenay model 5
1950Columbus model 5
1951Columbus 5M
1954Columbus 5B
1951Columbus 5A - this set
1954Courtenay 5B