The Ultimate RBK was manufactured by Radio (1936) Ltd in 1951, production ran for about 6 years.

5-valve broadcast band radio. 

Similar to 6-valve dual wave model RBY

Model nicknames include Sherwood Concord and Tawa

Valves (5):
Early: 6BE6, 6AR7, 6AV6, 6AQ5, 6X4
Late: 6BE6, EF41, 6AV6, EL41, 6X4

Intermediate Frequency: 460kc/s

Frequency Bands: 1

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

Early Model Schematic1951 Ultimate RBK

1951 Ultimate RBK

1951 Ultimate RBK


Late Model Schematic:

1951 Ultimate RBK


Late model chassis - including gram switch and input1956 Ultimate RBK Late Model Chassis inc gram input

1956 Ultimate RBK Late Model Chassis inc gram input

General Construction Notes for Radio (1936) Ltd: Early Radio Ltd. schematics did not show the models, just the year, valves and bands, so some sleuthing is required to find the right one.

Early 30's Ultimate models with three digit model numbers indicated both the number of valves in the set, and the price it retailed for - for example, the model 856 was an 8-valve radio which retailed for $56 pounds. The equivalent Courier models were reversed, so an Ultimate 856 was a Courier 568 (theoretically, at least). This was the Auckland price though, and often the sets would retail for 1 or 2 pounds more in other centres, presumably to cover the freight cost of moving them around the country from the Auckland factory.

Note the use of old resistance terminology on older schematics: ω means ohms and Ω means megohms.

Some 1936-onward 3-letter chassis codes vary the last letter between brands, for example:
BBU - Ultimate model BB
BBR - Rolls (and Golden Knight) model BB
BBC - Courier model BB
All use the same chassis.

Golden Knight, Courier and Rolls appear to use the same copper-painted chassis while Ultimate chassis' are painted silver

After the war a new model code system was introduced, whereby radio models all began with R - the first model being the RA, a dual-wave 5-valve set commonly released in a pressed tin cabinet.

All documented models using this chassis (2 in total)

1951Ultimate RBK - this set
1956State RBK