The Ultimate RBO was manufactured by Radio (1936) Ltd in 1953.

6 or 7 valve battery/mains portable broadcast band radio.

Early versions were 6-valve equivalent (selenium rectifier, no rectifier valve), while later models were 7-valve equivalent and used a push-pull output.

Technical Information

Valves (6 or 7 valve equivalent):
1T4, 1R5, 1T4, 1S5, 3S4, Selenium Rectifier or
1T4, 1R5, 1T4, 1S5, DL96, DL96, Selenium Rectifier

Intermediate Frequency: 460kc/s

Frequency Bands: 1

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

Service information (RL_-_RBO_-_6V_BC_AC-Bat_-_1953.pdf) here

Service information (RL_-_RBO_-_6V_BC_AC-bat_-_1954.pdf) here

1953 Ultimate RBO

1953 Ultimate RBO

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.