GULBRANSEN MODEL 720 'CORONA' (1940)

The Gulbransen model 720 was manufactured for H. W. Clarke Ltd by Collier & Beale Ltd in 1940.

Other radios based on the same chassis:

6 valve, with magic-eye tuning, dual wave radio

Almost identical to its successor model from 1942, the 722

It is assumed from the advertising imagery that the 720 has different artwork around the magic eye, and the name at the bottom of the glass, while the 722 has the name in the middle.  If you can clarify this, or have an actual example of this model then we would love to hear from you.

Gulbransen model 720 'Corona'
GISBORNE HERALD, 2 SEPTEMBER 1940

Technical Information

Valves (6 + magic eye):
6D6, 6A7, 6D6, 6B7, 42, 80 and 6U5 Magic Eye (some early variants)
6K7G, 6K8, 6K7G, 6B8G, 6F6G, 5Y3G and 6U5 Magic Eye
Also seen (possibly 722 variant lineup):
6U7G, 6K8, 6U7G, 6B6G, 6F6G, 80 and 6U5 Magic Eye

Intermediate Frequency: 465kc/s

Frequency Bands: 2

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

Service documentation for the model 720 is held, with a note (presumably by John Stokes?) stating that the model 722 is almost identical except for minor valve changes - it's not entirely sure what these changes are, however.

Gulbransen model 720 'Corona'

Gulbransen model 720 'Corona'

Gulbransen model 720 'Corona'

General Construction Notes for Collier & Beale Ltd:

Model numbering followed no real sensible scheme until around 1940 - and prior to 1934 apparently no model numbers were assigned at all.

From 1940 a 3- or 4-digit system was employed where the first digit indicates the number of valves, the second digit is the number of bands and the third is the year of manufacture.  From 1950 the last digit became two digits, eg: 5151 is a 5-valve broadcast-band only from 1951.

From 1957 model numbers were replaced with model names, ie the Pacemaker Buffalo - which makes the year of manufacture hard to determine unless service info is consulted (although C&B often released service info after the radio, and the date on the service info was for its release, not that of the model.

Other documented models using this chassis (4 in total)

YEARMODEL NAME
1942 Gulbransen model 722
1942 Cromwell model 722
1940 ARC-Victor model 720