The Mullard model 531 was manufactured for C. & A. Odlin Ltd by Philips Electrical Industries of N.Z. Ltd in about 1939.

Other radios based on the same chassis:

5-valve dual-wave set - equivalent of the Philips 155.  Very close to the Mullard 520 and 620 (Also Philips 152 and 153)

Technical Information

Valves (5, with magic eye on some): ECH3, EF9, EBC3, EL3N, AZ1

Intermediate Frequency: 472.5kc/s

Frequency Bands: 2

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

Philips 152, 153, 155 and Mullard 531, 520, 620 Schematic

Philips 152, 153, 155 and Mullard 531, 520, 620 Coils

Philips 152, 153, 155 and Mullard 531, 520, 620 wiring

General Construction Notes for Philips Electrical Industries of N.Z. Ltd:

Model codes are explained on the Philips brand page.  Philips early-mid century were probably the Google of their time - they had branches in many countries and a global brand that everyone knew - and were apparently happy to let engineers come up with new ideas and implement them.  Construction is often overly complex but very well engineered - although repairs can also take a complex path.  They used time-in-motion studies to find the most cost effective way to asemble sets and sometimes this means repairs can be nightmarish (if you've ever worked on a V7A Theaterette this will be all too aparent).  U suffix model numbers are transformerless (hot chassis) sets and great care should be taken, or the sets avoided altogether.

Other documented models using this chassis (6 in total)

1940 Philips model 152
1941 Philips model 153
1941 Philips model 155 'Super Five'
1940 Mullard model 520
1940 Mullard model 620