5-valve broadcast band radio - model 521 is dual wave version.
Photographed model is 501RN with the Radio-Nurse option - this allowed the radio to be used to listen in through a remote speaker - or use the radio and remote speaker like an intercom.
There is also a model 501B, which has an updated valve compliment, detailed below.
Intermediate Frequency: 455kc/s
Frequency Bands: 1