[Arran]

Mike;
  I noticed something that is rather unusual about the audio output stage in this radio, it has a resistor, a choke, and a capacitor across the primary of the audio output transformer, and on top of that it also has a cap between the plate of the audio output tube and ground. This, combined with the used of what looks like a Rola made loudspeaker, likely accounts for the nice sounding audio. It's curious to me that they would manufacture a 10 tube set, with an FM band, that has a single ended audio output stage though. This was probably why they felt compelled to add the extra tone correction components, in an attempt to eliminate some of the distortion that comes with a single ended stage. Brand Z was a strange company in this way, but at least this model used a proper rectifier tube.
Regards
Arran