[Arran]

I think that the model 91 is pretty similar to a model 90 circuit wise except that it uses 6.3 volt tubes instead of 2.5 volt tubes. The extra band is what they used to call the Police band, the lower end of which is now the upper end of the AM broadcast band so you kind of need it if you want to hear anything between 1500 and 1700 KC. The rest of that band between 1700 to 3500 KC is pretty much a dead zone, I think that WWV is about all you will find.
Regards
Arran