[Radioroslyn]

>Is B- just the same as the metal radio chassis?
Generally no. To do voltage measurements from the chassis ground to any point on the chassis will not give you an accurate reading. Always measure voltage from B-. If you look at the schematic most sets will have a large paper cap from B- to the chassis, it does 2 things. It isolates any dc voltage from the chassis and provides a rf ground from the chassis back to one side of the ac line. This is why sometimes by plugging the set in the other way around it will have less hum.
> should I plug the signal generator into the isolation transformer as well?
NO! This defeats the purpose of using it. Most just have one receptical for the output. That Viz unit has some outlets that are isolated and other that aren't. The object here is to have the radios ac source coming thru the transformer and the test equipment plugged in to the ac line.