Question, at a certain stage where he was testing the tone could be heard, but there was mixed in static/background noise. Would that stage still be considered fine, as long as you're hearing SOME of the generated signal at least?
In this particular case that would be true. By this I mean, if you had a dead radio and at least some signal was getting through then that stage at least is not killing everything. In this case his test lead was acting as a bit of an antenna and picking up stray noise and feeding it into the receiver along with the desired signal.
As a general rule, the farther back you go in the radio the less signal should be required from your signal generator to get suitable audio output. This is because you are getting more and more amplification as you work your way back through the radio stages. There are exceptions to this particularly for transisitor circuits (it's a weird impedance issue), but for tube circuits it is a pretty safe assumption.