1950 Dumont RA-109 Tuning Issue

[HiFiasco]

Hello! I've been in the process of documenting the restoration of a Dumont RA-109 I found recently. I completed the chassis rebuild without much incident, but was hoping to get some input on an apparent tuning sensitivity issue it seems to be having. I've made a quick video to help show what's happening:

https://youtu.be/r2SW5u6Ezcw


This is what I have:

-The TV tunes in a crisp bright picture with a battery powered pocket signal generator attached, even without a proper matching transformer.

-It won't display as much as snow with an RF modulator attached, even loosely coupled with wires laid on top of one another to try and eliminate the possibility that the signal from the modulator is too strong and throttling back the RF/IF gain. Blank raster only with no sound.

-Attaching the signal generator through the custom RF input cable I made instead of directly to the antenna jack works fine, so there doesn't seem to be an issue with the cable.

-With the signal generator routed through the modulator (modulator off) the signal is greatly attenuated, some picture with light interference.

The set uses the later style Mallory Inductuner without the ceramic shaft.

I feel like I've exhausted all my ideas on how to diagnose this thing. Unfortunately I don't have any alignment equipment handy. Does any one have any ideas or had similar experience with this type of problem?