Thanks for that Tom.
I've been round and round with this a few different ways, with a scope probe, with a coupling capacitor, disconnecting the IF cable from the tuner, and just get no sign of anything.
I decided to take a working set and try the generator on that to narrow down the problem. I'm using a solid-state Sony TV-110. Feeding an RF signal from the Philips generator (a UHF channel 26 aprox), I can tune it on the Sony no problem, so I know the generator's RF output is working.
I've followed the instructions, such as they are, in the Philips manual, for injecting IF, which says to connect the RF lead, without matching transformer, through an isolating capacitor, to the input of the first IF stage, and tune the RF output to the receiver's intermediate frequency, which in this case is 38.9MHz. For reference:
Connecting the Philips generator's RF output to the Sony's IF input, I get no sign of anything on the screen except for some faint snow. Now, I know this IF input is working because I can put the tuner back on it and it works as expected. I have tried using a scope probe on X1 and X10 in place of the generator's RF lead, I have put a couple of different values of capacitor (68nf, .1mf) in series with the input, and sweeping from the bottom of the generator's range way up to the top, there is absolutely no sign of any signal - this is the same behavior on the Philco set that is the subject of this thread.
The generator has two low-band (which include IF) presets, a high-band preset, and two UHF presets. I've tried on both of these low-band presets with the same non-results. The UHF preset, as mentioned before, works as expected.
It is looking to me like maybe the generator isn't working on the low band. Is there another way I'm not thinking of to verify its operation (my scope only goes to 20MHz)? It sucks not being able to trust your tools.
If I'm unable to to verify that the generator is working correctly, I'm thinking about trying to patch the tuner IF output from the Sony to the Philco's IF input. Is there anything I need to keep in mind about that approach? Just strip the ends off of some coax and go to town?
Thanks again to everyone who's been helpful here.