[PhilcoPhan1936]

I'm interested in the idea of adding an AUX input into the Philco 40-195 console I'm working on in order to play vintage broadcasts via an MP3 player/cellphone.

At a cursory look I'm seeing a few people discussing wiring a jack into the volume pot. Is there anyone willing and able to give me a nutshell description of how that is (safely) done?

As "Paperboy" mentioned, take a look at a Zenith schematic. Nostalgia Air has all the Rider's scanned. Look for 5S119. It has factory add-on info on the schematic. I know because I have this model and it has the switch and phono input added. Works very well. 

The other option is to get an AM transmitter kit. I have the SSTRAN, and it works great. As long as your AM radio is restored and working properly, an AM transmitter is the way to go. No mods of the radio needed. Just tune it in like a normal station....