I'd like to add a jack line-in to a Panasonic RF-2400 radio.
I'm wondering where I should connect this if it's doable.
There are pictures of the inside in the gallery here
https://www.radiomuseum.org/r/panasonic_panasonic_fm_am_2_band_receiver_rf_2400d.html
Thanks

 

Yes it can be done, Pin 25 is the input for the audio amplifier, try and lift + end of C17 and input a single there.

service manual here...
https://www.manualslib.com/manual/2433910/Panasonic-Rf-2400.html?page=22#manual

 

TS said line-in.
Did he mean line-out?

 

The chip has an internal electronic volume control, so the pot just makes a variable DC voltage. I think you could cut the trace between c16 and c17 to add a line input.

 

"B" is correct in that the volume control is not the audio input point, and will not work that way. Given that the entire radio circuit is contained in one IC device, the actual audio input voltage range is unknown. So while you could make the connection as described, I do not recommend doing it.