[Ron Ramirez]

Let's just repost that modified 38-40 schematic here for clarity.

[Image: https://philcoradio.com/images/phorum/Ph...840mod.jpg]

This mod uses a closed circuit 1/8" (3.5mm) stereo jack instead of an RCA jack. The jack takes care of the switching so you are correct, no additional switch is needed with this design. Just make sure you wire it up correctly.

I believe the 1/8" jack was chosen to not only provide the automatic switching, but also to better match the input from an iPod or other MP3 player. You can also use this to add Bluetooth capability to your radio.