There are many Radios that don't need a hack at all.
I will explain and show you here in this video below. Many old Full size radios ( Table Top Models) have a "phono" input on the back. It was for hooking your record player up to the speaker to get a boost in volume, the same way you hook up an mp3 player to a stereo today.
This is a guitar players GOLDEN TICKET!
It is just like buying a real cool vintage amp,but for just a few dollars....they made millions of old radios, before the internet and TV, every house had several old radios.
Here is a Silvertone, I once had a closet full of Silvertone's, they are some of the most available and best sounding Radios that make guitar amps, watch as I just plug into the "phono" input and play guitar.
watch this Video,