OTR (Old Time Radio) started fizzling out in the late 1940s when television was launched, but radio didn't go off entirely. There came a post period, which is to say, a middle time (MTR) after OTR but before NTR (New Time Radio), which is today's bland age of corporate schlock. The secret of MTR was to reduce the cast of radio programs to only two people, named Bob and Ray.
A lot of the OTR dramas ran into the early to mid 60s like Suspense and a few others. It took a while for TV to replace it and radio shows ran along side TV shows in the 50s and 60s. Some were adapted for TV shows like Gunsmoke, Our Miss Brooks, etc but I much prefer OTR to TV as you use your brain to create the picture. The CBS radio mystery theatre was created in the 70s by the creator of Inner Sanctum Mysteries, Himan Brown to try to revive OTR. As you know I run OTR shows every night. Yes unfortunately video did kill the radio star.