Just to clarify the sound affect, here's an audio clip of the 'echo', recorded on a Uher 4200 Report Monitor set to Stereo, using 2x Uher M518 mics.
1st radio was an Ekco PT378 Transistor radio, tuned to Radio5 (909) & the 2nd radio was a Dansette 222 Transistor radio, tuned to Radio 5 (693).
Both were in the same room, 3ft apart, one on one arm of my arm chair & t'other on the other arm:
When you click on the link below, it may take several seconds to play
http://www.plunder.com/Ekco-Affect-d...EJ2P7M5W4K.htm