This circuit makes use of a mechanical delay line to produce the reverberation effect. This is a '80s setup, showing both channels for a stereo system.
Among the alternative energy sources, one of the most promising is that represented by Astro-Rei....
This circuit is from the 1977 GE semiconductor manual. The components used are uncommon today....
Found in an Electronics World of 1968, this circuit is indicated for applications in photography...