The Aphex Aural Exciter was one of the first exciter effects. The effect was developed in the mid-1970s by Aphex Electronics. The Aural Exciter adds phase shift and musically related synthesized harmonics to audio signals.
There is not much information about these units . . .
But according to Gearslutz - The 602A and 602B units were not commercially available at first, these were rental units only licensed per minute of music, or per year. Later they changed their politics and allowed studios and broadcasters to buy their unit after a 5 year rental period. Not many could afford that; these are very rare.
The 602B originally sold for around US$2700 (approx $11,900 adjusting for inflation)
Apparently the 602B was used on Fleetwood Mac recordings.
If anyone has any extra information please let us know.