The EMT 140 echo plate was the standard reverb unit used in most professional recording studios and broadcast establishments since the 1960's
They are large, over 2 metres long, heavy, need to be isolated from loud sounds and only have one sound yet despite the efforts of many software designers working in various recording effects manufacturing companies it cannot be beaten for sound.
In its simplest description an EMT 140 consists of a mild steel plate connected to a metal frame and kept under tension, there is a driver in the centre ( imagine a loudspeaker with its paper cone removed ) also there is a pick up at each end, there is also a damping panel the same size as the plate which can be moved nearer the plate to shorten the decay time or moved away from the plate to lengthen the decay time, this all goes to provide a mono in stereo out superb reverb effects unit adjustable from 0.5 second to 5 seconds.
It sounds so simple which makes one wonder why studios do not make their own, there is nothing to stop this as the patent expired in the 1970's. Many have tried and many failed, in conjunction with bel electronics we made a couple in the 1970's and they sounded awful. Apparently the engineers at EMT used to visit their local steel foundry to select the steel sheets which may be the reason why they are superb sounding reverb devices.
This one comes with a remote control and motor to allow the decay time to be adjusted remotely, it came from one of London's premier studios and would have been used on many UK hits recorded n the past 30 years.