Good echo chambers were difficult and expensive to build, especially in urban locations where real estate was expensive and extensive sound isolation was needed to keep out traffic and other noises. Tape loops were sometimes used but they didnt provide the random, complex reflections that were needed to replicate real reverb in an acoustic space. As for springs...well, they sounded like springs.
In 1972, EMT released the very first digital reverb, the rack mount 144. The capabilities of this early unit were limited, and few survive. But just four years later, EMT blew a lot of minds by introducing the 250 Electronic Reverberator Unit. It looked like something from an UFO, and sounded fabulous. A free standing unit, it was three feet tall with black radiator heat sinks on three sides and a large, bright red power supply assembly. On the upper control panel, 4 oversize levers resembling aircraft controls adjusted main delay/decay time, LF and HF decay times, and added delay to the send. The software also included delay, phasing, chorus, slap, and space echo programs. It had one input and either 2 or 4 outputs, depending on the version ordered.
Despite its early 12 bit architecture, the 250 had a beautiful sound. Its design was a joint effort between EMTs engineers in Germany and a small firm in Massachusetts called Dynatron. EMT designed the converters, I/O, and power supply, while Dynatron designed the main digital/processor board. The Dynatron effort was led by Dr. Barry Blesser, then a professor at MIT (and later an AES President). The finished unit had nearly 500 ICs, and 3 cooling fans. To protect its revolutionary design, the part numbers and identification were scratched off most of the ICs on the digital board.
Four years later EMT released the 16-bit 251. Along with a new reverb program and an LCD display, the 251 had extended frequency response, more parameter controls, more programs, and a remote control port -- all in the same striking sci-fi package.The EMT digital reverbs were something else. They were Manhattan projects, the result of intense efforts in a short period of time. Despite their high costs they were very successful, and remain one of the few digital technologies that stand the test of time, for one simple reason the sound.
Though just a few hundred of these old girls were produced, it seems a safe bet that most units are still floating around -- who would throw out such an amazing looking machine? But as 250s and 251s pass the three decade mark, the attrition rate has caught up. Power supply problems, failed capacitors, aging ribbon cables, sluggish fans, dying RAM chips...those R2D2's can develop a lot of problems. Fortunately, they are all fixable and repair is well worthwhile.