As a post script, and since these units seem to be "in the news" again lately, I'd like to say a few words about the designer of the 250 and 251.
Though EMT was a German firm, they hired an American, Dr. Barry Blesser, to perform the design. At the time, Barry was a professor at MIT. Designing the very first professional digital reverb in the early 70's, with the limited chip technology then available, must have been a tremendous challenge. Barry has told me that he spent much time wrestling with a fundamental problem in digital reverb design -- emulating the 3 dimensional properties that make a room sound like a "room" as opposed to, let's say, a plate.
Barry wrote a landmark AES paper on digital audio in 1978, was involved with the founding of Lexicon, and served as an AES president in 1980.
Here's an archived audio recording of a talk he gave in 2000, at the Boston AES section. In it he discusses the future of pro audio and the impact of fast changing technology on what he calls career "threads". The Q&A session that follows it is interesting too. http://www.dplay.com/aes/blesser.html
Barry is truly a gentleman and a scholar. I have tremendous admiration for him and his work. Isn't it amazing that 30 years later, the 250, with hundreds of discrete logic IC's, no microprocessor, and minimal RAM, is still considered one of the best sounding reverbs that money can buy?