In 1977 band replaced their Binson Echorec 2 units with rackmount digital devices by MXR. MXR Digital Delays were usualy shipped with one 320 ms delay chip while the expansion model - containing four chips - produced up to 1.28 seconds of delay. I don't know about Waters but Gilmour's rig, for instance, included two MXR Digital Delay units and two upgraded MXR Digital Delay System II units working simultaneously, each with the different tap.more
David's MXR Digital Delay rack mount is seen in this photograph from the '70's. "We also have an old MXR DDL digital delay unit built into a rack unit. It has a digital readout, but it's really nowhere close to being accurate. Dave likes it because even though it's a digital unit, it still sounds a little dirty, like a tape unit." - [Phil Taylor, David Gilmour's guitar tech.](http://www.pink-floyd.org/artint/dagear.htm)more
I have several of these units since buying one working unit is as much as buying four bad units. This one is the System I, which came out in 1976, until it was superseded by System II. Watch out as these units can run hot, affecting your delay time!