Here is an example of the original grey case Echoplex, the EP-1, which was patented in 1964. It's a very early build, with serial number 957, and with the 'patent pending' label. The EP-2 came in with serial number 1549.
The first 500 units of the Echoplex were sold in 1959, so I am guessing this to be a 1960 or 1961 build.
The unit has been recently serviced, and sounds absolutely amazing! Very low milage, with negligible head wear, which makes the sound bright and 'alive'. Coupled with the original 110volt valve (tube) electronics, this is about as good as it gets! Delay pedals only try to emulate the real thing.
Fulltone now make what is virtually a copy of this unit - in fact, the endless tape loop is a high-quality Fulltone unit.
Sold to John