The big faults with the original quads are the conductive coating evaporating over time, the treble panels being overdriven and burned, and the bass panel diaphragm saran getting brittle. If you have a pair of original Quad ESL's, you have at least two of these problems.
With modern quads, it's typically easy to tell if a diaphragm or panel is in need of replacing, because the speaker will make noise when power on but nothing playing.
Sheldon
With modern quads, it's typically easy to tell if a diaphragm or panel is in need of replacing, because the speaker will make noise when power on but nothing playing.
Sheldon