I retailed the gear mentioned in the 1970s and early `80s, and still own and respect much of it today. The praise for many of the units mentioned above is deserved, even though I presently also use current Edge, Presence Audio, Manley, Rowland, Audio Note and others. Many of the designs back then were simpler inside (fewer parts), used more point-to-point OFC wiring (less circuit board paths), used less negative feedback, and often bigger power supplies. Maybe those are some of the reasons, but also, perhaps those designers knew more than we realize. And if the caps and some resistors fail- these units are still cheap to repair by any competent repair shop, as most all the parts are readily available.
Best,
Roy Johnson
Green Mountain Audio