I bought an Acoustic Research Amp new in 1969. I recently gave it to one of my sons and it is working OK, though probably out of spec given the age of the electronics.
I have an ADCOM GFA1 I bought new in the late 1970s in storage I use for backup when needed.
I have two Carver M 500t amps circa early 1980s currently in service in an office system and in an AV system for surrounds. Both were bought used.
Not to mention more recent buys.