Lancelock mentioned the Altec Lansing 1570B (170 Watt mono). I have a pair of the Altec 1568A (40 Watt mono), also about sixty years old and they sound beautiful.
These Altec theater amps had some of the finest transformers ever put in audio amplifiers but the power supplies were primitive. Tightening up the PS with new, larger electrolytics and poly bypass caps, maybe adding a choke, turned these into some of the finest sounding amplifiers, tube or SS, money can buy -
But not quite up to the level of a (modded) Harman Kardon Citation II (Stereo 60/60), again with superb transformers, probably THE best ever, which I am currently using and which replaced the Altecs.
There’s probably something to be said for vintage Audio Research and Marantz 9’s but those get crazy expensive and I haven’t had them in my system.
I have copious notes on the mods for both the Altec and HK which I’d be pleased to share if you’re interested.
Marc Stager
New York City
https://stagersound.com/silver