I kinda work on old radios.
Amps need impedance matched speakers.
Quite often transistors go bad and are easy to replace if you can solder.
Look for the transistor on your amp for physical defects.
I don’t really get to do much “work” cause nowadays we swap cards and assemblies instead of component repair.
But it’s pretty simple stuff.
Google the components to see on your amp and how to test them. I bet you can fix it.
And get a speaker with matched impedance. Lots of home stereo equip I remember seeing was 4 or 8 ohm.