Can an audio amplifier amplify DC?
Can an audio amplifier amplify DC?


Yes, I still have (and use) one, the Mitsubishi DA-A15DC (alt link) that I purchased in the early '80s and it's certainly not the only example of one.

It is a Direct Coupled amplifier (hence the DC in the model number) which means it allows DC/0Hz signals and doesn't have coupling capacitors.


  I would like an amplifier that can amplify AC (a square wave at
  ~50-100kHz)


To produce a reasonable square wave at 100kHz requires relatively flat frequency response out to at least 1MHz (probably higher) and that is far higher than any audio amplifier that I'm familiar with.  So, this seems to be the show stopper.