I found this Realistic MPA-100 at an auction for 9$.
I recently bought this PA amplifier at an auction. Here's an ad from the Radio Shack catalog. I'll take a look at why it was sold as-is and try to characterize its response. My scope has an FFT function but it is not great for measuring response. I think I am going to try trueRTA to check the response curve and see what makes it a PA instead of a music amp..