I found this Realistic MPA-100 at an auction for 9$.
![](https://static.wixstatic.com/media/f7190f_0d5bf7b7255e49fbae652c3940407df2~mv2.jpg/v1/fill/w_598,h_775,al_c,q_85,enc_auto/f7190f_0d5bf7b7255e49fbae652c3940407df2~mv2.jpg)
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..