I found this thing on e-bay some yrs ago and it still works. It is a 4 channel unit with High, Med High, Med, and Low with the ability to set the response rate. I know a little about the unit because the builder put the info inside as to who it was built for and when. It was built in 1974 for a club in LA. It works great and will handle up to 1k watts per channel. It has a big heat sink inside and a small fan. Here are s couple of pic's of it.
I know it dates me but I can remember when there was a complete wall of these at DisneyLand in the America Sings building that they used to entertain the people before the show started. It was quite something back then.
Steve Wall