Early 1980's vintage. Unit's case is aluminum with textured green finish. All knobs intact and turn as they should. Ex-military, its purpose was listed as follows: AN ELECTRRONIC DEVICE WHOSE AUDIO FREQUENCY INPUT SIGNALS CONTROL POWER FROM A SOURCE INDEPENDENT OF THE INPUT SIGNAL AND DELIVERS AUDIO FREQUENCY OUTPUT SIGNALS OF GREATER AMPLITUDE WITH RESPECT TO CURRENT AND/OR VOLTAGE. THE OUTPUT SIGNALS CHARACTERISTICS ARE UNIFORMLY RELATED TO THE INPUT SIGNALS. IT OPERATES AT FREQUENCIES OF 20 KILOHERTZS AND BELOW. IT MAY OR MAYNOT HAVE SIGNAL SWICHING CAPABILITIES. I plugged it in and heard slight static through speakers as knobs were turned other than that I have no idea of its working. Inside looked clean (see pics) cord/plug can use a good cleaning. Please look at pics closely before bidding to be sure you want this item. I'm not and electronics expert but this looks like it was a separate unit for larger modular A/V system.   Thanks for looking!