dynaco 120

Hey, guys’ im having a problem with my amp it is a home audio amp but it has been great and its 42 years old. I use it in my home as a test amp to make sure people car speaker’s work. The problem is when I hook it up it doesn’t put out any power it puts out just as much if I had my laptop go directly to the sub from the headphone jack. In addition, if I disconnect the speaker wire the amp still plays music with no speakers hook up to it. It plays the full music to not just a certain note the hole thing its pretty quite but I can make out lyrics and what not. If any one has an idea of what is going on let me know because I love this amp and wont to fix it. Sorry long post. Heres a pic and there is some info on the amp here. http://home.indy.net/~gregdunn/dynaco/components/ST120/index.html