This is old
Tesla amplifier, probably 40 years old, and has nothing to do with JJ, which was born on Tesla ashes after political changes in 1989. Funny coincidence some of audio gear were made within a stone's throw from where I'm typing this right now.
I'm not sure about the particular piece - it looks familiar, but I can't recognize this 6-channel variant. Cyrillic on Tesla gear is unusual too.
In my teens I enjoyed my share of repairing Tesla audio gear from former Czechoslovakia. I wouldn't touch it with 3,048m long pole again. My experience says that electrolytics will be dried out, connectors rusty, switches too, power cable is probably lost and unavailable in your country. PCBs made on cheap phenollic base and probably covered by conformal coating that is hard to solder through and smells absolutely horrific. As I'm typing this, I can still remember that stinch after decade or two. Random resistors may be dead and chassis seems to remember better days too.
50E is way too much, you'll need some more money to turn it into reasonable amplifier, so for PC speakers you better buy something else.