I got a 1993 50 watt JCM 900 SL-X. It works great except for that fact that there is no sound when FX loop is not being used. I currently keep a cable in the loop and it plays fine. Some people would recommend to do that any ways to improve the tone. However, I want my amp to be in proper working condition. Does anybody have any advice about what could be causing this? I am not qualified to do serious amp work, but could this be something minor enough that an unskilled person can fix it on their own?