One day I went to turn on my 1971 Marshall Superlead attached to my 4x12 cab (Stupid me was plugged straight in the wall) and NO RED LIGHT_NO POWER_NOTHING! I did everything I can do without sending it to my repair tech. I replaced the fuse's and pre-amp tubes and nothing. Is it a capacitor? Could it be a minor repair or is it over my head and needs to go to a professional repair tech? PLEASE ADVISE- THANKS!