That could be anything. Does your jewel light dim when it happens? More common issues could be a cold solder joint, failing plate resistor, or maybe a failing electrolytic cap. Do the ec's have any leaks or bulges? If you don't know how to troubleshoot, a tech is your best choice. I would start with my chopstick. I would also clean and make sure all pretube sockets were tensioned. Clean your pots also.