If I did not have bad luck with electronics I would not have any luck at all. So I have a president AX144 radio that has been redone by loosecannon. By the way if not for his generosity I would not have a radio to talk on right now. He placed a relay inside so I could key the lk500. So I finally got to use the lk500 with the radio yesterday everything was working right my SWR on input was 1.1 output SWR the same. Radio keying 4 watts going into the amplifier coming out I was seeing pep around 250 watts from the amplifier. Working very well until today. I always check my SWR first thing before using my equipment. I gave the amplifier 10 minutes to warm up SWR 1.1 input and output I was talking and out of nowhere, I hear this very loud bang. The cover was off the amplifier at the time. I was looking right at the tubes when it happens. Scared the living crap out of me there was no spark or smoke just a very loud bang. No smell coming from anywhere The sound sounded like it came from the right rear of the amplifier were the two tubes are located? Could one of the 3-500ZB tubes have gone bad? Do they make that kind of sound when they do go bad? Please, I really could use help on trying to figure out what happen to the amplifier. From what I can see there are no parts that look burned. Everything looks normal. The tubes were bought last year on 06/19/18 from K5SVC US government surplus as a matched set. 73,