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Hi, I have the above mentioned amp that has a problem. I have not used this amp for quite some time. Recently I turned on this amp to test a friend's guitar. I was testing for about a few minutes, when suddenly, a loud blarring and irritating sound started coming from the amp. It was only this sound and nothing else is coming from the amp. I tried turning off the channel and master volume but this sound is constant. After unplugging the guitar, I turned off the amp. After a while I turned on the amp and tried with my guitar with about an hour and it was fine. The following day, I tried with my guitar and after about an hour, the blarring sound came back again. This time I unplug the speaker connector and after about 2 to 3 secs, I plugged in back the speaker connector. The blarring sound was not there for a while and then came back again. This time I off the standy switch and on back again. Again it was OK for a while and then the blarring came back. Whenever I knock on the chasis of the amp, there is a crackling sound and when I knock hard the constant blarring sound comes on again. I started tapping on the 2 preamp valves and it was OK, When I tapped on the first power valve, it was OK but when I tap the second power valve, there is some crackling some from the speaker, I suspected the holder of the power valve could be loose. so I took out the valves and inserted the first valve onto the second holder and the second valve onto the first holder. So I tapped the now first valve and there was still the crackling sound, the other one was OK, So I concluded that it was not the holder but the valve itself. I thought there could be a dry joint somewhere, so I resoldered, the front board, the main board and the DSP board, but the problem is still there. I am wondering what could be the problem, could it be the crackling valve, the main board or the DSP itself. This problem is not consistent. After the earlier incidents, for the past 3 days it seems to work OK but the crackling from the same valve is still there. Could someone please advice. Thanks Carlos