So, my Marshall JVM 410c lately started making minor crackling sounds before creating a huge pop sound, and the level would be reduced until I changed the channel. This was concerning enough, and I had intended to have it checked out at my local shop, but then it began to hum and then produced the same pop sound last night. Even when I change the channel, no sound comes out now. Is there anyone who knows what's causing this? I'm not familiar with tube amplifiers, so I'm assuming this just means I need to replace a tube rather than the entire unit.
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Thank you for your comments, it sounds like faulty valves, I would suggest it is looked at by an engineer.