I've got a loaned Joplin amp here and after a few hours use it has blown a fuse. Half a second before it blew, I heard a brief, load hum and may have seen one of the valves flash or brighten out of the corner of my eye.
None of the valves has a short that shows up with a multimeter. Filaments are all fine. I've slipped off the bottom cover and I believe it's a factory build (red paint on all the screw threads) and it looks like a self bias circuit.
Can someone give me a tip on what to check? Cathode bypass caps and coupling caps are the obvious culprits to check. What else should I look at?
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Topic - Joplin blown fuse - jeff mai 02:46:42 10/06/09 (2)