So today I spent most of the day with one of the professors at my school and he helped me a great deal with my amp. First we build a tube tester circuit to check that the output tubes weren't completely fried. We found that the tubes should be good so we decided to continue with troubleshooting. We then next disconnected the rectifier, pre-amp tubes, and power transformer from the circuit. We then supplied our own 6.3v to the heaters and then replaced B+ with a power supply that we had set to 94v (All voltages were dc). We than measured the voltages at multiple pins on the output tubes. We found that the V5 tube grid, pin 2, was 8v while the V4's grid was .685v This confused us so we unsoldered the jumper from the turret board to the tube socket and the resistance reading read perfect. We reconnected this and the problem was still present. This had us stumped until we went out on a limb and tried removing the resistor and the jumper from the turret board and soldering them in the air. This miraculously worked and we saw milivolts on the grid, however the V4 tube then started to overheat. So we did the same thing and it started to work. We reassembled the amp completely and turned it on. All our reading looked normal and there was no noticeable red plating. There was a noticeable amount of sound coming through the amp with no guitar hooked up. Also if I turned up the normal channel volume the noise clearly got louder. Later when I had a guitar I played it through the amp. It sounded wonderful! I started to crank up the volume until the sound cut out and when I looked up there was smoke coming out of the amp. I didn't catch exactly what had been smoking on the underside, but I believe it to be the tube socket due to some burnt looking plastic. So I think I need a set of tube sockets. I want to get some ceramic ones so I don't have to worry about them melting. Is there a brand of ceramic ones you'd recommend? Also, what's the best way to find my grounding issues? (to eliminate the ambient sound and the sound from the normal channel)
It's almost done, Cooper C
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