Uploaded December 2019 | Updated September 2026, 1 day ago
Back to troubleshooting this guitar amp. I've had this old tube amp for years, and it always had a problem. It worked fine at low volume, but I couldn't turn it up very far on either channel, before it got to the point where it would break up uncontrollably on louder notes. In the last video, I pretty much rewired the whole amp. Partly to make room to take measurements, and partly to work through the schematic, checking that it was all correctly wired. Also, the lead dress was appalling, and may even be the cause of the problem. I also replaced the filter capacitors, since they were 20 years old, plus however long they sat on the shelf. Now it's time to begin trying to diagnose the problem. I'll begin by simply measuring DC voltage at the filter caps, and by measuring plate, cathode and grid voltages at each of the preamp tubes. I'll also plug in a guitar to record a demo of the problem
Back to troubleshooting this guitar amp. I've had this old tube amp for years, and it always had a problem. It worked fine at low volume, but I couldn't turn it up very far on either channel, before it got to the point where it would break up uncontrollably on louder notes. In the last video, I pretty much rewired the whole amp. Partly to make room to take measurements, and partly to work through the schematic, checking that it was all correctly wired. Also, the lead dress was appalling, and may even be the cause of the problem. I also replaced the filter capacitors, since they were 20 years old, plus however long they sat on the shelf. Now it's time to begin trying to diagnose the problem. I'll begin by simply measuring DC voltage at the filter caps, and by measuring plate, cathode and grid voltages at each of the preamp tubes. I'll also plug in a guitar to record a demo of the problem
