At 7:10, attaching a ground lug to a rusty bolt/nut and rusty chassis makes for a resistive ground, and leads to ground loop hum, and perhaps even an ungrounded chassis as the corrosion process continues. The chassis needs to be THOROUGHLY cleaned with sandpaper on both sides where the bolt passes through it, and the bolt and nut should either be wire brushed until shiny or replaced with clean modern hardware. The chassis ground for the terminal strip and filter caps looks far from being clean after a few seconds with sandpaper by hand ---- a Dremel tool and miniature sandpaper drum seems to be in order, and you need to clean both sides where the bolt passes through. The thorniest ground problem with old, rusty amps like this one is that the tube sockets are riveted to the chassis, and the mounting rings for the sockets are used as grounding tie points. The corrosion under these rivets, plus the relaxing and stretching of the soft brass, makes for resistive or intermittent grounds. It truly sucks to have to drill out the rivets and clean the ground points, but they do need to be reworked at some point ( the easier way is to lift the ground wires off of the socket frames and solder the wires *directly to the chassis*). The input jacks will also have a corroded, resistive ground where they bolt through the chassis; its not difficult to remove them and clean everything before reassembling....
At 7:10, attaching a ground lug to a rusty bolt/nut and rusty chassis makes for a resistive ground, and leads to ground loop hum, and perhaps even an ungrounded chassis as the corrosion process continues. The chassis needs to be THOROUGHLY cleaned with sandpaper on both sides where the bolt passes through it, and the bolt and nut should either be wire brushed until shiny or replaced with clean modern hardware. The chassis ground for the terminal strip and filter caps looks far from being clean after a few seconds with sandpaper by hand ---- a Dremel tool and miniature sandpaper drum seems to be in order, and you need to clean both sides where the bolt passes through.
The thorniest ground problem with old, rusty amps like this one is that the tube sockets are riveted to the chassis, and the mounting rings for the sockets are used as grounding tie points. The corrosion under these rivets, plus the relaxing and stretching of the soft brass, makes for resistive or intermittent grounds. It truly sucks to have to drill out the rivets and clean the ground points, but they do need to be reworked at some point ( the easier way is to lift the ground wires off of the socket frames and solder the wires *directly to the chassis*). The input jacks will also have a corroded, resistive ground where they bolt through the chassis; its not difficult to remove them and clean everything before reassembling....
I did enjoy the video!!! Killer