Re-tension Your Tube Sockets, Resolder Output Sockets
The main symptom is noise–crackling, static, pops, or hum when you wiggle the tubes. The noise is independent of the volume and tone controls. The spring contacts in tube sockets lose tension over time, and the solder joints can crack from expansion and contraction.
This is a particular problem with the output tubes because they run so hot. The heat conducted through the pins is enough to anneal the contacts, so they lose their grip. It occasionally happens to the other tubes, but less frequently. The output tube sockets are also prone to cracked solder joints because of the continual heating and cooling, expansion and contraction.To fix cracked solder joints, just reheat them with a soldering iron and apply a small amount of fresh solder. Take care not to melt the ribbon cables.
Re-tensioning tube sockets is easy. Make sure that the amp is discharged. If you turn it off while the tubes are warm enough so you can play through it, the amp will self-discharge through the tubes. See Removing the Circuit Board for more information.
You’ll need a small jeweler’s screwdriver, typically the smallest that comes in a set. Here you can see the size relative to the tube socket. The socket has a pair of springs in each position. The top of each spring is flared to guide the pin into the socket.
To re-tension the socket, gently insert the screwdriver between the socket wall and one of the springs. It doesn’t matter which spring, but one may have more room than the other. Choose the easiest one. Insert the blade far enough so that the tip is below the flare. Give the screwdriver a small twist, about 1/8 turn. This will bend the body of the spring inwards so it gets a better grip on the tube pin. You want to bend the portion below the flare, not the flare. Bending the flare will not help the tension and will make it difficult to insert the tube later.
You should probably clean the socket and tube pins at the same time. Use a nonlubricating contact cleaner such as DeoxIT 5. Do not use “tuner lube” or a lubricating contact cleaner. The oily residue will oxidize from the heat and cause poor contact. To clean the sockets, just spray the tube pins and insert/remove the tube a few times.
Cracked Solder Joints
The constant heating and cooling, expansion and contraction can also cause cracked solder joints on the output tube sockets. Reseating the tubes might have pushed the cracked areas together, but the expansion and contraction might have loosened them up again. The solution is to resolder the sockets, but be careful. Apply only as much heat as you need and a tiny amount of fresh solder to help things flow.
Don’t overheat the “dots,” the solder pads with no trace. Otherwise, they’ll lift and you’ll lose a bit of the support on the socket. Approach the other pads from the trace side, with most of the heat on the pin, so you don’t lift the pad.
Don’t melt the ribbon cables!