Re-tension Your Tube Sockets
The spring contacts in tube sockets lose tension over time. The main symptom is noise–crackling, static, pops, or hum when you wiggle the tubes.
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.
Great Website and really appreciate the dissemination of great (and correct) infomation. (I know I know, buy something aready!!!!!!;) Believe me I will………..Oh if I might suggest adding info to the “retensioning of tube socket is to also check the solder joints in the pcb to the sockets for cracks, “cold solder joints”. I’ve repaired a couple of these amps with this problem by reheating and adding more solder for better mechanical strenght. People like to “wiggle” the tubes to get a better connection and sometimes are little too robust in their excercise and contribute to a failure of the connection…………You gotta love that DeoxIT, best tool in my kit.
As a matter of fact, this section does mention resoldering the tube sockets. See above.
Thanks for all your info Bill! My BJ was making some awful noise and cooking one of my power tubes. I re-tensioned the socket and everything works great! you save me a ton of money.
Bill,
I’m about to purchase a BJ with your mods already done. It does have the black sockets which I understand can be problematic. Antique Electronics Supply has some ceramic sockets that will probably work. If you were swapping out sockets, which would you recommend?
Bill, I hear a rattle coming from the 12AX7 tubes when the tone is thick with low-mids and bass. It is more of a physical rattle rather than an electrical hum/hiss. It’s very annoying when recording. If I touch the tubes, the rattle subsides. Could this still be a socket issue in that the tube isn’t held firmly and is vibrating? Or could it be the tube guts vibrating?
That’s filament rattle or a loose grid. Your speaker is vibrating the tube; it’s a common failure for tubes in combo amps. You might be able to overcome it for a while with some silicone O-rings to damp the tube, but ultimately, you’ll have to replace it.
I am having the problem mentioned above. I have a Marshall jcm 900 running Groovetubes and the socket is loose. It runs about 10 minutes and goes quiet. If I press down the sound goes up again so I know its a loose socket. My question is should I re-tension the socket while it is “warm”. I see you should do this after the amp discharges, so I’m wondering if thats what you mean. Basically work on it while its warm?
Thanks and great forum.
Jeff
Your problem may be bad solder joints on the sockets, not loose springs in the socket.
To discharge the amp, just turn it off after you’ve been playing it. Leave the standby in “play” position and the amp will discharge itself. Unplug it. After that, you can work on it warm or cold.
Hi Bill. Just finishing up my mods, retentioning my tube sockets and inspecting solder joints. Sure enough V5 had a number of loose connections so I resoldered them. BUT… I noticed the pad of pin 6 raised from the board when the solder melted and figured I’d have to fix this one. Upon inspection it seems that pin 6 does not have a trace connected to it? I’ve been looking at Schematics on line but have not found a lay-out to check for use of this pin. V4 looks the same. Am I correct that it is not in use and I’m good to go? Thanks for all your help.
Right,
Pin 6 is unused. So are pins 8 and 1.