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Tube amp - tube socket problem

Hi fellow tube amp owners. Four months back I bought a used Primaluna Prologue 2 which I really enjoy listening to. I'm the 3rd owner and it was built in 2004. I have a problem with one of the preamp tube sockets. One day I was very lightly dusting the top while it was running. I barely touched the tubes, and I heard a loud pop/crackling noise. Turns out the left side 12ax7 socket is the culprit. In normal operation it's fine, no noise no problems. If I gently wiggle the tube it makes the noise. It then has to be returned to a precise position to return to normal. 

I contacted a local tech who said the sockets can become loose over time and/or get some contamination from the tube pins lodged down in there. He didn't seem too keen on working on it, but said he could try to clean it out. I wondered if there was a bad ground or short, so I opened it up and inspected all the solder joints involved with that socket and found nothing wrong. I don't really want to ship it to have it fixed if I can avoid it.  My main concern is that it could get worse overtime or lose some performance on that channel from not making good contact.

Any ideas? Has anyone had a similar issue? Thanks.
dtapo
tablejockey
3,934 posts
 
Patient to doctor- my leg hurts if I move it this way
Doctor to patient- then don't move it that way.
oldhvymec
5,101 posts
 
Clean and tighten the pin pockets, It’s not hard at all.
YouTube it..

If the noise is still there, you might need to have a solder joint repaired or the worst case a socket replaced..

Regards
millercarbon's avatar
millercarbon
12,531 posts
 
Agree, tweak the pin pockets. There's also some very fine pipe cleaner type wires that can be used to clean inside. Had mine so long, forget where they came from. I would also try and find a wire, same gauge as the tube pins, to slide into each pin pocket individually to figure out which one is loose. If you have an old tube on hand to sacrifice a pin that would be the way to go.
roberjerman
4,319 posts
 
Order a replacement socket from PrimaLuna. Install.
atmasphere's avatar
atmasphere
11,894 posts
 
You don't need a new socket. You have three options.

1) remove the tube and ever so slightly bend its pins inward so it grips the socket more tightly.
2) Remove the tube. Using a tiny screwdriver, work the bit in between the socket contact and the socket material, in such a way that when you tweak the screwdriver, you are able to bend the contact in such a way that it grips the pin of the tube with more force. Do this to all 9 contacts on the socket (unless it uses octal input tubes like the 6SN7, then do all 8 contacts).

3) Remove the tube. Using DeOxit in the red and black can, spray the socket contacts and then work the tube in and out of the socket a few times. Use as little DeOxit as you can- the stuff in the red and black can leaves no residue harmful to high voltage circuits. Do not use any other type of contact cleaner unless you **know** it leaves no residue- otherwise the application can destroy the socket and contaminate the circuit board. Isopropyl works too but is less effective. Dab up any left over liquid with a cotton swab.


Just be patient and take your time.

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