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Cleaning oxidized tube sockets on Fender Red knob twin tube amplifier

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  • #16
    Originally posted by jalexquijano View Post
    This is the socket that needs cleaning and tightening. As you see its a lot of wires to desolder and if i can clean it with deoxit d5 and GUM dental proxabrush it is more practical.
    Same amount of wires as any other 12AX7 socket. Not a difficult job to replace once you are in there, and a much more reliable repair if they are badly rusted.

    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    • #17
      Originally posted by g1 View Post
      Same amount of wires as any other 12AX7 socket. Not a difficult job to replace once you are in there, and a much more reliable repair if they are badly rusted.
      Preamp Tube socket that needs cleaning
      Attached Files

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      • #18
        Originally posted by jalexquijano View Post
        Preamp Tube socket that needs cleaning
        Just a typical Noval socket. Get Deoxit D5 and clean inside of contacts as advised. Also clean tube pins and re-tension socket contacts if necessary.
        I don't understand your problem.
        - Own Opinions Only -

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        • #19
          To follow up on my earlier post:

          I was working on an old Silvertone (which have notoriously shitty tube sockets), and accidentally broke off one of the terminal pins. In the past I would have ended up replacing the entire socket, or cross my fingers and try and solder to any exposed part of the pin which remained. ( <-- but who hasn't done that).
          Fortunately, my boss showed me a trick in how to replace the individual pin terminal using a donor socket. It is really simple, super handy, and works great. You can use this on any of the Belton/Cinch/Amphenol type of 7-9 pin socket - essentially, any of the types you can re-tension.

          Here is a photo of a Silvertone 1474. I broke pin 6 off, flush at the base of the phase inverter.


          .
          .
          I found a suitable donor socket. This one from a NOS 7-pin type.



          To remove the terminal, use a large pair of needle nose pliers, and clamp the jaws onto the terminal as flush to the base as possible. Gently straighten, and flatten the terminal while lightly pulling up.
          (This should straighten out the pin enough to feed it back trough.) Once you've done that, use the pliers to keep the terminal perpendicular to the base and press the pin back through. Like this:






          Insert it into the old socket. Use a small diameter dowel, centerpunch, or whatever tool you have lying around to press fit it in.




          Once you've inserted the new terminal, you may need to use some round nose pliers to re-crimp the pin on the other side, bending it slightly to keep it from being pulled back through. If there is a flange in the center of the terminal, you can use your tensioning needle to flare it back out enough to grip the base and prevent it from extraction.



          edit - correction: looks like the repair was done on the 6CG7 driver stage, right after the 12AX7 Cathodyne PI.
          If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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          • #20
            Just curious, how high are those 1megs? I have a 1472 or 1474 here, somewhere. I have a good pile of NOS carbon comp resistors. I usually don't use them for anything unless i can't find a certain value in metal/carbon film. Some of those dark bodied resistors, even though 20%, read better than the 10%/5% allen bradley types.

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            • #21
              Originally posted by mozz View Post
              Just curious, how high are those 1megs? I have a 1472 or 1474 here, somewhere. I have a good pile of NOS carbon comp resistors. I usually don't use them for anything unless i can't find a certain value in metal/carbon film. Some of those dark bodied resistors, even though 20%, read better than the 10%/5% allen bradley types.
              I don't have the amp to test them at the moment. It belonged to a good friend of mine who passed away of ALS a few months back. I worked on it about a year and a half ago.
              I'm pretty certain that I never measured those two particular resistors. However, thinking back on the work, I have a vague recollection of measuring some resistors(68k? 68Ω... something), and being a bit surprised that they that they had not drifted wildly out of spec.
              But, I'm with you. NOS, or even just OS carbons are a finicky beast. I haven't found a pattern as of yet to try and predict why some, which might look to be high quality and in great shape, will drift way past an acceptable tolerance. Yet, a 60 year old department store Silvertone, with a cabinet that can barely hold it together under it's own sound pressure, has carbon comps that will measure dead nuts.
              Mozz, we get Silvertones in fairly regularly, so I'll try and keep an eye out to make a note of what I find and give you the heads up

              If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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              • #22
                I am not even sure that the resistors seen in the picture are actually CC types, though they look similar. There was a type of carbon film resistors (in the 70s I think, made by Philips) that looked exactly like the ones in the picture: rounded edges, lengthwise center seam, somewhat shiny surface. When you crack them open you might find a slim CF resistor element inside surrounded by mold.
                - Own Opinions Only -

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                • #23
                  Oxidized tube sockets are a nightmare for the amplifier and for the owner, because in most cases the amp behaves unsafe.

                  Cleaning oxidized tube sockets, involves disassembly, desoldering, degreasing and finally scrape the rusted pins.
                  When scraping the rusted pins, pins electrolytic protection is damages, and sooner or later the oxide reappears on the tube sockets. Lots of work with an uncertain outcome.

                  Re-sockets, no matter how is demanding the job, is the only correct job. New is new.
                  It may be slightly expensive option for the owner, but the owner gets the correct amp for the long run and there are no complaints about the job done.
                  A slightly cheaper variant is cleaning oxidized tube sockets in ultrasonic cleaning baths.
                  Who does not know and knows that he does not know - teach him Confucius)
                  Who knows and does not know that he knows - wake him Confucius)

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                  • #24
                    Originally posted by vintagekiki View Post
                    Re-sockets, no matter how is demanding the job, is the only correct job. New is new.
                    It may be slightly expensive option for the owner, but the owner gets the correct amp for the long run and there are no complaints about the job done.
                    A slightly cheaper variant is cleaning oxidized tube sockets in ultrasonic cleaning baths.
                    Replacement, while might appear to be the ideal option, is not always the practical or warranted.
                    Consider as an example, the Silvertone amp in the photos above. Amps built like that one are constructed with many of the component leads wrapped and soldered directly to the socket terminals. Forget for a moment, that unsoldering and moving/removing the components risks breaking or shortening leads making reassembly more difficult. But many of these sockets are riveted to the chassis.
                    Even if they are not, the whole process of clearing the leads, removing the socket, installing a new one, and reconnecting all the components is going to add... at LEAST a 30-45 minutes of labor (but could very reasonably take over an hour.).
                    Is the customer going to go for the cost of my labor in addition to the socket, if it is not a necessity? If so, I'm happy to do the replacement for them; I love doing that kind of work. But we (and almost all other repair shops) have hourly rates, and I'm not doing it for free.
                    Consider another issue: What if the socket is not identical to the original? In the case of many Fender octals of a certain vintage, identical replacements which have the same base diameter and mounting hold dimensions are not always readily available. Plus, if the amp is installed with black phenolic sockets(as an example), and a brown phenolic or ceramic socket were installed, it is an obvious modification to the original and will most certainly effect the value of a vintage amp. Is it perfectly acceptable as a functional replacement? Yes. But I've see replacements that are mismatched that look like shit, and it could be of great concern to many customers.

                    I considered building an ultrasonic bath for just this purpose, and we talked about it in a thread several months back. I think Helmholtz mentioned having one. If I remember correctly, he doesn't use it for cleaning terminals and sockets like this. I can't remember exactly why, but I was dissuaded enough to put aside the idea

                    edit: found the thread.
                    https://music-electronics-forum.com/...cts#post784110
                    (I certainly respect his expertise, but perhaps some experimentation would be warranted to confirm his suspicion before I disregard the idea totally.)
                    Last edited by SoulFetish; 07-26-2020, 08:02 AM. Reason: found link
                    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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                    • #25
                      Ultra-sonic bath would still require all the work, and only solve the issue of hard to find part I think?
                      For myself, when I said these sockets are not too difficult to replace, I was referring specifically to experience with the Red Knob Twin model. The sockets are screw mounted, the wires are not even wrapped at the pins. Very quick compared to many other preamp tube sockets.
                      "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                      Comment


                      • #26
                        Originally posted by g1 View Post
                        For myself, when I said these sockets are not too difficult to replace, I was referring specifically to experience with the Red Knob Twin model. The sockets are screw mounted, the wires are not even wrapped at the pins. Very quick compared to many other preamp tube sockets.
                        You’re right. It still requires all the work. When I was looking into building one (ultrasonic bath), what I had in mind was using it for large multi deck switches end new old stock sockets and terminals I had around. It would certainly take less time to just.transplant each pin, than removing the socket and giving it a bath.
                        i agree with you on the red knob as well,
                        most fender amp sockets are easily accessible, which is nice
                        If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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                        • #27
                          Originally posted by Helmholtz View Post

                          Deoxit D5 is safe on sockets and plastics. But you shouldn't flush the whole socket anyway, just apply a drop to a slim (smallest size for Noval) interdental brush (https://www.amazon.com/TEPE-Interden...451085&sr=8-10 )
                          I just received that package of TEPE interdental circular brushes. Those are really nice! I haven't yet used them, but look to be well made. Thanks for the suggestion!
                          Logic is an organized way of going wrong with confidence

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                          • #28
                            I use wound guitar strings, usually an .026 D string is the right size, like a small round file.

                            Same for cleaning my vacuum desoldering gun.

                            working on an old Sano 50WR, every frickin' preamp socket is oxidized and not making a good connection, it's bizarre!

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                            • #29
                              Click image for larger version  Name:	image_51424.png Views:	4 Size:	57.9 KB ID:	911047 Click image for larger version  Name:	image_51425.png Views:	4 Size:	58.8 KB ID:	911048
                              Cleaning the socket by scraping the rusted socket pins, electrolytic protection is damaged, and sooner or later the oxide reappears on the tube sockets.
                              Just scraping the rusted pins without degreasing the socket body socket is not a job.

                              Since tube socket during operation are exposed to extreme temperature changes, socket pins (red arrow) over time lose their elasticity, so the compound of the tube with the socket can be unreliable.
                              Tighten socket pins do not help because the elasticity is irreversibly lost.

                              I have a habit to tell a user who has brought a messy, neglected amp, that it's time to make amp happy for his birthday. Such as car has servicing on the traveled km, so in the amp must be replaced socket for power and rectifier tubes, because they suffer the greatest strain.

                              When realistic see, cleaning the socket is lot of work with a short-term outcome.
                              Who does not know and knows that he does not know - teach him Confucius)
                              Who knows and does not know that he knows - wake him Confucius)

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