HELP - new tube amp owner managed to break tube guide pin in socket

Discussion in 'Audio Hardware' started by CraigVC, Jul 24, 2021.

  1. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    Well, my first attempt to remove and reinstall a tube on my first-ever tube monoblock amplifier, resulted in complete failure. See photo below.

    Any advice to help me solve this problem I've gotten myself into, hopefully avoiding having to take this amp in to a repair shop?

    PROBLEM: The plastic guide pin of the tube has broken off into the socket when I tried to reinstall it. :oops:

    I rocked the tube gently to get it out, and it came out easily enough, but trying to put it back in wasn't working, so I (probably stupidly, in retrospect) tried to rock it back in, and that's when the plastic broke off. This tube dates from circa early-1940s, as I best I've been able to find via online research.

    So then (maybe also stupidly?) I got a pair of needle-nose pliers and tried to carefully pull out the broken piece ... which basically broke another little piece of the guide pin off every time I tried, so now I have a plastic baggie of shards of brittle broken plastic.

    These are the tubes that came with the amps when I purchased them used. (This particular amp uses one tube per amplifier.) I was trying to troubleshoot why the left channel amp was quieter than the right channel amp.

    These tubes appear to be RCA VT-231, which according to VT- 231, Tube VT-231; Röhre VT- 231 ID16589, Double Triode is a6SN7GT type.

    The amps' manual recommends: 6SN7, 6SN7GT, 6SN7GTA, 6SN7GTB, 6SN7WGT, 6SN7WGTA, ECC32, 5692, 6180, CV1986, and CV1988.



    [​IMG]
     
  2. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    Also, any guidance on the proper, safe way to install tubes into those sockets would be appreciated. :hide:

    I'm planning to buy a matched pair of tubes to replace these, in hopes that the lower volume in the left channel would be resolved by doing so, and the last thing I want to do is spend money on another pair of tubes that I promptly break in a similar way!
     
  3. Davey

    Davey NP: Celer ~ Malaria

    Location:
    SF Bay Area, USA
    I'm guessing you tried to put it back in without it indexed correctly and so that is why the guide pint is jammed in the hole. If you can't pull it out, then either just break it apart and take out the pieces, or open it up and knock it out from the bottom with something like a chopstick and hammer.
     
  4. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    I checked but couldn't tell that there was any index position for the guide pin. I felt for and visually looked for a groove or slot but didn't notice any. I definitely could have looked more closely though. Now I know there should be one on a tube guide pin, I will make sure I've found it (and the corresponding other groove inside the socket) before attempting any future tube installs. Sigh.

    At least I was able to learn pretty quickly that it's a guide pin with no electronic purpose. Otherwise I wouldn't be able to sleep so easily tonight.

    Thanks for the advice and info. I'll dig back in tomorrow after a good night's sleep. And I'll go ahead and order new tubes... thinking about some vintage Sylvanias.
     
  5. Davey

    Davey NP: Celer ~ Malaria

    Location:
    SF Bay Area, USA
    Well, they usually have an index tab on the guide pin, and the guide pin usually extends below the tube pins. I just checked your link, and it does show an index tab, can't tell how far past the pins it extends, normally you rotate the tube until the guide pin drops in place and then it should easily go in ... you can clean the pins, just use a little paint brush and coat the pins and then install and remove a couple times, or first use some Deoxit, I've done that in the past, but always follow up with some IP alcohol to clean the pins ...

    [​IMG]
     
    Last edited: Jul 24, 2021
  6. vinylontubes

    vinylontubes Forum Resident

    Location:
    Katy, TX
    Did you set the bias to the proper voltage for each of the amps?
     
  7. slovell

    slovell Retired Mudshark

    Location:
    Chesnee, SC, USA
    If you can get the plastic guide pin out you can super glue it back on the tube, just make sure it's oriented correctly. You can compare it to another tube to be sure. The guide pin has no electrical contact. I did the same thing to one of mine several years ago and it's still working just fine.
     
  8. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    The owner's manual for these amps (which is written to cover both the WT100 stereo and WT350 mono variants) mentions in several places that "the tubes do not require biasing":

    This particular sentence stings with embarrassment for me to read, the morning after my error last night that broke the guide pin: "Make sure that they are oriented correctly before inserting them in their sockets."
     
  9. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    Unfortunately, the plastic is so old and brittle that the broken piece of the guide pin has been disintegrating into little shards. So sadly the opportunity to glue two intact pieces back together is lost.

    Anyone else have any clever, effective ideas for me to extract the remaining piece of guide pin out of the socket, knowing that it's old and brittle plastic?
     
  10. Apesbrain

    Apesbrain Forum Resident

    Location:
    East Coast, USA
    You might try approaching it at a different angle: rest your needlenose on the top of the socket with the open jaws on either side of the pin and, without squeezing tight enough to break the pin, try to gently lever it up.

    A very small amount of lubricant applied only to the center pin might help.
     
    CraigVC likes this.
  11. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    So far, "just break it apart and take out the pieces" is the leading strategy for me to try today. I'm mainly concerned that it will work to break off more pieces until getting to inside the hole of the socket hole, then it will become difficult to break off more pieces that are tightly wedged in there.

    Regarding "open it up and knock it out from the bottom with something like a chopstick and hammer" ... take another look at the photo above: The white plastic socket seems to be affixed to a metal riser, which is soldered to the circuit board. So does "open it up" mean - in my specific situation - detatching the socket from the circuit board? I'd be VERY nervous to do that. Unless I'm misreading this suggestion, I am ruling it out for now.
     
  12. Davey

    Davey NP: Celer ~ Malaria

    Location:
    SF Bay Area, USA
    Yea, I forgot they were PC mount sockets so probably no hole in the middle of the board. If you had a bolt of the right size, may be able to screw it into the broken plastic piece and use it to pull out the remainder. Worse case would be to unsolder the socket and then knock it out, or replace the socket while it is off, but that is a much bigger job, and likely beyond what you can do on your own. Hopefully you can pull out the remainder, maybe using two sets of pliers, one on each side. Or maybe around the outside, not squeezing too hard, just try to massage it out.
     
  13. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    Drill a small hole in the center of the plastic, and install a small screw. Pull out.
     
    BeauZooka likes this.
  14. indy mike

    indy mike Forum Pest

    Once the snapped off guidepin is removed. I wouldn't recommend using glue to repair the tube's guidepin - that crack will give way again. There are gizmos called socket savers which you mount to the base of the tube after clearing away the remnants of the damaged guidepin. I use a thin layer of high temperature automotive gasket sealant spread across the saver (keep it away from the holes for the pins to go through), orient the pins so they slide through the saver, seat the saver in place, let the sealant set up and you're good to go. You can snag the sealant at an automotive parts store - the socket savers look like this:

    6 Pcs Vacuum Tube Octal Socket Saver Missing Broken Guide Key Fix Repair Keyway | eBay
     
    Strat-Mangler and Davey like this.
  15. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    Thanks for the suggestions.

    Here's this weekend's plan:

    1.
    I put the amplifier on my partner Sara's desk; she has offered to work on removing the plastic. She's truly brilliant at solving these sorts of challenges, so I have full confidence in her. Even though I'm the audio fanatic in the family, I consider this high-end audio equipment ours because we discovered and fell in love with it together. Plus, she had an early post-high-school job working at an electronics boards fabrication and assembly company, so she had a really good electronics toolkit that includes a variety of pliers, forceps, etc., designed to work with tiny delicate things.

    2.
    Having isolated the source of my "left channel volume is lower than right channel" to the pair of mono amplifiers, I am following my hypothesis that it's specifically a tube issue, and not an issue with some other part inside the amplifier. So I ordered the following pair of vintage tubes from Tubedepot.com:
    Sylvania VT231 / 6SN7GT - 1945

    Ideally, we get this broken piece of plastic out of the socket without any harm to the amplifier, the Sylvania VT231 tubes arrive in a week or so, and I successfully can install both of them without breaking them. And the channel volume issue will be resolved by this.

    Less ideally, all of the above happens, but the lower left channel volume is still an issue. I think if it reaches that point, I'll reach out to repair shops for a diagnosis.
     
    patient_ot and jonwoody like this.
  16. DaveyF

    DaveyF Forum Resident

    Location:
    La Jolla, Calif
    This is exactly the kind of thing that haunts us all with tube amps. The older the tube, the more likely something like this is to happen. I would think the safest and most likely best way to proceed would be to go to a tech and have him remove the socket and replace the socket/remove the broken guide pin. ( BTW the odds of a sheared off metal pin are just about as great ( particularly with small signal/driver tubes), specially if the tube pins are not straight, are gunked up and or have been somehow weakened in the past, all of which IME are quite common!)
     
  17. CraigVC

    CraigVC Senior Member Thread Starter

    Location:
    Portland, OR
    Yeah, this makes me nervous about continuing to go down the vintage/NOS tubes path. I've just experienced how 70+ year old plastic can degrade and become susceptible to breaking like this. And yet I just invested a significant amount of money in another, even more exotic, pair of vintage tubes, chasing that magical 3-D sound that the Sylvanias are touted to have.

    It's probably likely that at some point I'll be getting acquainted with local technicians who specialize in tube gear. Perhaps sooner than later, either for this problem, the left-channel volume problem, or for a general checkup to make sure everything's working in tip-top shape.

    It seems like Echo Audio - Your source for the finest Home Audio and Hi-Fi Audio Equipment , located just a few miles from where I live, is a good place to take tube gear for service/repair.
     
  18. DaveyF

    DaveyF Forum Resident

    Location:
    La Jolla, Calif
    IMHO, with all gear, tube or ss, particularly tube, it pays to know a good nearby tech.
     
  19. Echoes Myron

    Echoes Myron Forum Resident

    Location:
    USA
    I would not open the amp for fear of shock.
     
  20. Blue Devil

    Blue Devil Well-Known Member

    Location:
    Tuxedo Park NY
    Try using a vacuum cleaner.
     
  21. avanti1960

    avanti1960 Forum Resident

    Location:
    Chicago metro, USA
    you got off easy. could have been a lot worse. i would squeeze gently with a set of cable strippers that capture the outer diameter of the pin in its jaw blades while simultaneously prying it up using the tube socket as the fulcrum. gently.
    next time you install tubes have proper lighting to see exactly where the index tab goes.
     
  22. trd

    trd Forum Resident

    Location:
    Berkeley
    Just turn it upside down, the pieces will likely fall right out.

    This happened to me once and I got small tweezers and couldn’t get it. Didn’t use adhesive for fear of leaving behind. I was fairly pissed at myself and trying to figure out when I could get to my tech when i decided to just turn it over. Voila!
     
    patient_ot likes this.
  23. allied333

    allied333 Audiophile

    Location:
    MI
    I re-attach the tube pin with super glue.
     
  24. avanti1960

    avanti1960 Forum Resident

    Location:
    Chicago metro, USA
    another thing to try is to insert a screw that is just bigger than the inside of the pin, get the threads started with a screw driver a few turns, then carefully extract by pulling straight out.

    also- don't let this discourage you! the sound of tube amps make them more than worth their minor foibles.
     
    Ingenieur likes this.
  25. indy mike

    indy mike Forum Pest

    Old plastic/new plastic - both can/will break. Lining up the guidepin so that you're positive the raised guide is lined up with the slot takes care of a primary source of pins getting snapped off. Try not to rock the tube excessively back and forth a lot to pull out a tube from a socket - while you're lifting up, gently rock the tube. I like using a clean cotton cloth (shout out for buying a pack of cotton diapers for this purpose - helps keep finger/hand oils off the glass), don't remove the tube immediately after shutting down, give it cooling off time.
     

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