cold solder joint ?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by cbnutt, Apr 21, 2016.

  1. cbnutt

    cbnutt Member

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    Early 70,s Deluxe Reverb , about any where I tap or hit the amp I get crackling , static noise , top of cab , on chassis etc . sometimes when playing , most likely a solder joint ?? thanks .
     
  2. zenas

    zenas Member

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    I look for a microphonic tube first.
     
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  3. cbnutt

    cbnutt Member

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    that would be more of a squeal , this is crunching , crackling ,
     
  4. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    Not much use to talk about 'em, you just have to get in there and find it. Usually you can poke your way into finding it with a chopstick. One thing to be aware of though, some cold joints only act up if they haven't been messed with much. For instance, assume the lead of a resistor has fractured loose from the solder blob in an eyelet. It over time acquires a slight oxide coating and starts acting up intermittently. If you agitate it too much during the troubleshooting causing the lead to move inside the solder blob and scrub away the oxide, it may start behaving itself (and be tougher to find, if you didn't find it before).
     
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  5. tresspassor

    tresspassor Member

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    It could be a number of things. Bad tube, loose or oxidized tube connector contact, bad plate resistor, bad solder connection, etc. I would start by rolling tubes and cleaning the tube sockets since you can do that while the amp is assembled. Tubes can crackle, pop, crunch or squeal depending on their mode of failure. After that, you'll have to open up the chassis and start chop sticking (Only if you know what you are doing!), or take it to a tech for service.
     
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  6. cbnutt

    cbnutt Member

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    ill try my old tubes first , "guessing" its not that as I put in some NOS from KCA awhile back, but of course its possible .
     
  7. swiveltung

    swiveltung Member

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    It can be a tube... they don't just squeal. This is one of the harder things to diagnose. I had one that drove me crazy late last year. It would come and go. I finally did like a 4th chopsticking on it. The whole board had some noise, some caps were noisier than others. I'd replace a cap and play it for an hour or two, think it was fixed... then it would start again! I ended up resoldering the whole board. Finally I was chopsticking, much of it was microphonic or crackling this time. When I hit one tab on the preamp tube socket it got really loud crackling. I had to look at it with an eyeglass... the wire would move just slightly in the glob of solder.. to the eye it looked perfectly soldered. resoldered that tab.....that was it!
     
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  8. kjt1776

    kjt1776 Member

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    V1, first pre amp tube closet to guitar input
     
  9. VaughnC

    VaughnC Supporting Member

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    Yup, this is one of the things I try to warn people about when they build their own amps and don't wrap & crimp terminal connections before soldering. In electronics school, they taught us that solder should be used to stabilize a connection, not make the connection. You need a good electrical connection first. I've found this issue in many vintage Fender amps...wire would just pull out of a solder connection after years of heat/cool cycles. Wouldn't have happened with a proper wrapped/crimped connection.
     
    Last edited: Apr 23, 2016
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  10. UsableThought

    UsableThought Supporting Member

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    That rubric has it backwards. There may have been a pedagogical reason your teachers put it that way, but the resulting inaccuracy is less than helpful for beginners learning to solder in today's world, where point-to-point is a rarity & even through-hole is losing ground.

    Consider surface mount components, or through-hole PCB mounting where the lead goes through a hole but is never crimped or wrapped. Solder is all that's needed for an electrical connection. Of course SM are very light so need little support. But even very large filter caps mounted to a PCB often do not have their leads crimped in any way. Instead, a solid mechanical connection is created via glue or goop. This keeps the solder joints from being stressed, and once again has nothing to do with the electrical connection as such.

    Turret or eyelet or similar point-to-point connections, because of their quasi-suspended nature, certainly do require a solid mechanical connection to avoid stressing the solder joint - and that is one thing wrapping & crimping provide. If that were all that was necessary for an electrical connection, such joints would then not be soldered - much as nut-and-bolt chassis connections may be left unsoldered. In addition to long term mechanical stability, another benefit of wrapping and crimping for terminals or indeed all hardware is immobilizing the joint so solder will set properly - thus minimizing one of the causes of cold solder joints.

    To sum up, you're right about the necessity of crimping & wrapping where appropriate, but the electrical connection this provides is mostly incidental; the real contribution is mechanical. My guess is, your teachers put the order in reverse as a kind of EE judo - a trick to get students to make something tedious into a priority, rather than slough it off.
     
    Last edited: Apr 23, 2016
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  11. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    That's one thing turrets have going for themselves over eyelets -- you can wrap a turret, but you can't wrap or crimp an eyelet connection.
     
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  12. damian1

    damian1 Member

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    Not to mention it is a MAJOR pita to ever change a component when they are wrapped and crimped all to hell. I have a couple true point to point vintage amps and they are the worst to work on. I'd take working on a pcb all day in comparison.
     
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  13. paulg

    paulg Supporting Member

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    A proper soldered connection requires metal to metal contact. The solder flows between the connection and creates a "new" metal. This provides the best electrical transfer. Using solder as "glue" may work but it's not the correct way to make a good connection. Fender amps with eyelets are not the best by a long stretch. I don't think that method was ever "mil-spec". Turrets were in their day because of the metal to metal contact.
     
  14. zenas

    zenas Member

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    I don't know maybe tag boards suck. But judging by the 50 year old Fenders I see thay don't really suck too bad.
     
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  15. UsableThought

    UsableThought Supporting Member

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    New metal? See Wikipedia:
    EDIT: But also see John Coloccia's comment which follows - he agrees w/you that there is something like this at work and adds supporting detail. I should know better than to trust Wikipedia too much.

    As for what is "proper," think "best practices" instead. If the problem is "how do we solder a PCB so it will last," we can't be saying there has to be metal-to-metal. See the videos in the Mega Soldering thread posted by @John Coloccia, over in the luthier's forum.
     
    Last edited: Apr 24, 2016
  16. John Coloccia

    John Coloccia Cold Supporting Member

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    Both descriptions are accurate, believe it or not. Melted solder acts as a solvent. Tin is especially good at dissolving other metals. At the interface, you do actually get a new alloy even though the base metals are well below their melting point. Ideally, there's intimate contact between the two surfaces you're joining, but for through hole PCBs it doesn't really matter IF your joints meet some basic standards. The joint will actually be much stronger than the through hole because of the huge surface area and the geometry of the joint. With a typical surface mount device, it's far more critical that you have a very good joint as it's very easy for the joint itself to be the weak link.

    When you need a lot of mechanical strength from the joint, it becomes important to have the pieces you're joining in very close contact with each other because the solder itself is very, very weak. Building cables comes to mind. If you want them to last a long time, you need to do a good job of properly dressing and preparing the ground connection as you actually get a good bit of strength from there and it needs to be rock solid.
     
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  17. UsableThought

    UsableThought Supporting Member

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    Thanks - I learned something new. I'll correct my earlier post.
     
    Last edited: Apr 24, 2016
  18. J M Fahey

    J M Fahey Member

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    FWIW metals dissolve into each other well below the melting point of at least one of them, no need for both to be liquid by any means.
    In a particular case, naked (bare copper) soldering iron tips dissolve in solder wire tin and quickly (just days) develop huge "cavities" , it was a nightmare in my early days (late 60's , early 70's), also including Fender, Marshall and anybody else, nobody was free from it.
    [​IMG]
    So much so that a coarse file or a rotary grinding stone was a standard part of any Tech bench , or even hobbyists, to keep soldering iron tips in proper shape.
    Then of course, iron coated "ceramic/long life" tips were developed.
     
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  19. zenas

    zenas Member

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    Interesting thread.

    I wonder if the OP has had any luck with his amp ?
     
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  20. paulg

    paulg Supporting Member

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    I wonder if the solder they use in wave construction for pcp and surface mount is specially formulated so the metal to metal connection is not necessary.
     

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