25th Jan 2023, 12:02 pm | #1 |
Pentode
Join Date: Jul 2006
Location: Bangalore, India
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Desoldering
Dear friends
I have been restoring vintage radio sets mostly Philips holland and India since many years. One difficulty which I face is desoldering of the components. In Philips radio sets the wires are put into the lugs and the ends are bent. It becomes very difficult to remove the wire without overheating them. In case a valve base has to be replaced it is very difficult to remove the wires which have been bent. So the only solution remains is to cut the wires and thereby reducing the length. Same problem comes when changing a resistor or a capacitor. Ultimately it ends up in over heating the wires and melting the insulation. Sometimes in each lug there will be two or three wires making the removal still more difficult. The modern desoldering pump is not very helpful. Can the forum members suggest suitable solution to this problem? Regards P.rajan |
25th Jan 2023, 12:26 pm | #2 |
Dekatron
Join Date: May 2010
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Re: Desoldering
It's something we all struggle with to some extent, and it all comes down to the tools and techniques.
Speaking of tools, who remembers, or has still got the red desoldering tool cover gift given with one of the magazines? It looked like a pen, and had an aluminium bit at each end, one pointed and the other slotted.
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25th Jan 2023, 12:46 pm | #3 |
Nonode
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Re: Desoldering
I use a simple desoldering tool “ solder sucker” , see picture, it helps, but it can still be difficult to avoid damaging components. Hope that helps.
John |
25th Jan 2023, 1:05 pm | #4 |
Octode
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Re: Desoldering
Many of us on here will also remember those post-war surplus units, where the original production-line assemblers seem to have been under strict instructions to practically tie knots in the component leads when soldering to tagboards, with leads sometimes wound two or three times through the tags. This made good sense in terms of minimising contact resistance of joints, but made removal/replacement of components an “origami” nightmare. There was also a general dictum that soldering should only be done to a joint that was already mechanically unbreakable (this seems to have been conveniently forgotten when PCBs arrived on the scene).
Mike |
25th Jan 2023, 1:18 pm | #5 |
Dekatron
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Re: Desoldering
Yes, this is always a problem. Sometimes PVC insulation will melt a bit, sometimes it's safer to "give up", use flush cutters to cut the terminal off the defective terminal and then solder the whole lot to the new component.
My current method is: -Use a suitable iron. I love my old Weller TCP which is thermostatically controlled. -Add a little bit of fresh flux-cored solder, and/or some liquid flux designed for electronics (NOT plumber's flux which is corrosive). -Heat the joint and suck off most of the solder in one go, using a solder sucker with a silicone tube tip (which adapts well to the joint). -Use good quality desoldering braid (I use Servisol Soldamop on the red reel) and the iron again, to blot away the remaining solder. -Carefully unpick the wire(s). It helps if you cut through the component first, so that the wire you're retrieving is only attached at one end. Sometimes it also helps to wiggle it while heating the tag, so that it frees itself. Good luck, Nick. |
25th Jan 2023, 1:22 pm | #6 |
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Re: Desoldering
An alternative is to snip off the leads close to the old component. You can then solder the new component to the old component's leads. You have a choice of forming umbrella handles on the old and new leads then interlocking them, wrapping the new leads round the old ones, or for a really good job wrap coils of wire round the overlapping leads.
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25th Jan 2023, 1:30 pm | #7 |
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Re: Desoldering
I saw this tip many years ago and use it on new homebrew stuff.
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25th Jan 2023, 1:41 pm | #8 | |
Dekatron
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Re: Desoldering
Quote:
N.B. The 2-D photo doesn’t do it justice, the new caps are NOT touching the hot resistor, and the bare wires are NOT in danger of touching one another. P.S. if you need to sleeve wires, try to find SILICONE sleeving, as it doesn't melt with the soldering process like PVC can. |
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25th Jan 2023, 1:45 pm | #9 |
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Re: Desoldering
A nice neat job.
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25th Jan 2023, 2:21 pm | #10 |
Dekatron
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Re: Desoldering
Thanks. As I said, it looks much more satisfactory "in the flesh".
I made up the coils using a jeweller's screwdriver as a "former", but I can't remember whether the coils were seperate entities slid over the wires before soldering, or whether I formed them out of the capacitors' leadouts themselves. The sole purpose of the coils is to hold the wires in contact and dead still while soldering takes place. These 1950s Marconis are wired in a "rats' nest" kind of way, so this kind of repair is quite acceptable aesthetically. I probably wouldn't do it on a nice set with neat, tagstrip construction though. Last edited by Nickthedentist; 25th Jan 2023 at 2:27 pm. |
25th Jan 2023, 2:42 pm | #11 |
Dekatron
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Re: Desoldering
With component leads that are tightly wrapped or threaded-through-holes, I generally use side-cutters to cut away as much as possible of the wrapped/threaded-through lead as possible before reaching for the soldering-iron/blunt-seeker/sucker to remove the remains.
I vaguely remember reading somewhere that one reason for the tightly-wrapped/threaded-through-and-bent-over assembly style was that there were often different pay-rates for 'assemblers' and 'solderers'; the solderers being seen as higher skilled and so getting the higher wage. So it made sense to have 2 or 3 lower-skilled/lower-paid 'assemblers' doing the time-consuming bit of fitting parts to a chassis, then passing them down the line to a single solderer to do his [or more usually her] thing with the iron without the time-consuming task of all that wrapping/threading.
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25th Jan 2023, 2:49 pm | #12 |
Dekatron
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Re: Desoldering
When I was at college in the 70s, we were taught that connections needed to be threaded through the holes and bent round for mechanical strength. We would have had our backsides kicked if we'd done it any other way. However, the truth is that it really doesn't mater in the grand scheme of things whether you just snip the component off and solder the new one onto the old solder connection or whether you do the very neat method of the wound coil as shown, which is probably the best method.
I'm not a blanket cap/component swapper, so I can if I want take my time with the solder sucker (and sometimes wick) with fine forceps and long nose pliers, remove all the solder and unwind and unthread the old component wire from the tag. If the area is 'delicate', then for least possible damage risk I'll just snip the part out and solder the new one onto the old solder joint. This type of repair/joint can always be returned to at a later date and done as originally manufactured if need be, and if time permits, so no originality lost, as the repair is reversible for anyone that wants to do it again in the future. In the old days we were always taught that good mechanical strength was important and not to just rely on the solder, hence why you find these connections wound round and through the holes in solder tags - it was the generally accepted method back then. Perhaps some of the thinking was that an overheated component could melt its solder and drop off, possibly shorting out another part of the circuit, if it wasn't securely wound onto the tag - and this sometimes did happen. Certainly when it came to bridging o/c droppers with the RS polo types, securely winding the bus bar tinned copper wire before soldering was essential! |
25th Jan 2023, 2:57 pm | #13 |
Pentode
Join Date: Sep 2011
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Re: Desoldering
If you are replacing a valve base, then when you have removed the solder as best you can, just cut up the tag itself, releasing the wires, and then deal with each wire individually.
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25th Jan 2023, 2:58 pm | #14 | |
Dekatron
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Re: Desoldering
Quote:
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25th Jan 2023, 3:02 pm | #15 |
Dekatron
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Re: Desoldering
Here is a short video on space grade splicing https://www.youtube.com/watch?v=O-ymw7d_nYo
There are other methods apart from the "linesman's splice" though. The other acceptable method is to use a thin wire to lash the ends of the wires to hold them in place while soldering. A bit like Nick's method with the replacement capacitors. Craig
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25th Jan 2023, 3:28 pm | #16 |
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Re: Desoldering
I remember being taught that solder should be treated as an insulator and mechanical contact was important.
Clearly not true as PCB's demonstrated,
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25th Jan 2023, 3:35 pm | #17 |
Heptode
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Re: Desoldering
One reason for the tightly wrapped wires before soldering is that some equipment was tested before it was soldered, so mistakes could be more easily rectified.
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25th Jan 2023, 4:03 pm | #18 | |
Dekatron
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Re: Desoldering
Quote:
Pretty sure it was a PW offering in the '60s sometime.
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25th Jan 2023, 4:42 pm | #19 | |
Dekatron
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Re: Desoldering
Well done Chris, I knew someone here would still have one!
Quote:
I'm interested in this kind of social history. There is a film about the radio manufacturing industry where it's made very clear to the audience that although we can see the radios being made, aligned, and tested by female operatives, we must not form the opinion that they know anything about them. Does anyone know the title of the film I'm referring to? It's online somewhere but I've lost track of it.
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25th Jan 2023, 4:44 pm | #20 |
Octode
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Re: Desoldering
I had been struggling with desoldering for ages, and the desoldering braids I was using were all hit and miss. Sometimes they worked, sometimes they didn't.
Until I found out, mostly by accident, that if you smear the braid in cheap Silverline soldering paste, it'll suck up solder from the joint like magic, whilst also acting as a heat sink. It will totally clean up the joint. In sets with components in hard to reach places I use the Philips method of creating a tunnel with one of the ends, but I prefer a good wrap around joint where possible. |