Desoldering

[Station X]

I have to confess to melting solder joints with an iron and then blowing away the solder with a jet of compressed air. It leave joints very clean.

Of course it leaves "granulated" solder everywhere, but it's easily cleaned off.

[Katar83]

Well, that is something I've never heard off or even considered

The only method that works for me is desoldering wick, excess removed first with a pump, etc then wick to finish it up and free the wires. I only use the blue case soldering wick, called chemwik or chemtronics, I've tried many over the years and only these are good.
I've got proper soldering station here so not a problem with overheating pads but for old radios tend to use a proper transformer soldering gun with a thick copper tip as its just quicker.

[Herald1360]

Originally Posted by Gabe001

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.

The flux embedded in desoldering wick loses its efficacy with time, even the "good" stuff.

I keep one of the flux pens handy and run it over an inch or so of my mostly time expired wick to restore it to" fresh out of the pack" performance when need to deal with the odd old joint. Works almost as well with plain/tinned copper braid from old coax too.

Any old flux paste will work but if it's not electronics grade it may be corrosive

[John10b]

Graham, like Katar83 I have never come across that technique before, obviously if it works for you so be it, I would be concerned with the bits getting everywhere, and causing problems down the line, so to speak.
John

[G6Tanuki]

Must admit, I've never been happy with "Desoldering braid" - you need to whack rather more heat into it than I am happy with, and I've seen too many cases where it's stuck to and lifted away PCB tracks.

A *good* solder-sucker has always been my preference. Get used to replacing the nozzles, sometimes every couple of days in a 'production' environment.

[Nickthedentist]

Originally Posted by Station X

I have to confess to melting solder joints with an iron and then blowing away the solder with a jet of compressed air. It leave joints very clean.

I've not heard of that, but I have resorted to getting joints hot, then turning the chassis the right way up and slamming it hard onto the bench, to dislodge most of the solder.

Look after your eyes when de-soldering: the plunger handle of unshrouded desolder pumps can poke you in the eye. And don't do what I did as a child while desoldering some co-ax from a CB aerial plug and hold it up to the ceiling light to see whether the central pin was clear of solder. It wasn't, until a large ball of molten solder dropped out, missing my eye (and head) by a couple of inches.

[Station X]

Originally Posted by Nickthedentist

Look after your eyes when de-soldering: the plunger handle of unshrouded desolder pumps can poke you in the eye

In my case it generally hits the underside of the bench magnifier!

[Lucien Nunes]

With the usual situation of a solid component lead pushed through a tag, if I want to save both the tag and the full length of the wire, I remove the bulk of the solder and then tease the wire out without necessarily keeping the solder molten throughout the process. Solder is very weak and the wire can be prised free from a thin film of it when cold, using a pair of fine needle-nose pliers, a small flat screwdriver blade and a mounted needle / dissection seeker.

If I want to preserve enough of the lead to remake the joint, but not necessarily wrap it fully around the tag again, I locate the point where it emerges from the first pass through the hole and cut it in situ with pointed flush cutters, along with any adhering solder, then cut through the detached wrapped section to enable it to drop off the tag when heated.

Regarding the merits of a secure mechanical joint, the main advantage is to make the solder interface as large in cross-section and as small in path length as possible, to reduce the tendency to embrittle and fatigue especially in the presence of vibration or heat. For static equipment like a domestic radio it's really not very important, but where there is movement, even of small amplitude, avoiding forces transferring via the solder can improve reliability.

[emeritus]

I was taught on a workshop course that old solder is often difficult to melt because copper progressively diffuses with time from the leads and tags into the solder, thereby raising its melting point significantly. That is why applying fresh solder, preferably tin/lead, can help on really old equipment. The solders used during the 1940's had less tin than the usual 60/40 stuff to conserve supplies of tin, so had a higher initial melting point anyway.

[prajan]

Dear friends
Thanks everyone for the reply. One thing I would like to mention here that the amount of solder to be sucked when we are working on PCB is very less so a normal desoldering pump works very well but when the same pump is being used to suck the solder from the connector strips, valve bases, various other components of vintage radios , the quantity of the solder to be sucked is more and here the normal desoldering pump fails. Is there some other electric desoldering pump available which can suck out larger quantity of solder?

Regards
P.Rajan

[davidw]

Originally Posted by Station X

I remember being taught that solder should be treated as an insulator and mechanical contact was important.
Clearly not true as PCB's demonstrated,

I suspect Graham and I were taught at the same place -Bletchley Park POTs training school- late 60s in my case where I remember being told a joint should be mechanically and electrically sound before it is soldered.

[David G4EBT]

When I need to replace components attached to valve-holder tags, for some years now I've snipped off the old component leaving about 1/4" of wire attached to the tag, then coiled the wire on the end of the new component and soldered it to the remnant of wire, leaving the tag undisturbed.

To try to unsolder wires on thee rather fragile tags of B7G B8A and B9A (Loctal) valve-holders is just inviting trouble.

On the tagboard of the Bush DAC90A, (sorry - I'll put some money in the swear box!), the solder tags are doubled-ended, with the inner ends flat and disused from new. The old capacitors can be snipped off the outer end of the tags, the flat inner ends of the tags carefully bent upright, scraped clean and tinned, then the new component soldered to the inner end of the tags. That way, there's no need to de-solder anything and no risk of other wiring on the tagboard being disturbed.

On compact equipment with 'rat's nest' wiring, it's a big enough challenge to diagnose and rectify faults, and the more disturbance we create, the greater the risk of introducing new faults that weren't there before we started.

Pic 1: Examples of coiled joints on a Heathkit RF1-U signal generator (ECF50, 12AT7).
Pic 2: Examples of coiled joints on a Figaro Special. (ECH81, EBF89, ECL82).
Pic 3: Sketch of the DAC90A spare tags on tagboard.
Pic 4: The last '90A I worked on had previously had the caps replaced in what, to my eyes, was an untidy fashion, albeit functional. I removed them, fitted more compact caps, soldered to the spare tags. A bit 'OCD ish'? Maybe, but my time's my own.

Hope that's of interest.

[Cathovisor]

Originally Posted by Gabe001

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.

The only braid I have found from long experience that works reliably time after time is Chemtronics - I use it all the time.

[Cathovisor]

Originally Posted by prajan

Dear friends
Is there some other electric desoldering pump available which can suck out larger quantity of solder?

Well, there are the Weller types which work with a vacuum pump but they are not cheap. Other brands are available.

[Cathovisor]

Originally Posted by Lucien Nunes

With the usual situation of a solid component lead pushed through a tag, if I want to save both the tag and the full length of the wire, I remove the bulk of the solder and then tease the wire out without necessarily keeping the solder molten throughout the process. Solder is very weak and the wire can be prised free from a thin film of it when cold, using a pair of fine needle-nose pliers, a small flat screwdriver blade and a mounted needle / dissection seeker.

If I want to preserve enough of the lead to remake the joint, but not necessarily wrap it fully around the tag again, I locate the point where it emerges from the first pass through the hole and cut it in situ with pointed flush cutters, along with any adhering solder, then cut through the detached wrapped section to enable it to drop off the tag when heated.

You and I use the same technique, Lucien.

[Takapuna]

I too have one of the soldering tools identical to the one one Chris pictured from the front of a magazine many years ago. I still use it, especially the slotted end for bending component wires to the correct pitch before fitting. I thought my one came free with Everyday Electronics (remember that?) but it might have been one of the others. Perhaps each of the magazines: Practical Wireless, Practical Electronics and Everyday Electronics gave one as I believe they all belonged to the same stable.

I remember a prize competition in Everyday Electronics (I think) where the prize was a small screen CTV which was very desirable at the time. To win you had to place in order of importance items from a list of "things you should do when soldering". There were the obvious ones, such as making sure the items to be soldered were clean, tinning the wires before soldering etc. However, I do remember one point which was "to ensure a good mechanical joint has been made before soldering". The "correct" order for the answers was to be judged by a panel of experts and then a winner from those with matching answers drawn from a hat. I sent in my entry expectantly but I'm still waiting for confirmation that I've won! Regarding the date, I remember the prize TV shown displaying a picture of the Ladies Wimbledon Finals winners shield held high by either Anne Jones in 1969...too early I think, or Virginia Wade in 1977...which is later than I though.

Phil
----

[Craig Sawyers]

Originally Posted by Station X

I have to confess to melting solder joints with an iron and then blowing away the solder with a jet of compressed air. It leave joints very clean.

Of course it leaves "granulated" solder everywhere, but it's easily cleaned off.

There is a hidden peril in using that method in radio sets. Solder flakes can get stuck between the tuning capacitor vanes or air dielectric trimmer capacitors. Which can give surprising and smoke generating results.

Craig

[PaulR]

I seem to remember seeing commercially produced coils to enable new components to be attached to the stubs of the old leads in the same way as Nicks very neat approach. You might think he was skilled at doing precise procedures in a confined space!

I must overcome my obsession of trying to remove every trace of the old component!

[Station X]

There's a thread somewhere in the forums showing how to make a simple winder for those coils.

[Nickthedentist]

Originally Posted by PaulR

...Nicks very neat approach. You might think he was skilled at doing precise procedures in a confined space!

Thanks for the kind words but the nice thing about these is that you can make them up "on the bench" then fit and solder them with ease.

Originally Posted by PaulR

I must overcome my obsession of trying to remove every trace of the old component!

You're not the only one. Having tags break off helps you reappraise though!