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Old 30th Dec 2011, 7:25 pm   #21
kalee20
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Default Re: Accepted restoration methods

Personally, I tend to make a 'fair' (as opposed to a 'good') mechanical joint. In a typical valveholder tag, that's push the lead through, bend it 90°, and snip off.

As others have mentioned, the possibility of damage to the tag/valveholder/other components, trying to desolder and unwind a doubly-wrapped lead, is quite high.

If the joint is good enough to not move while it's being soldered, and will have a pleasing-looking profile afterwards, generally, that is my target condition.

If you need a 'good' mechanical joint before soldering, then to me there's something wrong - is the component itself too heavy? An example might be a chunky axial electrolytic capacitor - if supported by its leads then yes a good mechanical joint would be necessary. But in this case, far better to support the component by a clamp or a P clip, leaving the connection again by no-more-than-necessary wrapping and soldering.

If the joint is carrying high currents, such as heater wiring, then yes a complete wrap around tags might be justified. And if the joint is likely to run hot (such as a tag on a mains dropper), then again yes. Finally, a high-vibration environment, the joint should be well wrapped, with possibly a strain-relief loop. But these are the only cases where I would bgo for a 'good' mechanical joint.
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Old 30th Dec 2011, 7:29 pm   #22
Keith
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Default Re: Accepted restoration methods

"Of course there's no wrapping on most PCBs"

There's certainly not much wrapping involved in surface mounted components which probably comprise >99% of the solder joints in today's households!

Seriously though, I suspect that the insistance on mechanical wrapping of leads on tags was more about the prevention of relative movement whilst the joint cooled, the latter being a virtual guarantee of "dry" joints.
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Old 30th Dec 2011, 8:58 pm   #23
2E1CIH Mike
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Default Re: Accepted restoration methods

Gentlemen,

Thank you for your interesting comments.

I am about to embark on desoldering several wires as a means to disassemble my receiver into two manageable sub-assemblies. It has crossed my mind (thinking about it over the Christmas break.....as one does) that to disconnect some of these connections will be fiddly, and may well require the application of prolonged heat. I'm concerned about the possibility of damage due to this.

With David's comments in mind, would the method he has described for caps be suitable for the disconnection of several wires? These are mostly soldered (and well wrapped) to tags on switches etc.

Season's Greetings.....Mike
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Old 30th Dec 2011, 11:37 pm   #24
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Default Re: Accepted restoration methods

Gents,

To Mike's comment, I might suggest snipping the wires at a point where it would be convenient to make a neat in-line splice but be sure to remember to slip an appropriate sized piece of heat shrink tubing over the wire first, make the joint, "twist and solder", then slip the heat shrink tubing over it and have at it with a hair dryer. If you slip a large metal spoon behind the wire and then apply the blow dryer the spoon will reflect some heat and you can get more rapid heating and shrinking and protect the surrounding area as well. Obviously there are other ways, and if this is going to be a common practice there are very nice small heater/blowers expressly for this purpose.

As much as it bothers me to do it this way, rather than being a purist, I am reminded of the sinking feeling a few months ago when, in the midst of undoing a joint at a tube socket, the soldering lug broke off the socket. That meant seven other set of leads had to be removed, a socket acquired, drilled out and replaced (yes it was riveted in) and the process re-started.

Best of luck.

David

P.s. I did not mean to imply that solder was not a conductor, just not a very good conductor, of course that was based on the old 60-40 lead/tin solder formulations. Some of the new solder also contains silver which I assume is to improve the conductivity and strength of the joint on PCB's.

DS
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Old 31st Dec 2011, 9:02 pm   #25
2E1CIH Mike
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OK, many thanks David. I favour your train of thought.

I believe there's a pint of beer (warm, of course....a British speciality) with my name on it downstairs. The new year approaches. Your turn soon after.

All the very best for 2012.

Thanks again and kind regards.....Mike
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Old 31st Dec 2011, 9:22 pm   #26
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Default Re: Accepted restoration methods

Mike--

Enjoy the pint--I spent many a visit to London doing the same and I wish I were back there now.

Cheers,
David
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Old 31st Dec 2011, 10:06 pm   #27
kalee20
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Default Re: Accepted restoration methods

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Originally Posted by Fix2Relax View Post
Some of the new solder also contains silver which I assume is to improve the conductivity and strength of the joint on PCB's.
Strength - yes (as below). Conductivity - no.

It's also there to improve flowability. And occasionally it is there to stop silver leaching out of terminations when they're soldered - such as metallising on ceramic substrates.

While silver is the best metallic conductor, adding a percent or so to solder alloy does not make a material improvement to conductivity - and in fact adding a random metal to an alloy is just as likely to make things worse as to make them better, owing to metallurgical changes in crystal structure.

Getting back on topic, for any restoration, the solder to use is almost certainly 60/40. Modern lead-free solder should not be used - at the best of times it is not nice to use, but on old equipment, made with leaded joints, using lead-free solder will result in a really bad joint (lead must either be virtually not there at all, or there must be a fair bit. Between certain limts there's a "no-man's-land" concentration of lead, which results in weak, brittle joints.
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Old 1st Jan 2012, 8:58 am   #28
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Quote:
Originally Posted by 2E1CIH Mike View Post
OK, many thanks David. I favour your train of thought.

I believe there's a pint of beer (warm, of course....a British speciality) with my name on it downstairs. The new year approaches. Your turn soon after.

All the very best for 2012.

Thanks again and kind regards.....Mike
Greetings Mike, how about a Kiwi home brew?

Out of direct interest I noted this thread and have followed it through. From the outset I knew where you were coming from and agreed with your thinking. Disconnecting an existing component pig tail or lead, can very often causes unwarranted damaging to what is original, particularly if access is difficult. That fact that repairs have been necessarily made must be obvious, why cause unnecessary damage, how can a neat electrically efficient joint be criticised? A tiny hook in both wires, crimped to hold while properly soldered, is the way to go.

I owned and operated a Company building control systems on which life depended. There was never any consideration of a soldered joint requiring mechanical attachment. Countless joints were involved and not once did a faulty connection cause a problem, or was a dry joint reported. All is absolutely in the hands of the operator who observes the making of the joint, molten and as it cools. Subsequent inspection is not the answer. Furthermore a mechanical connection often can disguise the required result.

Mechanical support under a soldered connection has no purpose other than to to facilitate retention during soldering, as was often required during the original assembly of valve radios. In actual fact the rigidity of the joint within an otherwise flexible connection, is within itself a very real problem.

Trevor, down under.
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Old 1st Jan 2012, 10:50 am   #29
2E1CIH Mike
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Default Re: Accepted restoration methods

OK "Kalee20", thanks for that.

As Big Ben struck mid-night, another thought occurred (only joking); Would a combination of the wire cutting/splicing idea, and the small coil idea for replacing caps be deemed OK? To clarify; I mean how about making tiny coils to slip over, and crimp/solder to the two cut ends of a cut wire?

This has turned out to be a lengthy (but very useful.....to me) debate. Thanks to all for your patience.

Regards.....Mike
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Old 1st Jan 2012, 1:01 pm   #30
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Default Re: Accepted restoration methods

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I mean how about making tiny coils to slip over, and crimp/solder to the two cut ends of a cut wire?
Like this?
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Old 1st Jan 2012, 8:46 pm   #31
2E1CIH Mike
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Hi Col,

What an excellent idea! They say the simple ideas are the best, and this must surely be a prime example. I bet you could patent it.

Thank you for letting me know about your detailed description, and for your empathy. I will make one (before the patent is issued).

Thanks again.....Mike
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Old 1st Jan 2012, 10:14 pm   #32
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Default Re: Accepted restoration methods

Hi everyone,

Interesting. I also was taught to wrap wires before soldering by C&G lecturer at Stoke on Trent tech colleage. However what about Philips TV's and others that mounted the cathode resistors for the frame output valve on stand off arms? The idea being that if the resistor got too hot due to a fault condition the solder melted, the resistor fell off, so isolating the faulty stage. Also a lot of high wattage resistors had a spring loaded wire on the top, soldered together, again over heating would switch off the stage.

Regards

Derrick
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