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Old 24th Feb 2017, 4:49 pm   #1
DonaldStott
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Default Vintage Radio Solder Joints

What happens to solder joints in vintage radios after 70+ years?

Currently restoring a Bush AC91 c.1946 and have come across a number of components/wires where the solder joints simply won't melt!

Had to end up cutting the lead or wire and tidying up the tag as best as I can.

No doubt there is some change in the chemical composition of the solder as what remains is no longer metallic and shiny.

Just curious ...
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Old 24th Feb 2017, 5:00 pm   #2
vidjoman
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Default Re: Vintage Radio Solder Joints

You need to add fresh solder with flux and it'll blend and melt.
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Old 24th Feb 2017, 5:44 pm   #3
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Default Re: Vintage Radio Solder Joints

Copper progressively migrates into the copper over time, and the resulting alloy has a much higher melting point than the original solder. Likewise, lead and tin migrate into the copper. As vidjoman says, just apply more solder to dilute the old stuff and lower its melting point.
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Old 24th Feb 2017, 5:54 pm   #4
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Default Re: Vintage Radio Solder Joints

It appears to me that some component leads in old sets go crystalline and break very easily. Others refuse to take solder no matter how much you clean them or how much flux you apply.
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Old 24th Feb 2017, 6:33 pm   #5
The Philpott
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Default Re: Vintage Radio Solder Joints

I wondered why this occurred, i thought it was a different solder used.

I can totally believe that copper migrates into a lead-tin alloy, i was one told by my science teacher that lead and gold clamped together start to migrate into one another. Particularly on WW2 equipment several times i have had to abandon the 15watt 'iron and use the 25watt one instead.
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Old 24th Feb 2017, 8:57 pm   #6
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Default Re: Vintage Radio Solder Joints

The first sentence of my post should of course have started with "Copper progressively migrates into the solder..."

The phenomenon is referred to as "Solid solution" and I learned about it in a lecture that was part of a workshop course that Plessey sent me on when I joined them. Later a work colleague lent me an old book from the Victorian era by a Mr. Ganot, "Principles of Physics" I think was its title. It described, without going into maths, a large number of experiments that the early investigators had done, like how water will ooze through solid gold if high enough pressure is applied. It did describe how, if you put a thin sheet of copper between two silver discs, clamp them together, and apply heat to one side, the copper will disappear, having migrated beneath the surface of I think the cooler disc, but that you could reveal it by etching away the surface with acid. Another one demonstrating how one metal could flow through another was, if you dip one end of a piece of solid Lead wire into a beaker of Mercury, with the other end over another beaker at a lower level in the configuration of a syphon, after a while drops of Mercury will drip from the lower end.

I did think it would have been interesting to repeat some of them myself, but many of them involved stuff that was ether too expensive (like Gold and Platinum ) or too difficult to obtain (like Mercury).

Last edited by emeritus; 24th Feb 2017 at 9:03 pm.
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Old 24th Feb 2017, 9:17 pm   #7
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Default Re: Vintage Radio Solder Joints

A very interesting post emeritus! This is all new to me. How bizarre. It must occur at molecular level I suppose.
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Old 24th Feb 2017, 9:43 pm   #8
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Default Re: Vintage Radio Solder Joints

A frustrating problem that might just be related is the embrittlement of phosphor bronze valveholder contacts.

I'm sure that many of us have tried to tighten up a bifurcated contact from a reputable 1960s valve-holder (McMurdo etc) only to have it fracture and require replacement. This age-related embrittlement has always been a puzzle to me. What causes it? Could it be related to copper migration from the phosphor bronze into the solder joint? If so, it shouldn't happen on contacts without a soldered connection.

Can anyone shed light on this?

Martin
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Old 24th Feb 2017, 9:55 pm   #9
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Default Re: Vintage Radio Solder Joints

This latter phenomenon seems to be particularly common on battery valve sets.
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Old 24th Feb 2017, 11:35 pm   #10
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Default Re: Vintage Radio Solder Joints

Yes, Nick, I've come to the conclusion that some sort of fumes released from zinc-carbon batteries as they approach the end of their life causes this damage, to valveholder pins and to other metal components in battery valve radios.

The other issue is soldering iron power and heat storage capacity. Many old sets were built using relatively hot and high-powered irons, rather than the 25 watters we tend to use for repairs. A big joint will conduct heat away from the bit tip faster than the element can respond, meaning that the tip temperature drops. I have a 60 watt iron with a large copper bit which acts as a heat reservoir, and this has been able to melt joints that even my 100 watt Weller gun has failed to do.
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Last edited by Phil G4SPZ; 24th Feb 2017 at 11:36 pm. Reason: Clarity
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Old 24th Feb 2017, 11:50 pm   #11
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Default Re: Vintage Radio Solder Joints

In some times and places (and wartime/immediate post-war Britain may have been one of them), shortage of tin may have forced the use of high-lead alloys, which would be harder to melt Also, humid conditions (maybe aggravated by e.g. coal fire fumes) can make a stubborn dull grey coating on high-lead solder which can hinder good heat transfer.
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Old 25th Feb 2017, 12:04 am   #12
Craig Sawyers
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Default Re: Vintage Radio Solder Joints

There is an identified phenomenon in mil spec or aerospace, called "red plague"

https://en.wikipedia.org/wiki/Red_plague_(corrosion)

What is happening in vintage radio sets might well be a variety of the same phenomenon.

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Old 25th Feb 2017, 12:08 am   #13
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Default Re: Vintage Radio Solder Joints

i consider it an honour to work on assemblies that have been in existence for so long that they actually encounter such queer changes!

Fortunately one doesn't have to deal with gold-aluminium intermetallics unless fault-finding relatively modern equipment. White plague and Purple plague. Nasty.
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Old 25th Feb 2017, 12:10 am   #14
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Default Re: Vintage Radio Solder Joints

https://en.wikipedia.org/wiki/Red_plague_(corrosion)

I'm sure I've seen that in old ex-WD equipment. Fascinating, thanks!
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Old 25th Feb 2017, 12:55 am   #15
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Default Re: Vintage Radio Solder Joints

Not exactly the same but a similar problem...In the Vestel manufactured Analog TV's such as the 11AK17, 11AK15, etc that used BU 508's in the loptx stage. The "S" Correction capacitor or the Line Lin coil would go dry solder.... a neat hole in the pad with the component pin sticking through. Obviously... to me any way...there was metal migration in the solder, due to hi voltage pulse voltages and line current. The O/C always caused to BU508 to fail....It happened for years....Vestel either didnt care or had no way of fixing it.
Then when they moved to the 11AK22... the fault stopped... and another... cropped up in the frame stage, but not solder related.
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Old 25th Feb 2017, 1:02 am   #16
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Default Re: Vintage Radio Solder Joints

I doubt very much if there is significant copper diffusion in solder, The temperature is much too low.

[B]Season cracking[B]
Brass, and probably other copper alloys are prone to season cracking. This was so named when the shells in the indian army split during the monsoon. The reason was that the shells were stored in the stables next to the horses which produced ammonia.
All metals are crystalline and the grain boundaries are at a higher energy state since the atoms do not fit perfectly. This is exacerbated if the stress of manufacture had not been reduced by annealing. The higher energy grain boundaries are corroded by the ammonia leading to splitting. I would think that other corrosion couples are possible.
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Old 25th Feb 2017, 1:12 am   #17
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Default Re: Vintage Radio Solder Joints

Red Plague would probably explain the disintegrating tubular contacts to the 10" fluorescent tubes that were fitted to the already rather elderly motor caravan that we had in the 1990's. I had similar problems with disintegrating contact pins on the chokes of some of the double 5' fluorescent fittings that I got from the scrap bin (10p each) when they replaced all the fluorescent fittings with same-sized slim-line fittings. The pins snapped off at the Paxolin plate where the connections fed through inside the metal casings and were very brittle and somewhat reddish.

I guess one reason for the continuing use of lead-based solders in high-reliability equipment is that the natures of the interactions between conventional Lead/Tin solders and other metals is well known from years of actual experience. As has been mentioned in other threads, pure Tin can grow whiskers that can cause short circuits, and there may well be similar problems with the new lead-free solders that might take some time to develop.

I just remembered that about 20 years ago there was some correspondence in the "Railway Modeller" about problems that people had been experiencing with white metal kits. Some had used solder to fill some oversized holes for handrail supports on loco boilers. A few months after the models had been finished and painted, very noticeable raised rings appeared under the paint where the solder filling had been used, and these, not only re-appeared after the surface had been rubbed down flat and re-painted, but migrated outwards. A reader who was a professional metallurgist said that this was due to the formation of intermetallic compounds at the junction of the solder and the white metal that had a lower density, and therefore occupied a larger volume, than either of the original metals. If nothing were ddone, the rings would continue to grow in size as the solder progressively diffused into the white metal, and the only solution would be to drill out the regions affected by the solder and use a non-metallic filler or a specific alloy that the writer identified which he knew would not react in that way with the type of white metal used in model kits.
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Old 3rd Mar 2017, 9:02 am   #18
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Default Re: Vintage Radio Solder Joints

We had a Toshiba TV that blew its line output transistor. Examination revealed that the line output transformer mounting pins had clear void rings in the solder connections, there were poor contacts on them all. A new transistor was fitted but failed to work, the transformer itself had gone open circuit presumably due to the intermittent contacts. A new one was fitted and it was noted that the holes in the copper tracks were hugely oversize. The connections were remade with tiny brass washers on every pin, soldered on to the tracks. It never failed again. Whether this was due to poor etching or whether the copper had migrated into the solder was not established.
Perhaps the high voltages had something to do with it?
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Old 3rd Mar 2017, 10:40 am   #19
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Default Re: Vintage Radio Solder Joints

Quote:
Originally Posted by turretslug View Post
In some times and places (and wartime/immediate post-war Britain may have been one of them), shortage of tin may have forced the use of high-lead alloys, which would be harder to melt Also, humid conditions (maybe aggravated by e.g. coal fire fumes) can make a stubborn dull grey coating on high-lead solder which can hinder good heat transfer.
Another point to remember is that some components (I am thinking mains droppers here) may have been soldered with higher melting point solder for reliability.
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Old 3rd Mar 2017, 11:19 am   #20
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Default Re: Vintage Radio Solder Joints

Quote:
Originally Posted by Boater Sam View Post
We had a Toshiba TV that blew its line output transistor. Examination revealed that the line output transformer mounting pins had clear void rings in the solder connections, there were poor contacts on them all. A new transistor was fitted but failed to work, the transformer itself had gone open circuit presumably due to the intermittent contacts. A new one was fitted and it was noted that the holes in the copper tracks were hugely oversize. The connections were remade with tiny brass washers on every pin, soldered on to the tracks. It never failed again. Whether this was due to poor etching or whether the copper had migrated into the solder was not established.
Perhaps the high voltages had something to do with it?
I'm sure that I'm not alone in having experienced the apparent 'evaporation' of solder from relatively high voltage connections such as the LOPT above or a CRT base. Sometimes it can leave the joint completely free of solder. I guess that solder molecule migration is linked to some local ionisation.

Martin
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