Old Solder

[Rhodesplyr]

In a 1952 amp I've been restoring, the solder I've needed to remove comes off as grainy chunks rather than as a liquid, and I have to use the trick of melting fresh rosin-core solder into the old solder to get it to melt at all. I've encountered old solder before that was hard to melt (hence being familiar with how to deal with it), but I've never run into anything quite like this stuff.

In such a case, on a fairly simple amp, would it be better to leave existing joints alone if I don't need to desolder them, or would there be a compelling reason to desolder and resolder them all for the sake of future reliability?

[R.G.]

Odd that you should mention that. Just yesterday, I was removing some wires from terminals in a chassis and noticed a similar issue, which got me thinking about it.

In my case, I believe that they used 50-50 solder and not 60-40. 63% tin, 37% lead is the eutectic point for tin-lead solder. Any change in composition either direction makes the melt temperature rise. In fact, this is so predictable, you can readily tell what the tin-lead mix is by just measuring the melt temperature. I once used this to prove that some plumbing was done with 50-50 plumbing solder instead of lead-free solder.

In my case, I reached over and twisted up the temp control on the iron. Then it started melting OK. But at the setting I use for new construction with 60-40 rosin core solder, it was just getting slushy and grainy. The grain is crystals of the excess metal forming in the liquidus, which *is* composed of 63-37 tin lead in all cases.

If it ain't broke, don't fix it. If the joint looks like it was flowed smoothly and well into the wires, and you don't have to replace it, leave it. It's not degrading any more than it already was. But if you have to fix a joint, clean off the old stuff and use fresh 60-40 and rosin flux to get a proper joint. If you partially melt an old joint that had high-temp solder like this, it gets really bad unless you can get it hot enough to flow again. Turn up the heat if you can do it without burning the wires/joints up.

[Enzo]

[Tim Allen] Ah ah, 140 snorting snarling watts of Weller gun power ought to convince the stuff. If not, I still have the 200 watter.[/Tim Allen]

[R.G.]

MORE POWER!!

Tim Allen is one of my personal heroes.

As a side note, I have found that for me, it's better to have an iron that's too hot than just solder melting temp. Heat takes some time to travel through the distributed thermal resistance/capacitance down wires, and if you can heat the joint locally and FAST, you can make a joint before the heat has time to travel up wires to something else. So for me, a really hot iron paradoxically keeps everything else cooler.

The only reason I ever turn my iron temp down is that if the temp is too hot, the oxide formation rate on the tip un-tins the iron too fast.

But it does take a quick, deft touch to get in there, make contact, solder, then get out before things start smoking.

[Enzo]

So for me, a really hot iron paradoxically keeps everything else cooler.

Oh, AMEN.

One thing I try to tell trainees is "solder with confidence." A nice hot iron, clean tip. Put it on the joint until the solder melts. Leave.

It isn't the 800 degree solder iron tip that kills parts and pc boards, it is the fiddling around: Melt some solder onto the joint, stir it around with the tip, maybe it doesn;t look quite right, stir some more, maybe add some more solder. And maybe even more solder, looks like maybe room for some more over here too, now slide the tip up and down the wire leads, feel compelled to plate the entire length of the wire if you can. Hey, the cheap crummy pc board just had the copper come loose. I ain't buying that brand any more. Maybe I better suck all that solder off and try again...

[bob p]

[Tim Allen] Ah ah, 140 snorting snarling watts of Weller gun power ought to convince the stuff. If not, I still have the 200 watter.[/Tim Allen]

I would have expected the ToolTime guy to solder with a blowtorch. After all, he does plumbing, right?

edit: wow. old thread.

[km6xz]

Well, it still applies and is a good refresher for those who claim pc boards are lousy because they lift traces.

Back in the day of Germanium transistors like CK722 which were pretty heat sensitive, they frequently were ruined by too much heat. With all the warnings about heat, techs would lower their iron or gun temperatures "just to be safe" and ended up ruining perfectly good transistors by having too little heat so the time the joint was heated was extended, which in turn gave the heat a longer time to conduct up the lead to the semiconductor itself.
In old gear, point to point wiring was done well in that mechanical connections were secured before solder was applied. That means the electrical contact resistance was low due to the metal to metal contact, and not dependent on solder except for immobilization and reduction in oxidation. Otherwise, most gear could have worked just fine off the assembly line with no solder used at all.

[soundmasterg]

Well, it still applies and is a good refresher for those who claim pc boards are lousy because they lift traces.

Back in the day of Germanium transistors like CK722 which were pretty heat sensitive, they frequently were ruined by too much heat. With all the warnings about heat, techs would lower their iron or gun temperatures "just to be safe" and ended up ruining perfectly good transistors by having too little heat so the time the joint was heated was extended, which in turn gave the heat a longer time to conduct up the lead to the semiconductor itself.
In old gear, point to point wiring was done well in that mechanical connections were secured before solder was applied. That means the electrical contact resistance was low due to the metal to metal contact, and not dependent on solder except for immobilization and reduction in oxidation. Otherwise, most gear could have worked just fine off the assembly line with no solder used at all.

Yeah I agree with you. I've seen a lot of old military tube gear here that was made super well, and I've read that one of the requirements was a full power test of the device before any solder was applied to the joints. By and large most of the gear was made with turret construction with leads wrapped around turrets. If you have a sorted layout and circuit, thats still a great way to make your amps!

Greg

[big_teee]

Yeah I agree with you. I've seen a lot of old military tube gear here that was made super well, and I've read that one of the requirements was a full power test of the device before any solder was applied to the joints. By and large most of the gear was made with turret construction with leads wrapped around turrets. If you have a sorted layout and circuit, thats still a great way to make your amps!

Greg

Unless you have to work on it.
I put my pickups in a mexican Tele a while back.
They wired the pots and switches wrapped and soldered.
I about destroyed the switch getting the old wire off.
They went through the holes and gave a wrap or two on the small switch terminals.
I try to build everything when it can be maintained and worked on.
I do a little more wrapping on the power tube sockets, because of the heat, but not inside the guitar.
T

[Mick Bailey]

The parent material also alloys with the molten solder, as does the bit material to some degree (hence the development of Savbit solder). A tinned terminal will alloy some of that tin into the joint, and the tin itself will be contaminated with the base metal that it's deposited on. In the days of hot-dipped tinned terminals there was a fair deposit of tin. The irons used would have been pretty hot to give the speed of assembly and reliability the joint and it's my theory that all of this could contribute to the higher melting point of a soldered terminal.

[Alex R]

I do wonder about 'military spec' wiring. Durable yes, easy to repair under fire, er no. Not just the three-turns-and-crimp under the solder but the way (I'm thinking of the old Hiwatts) the wiring itself is neatly hidden under the tagstrips so yo can't see what's connected to what.

[Mick Bailey]

I also wonder about older wiring to tags and terminals. It was seen as good practice, but just how many wraps does a wire need once it's soldered? Especially considering the forces applied to many of the joints. Some of the old radios I work on will have three or four leads all wrapped around a tag three times and are almost impossible to pull apart.

So, the relative strength between;

a) No wraps - wire passed through a tag and soldered to the point at which the solder fills the joint
B) A single wrap
C) Three wraps

I bet in every case the component lead will fail before the joint. Once that wire is entombed in solder, the stress point is the interface with that solder, which is fairly abrupt.

Now, if you were assembling equipment you could either fit a component or two, pick up your soldering iron, solder the joints and then put your iron down to repeat the process. Or, someone could wire a significant number of components and pass these on to an operative who just solders. In this case it would make sense to fix components in position by wrapping. I'm not certain that much of the wrapping that went on wasn't just to make production quicker, especially with consumer goods.

It's another matter if the gear needs to hold together under heat for as long as possible, but how much equipment is designed to continue operating after the solder has melted out of the joint? Certainly not guitars and amps.

[rjb]

I do wonder about 'military spec' wiring.

FWIW, NASA spec was never "wrap it a million times".
http://www.protostack.com/download/N...0Soldering.pdf

Here's what it says for hook terminals:

Slide the wire off the terminal. Usingwire cutters, flush cut the bent wire so that it
will only make contact with the terminal for
180 degrees minimum (1/2 turn) to 270
degrees maximum (3/4 turn).
26 AWG and smaller wire shall be 180
degrees minimum (1/2 turn) but less than one
full turn 360 degrees maximum (1 turn).

For pierced terminals, they outline procedures for 180 degree (1/2 turn), 90 degree (1/4 turn) and 90+90 degree (Z bend) entry.