Soldering Buss Wires/shields to Potentiometer Cases

[nevetslab]

I'm now at the step in re-building the Lombardi 8-Ch Mixer that has the Binson Echorec Magnetic Disc Delay System, where having earlier unsoldered 20AWG Ground Buss wires from the pot cases (which are mounted to fully grounded panels)....now attempting to restore those ground buss wires for each channel...which runs from the Echo Send pot, picks up the Treble and Bass pots on it's way down to a ground terminal, and then down to the case of the Slide Pots. I had already wire-brushed the surfaces of the pots, applied liquid flux just prior to attempting to re-solder the ground buss wires that had been soldered to the cases. WILL NOT SOLDER! Turned the iron (3/16" freshly tinned tip) from 750 Deg up to 900 Deg, and still WILL NOT SOLDER! I've gotten really good at creating drips of solder plopping down onto the lamps below that illuminate the slide pot panel surface, but bonding to the steel case of the pots? Not a chance.

CTS Pots. Date code from 1974-1975.



Now granted, what I saw during unsoldering those buss wires in preparation to unsoldering them, I didn't see fine solder work there. I figured getting past the 45 yr old surface to fresh metal with a wire brush, and using Kester Liquid Flux to assist would have gotten solder to flow. An exercise in futility here, I'm afraid.

[Enzo]

Only thing comes to mind is that temperature is only part of it. A 900 degree tip with only 20 watts behind it is still only 20 watts. I use my ancient Weller 100/140 watt gun for such joints.

[nevetslab]

While I thought about that, there was NO WAY to fit that beast of an iron into the space with all those lead wires and components in the chassis. I hadn't thought about the mere 20 watts behind the Pace iron in use. Good point, if it was feasible without destroying the neighborhood in the process.

[Enzo]

When I was a kid, I used my dad's soldering iron. One of those big things about an inch in diameter with the pyramid tip. But my Weller gun had that formed wire sort of tip, that could poke into smaller spaces, and if I needed to I could bend it into a curve. 140 watts on the high trigger click.

I have had that gun over 60 years. Bought it from Montgomery Wards. Peeled the MW label off it to expose the Weller label. Over the years I dropped it too many times and have replaced the plastic sides. I have made countless new tips from 12ga bare wire. I replace the power cord with a longer one. And even had to put a new trigger switch in it. But by god it has been a good one. The transformer at its core is still original.

[The Dude]

............ and they have a light! I still have one of those myself that I bought in grade school and it still works. My story is similar to yours- broken plastic, replaced power cord, etc.. but still kickin'.

[Enzo]

That screw in bulb with the lens tip? A #222 I think? (Oh, I'll go look it up) YES, a #222.

Note the formed wire tip is offset towards the top? I always mounted the tip upside down so the end was in the "beam" of that little bulb.

And when the tip burns out, it is always at the tip, results in two wire pieces pointing into space. SOmetimes you could bend them to touch and solder another joint or two. But leaving them not touching, you could shove them against your work and do resistance soldering. The current flows through th work, between the poke points and it heats itself up.

SO have we sufficiently derailed your thread nevets?

[Jazz P Bass]

I like the flat spade tip that they offered for melting plasitic.

[Jon Snell]

I'm now at the step in re-building the Lombardi 8-Ch Mixer that has the Binson Echorec Magnetic Disc Delay System, where having earlier unsoldered 20AWG Ground Buss wires from the pot cases (which are mounted to fully grounded panels)....now attempting to restore those ground buss wires for each channel...which runs from the Echo Send pot, picks up the Treble and Bass pots on it's way down to a ground terminal, and then down to the case of the Slide Pots. I had already wire-brushed the surfaces of the pots, applied liquid flux just prior to attempting to re-solder the ground buss wires that had been soldered to the cases. WILL NOT SOLDER! Turned the iron (3/16" freshly tinned tip) from 750 Deg up to 900 Deg, and still WILL NOT SOLDER! I've gotten really good at creating drips of solder plopping down onto the lamps below that illuminate the slide pot panel surface, but bonding to the steel case of the pots? Not a chance.

CTS Pots. Date code from 1974-1975.



Now granted, what I saw during unsoldering those buss wires in preparation to unsoldering them, I didn't see fine solder work there. I figured getting past the 45 yr old surface to fresh metal with a wire brush, and using Kester Liquid Flux to assist would have gotten solder to flow. An exercise in futility here, I'm afraid.

Many years ago, before Zinc Chloride was a known corrosive chemical, we used to use Bakers Soldering Fluid. A mixture of chlorides and Zinc. After a few years, it would actually eat its way out of the metal container!
But, it allowed the soldering of tarnished and corroded metals.
It was so agressive, it would ruin a good soldering tip, so keep a file handy when using your prize copper bits heated on a brazier.

[Mick Bailey]

Are those pots zinc plated, rather than tin? They look like zinc from the picture, which is a problem to solder, though once soldered should reflow OK.

This reminds me of some Switchcraft sockets I bought a few years ago in bulk. The ground tabs soldered fine, but the tip connections would not solder under any circumstances. For each one I had to completely remove the plating down to base metal to get a joint to flow.

[nevetslab]

Ah....I hadn't thought about my Weller Soldering Gun. 140W. I had been using that for cutting Tech Flex, before buying a bench Hot Knife to make it easier when we were wiring up custom cables for all of the Meyer Monitor Wedges a few years ago here at CenterStaging.

I also have made several alternate tips from Copper Buss Wire. I suppose I could tempt fate and try again on the re-soldering the ground buss wire to the case.

I too would guess the pot cases are zinc plating. The original soldering job done 45 years ago wasn't what I could call a quality soldering job.



I'll have to see how it behaves on a couple other CTS pots I have here before diving into redoing the attempted re-soldering job.

Good suggestion!

[Leo_Gnardo]

I too would guess the pot cases are zinc plating. The original soldering job done 45 years ago wasn't what I could call a quality soldering job.

Photo tells all - solder didn't adhere to the pot's metal. I hope you've tried removing the lousy solder connex, and re-prepping the metal surface with a wire brush scrub or super fine sandpaper scratchup, then solvent clean, then apply your favorite solder/flux combination.

My 33W bench iron handles all sorts of pot covers well. Sometimes I'll switch to a 45W heater with big tip if the job seems extra tough.

[xtian]

where having earlier unsoldered 20AWG Ground Buss wires from the pot cases (which are mounted to fully grounded panels)

Why do we want to ground the pot bodies if the panels are also grounded?

[Enzo]

Not all pot covers have electrical connection to mounting bushing.

[J M Fahey]

Why do we want to ground the pot bodies if the panels are also grounded?

It´s the other way: the bus wire GETS ground from panel/chassis through pot cases.

* Cleanliness first, use a small wire brush to remove years of unsolderable surface crud, zinc sacrifices itself to protect the rest but becomes a whitish salt; or absolute worst case use a mounted stone to reach bare metal as suggested above.

* You need power and copper mass more than plain temperature, buy a cheap Chinese 100W soldering iron, the kind Fender assemblers used for eyelet, chassis, pot soldering.

* Cheat. Order at a jeweller´s/Art supply store a small bottle of "soldering enhancer" or something, not "flux" which is mild, rosin and alcohol based but the water based nasty solution, most probably containing Zinc Chloride salts.
It won´t say so in the label, probably a mystery/house/no brand coming from a garage/backroom "chemical factory" he he.
They still make it, one way or the other, because nasty as it is, nothing beats it.

Never use near copper so no direct on a PCB or stranded wire which suck it by capillarity but become green corroded later, only for chassis/pot work, just to get the initial solder coat, then you wipe it off with a damp cloth and continue as usual.

[nevetslab]

Why do we want to ground the pot bodies if the panels are also grounded?

I've been asking the same question. The bushing plate is most assuredly grounded to the case, and that's mounted to the metal chassis. This was Lombardi's brilliant way of grounding. When I saw components on the ground side of the preamp PCB in contact with the mounting bracket, so even there, there's additional ground paths that became in parallel to the wired grounds, I moved the PCB to the other side of that bracket, and elevated it so the solder pads weren't in contact, leaving the PCB ground circuit defined by the wiring, and not by happenchance mechanical means.