[Collins] (no subject)

[Gerald]

On Sat, 2005-12-31 at 18:06 +1030, L.D. Ritta wrote:
> Just what is the Collins soldering techniques and how do I find out?
> Is there a book somewhere, you have me curious.
> 
> Lee
> 
NASA had a book. The NASA way would take 20 times longer than the
Collins way, though when I was at Cedar Rapids, inspectors for HF
transmitter products often came over from inspecting Apollo flight
equipment and so were EXTREMELY picky.

In a way, Collins production cheated. First the parts were clean. The
leads hadn't sat in a paper sack in a basement for 30 years. Much of the
detail in the NASA book was on cleaning the surfaces to be soldered. Not
depending on heat and soldering flux to do the cleaning. Then they
tinned the component leads before assembly to be sure the surface to be
soldered was very fresh and clean. Nothing there but solder without
oxides and scum.

Then there's the heat source. I believe ham rig production probably used
100 to 150 watt Hexacon hatchet soldering irons. Bent at right angles.
Probably with pyramid tips. At least I saw lots of those irons at
Collins Surplus in those days. Too small an iron cools off doing each
joint and causes a much longer heat soak of the joint and components
than necessary and if the solder isn't really molten it won't wick into
the wrapped joint. It my opinion that ARRL suggestions of using only 25
watt irons for printed circuit board work are WRONG unless one is only
using Unger ceramic screw in heating elements that run at higher
temperatures for the higher power elements. Those are just bad choices
of tools.

The solder, likely they used a eutectic, 63/37 alloy. It has the lowest
melting temperature and no pasty range, its either melted or solid, so
its hardest to make a "cold" solder joint by having pieces move while
the older is solidifying. Solder strength in the pasty temperature range
is very small.

Of course Collins soldering rules required every joint to be
mechanically sound before soldering so movement didn't accidentally
occur.

Flux. I don't remember what solder and flux I grabbed from lab techs for
soldering. I used whatever they did and it worked. Classically, assembly
used plain rosin flux (leaves a characteristic odor in vintage General
Radio wooden cased equipment) but there is where cleanliness before
soldering is most important. Soldering is more fun with an activated
rosin flux that will do some cleaning on its own.

On my own workbench, I allow only Ersine Multicore Savebit with
activated rosin flux. I despise most other solders, especially Kester
44. Its getting harder to find. For vintage radios, 1/16" diameter is
right, for PC boards 20 gauge is about right.

For a soldering iron, I keep two on the bench, one 60 watt Weller
temperature controlled and one 100 watt temperature controlled Weller.
The 60 watt for little stuff and the 100 watt for vintage radio work.
They are both of the style without a control box, the 100 watt is often
sold for soldering cames of leaded glass windows.

Technique: With all the parts to be soldered cleaned (by fiberglass
brush or knife scraping when necessary) and made solid (by Collins
rules, not necessarily mine), wipe the soldering iron on a damp sponge
or cotton towel, then melt a drop of solder on the iron. It takes that
drop of solder for heat transfer. Apply that solder (which won't have
any flux left) to the joint and so apply heat to the joint. Apply wire
solder to the other side of the joint. As the joint heats it will melt
the wire solder and pull the solder in. If solder doesn't pull into the
joint, its not hot enough or not clean enough. Then inspect. If there
are solder balls, the joint hasn't been hot (or clean) enough and the
solder hasn't wetted. Those balls often enclose unmelted flux, hence
such joints are called "rosin joints." When heated enough the solder
will for an nice fillet to the flat surfaces and the wires.

When multiple (especially) wires are crimped to a lug, it is easy to get
solder on the surface, but not through to the lug or to all the wires.
I've come to appreciate Tek tube type scopes were there was never a
crimped wire, but all connections depended only on solder. That makes
for real easy testing of a connection. Just tug on the wire. If it
soldered it doesn't move. If its not soldered it comes out.

Heathkit assembly manuals had a decent page on soldering too.

Well, I just wrote chapter one of my next book on radio restoration.


-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer