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To All from PA0SE
May I inject an item on a low-tech subject into the stream of
high-tech stuff that has been coming to us via the
reflector?
I know that soldering litz wire has been discussed extensively
lately but by chance I came across an article on the subject written by a
professional that may interest you. It relates to litz wire with strands covered
by enamel. Modern litz has a coating that dissolves in molten solder
and soldering is no problem.
I found the article in the 1949 edition of ELECTRONICS MANUAL
FOR RADIO ENGINEERS (McGraw-Hill).
I wish you and yours a happy and healthy New Year with extreme
DX!
73, Dick, PA0SE
JO22GD
Soldering Litz Ends
By EMERICK TOTH
The writer had occasion to design a receiver for
aircraft using coils of litzendraht wire. These coils ranged in diameter from 12
inches, wound with litz of about 180 strands of number 38 wire, to little
fellows of 1/2 inch ID using 7/41 litz. Over 150 coils were involved, a total of
more than 300 coil ends, thousands of individual strands that must be properly
tinned and soldered. Careful tests were made of the following three
methods:
(1) Cautious removal of the silk and enamel
from the coils end by abrasion against a relatively soft high-speed rotary
wirebrush.
(2) Heating of the coils end in an alcohol
or Bunsen-burner flame and subsequent plunging of the hot coil end into
alcohol.
(3) Application of a small quantity of a
paste of zinc chloride and water to the coil end and heating with a soldering
iron, immediately followed by tinning with rosin-core solder while the
resulting zinc chloride and enamel mixture was still boiling. The silk
insulation was burned and stripped off by a very short exposure to a flame, and
subsequent wiping with a rag prior application of the zinc
chloride.
Method (1) was found to damage individual strands
excessively, and did not clean all strands in sizes of litz with many strands,
such as 70/38 and 180/38.
Method (2) was difficult to control. Insufficient
exposure to the flame resulted in the enamel not cracking off when the hot coil
end was plunged into cold alcohol. Overheating caused individual strands to burn
off. Even when satisfactory cleaning was obtained, the copper was left so
brittle that soldered coil end would break easily.
Method (3) provides easy and effective tinning.
The appearance of the tinned end was neat and clean after the residue of
zinc chloride, enamel, rosin, and solder had been wiped off while still hot with
a damp rag. The ease of tinning even 180/38 litz suggested that
inside strands were not properly coated. Several samples were cut in
cross-section but all strands appeared to be clean of enamel and
tinned.
Samples were placed in a salt-spray chamber and
subjected to the Navy's standard salt-spray test for two hours. It was found
that except for a light accumulation of powdery salt the samples were in no
way affected by the test and all 300 coil ends were processed as outlined
in method (3) above.
Eighteen months after delivery, one equipment was
examined which had been in service in Panama for a year. No trace of
corrosion or any other damage was found.
Zinc chloride is very hygroscopic and
should be kept in a suitable well-stoppered glass bottle, with only as
much paste prepared at one time as is needed for a few hours use.
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