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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.