[Milsurplus] Fw: I've got a question about a particular failure mode in ARC-made radios of WWII vintage

[Brad Latta]

 Leidecker, Henning W. (GSFC-5600)
 henning.w.leidecker at nasa.gov
 wrote:
 
 I've been searching for documentation of shorted
 tuning
 capacitors (well, 'condensors' in WWII talk):
 air-space
 variable capacitors.  Aircraft Radio Corporation
 used
 cadmium plating on (at least) some of their
 capacitors, and
 these cadmium coatings sometimes grew metal whiskers
 that
 shorted the rotor and stator plates.  Other
 manufacturers of the time might have also used
 cadmium
 platings and had the same problem?
 
 I'd like to find anything that has been written about
 this.  Perhaps there would be mention of this in a
 field manual or in some "Unsatisfactory Reports"
 item? 
 
 
 Perhaps folks restoring equipment that used
 cadmium-plating
 (to resist corrosion of the base materials) have
 found
 shorts or high leakages in air-spaced variable
 capacitors,
 or other items subject to shorting by whiskers?
 
 Here is some background...
 
 Jay Brusse runs the "Metal Whisker" web site at
 Goddard
 Space Flight Center:
     http://nepp.nasa.gov/WHISKER/
 He gets some help from Michael Sampson and from me.
 
 Whiskers are thin filaments of metal that sometimes
 spontainiously grow from coatings of tin or zinc or
 cadmium
 (and more rarely, other metals) applied over base
 metals
 (such as copper or iron) that would corrode if not
 protected.  These whiskers reach lengths of
 millimeters
 (or, more rarely, centimeters) and have caused
 electrical
 short circuits.
 
 The first report that we have found of failures
 induced by
 spontainious whisker growth was an article in 1946 by
 Cobb,
 writing of experiences of the Aircraft Radio
 Corporation
 (ARC), where cadmium was applied to the plates of
 air-spaced
 variable capacitors, and its whiskering had caused
 failures.  A few years later, an author of a report
 from Bell Labs (Murry Hill, NJ) mentioned that
 cadmium
 whiskers had caused failures of radios used early in
 WWII.  Bell Labs (Murry Hill) is less than 20 miles
 from ARC, who got an order for many radios at the
 start of
 WWII, and got production help from both Bell Labs and
 from
 Western Electric.  And it seems likely to Jay and me
 that the cadmium-whisker-induced failures mentioned by
 Cobb
 were happening in the radios that ARC (and their
 co-producers) that were delivered into aircraft used
 in
 WWII.
 
 As part of our effort to detail harm caused by metal
 whiskering in electronic equipment, Jay and I have
 been
 looking for any details of these radio failures.  We
 have heard rumors that the repair manuals for ARC
 equipment
 spoke of ways to identify shorting problems in the
 air-spaced tuning capacitors, and spoke of ways to fix
 these
 when found.  But we do not have any specific texts.
 
 I have found mention that "Engine and radio problems
 caused
 delays, but on April 15, 1943, the first Thunderbolt
 kill
 was made by a 4th Group leader."  But that is too
 vague
 to be of help to us.
 
 Sincerely,
 Henning Leidecker
 

   
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