JS and JA (1940 to 1954) Previous
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In 1940, the HFS and HFA meter were replaced by the JS and JA meters. The basic concepts behind the HFS and HFA meters were retained and updated. Initially, these meters were to be produced with chrome steel magnets, but just prior to production, these magnet assemblies were replaced with new Alnico magnets. The steel base on the HFS (which was prone to rusting out) was replaced with an aluminum base on the JS.
 
JS
Pete Mallet collection
JA
Photo by David Dahle