Hi y'all,
Mostly as an excuse to fiddle with my new inexpensive Fuji Finepix A350 digital camera, I took these pictures of a rare diaphragm. This is believed to be a prototype D-175 diaphragm, hand built by Jim Lansing in about 1946. It was formerly owned by Hal Cox, and was given to him years ago by William Thomas, longtime owner of JBL. Thomas gave his friend Hal a whole bunch of stuff at one point that had reportedly come out of Jim Lansing's work area in the old Fletcher Drive factory.
Most noticeable difference from typical late 1940s 175 diaphragms is the lathe turned brown phenolic mounting ring; all of the production items I have seen used a cast black phenolic ring. Next unusual feature is the way the leads are dressed. Instead of beryllium copper lead outs, the voice coil wire itself is dressed across the tangential compliance and up the outside of the mounting ring to the screw terminal. There were pieces of black electrical tape covering the wires on the outside of the mounting ring, but the tape has fallen off on the side I photographed. This style of dressing the leads is similar to many of the Western Electric 555 diaphragms.
Jim Lansing's handiwork was always meticulous, and this diaphragm is as good an example as any. The edgewound aluminum voice coil looks like a single band of metal, it is so smoothly wound. The only crude aspect is the haphazard way in which the shims beneath the mounting screws were fashioned. Perhaps they were added by someone else later on.
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