The First Strain Gauge?

On a recent trip to NYC, Frank (the guy who suspends a broomstick from a piece of fishing line and calls it a tonearm) brought me a very special gift from the Pfanstiehl Chemical Company of Waukegan, Illinois.  Inside this box is to date the earliest sample I have seen of a strain gauge phono cartridge and matching power supply.

For one year in 1946 Capehart used a Pfanstiehl strain gauge cartridge in one of their high end 78 record changers before switching to a GE variable reluctance cartridge.

Since the phan-Tone is a flip-over cartridge (with two individual gauges) that can play both 78's and 33/45's it must date a few years after the Capehart misfire so there still may be earlier ones out there.   This one is still a very cool vintage mono cartridge with a sapphire stylus on either side that tracks at a mere 7 grams and I want to thank my brother for the wonderful gift.