K.D. Smith and the Telephone Click Reducer
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K. D. Smith and the Telephone
Click Reducer

 By Dave Smith
 (c) SMEC / SMECC Reprinted from SMEC Vintage Electrics Volume 2 #1

One of K. D. Smith's early contributions was the observation, while experimenting with copper oxide diodes, that the diodes had at low voltage initially high impedance in the forward direction. This meant that a relatively high voltage was required before electrons started moving in the proper direction through the diode. 

This characteristic proved useful, as it prevented the passage of low voltage voice signals through the diode that was in parallel with the earphone but would clip the higher voltage level of the clicks and static sending their currents through the diode to ground.

This diode, was for decades, installed in every telephone handset in the world. It proved to be the cheapest noise filter until the silicon click reducer diode came along. This silicon click reducer was also a contribution of K. D. Smith!

The Bell Telephone Laboratories was greatly impressed by K. D. Smith's ingenious use of this casual observation, and K. D. Smith a handsome raise early in his career. - DS

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