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From: John Davidson
Date: 9/3/99
Time: 10:54:28 AM
Remote Name: 206.16.140.254
Jim Your view on a metal junction detector was of interest. Several of us, and especially Mr. Pizzella, are trying to understand how galena works as a point contact junction detector. My understanding of a Fe point on razor blade is that the selenium protective coating on the old time blades was the semiconductor. In fact, I heard that is how International Rectifier decided to try to make selenium rectifiers. Now, since blades are no longer coated with Se, it is rusty spots that contribute (and not so well) the FeO2 as the semiconductor. I have noticed that only special kinds of rusty spots work well.
Your explanation of the point emitting electrons is interesting, as I have seen it, although I thought that only occurred at HV, but indeed HF aggrivates it. We have only a volt of so and it seems the iron blade would interfere with that field.
I always suspected that galena, as a semiconductor, simply forms an ordinary point contact (Schottky barrier type) junction with the PbS. (As you may know, point contact junctions operate slightly differently from planar 'grown' junctions.) My explanation fails to account for the hot spots, and cold spots in galena. Others say I am wrong, they suspect germanium impurities form the junction. ... and the quest continues.
Regards, John
From: John Nix
Date: 3/18/99
Time: 8:19:19 PM
Remote Name: 208.158.229.4
Have any of you tried to build a crystal loudspeaker? Article on same: (title lost in Xeroxing), by William J. Millard, Elementery Electronics, May-June 1968 P.49-55.