rrw@naucse.UUCP (Robert Wier) (12/07/89)
Having seen discussions recently on the use of galena crystals in crystal radio sets, I thought that I would note the following: On page 27 of the current "Nuts and Volts" magazine, there is an ad by Yeary Communications of a "Cat Whisker" kit. Copy says "Authentic Cat Whisker and Galena Crystal Detector and Stand with All Brass Mechanism and True Woods Metal Crystal Mounting" circular and oval forms available: $19.95 & $5 s&h. address is 12922 Harbor Blvd, #800 Garden Grove, Ca 92640 Disclaimer: I don't know anything about 'em... just saw the ad... x --------------------------------------------------------------------- - Bob Wier Northern Arizona University summer:Ouray, Colorado winter:Flagstaff, Arizona USENET: ...arizona!naucse!rrw | BITNET: WIER@NAUVAX | WB5KXH
commgrp@silver.bacs.indiana.edu (12/09/89)
>On page 27 of the current "Nuts and Volts" magazine, there is an >ad by Yeary Communications of a "Cat Whisker" kit. Copy says >"Authentic Cat Whisker and Galena Crystal Detector and Stand with >All Brass Mechanism and True Woods Metal Crystal Mounting" > >circular and oval forms available: $19.95 & $5 s&h. >address is 12922 Harbor Blvd, #800 Garden Grove, Ca 92640 > >- Bob Wier Northern Arizona University Galena crystals are available cheap at "rock swaps" (like hamfests for rock collectors; ask a geologist where to find one). I bought a beautiful one-inch cube of it for about $1.50. Rock shops in cities have them for 4x - 8x that price. Some crystal-set plans use a metal tube with a setscrew to hold the galena. It's better to embed the crystal in low-temperature alloy (e.g., Wood's Metal: Bi 50%, Pb 25%, Sn 12.5%, Cd 12.5% by weight; melting point 70C. See CRC Handbook of Chemistry & Physics). The "cat whisker" is any sharp-pointed metal needle, mounted with a spring to maintain tension. If you do not insist on historical purity, a 1N34 point-contact germanium diode works much better. -- Frank Reid W9MKV reid@gold.bacs.indiana.edu
mmm@cup.portal.com (Mark Robert Thorson) (12/09/89)
For those who might be curious what Wood's metal is, it's an alloy of bismuth, tin, and cadmium which can be had in forms that melt in boiling water. Commonly used for the safety plug of pressure cookers and the part which opens up ceiling sprinklers for fire extinguishing. I hadn't known that they use it for mounting galena crystals, too. The comment about the diode drop of a galena crystal being about 0.05 V makes me wonder why they're aren't commercial devices with similar performance. Is there no application for such a thing? (Other than crystal sets, I mean.) And how exactly does a galena crystal work? With such an incredibly low diode drop, I assume there aren't any PN junctions in there. Is it anything like a MOS transistor with the gate and source connected together?