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Mullard 0A81 OA81 germanium diode, crystal set projects
Mullard 0A81 / OA81 Germanium Diode for Crystal Sets and other Radio Projects
As described above, an old style germanium signal diode removed from a radio suited for any crystal radio project having several advantages over the modern replacements, those being:
Unambiguous red coloured markings for the cathode, the "pointy end" of the diode.
Bigger physical size making it easier for kids, or in fact anyone to handle.
The paint can be scraped off to reveal the cat's whisker wire making contact with the germanium crystal.
I have checked all of these with a modern diode tester for forward voltage less than 500mV and low reverse leakage.
Here is a sensible crystal radio design:
http://homepage.ntlworld.com/henry01/loud_crystal_set_radio/loud_crystal_set_radio.htm
This is also exactly the part for including in a recreation of the H.C. Dobbs "Making a Transistor Radio" Ladybird book regenerative receiver, and you can see an example here:
http://homepage.ntlworld.com/henry01/ladybird_radio/ladybird_radio.htm
