Mullard 0A81 Germanium Point Contact Crystal Set Diode Tested OA81
$2.61
This is one item of used Mullard OA81 diode recovered from a 1960s transistor radio. You might prefer to use one of these original larger germanium point-contact types if you're making a crystal set. These have all been tested for less than 500mV Vf at 0.89mA. The paint may have flaked a little in places and the picture shows a typical item. If your design specifies an OA91, the OA81 will do fine as according to the 1969 Mullard data book, the OA91 is just a physically smaller version. The higher pack quantities are cheaper per item.
There are various crystal set experiments and musings available on my websites:
Crystal Set 1
https://www.interestingelectronics.com/old/henrys_interesting_electronics/loud_crystal_set_radio/loud_crystal_set_radio.htm
Crystal Set 2
https://www.interestingelectronics.com/old/henrys_interesting_electronics/crystal_radio_v2/crystal_set_radio_v2.htm
Crystal Set 3
https://www.usefulcomponents.com/main_contents/projects/choccy_block_crystal_radio/choccy_block_crystal_radio.html
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