Mullard 0A81 Germanium Point Contact Crystal Set Diode Tested OA81

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.

There are various crystal set experiments and musings available on my websites:

A Good Loud Crystal Radio Design With Some Justifications And Digressions

The More Standard Parts Crystal Set Version 2

The HJW Electronics Choccy Block Crystal Set Radio Kit CBCSRK-1T