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What specific type of diode (presumably) is the logo for Electrical Engineering Stack Exchange?

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    \$\begingroup\$ Nothing really as far as I can tell. \$\endgroup\$ – DKNguyen May 28 at 19:01
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    \$\begingroup\$ That's a 1N4148. Or maybe a '914. Hard to tell exactly! \$\endgroup\$ – SteveSh May 28 at 19:13
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    \$\begingroup\$ With the circle round it, I think it's old enough to be an OA45. \$\endgroup\$ – Brian Drummond May 28 at 19:25
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    \$\begingroup\$ I suspect it is a relic from vacuum tube days (5U4GB, for example.) When semiconductors appeared on the scene, the cathode and anode needed to be replaced with something distinctive, while keeping the basic diode/triode/etc symbol recognizable to those more familiar with tubes. But I'm no historian. I hear Don Lancaster is still alive (Spehro?) He'd know. \$\endgroup\$ – jonk May 28 at 19:45
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    \$\begingroup\$ @jonk, I looked up Don Lancaster's site here: tinaja.com/whtnu20.shtml. Since he posted on may 26, proof of life as it were. Even if the site design made my eyes bleed, even by Web 1.0 standards. \$\endgroup\$ – hacktastical May 28 at 20:06
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"Standard" diode.

Not LED, not schottky, not zener, not TVS...

The circle is an optional style that was popular a while back, but now diodes are mostly drawn without the circle around them.

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    \$\begingroup\$ I've seen some styles that call for the circle to indicate a "real" device where the uncircled version is an ideal device. \$\endgroup\$ – The Photon May 28 at 20:27
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    \$\begingroup\$ @ThePhoton That's interesting! Do you have a link you can share? \$\endgroup\$ – Aaron May 28 at 22:16
  • \$\begingroup\$ is the unfilled triangle significant? \$\endgroup\$ – stib May 29 at 3:49
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    \$\begingroup\$ In a rather informal convention, a circle around the element means a discrete element, no circle means it is a part of an integrated circuit. Transistors are for sure drawn like this and the circle means packaging. One can see a Darlington transistor to be drawn with a circle around both transistors. \$\endgroup\$ – fraxinus May 29 at 9:02
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    \$\begingroup\$ Many years ago, the circle was used to denote a discrete device. Symbols without them were part of an integrated circuit so when looking at the circuit of a TTL part (to understand how it operated, which is still a good idea) there were no circles. This was almost universal in the 70s and early 80s but slowly fell out of use when ICs started to simply show an equivalent circuit in the datasheets (and designers couldn't be bothered to draw a circle that started to have no real meaning). \$\endgroup\$ – Peter Smith May 29 at 9:31

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