What is a ISS85 Diode

According to my schematic, D20 in a 25LTD Classic is a 1N4148.

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In the USA, a manufacturer who dreams up parts like diodes will "register" the design and the specs for it with a standards agency. Pretty sure this habit originated with the military, needing to impose some kind of order on the chaos of the 1950s semiconductor industry. Any other outfit who wants to license the thing, build and sell them now has a ready-made market if that part becomes popular. Everyone knows what a "1N4001" is without worrying who made it. And the radio designer who depends on what that part does won't have to first ask "who made this diode?" to have dependable specs for how it behaves.

In the USA, the industry's agency for this kind of registration is called JEDEC, for Joint Electron Device Engineering Council. You can thank them for all the "1N", "2N", "3N", etc type numbers.

In Japan, they have a similar setup called the "EIAJ", for Electronics Industries Association of Japan. They use a different prefix format for their registered semiconductor type numbers. A "1S" prefix just tells you it's a diode. A "2S" tells you it's a transistor with three legs. A "3S" tells you it has four. One more letter follows the "S". That letter tells you what kind of transistor or diode. A 2SA is a high-frequency PNP junction transistor. A 2SB a low-frequency PNP. 2SC high-frequency NPN ,and 2SD a low-frequency NPN.

Just can't remember what the second "S" in "1SS" tells you.

73

I’m showing D20 as a 1S2075 diode. That’s basically the same as a 1N4148. On the other hand, 1SS85 is a Silicon Epitaxial Planar Diode. Some dealers are classifying that one as a Varicap diode. Double check…Are you sure a 1SS85 was placed at the D20 location. I don’t have any problem using a 1N4148 at D20, but I would be hesitant substituting anything other than a1SS85 without further research.

This is the spec sheet on the 1SS85…
https://datasheet.octopart.com/1SS85-Hitachi-datasheet-103826.pdf

sunbulls said:

1SS85 is a Silicon Epitaxial Planar Diode

Click to expand...

Pretty sure the 1N4148 is, too. Datasheet doesn't state it as such. Just means the junction layers are grown by condensing vapor onto a crystal surface.

Thanks for the link. Didn't think to check there.

A varactor that only changes from 1.5 to 1pf would have a limited range of useful applications. I remember a gadget that was being sold to stabilize the analog VFO in old ham transceivers. Worked by hijacking the radio's RIT potentiometer circuit. If the radio lacked a variable-voltage RIT circuit, you would add it by using a 1N4001 rectifier diode as the varactor. Idea was that you didn't need a wide tuning range.

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A Diode with a true PN junction!

Rare treat to see these days!

The Older PN diodes with their P-I-N layers are being rediscovered as varactor's.

Thanks for the link!