rare components and mysterious electronics applications

[pir]

please do a blog about some of not well knowned and mysterious-rare electronics like:

tunnel diodes
varicaps
Lambda diodes with FETs...e.t.c.

and some uses of them
like dip meters
dynatron  oscillators...e.t.c.

in short words ...the most hockus-pokus ever

[SeanB]

How about backwards diodes, our good old Gunn diode ( which is not really a diode other than it has 2 terminals) and Impatt diodes.....

[pir]

How about backwards diodes, our good old Gunn diode ( which is not really a diode other than it has 2 terminals) and Impatt diodes.....

 
i love it..!!

complex tunnel semi roX

[xDR1TeK]

There are many components that in today's standards are few in numbers. Some are deprecated and no longer in production (discontinued).
The only ones I truly miss are the the phosphorus 7 segment displays found on calculators and such.
Not rare though but they were memorizing mesmerizing.

[SeanB]

And then you come to holloware and the many funny units that are available in that form, with assorted functions. There are so many ways to make a simple diode do things.

[jeroen74]

The only ones I truly miss are the the phosphorus 7 segment displays found on calculators and such.

Vacuum Fluorescent Displays are still widely used in home AV equipment, Point of Sale terminals, industrial equipment, lab equipment, those printing desktop calculators etc. So it's far from an obsolete technology.

The reason you don't see them in battery powered calculators is simply power consumption. LED and VFDs in that application disappeared overnight when LCD technology took off.