Post by Michael BlackPost by J.B. WoodPost by philoAs a kid I was an avid reader of Popular Electronics and built
projects often.
One day they featured a new item called a tunnel diode.
When I went to the local electronics stores they did not stock them
nor did they want to place a special order....just for a kid. They
were not rude but told me they simply could not obtain such a part.
Fifteen years later, as an employed adult working as a service
engineer for a major corporation I needed a tunnel diode for a repair
job. Much to my surprise I was still treated as a kid and politely
told they could not obtain such an item.
In frustration I said, "But it's for A.O. Smith."
Their immediate reply, "How many do you want?!"
I still have the spare.
Hello, and I remember a few magazine electronic projects calling for a
tunnel diode. IIRC one such project was for an FM bcst tuner. One of
my EE undergrad profs termed the device an "electronic Edsel". A
device in search of a practical application(s). Maybe a one-port RF
amplifier (like a circulator-MASER combination)? Sincerely,
I think that's a fair assessment, with some exceptions.
For about a decade, the hobby magazines covered the tunnel diode. It
was a novelty item, and the projects never amounted to anything much.
Any use we saw in hobby magazines could be done with some other device,
wireless microphones, receiving converters, "grid dip oscillators",
whatever. Sp the projects were all simple. GE had a section in one of
their early sixties transistor manuals devoted to tunnel diodes, that
also probably helped. I think they issued the section as a separate
book at one point. It was full of circuits that used the diode, but
again nothing out of the ordinary. That was a source of many of the
magazine articles, "101 things you could make with tunnel diodes".
There was an interesting FM broadcast receiver, a tunnel diode as a
mix/oscillator dropping to about 200KHz IF, the IF was RC coupled, and
then a pulse counting detector. It was neat because it was different,
not because of the tunnel diode. Oddly, much later I found an article in
a late forties QST about a similar receiver, except using tubes, and it
originated from GE too.
I do have a Sony "portable" AM/FM radio, nice and heavy, that even
mentions "esaki diode" on the front panel, but that's probably about the
only consumer device that used it.
On the other hand, it was much later that I came to learn that tunnel
diodes had seen use in lab equipment, I think triggering devices in
oscilliscopes and probably elsewhere. Probably at the time they offered
some advantage, but it sure wasn't novelty.
Maybe when they first arrived they offered some advantage in terms of
how high in frequency they went, but it was a blink, and soon
transistors took over in that area.
And yet, even twenty years ago it was common in sci.electronics.basics
to have people ask where they could get tunnel diodes. It would turn
out they saw some schematic somewhere "on the net" and probably liked
the simplicity. But since it was just a schematic, it offered no
insight into the fact that tunnel diodes were a mostly passing phase and
if you could get them at that point, they'd be expensive.
Michael
For the repair I did at A.O. Smith the tunnel diode was in a charger for
stationary batteries. I at first replaced it with a standard diode not