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Michael Black[_2_]

On Wed, 5 Apr 2017, wrote:

It seems the most "famous" germanium diode was the 1N34(A). Heck, I
remember that number from way back....

I googled up a data sheet for ALL germanium diodes. (Assuming they are
all listed), it seems there are about 20 of them.

The 1N60 is another common one, along with 1N270.

Anyhow, my reason for an interest in them is because I'm making up some
RF probes for my old oscilloscope and other test gear. These probes are
very simple, a cap, resistor and a diode. Making up a suitable housing
is more troublesome than the electronics within them.

I downloaded a bunch of schematics from the old Heathkits and Eico kits
and others. They are all pretty much the same, except some use the 1N34
while others use the 1N60. One of these has a slightly higher PIV (I
forget which one). Otherwise they dont seem too much different.

I am just wondering why some use 1N34 while others use 1N60? (and none
use any of the other germanium diodes). Is there any advantage or
disadvantage to either of them?

The 1N34 was available to hobbyists early, probably because Rufus P.
Turner was connected to its development.

Realistically, what's being referenced is a germanium diode. The part
number was a descriptor, when you saw it you knew it was a germanium
diode, and that was really all that mattered. The number kept being used
because it had been used, and diodes with that number were available
through hobby outlets. I have no idea if they were all 1N34s, but they
would have all been germanium small signal diodes.

For the hobbyist, it didn't matter. They'd be used for "crystal radios",
field strength meters, rf probes, and maybe diodes in the detectors of
superhet receivers. It was never a fussy thing, except that they be
germanium. I guess the 1N82 was germanium, seen in UHF tuners as a mixer,
and used in such hobby projects where a high frequency diode was needed,
like crystal radios intended for the aircraft band. So I guess a lot of
UHF tuners in the old days had a germanium diode in them. I found a bunch
in the FM detectors of various FM broadcast radios, at a time when I would
have though silicon had taken over, indeed transistors in the same radios
were silicon.

Also, why dont they use Silicon Diodes?

Because the germanium diode has a lower forward voltage drop.

Schottky diodes have lower forward voltage drop than silicon, though I
can't remember if it's lower than germanium. A DMM with a diode function
will easily separate them, all three diodes have a distinct voltage.

I went through a bunch of boards at one point, and uncovered a lot of
germanium diodes this way, certainly more than I expected.

Michael