1N34A diodes. Cheap vs expensive.

[Rob Strand]

https://www.radiomuseum.org/dsp_more_tubepix.cfm?tube_pk=8526&type=T
https://www.radiomuseum.org/dsp_more_tubepix.cfm?tube_pk=34150&type=T

For the package you won't get Schottkys in the glass cases (the fakers haven't gone that far yet).  So a glass case is a good indication you have real germaniums.

It you get diodes that look like 1N914's or small Schottky's BAT46's the chances are they are not germaniums.   The only old school package which even looks remotely like these is the your middle-left pic but if you look at it closely it still doesn't really look like the modern packages.

[PRR]

> glass case is a good indication you have real germaniums.

1N914?

[Rob Strand]

> glass case is a good indication you have real germaniums.

1N914?

I mean the glass case styles in your pic   The common germanium package.
In other words if it looks like a germanium it is probably a germanium!

[iainpunk]

So a glass case is a good indication you have real germaniums.

i guess my 2N4148's are germanium now, haha,

cheers

[PietS]

Thanks everybody for all the tips and pointers.

I got a few that were sold as 1N34A for $0.40 a piece at a local electronics shop. Glass casing, black line with red in center. They didn't look newly made so had good hope.

Forward voltage with diode test setting on cheapo DMM reads 160-170mV, nothing in reverse. Basic resistance measurement with DMM reads around 2K in forward direction and around 35k in reverse.

Then I tested forward voltage drop using a 9V battery and a 1k and 10k resistor. At 0.9mA there was a 0.16-0.18V drop and at 9mA a 0.25-0.30V drop. The different individual diodes I tested were quite consistent.

Reverse biased with 9V, I got about 5-6uA leakage current.

I'm not sure what to think. They looks the deal and they seem bit leaky like Ge diodes should be but the voltage drop with 9mA seems more like a Schottky.

Edit: I heated them up with a lightbulb while measuring forward voltage, and forward voltage actually dropped about 15mV instead of going up. Also found out that leakage current at 9V for germanium diodes should be in the range of 50uA instead of 5. Bummer.

Edit2: Measured leakage using a 1.35V battery and got 4uA which is too high for a Schottky. Maybe it's new production with better characteristics?

Pic of the diode:

[anotherjim]

At higher current, the Vf does go up. Can reach 1v for some Ge. Si diodes can do this also. Schottky can equal ordinary Si junctions at higher current.
With glass Ge diodes, the point-contact structure can usually be seen...

The path through a diode will have some ordinary resistance, so voltage drop over that will increase with higher current and add to the apparent Vf.
.

[iainpunk]

>35k in reverse

that could be realistic, i have some real vintage AA119 diodes, they read 1.8Mohm in reverse, despite being Ge, that could just be up to the DMM
i did measuere reverse leakage at 10v with a 100k trim pot, i read about 5v over the diode, when the pot reached 24k
some Ge's leak more, some less.
schottkeys on the other had had OL readings on the highest settings, and had 0v when using a 10M resistor at 10v.

cheers, Iain

[PietS]

With glass Ge diodes, the point-contact structure can usually be seen...

[/quote]

I've added a pic to my post. Can't get bigger closeup but I don't see that thin bendy wire when using a magnifier.

[Phend]

"In a small silicon diode operating at its rated currents, the voltage drop is about 0.6 to 0.7 volts. The value is different for other diode types—Schottky diodes can be rated as low as 0.2 V, germanium diodes 0.25 to 0.3 V, and red or blue light-emitting diodes (LEDs) can have values of 1.4 V and 4.0 V respectively."

Here are 3 picture of 3 diodes, one is a real 1N34A. Others 1N914 1N4005
(Note on the meter Uf should be Vf and the symbol is reversed. (correct me if this statement is not correct))

[iainpunk]

"In a small silicon diode operating at its rated currents, the voltage drop is about 0.6 to 0.7 volts. The value is different for other diode types—Schottky diodes can be rated as low as 0.2 V, germanium diodes 0.25 to 0.3 V, and red or blue light-emitting diodes (LEDs) can have values of 1.4 V and 4.0 V respectively."

Here are 3 picture of 3 diodes, one is a real 1N34A. Others 1N914 1N4005
(Note on the meter Uf should be Vf and the symbol is reversed. (correct me if this statement is not correct))

Uf is absolutely scinetifically correct, the symbol for electrical tension is U. english is one of the few languages where tension is replaced by the word voltage, but that's technically incorrect.

cheers

[rankot]

"In a small silicon diode operating at its rated currents, the voltage drop is about 0.6 to 0.7 volts. The value is different for other diode types—Schottky diodes can be rated as low as 0.2 V, germanium diodes 0.25 to 0.3 V, and red or blue light-emitting diodes (LEDs) can have values of 1.4 V and 4.0 V respectively."

AFAIK, Ge diodes can vary A LOT with a Vf value - from 0.2 to 0.8V. I have a lots of them, some bought in Russia, some in China, they are definitely Ge diodes (according to the package and that you can actually see point contact inside), but they vary a lot. So it is always good to measure, or even better, to socket them and listen how they sound in a particular circuit.

[anotherjim]

Not all Ge diodes have the "cats whisker" point contact. There are other methods that are not so obvious.
I have some old Si diodes that look like what you have, but I can tell by the Vf they are definitely silicon.

Old semiconductors were either in glass or metal. I could be wrong, but I wouldn't expect to find Schottky diodes in the larger bottle glass casing - they are comparatively recent aren't they?

[PRR]

Here are 3 picture of 3 diodes, one is a real 1N34A. Others 1N914 1N4005
(Note on the meter Uf should be Vf and the symbol is reversed. (correct me if this statement is not correct))...

Symbol IS correct. (Though parallax makes it hard to tell 1 from 2 on the socket.) Stripe on diode is line on symbol.

[Rob Strand]

I've added a pic to my post. Can't get bigger closeup but I don't see that thin bendy wire when using a magnifier.

It looks like a solid "bar" inside instead of the wiggly wire like the pic anotherjim posted.

I've been doing electronics a long time and I've never seen a diode like that, not with the clear glass and "real germanium case" styling.    I'm thinking it's a Schottky with a casing designed to deceive.   The measurements look more like Schottky.

(Note on the meter Uf should be Vf and the symbol is reversed. (correct me if this statement is not correct))

Europeans have used U for voltage for a *long* time and everyone else uses V.   Both are correct, maybe think of the U as V with a European accent.    The IEC standards will push for U as they are fundamentally European.


EDIT 1:
Here's some yabbering on the topic,
https://electronics.stackexchange.com/questions/99584/where-does-u-for-voltage-come-from


EDIT 2:
It's possible the odd casing is the same as a photo-diode.

[iainpunk]

"In a small silicon diode operating at its rated currents, the voltage drop is about 0.6 to 0.7 volts. The value is different for other diode types—Schottky diodes can be rated as low as 0.2 V, germanium diodes 0.25 to 0.3 V, and red or blue light-emitting diodes (LEDs) can have values of 1.4 V and 4.0 V respectively."

AFAIK, Ge diodes can vary A LOT with a Vf value - from 0.2 to 0.8V. I have a lots of them, some bought in Russia, some in China, they are definitely Ge diodes (according to the package and that you can actually see point contact inside), but they vary a lot. So it is always good to measure, or even better, to socket them and listen how they sound in a particular circuit.

i have noticed the HUGE range of forward voltages as well, i have Ge's measuring up to 1.1v in my power diode stash. weird package, one lead and a threaded metal case.

Europeans have used U for voltage for a *long* time and everyone else uses V.   Both are correct, maybe think of the U as V with a European accent.    The IEC standards will push for U as they are fundamentally European.

the Europeans have used U for tension/potential since before the Edison decided it was cool to not use the global standards.
south America, Africa and large parts of Asia also use U, the Brits and US are the odd ones out, at first using T instead of U, and then transitioning to V in the 1880's.

cheers, Iain

[Rob Strand]

Here's what we are dealing with,

From
https://www.forosdeelectronica.com/threads/amperimetro-para-medir-potencia-de-un-transmisor.14897/

That sparked my memory, there's diodes call "Hot Carrier" diodes which came in a lot of odd casings.  They are basically a form of Schottky diode.

the Europeans have used U for tension/potential since before the Edison decided it was cool to not use the global standards.
south America, Africa and large parts of Asia also use U, the Brits and US are the odd ones out, at first using T instead of U, and then transitioning to V in the 1880's.

When I was a kid I had a lot of databooks/brochures/catalogues/publications from Siemens so I'm used to the European style and symbols.   When you deal with electro-acoustics the electrical V symbols are good because they don't clash with u and U symbols for velocity and Volume velocity.

[PietS]

I've added a pic to my post. Can't get bigger closeup but I don't see that thin bendy wire when using a magnifier.

It looks like a solid "bar" inside instead of the wiggly wire like the pic anotherjim posted.

I've been doing electronics a long time and I've never seen a diode like that, not with the clear glass and "real germanium case" styling.    I'm thinking it's a Schottky with a casing designed to deceive.   The measurements look more like Schottky.

You're probably right. Using a magnifier they do look like a junction diode and I don't see anything that resembles the cat whisker of a point contact diode. However, I've read that junction diodes were sometimes made with germanium so maybe these are like that. The leakage currents seem to be in the range expected from germanium. A long maybe but with a bit of luck these are germanium junction diodes with some of the desirable germanium properties at stompbox voltages. I don't know, I'm just brain storming.

I got some more stuff incoming, including breadboards and parts, some schottky diodes and a pair of expensive point contact 1N34A's from a reputable music store. I'll built a small circuit to test them using a range of small forward and reverse voltages (10-500mV) and see if the I-V curves at stompbox voltages look like Schottky's or more like real 1N34A.

[Rob Strand]

Using a magnifier they do look like a junction diode and I don't see anything that resembles the cat whisker of a point contact diode. However, I've read that junction diodes were sometimes made with germanium so maybe these are like that. The leakage currents seem to be in the range expected from germanium. A long maybe but with a bit of luck these are germanium junction diodes with some of the desirable germanium properties at stompbox voltages. I don't know, I'm just brain storming.

It's possible to make diodes like that but I just haven't seen any.

It's actually an interesting dilemma   What measurements can we make to determine if it's Germanium or Schottky?    Why do we care, what characteristic makes the difference, and if there is a difference why can't we measure it!

One difference is the incremental slope of the V vs I curve.   Probably need to cover 1uA to 10mA.

Normally we can see a difference between the two diode types at a test current of 10mA.  The funny thing is not many circuits actually push the diodes that hard.  It's just a convenient test to see the difference.

I had some thoughts that the band-gap voltage of silicon and germanium are different, which shows up in temperature tests.  However, Schottkys aren't exactly like silicon and the effective band-gap voltage ends up being a lot like germanium.  Reverse recovery is another difference but it needs a very careful set-up of the experiment, probably not practical for hobbyists.

[amptramp]

If I wanted to get a germanium diode that would not be likely to be counterfeit, I would select a 1N295 which was the standard detector diode for transistor radios, both AM and FM, and forget about the 1N34 and all its variations.  Many of these diodes have the colour code (red, white, green) on the cathode end serving as the cathode band, so it is hard to get confused.

The 1N60 was the standard video detector diode for televisions for a couple of decades and these are low-capacitance, low forward current devices.

I also have a stash of devices labelled "germanium" with forward voltages in the 0.6 to 0.7 range, so either deceit or confusion has caused this to happen.  I also have some in the 0.27 to 0.35 range that I believe are germanium, so measurement is your best protection against fakes.

[Phend]

Picture of a 1N34A that I have. Also it being measured, both directions, in cheap tester.
Note black band on diode and symbol on tester. No big deal.............