I am in a little trouble and seeking some help. I got a bunch of mixed up diodes from an old collection. I know there are few diodes which are Germanium Diodes. But they look so similar to 1N4148 and similar transparent case diodes. The problem is, the diodes are old (but working) and it's very difficult to read the numbers printed on them. How can I identify and distinguish Germanium diodes? Can I measure something with a multimeter, or create a simple circuit to identify the Germanium diodes. I am looking for identifying diodes like 1N60 and 1N34A. I would highly appreciate your help!
Use this schematic to test the diodes. You can easily distinguish Silicon and Germanium Diodes. Silicon diodes should read approx 0.7V and Germanium diodes should read 0.3V. A little difficult to distinguish Schottky diodes though. They should show approx 0.2V which is close to 0.3V. If you have a very stable power supply and a good meter you can distinguish this as well!
Germanium diodes have a lower forward voltage drop than silicon diodes. Rig up something that puts a little current thru them, and measure the voltage.
For example, a 5 kΩ resistor in series with a 5 V supply should do quite well. The current will is limited to 1 mA, and the reverse voltage to 5 V. Neither should hurt any of the diodes you have.
Silicon diodes will have around 650 mV forward drop. Germanium will have about half that.
Note that silicon Schottky diodes have about the same voltage drop as germanium diodes. If you think there might be some Schottky diodes in the mix, then it gets more complicated.
The continuity test function on many multimeters has a "diode" setting that will tell you what the forward voltage is, from which you can infer the type of diode.
Using diode test mode on a DMM is the best way. It will use some standard fixed current like 1mA to measure voltage up to maybe 3V. This is also useful for comparing LEDs. If you dont have a DMM, get a good one.
There is no real need for old Ge , as Schottky performs better and diode capacitance * forward Rs= (ESR) resistance , which is relatively constant is better on Schottky and ESR=k/Pd for power rating Pd.
In fact some manufacturers are making the 1N60 with Schottky Silicon instead of the original Germanium.
Real world germanium diodes (even recent production) almost always come in a larger glass body (diameter about equal to or even thicker than a 1N4007, slightly longer. Not unlike a small reed switch), either left clear or painted black. With clear case examples, the insides will appear mostly see-through hollow (instead of mostly filled with red/orange copper tampers, like you will see on a 1N4148 or similar), sometimes with a visible hair thin wire going towards the actual semiconductor element.
This old case style has been used for silicon parts too, but is VERY uncommon for them.
Germanium semiconductors in molded plastic cases are an ABSOLUTE exception (only one I am aware of is the AF279 HF transistor), since most germanium parts were made in processes that require the part to be kept in a clean, hermetically sealed case (which plastic molding does not reliably provide). So, anything plastic molded will be silicon.
For power diodes, the same style of metal cases have been used for both Si and Ge devices.
If the labelling is partially readable: european parts whose designation starts with "A" are always germanium, "O" is so old that is is LIKELY germanium, "B" is silicon.