[sdiy] Ge transistor tester weird results

[René Schmitz]

Hi cheater cheater,

On 07.02.2022 18:46, cheater cheater via Synth-diy wrote:
> Hi all,
> I recently bought and tested a few Germanium transistors in my small
> semiconductor tester and I got weird behaviors.
>
> I have this transistor tester:
>
> https://www.amazon.de/ARCELI-LCR-T4-Transistor-Kapazit%C3%A4t-Induktivit%C3%A4t/dp/B07J2Q4VY9/
>
Those testers are mostly based on an open source firmware that came from 
here:

https://www.mikrocontroller.net/articles/AVR_Transistortester

If you want to know more how they detect and measure that is a good 
starting point.

(There are English and other translations.)

I don't think Germanium was not on their check list, even if it came 
from a German forum. :)

> In addition to that, out of the AF306's I tested, there are some in
> the hFE 10-40 range, some (fewer) in the 40-100 range, and then there
> was one that's hFE 100, one that's around 250, and a couple that's
> 400-500. I don't know how to explain the ones that are hFE > 100.
> What's going on here? Are they really that strong? Are they broken?
> Also worth mentioning at hFE 500 the tester gets confused and assumes
> the device is a P-JFET.

hFE of 50 - 200 I would consider normal, but the higher values look 
suspicious.

It is possible that this device is not drawing any (or much) base current,

yet has enough CE leakage current to be detected. hFe = Ice/Ib.

This can be interpreted as a high hFE, or mistaken for p-jFet, or plain 
broken Ge PNP.

To test this: It should make a difference when the base is not connected.

You can also try to measure the BE diode alone.

> My guess is that once the tester figures out this is a transistor it
> will just test hFE with a DC voltage and a very small current. So
> given that is the case, and that a lot of the Germanium transistors
> are in the right range, I don't think that the very high hFE
> measurement has to be off... but I don't know what might be happening.
>
> My main worry is that those transistors are broken and if I put them
> in a reasonable circuit they'll try to output so much power they'll go
> up in smoke. Or maybe it's something more subtle, like a lot of noise
> being read by the ADC as high output current, or something like that.

Depends, in a power stage you might get smoke. In small signal

circuits, there should be resistors delimiting the amount of current,

even if the transistors became dead shorts.


> How does one explain the weird drift and the super high hFE?

Ge has lower intrinsic resistance compared to Si, and hence more leakage.

And consequently you notice more temperature effects.


Best,

  René


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