[sdiy] Ge transistor tester weird results

sleepy_dog at gmx.de sleepy_dog at gmx.de
Mon Feb 7 19:04:15 CET 2022

I remember reading something about hFE measurements, done by usual
testers for SI stuff,
being unreliabe, due to larger leakage current than n Si.
IIRC that's also temperature dependent, so testing them a lot might
cause changes?
Soldering damages those old things more easily than more modern
transistors. I'd socket them.

cheater cheater via Synth-diy:
> 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/
> As you can see, it's a simple device that has a ZIF socket. It will
> auto-find the device's pinout and can figure out what sort of device
> you put in it. For a transistor it will calculate the Vf and the hFE.
> When I test a new Si transistor, say a BC558, it will auto-find the
> BCE pins and show a schematic diagram of a PNP transistor. The hFE
> might drift between tests a little, up to 1%.
> I also tested the 20 AF306's I got, which are Ge transistors, with hFE
> min 10, and they have the same TO-92 package as the BC558. First of
> all, the schematic shown always shows the transistor in parallel with
> a diode. I assume that's because the Vf is ~0.3V, and the tester
> assumes Si, so it guesses there's a diode there.
> Second of all, the hFE on those drifts a LOT between tests. As I keep
> on repeatedly testing, it will drift up or down by maybe 10-20%, first
> quickly and then slowly. The direction of drift is always the same for
> the same transistor, but it will be different between transistors. As
> the hFE drifts, the Vf drifts with it, too. If I take a small pause of
> several seconds, the hFE will drift back close to its initial value,
> but if I resume rapid test runs, it will drift away to its "final"
> value more readily.
> 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.
> 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.
> How does one explain the weird drift and the super high hFE?
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