[sdiy] Ge transistor tester weird results

cheater cheater cheater00social at gmail.com
Mon Feb 7 21:06:30 CET 2022

I don't know that heat's the deal here, I mean they're not hot to the
touch, and a single test is very short. I mean, they might have warmed
up, who knows. But I haven't noticed anything special.

On Mon, Feb 7, 2022 at 7:07 PM Steve via Synth-diy
<synth-diy at synth-diy.org> wrote:
> 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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