How to test Germanium transistors? Ambiguity all over

Описание: CORRECTION to the video: on 2.14 I say “we have here the Silicon transistor” but of course I mean: “The Germanium transistor” (!), also when explaining that further..

Measuring whether a Germanium transistor is good or bad. Is it good or bad? Ambiguity all over.

Measuring Germanium transistors can give very doubtful results. This video gives some rules of thumb.

Test procedure:measure the resistance with an Analog (not digital) Ohms meter between C and E, probes + and – reversed or not.

After that check the diode-functions inside the transistor by measuring the resistance with that Analog Ohms meter between B and E and B and C. One direction: low resistance (current flows), the other direction (probes reversed): no current flows (=high resistance). Refers both to NPN and PNP, Silicon or Germanium, though Germanium can “leak” current in the reverse-mode-measurement: when you expect endless resistance it is 200 K or 500 K.

Conclusion: when you measure Ohms resistance between C and E of a Germanium transistor: don’t throw it away, unless you measure in both (!) directions (C-E, probes +/-reversed and not reversed) a low resistance, say: 100 Ohms or 1 K or 5K. If so: there is a shortcut between collector and emitter of the Germanium transistor. Measurements also depend on temperature: Germanium transistors are extremely temperature sensitive, current between C and E rises substantially depending on the temperature (Silicon: no problem or a minor problem).

When you measure any resistance between the Collector-Emitter of a Silicon (!) transistor (PNP or NPN: throw it away (probes +/- of the analog Ohms meter reversed or not).

You can, by the way do the same measurements on the basis-emitter diode and the basis-collector diode. It could even be that (in a peculiar case) one of these diodes is defective (shortcut) while you measure a high Ohms value between C and E. In case of Germanium this is (more or less) impossible.

When a Germanium transistor shows defectives inside the B-E or B-C diode, this will be visible in the Ohms resistance between the C and E (probes +/- reversed and/or not reversed).

So use an Ohms meter with a 3 Volt battery inside, if not 3 V it could be that the barrier voltage of a transistor is not reached, conduction measurements get cumbersome and ambigue .

The voltage with which Ohms measurements are made in hobby (and professional) meters depend on the construction of the Ohms meter. Many hobby meters measure Ohms resistances with a 3 Volt battery, no problem in that case.

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Test a Germanium transistor in an oscillator circuit
   • Test circuit for (PNP) germanium transisto...  
But there are - of course- easier to make Ge trans oscillators.