My Transistors, original or copy?

MPSA42 from China "New Stock":

Tested with a cheap tester: hFE 160, Ie 1.2mA, Ube 579mV
High chance it is fake, but if so, what real transistor is underneath that plastic?
Who the hell knows? Might even be “real”.

Put it on a 300 volt DC supply collector to emitter, in series with a 100k resistor. Measure the leakage current. If it’s well under 1 uA, go ahead and use them. If not, stick with lower voltage, non-critical useage. Measure the actual vceo (where it zeners) and stay well under it. This sort of test jig won’t blow a 2N3904. It’s not good for it, as you can degrade the hFE and noise over time with the test.
Yes, it actually is. Keep Pdiss under control, and keep the test short. I used to grade “ungraded” TIPs, salvage, and grab-bag parts from Poly-Paks that way. As well as using Radio Shack parts above Vceo. The old RCA data books used to explicitly state against testing “on a curve tracer” because you can very easily get it into second breakdown as the current rapidly climbs. Limit with a high value resistor or current source and the only thing you could do to it is degrade the hFE. Don’t grade low noise input stages that way. But i have graded 2N3904’s and 2SC945’s for higher voltage operation this way and had them still work as expected. Was the noise figure degraded? No idea. Theory tells you it would, but it didn’t make anything hiss more than I’d expect. If an application is critical, you just don’t resort to these tactics.

This will not tell you anything about second breakdown. But no TO-92 known to Man as its S/B limit inside of its Ta limited thermal limits. Tc yes, but that’s not how you use parts like this. When you have to go heat sinking a TO-92 you’re using something too small to begin with. It’s very tempting to use the simple vceo to determine “what I can put on this unknown or potentially fake TO-3”. It must be supplemented by an operational test, such as a 50V/3A test jig. That was my old “golden standard” in the early days - it passes that and you can make an amp out of it. It fails, nothing is really lost…..
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