On Saturday, 13 March 2021 at 06:00:06 UTC-8, Bill Sloman wrote: ..
Thanks.
I found a stash of newer generic transistors I'd forgotten about so I tested a few of those for breakdown voltage.
The others I had tested were 30 or so years old that I got when a company I was at stopped doing hardware development and cleared out their labs.
Interestingly the breakdown voltages are much higher with the new ones, more in line with Fred's estimate.
Also interesting is that the breakdown voltage drops by ~30mV in the first minute of applying the current. It is somewhat reversible; resting it a few minutes seems to allow it to largely recover.
I wondered if there was concurrent change in Hfe as has been reported, but I could not measure any significant change.
Reverse Base Emitter Breakdown voltage @ 100uA
2n4401 NPN 1) 7.851 NSC old - Rise a few mV at start 3) 7.854 NSC old 2N3904 NPN 1) 7.599 Motorola old 2) 7.276 Motorola old 3) 7.579 Motorola old 4) 10.913 Generic new (-30mv during first few seconds + tempco) 5) 10.915 " " 6) 10.881 " " 2N2222 NPN 1 7.452 NSC old 2 6.902 NSC old 3 7.856 NSC old 4 8.755 Generic new (-30mv during first few seconds + tempco) 5 8.766 Generic new " 6 8.738 Generic new " 2N3906 PNP 1) 7.395 Fairchild old 2) 7.438 Fairchild old 3) 6.746 Motorola old 4) 11.469 Generic new 5) 11.395 Generic new (Hfe 296/296 -30mV) 6) 11.441 Generic new (Hfe 304/302 -30mV) kw