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Pimpom Pimpom is offline
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Default Vintage transistors and tin whiskers

On 5/17/2020 7:45 PM, Cursitor Doom wrote:
Gentlemen,

I have some old OC171 transistors from an old Eddystone short wave radio
I'm restoring. The problem is I suspect they've developed whiskers, as
the resistance readings from e,c and b to the screen connection are all
far too low (sub 10 ohms). A colleague has suggested blasting the
whiskers by tying the ecb leads together and zapping them against the
screen with a 500nF cap charged to 500VDC. Now this seems a bit counter-
intuitive to me and I'd have thought higher current lower voltage would
be safer for these delicate germanium devices, but WTF do I know?
Is it feasible to remove the whiskers by this sort of method or any other?

Thanks,

CD

I don't know about the whiskers but Ge transistors have high
leakage and no sharp knee at low currents. I wonder if 10 ohms is
too low depending on the voltage applied by your meter. I have a
few of the later AC188 types. I'll dig them up tomorrow and
measure their resistances.

For quick go-no go checks of transistors, I prefer analog MMs.
The static forward resistance depends highly on the current
applied through the probes.

I used to have some OC71s and OC72s a long time ago. They made
neat phototransistors with the paint scraped off from their glass
enclosures.