MIKE ROSS wrote in a message to Greg Mayman:

 MR> That's true. I've only run across some really strange small devices
 MR> once or twice which I was hard pressed to identify which leads were
 MR> which. One device turned out to be an SCS, a Silicon Controlled
 MR> Switch, basically a PNP and NPN transistors in series (C-p to B-n &
 MR> B-p to C-n), sort of like an SCR except you can turn it off.

You can turn an SCR off.  Just gotta hit it right...

In fact there were some sold as "gate-turn-off" devices as I
recall.  I can't remember part numbers or what was specifically different
about them,  but...

And then there was the circuit I breadboarded one time,  had a couple of
SCRs with small lamp loads,  and the anodes were coupled by a capacitor, 
something like 100nF.  Turning one on would usually turn the other one off.

I'd call an SCS sorta like an SCR but with an "anode gate" as
well as the typical "cathode gate".

I knew there was a way to envision both of these devices as a pair of
complementary cross-connected transistors,  couldn't remember how it went
until I finally happened across it on a website (4QD).  The resulting
device can also be considered a PUT,  as well.  I think this is pretty
handy...

Out of a fair number of parts that I was recently sorting,  there was *one*
UJT,  and *no* SCRs,  though there were a few TRIACs.  So now if I need a
UJT or an SCR I can "make" one by using a couple of bipolar
transistors,  and get pretty much the specs I want.

 MR> Another was in a batch marked as RF transistors. It had a 
 MR> relatively low static HFE, and I really couldn't figure out which
 MR> was the collector or emitter but the clue was that in most 
 MR> transistors the collector to base has a slightly higher resistance
 MR> reading on an ohm-meter.

Do they?  I'll have to keep that in mind.  Though I don't do much with RF devices.

 MR> To make things worse it even had a diode from emitter to collector 
 MR> sort of like the damper diode built into horizontal output 
 MR> transistors.

And it was an RF part?  How odd.  I don't think I've ever encountered one like that.

For the ones I can't identify,  there are a couple of TO5 cans with 6
leads.  The only diagrams I have of 6-leaded TO5 cans are showing the
little tab as being in one of the gaps between the leads,  but that's not
what I have here, the tab is at one of the leads in the middle of one
group.  Resistance readings are rather odd,  too -- very low resistance
between the middle one and the end one in one group,  but not the other. 
Very odd.  And I have two of these,  longish leads,  never been soldered
(new?),  and they both read the same.  I'll find out eventually,  I guess.


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