The asymmetry is, in fact, the only thing that makes
one end a
collector and the other end an emitter. If it were truly
symmetrical, it genuinely wouldn't matter which way you placed it.
But yes, it will (sorta) work placed backwards; I've had a number
of maddening debugging sessions that all boiled down to "I forgot
the standard pin ordering on a TO92 package", since the transistor
will *work* backwards, but is much weaker than expected.
I was 'led a merry dance' by this a few weeks back. I was working on a
1970s telephone answering amchine, a RecordaCall Bantam
The control system of that unit uses a number of interconencted SCRs
(thyristors). I found one that was certainly defective nad bought what I
believed to be identical replacements.
Upon fitting one, I got crazy results. That DCR seemed ot be turned on
all the time. Noting would turn it off. I disconencted the gate drive and
pwoered up. It was turned on. I shorted anode to cathode, it stayed
turned on when I removed the short. And so on.
After a lot of testing I found out what was going on. What I had fitted
was not an SCR at all, it was a PNP bipolar transistor.
The circuit had the cathode of the SCR conencted ot the -ve rail. A 470
ohm resisotor form gate to cathode. and a load resisotr from anode to the
+ve rail.
The SCR was in a TO5 metal can. So was the transistor I mistakenly
fitted. The cathode conenction (-ve rail) went to the mitter, the gate to
the base and the anode to the collector. Yes, that meant the trnasistor
was the wrong way round, but it still worked poorly. And that 470 ohm was
now between the point acting as a collector and the base. Not sruprisingly
that transistor was aturated.
Once I had fitted a real SCR, it all worked...
-tony