"Greg Mayman" bravely wrote to "Roy J. Tellason" (02
Jan 04  08:17:00)
 --- on the heady topic of "*BIG* TRANSISTORS"

 -=> Roy J. Tellason said to Greg Mayman
 -=> about "*BIG* TRANSISTORS" on 12-25-03  04:06.....

 GM> It's time to set up for some DC tests with a power supply and
 GM> resistors, and see if they act like NPN transistors.

 RJT> Don't need a power supply and resistors -- testing with an ohmmeter is
 RJT> quite enough.

 GM> DC tests can show you which is collector and which emiter -- the
 GM> base-emiter usually shows a reverse breakdown of about 6-8 volts,
 GM> the collector-base junction is a lot higher. There aren't many
 GM> ohmmeters that can check these aspects.

 GM> And with DC tests you can measure the current gain of the
 GM> transistor, which you can't do with an ohmmeter...

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

Another was in a batch marked as RF transistors. It had a relatively low
static HFE, and I really couldn't figure out which was the collector or
emitter but the clue was that in most transistors the collector to base
has a slightly higher resistance reading on an ohm-meter. To make things
worse it even had a diode from emitter to collector sort of like the
damper diode built into horizontal output transistors.

 Mike
 ****

... I am Ohm of Borg.  Resistance is V/I...
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