My setup is simple: a NPN transistor is connected to a DC motor and a battery. The series goes like this: positive terminal - motor - collector; emitter - negative terminal. The transistor base is a loose, long wire.

I would assume that shorting the base and collector would turn the transistor into a diode, allowing current to pass. However, this does not happen. Instead, shorting the base and emitter makes the motor turn. Is it possible that this is not a NPN transistor and some other type instead? Or am I mistaken somewhere else?

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    \$\begingroup\$ What is the part number on your transistor? \$\endgroup\$ – Dave Tweed Apr 4 '13 at 21:24
  • \$\begingroup\$ Easy to tell NPN from PNP (and positively identify the base) with a multimeter. \$\endgroup\$ – Brian Drummond Apr 4 '13 at 22:19
  • \$\begingroup\$ The part number is КТ361Б. I salvaged it from a Soviet alarm clock. Google says that it is, in fact, a PNP. Silly me. \$\endgroup\$ – Moshanator Apr 5 '13 at 7:59

Maybe it's PNP and upside-down (or right way up): -

enter image description here

As soon as you conect the base, the current flows from emitter (or collector) through the base. In other words it's acting like a diode


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