[Boatanchors] transistor help needed

[Brian Clarke]

Hello Gene,

Here is a simple technique for discovering the connections to small signal 
transistors.

Turn on your trusty Ohmmeter. Measure the resistance between each possible 
pair of wires, swapping the Ohmmeter lead polarity for each pair. The wire 
that shows low resistance when the Ohmmeter leads are connected one way and 
high the other way to the other two wires is the base. If this wire is in 
the middle, you can safely assume the underbody connections are E - B - C. 
If the wires emerge as on a semicircle, then E is at 0900, B is at 1200 and 
C is at 1500. Provided your Ohmmeter does not cause too high a current to 
flow, you can use this same method to test transistors in circuit. With 
four-wire shielded BJTs or dual gate FETs, you need the tag or some other 
sign, eg, a white paint dot - usually the emitter; some four-wire 
transistors have variable spacing between the wires rather than a paint dot 
or a tag.

This method can identify E, B and C connections for power transistors, too - 
but they won't necessarily fall into the E - B - C configuration. In this 
case, if there is a metal heatsink tag [eg, TO-220] or the case is one of 
the connections [eg, TO-3], this is almost always the collector.

73 de Brian, VK2GCE.