During my previous project, the slayer exciter, I kept blowing transistors trying to pump too much current through them. While I was troubleshooting the circuit, I needed a quick way to test the transistors I was using, so looking around, I found this simple transistor tester circuit using a 555 timer.
The 555 drives the transistor in order to blink the led. If the led is full on or off, then the transistor is dead. There is a 10k pot that will adjust the timer speed so the led will speed up or slow down as an additional verification that the transistor is working.
I built it on a small breadboard to make sure the circuit worked okay.
Everything looked good, so I made it a bit more permanent. I built the circuit out an a piece of perf board and added sockets for easy testing of different transistors.
To make it a bit more portable, I added a 9 volt battery connector.
It has made checking transistors much quicker than before and I would definitely recommend knocking one together for the bench.