TRANSISTOR TESTER - 1
Transistor Tester - 1 project will test all types of transistors including Darlington and power. The circuit is set to test NPN types. To test PNP types, connect the 9v battery around the other way at points A and B.
10mH choke with 150 turns for the secondary
The transformer in the photo is a 10mH choke with 150 turns of 0.01mm wire wound over the 10mH winding. The two original pins (with the red and black leads) go to the primary winding and the fine wires are called the Sec.
Connect the transformer either way in the circuit and if it does not work, reverse either the primary or secondary (but not both).
Almost any transformer will work and any speaker will be suitable.
If you use the speaker transformer described in the Home Made Speaker Transformer article, use one-side of the primary.