Based on a PNP Germanium or silicon transistor of any kind, taken advantage of some out-of-the-way device such as an old tape recorder, we can assemble this useful component tester.
As examples of transistors that can be used in this project, we cite the 2SB75, 2SB175, OC71, OC74, AC128, AC188, AC17, AC125, and many others. By consulting the datasheet you should check if the transistor is PNP and if your collector current is at least 50 mA. In figure 1 we have the taster circuit.
The actual appearance of the assembly is shown in figure 2.
Probes can be improvised with large nails or peeled strands. For ease of use we suggest that the unit be mounted in a plastic box.
To use the tester, simply place the test leads on the terminals of the component under test, taking into account their characteristics. If the LED lights up, the component is conducting the current. Remember that not always lack of current indicates a bad component, as in the case of capacitors.
Material list
Q1 - Any germanium PNP transistor
B1- 3 or 6 V - 2 or 4 small batteries
S1 - Single switch
R1 - 10k ohm x 1/8 W- resistor - brown, black, orange
R2- 470 ohm x 1/8 W - resistor - yellow, violet, brown
Miscellaneous: terminal bridge, battery holder, probes, wires, solder, etc.
