As I child, I had this electronic construction kit called Elektronik 1. It was manufactured in former Czechoslovakia, based on resistors, diodes, BJT transistors, capacitors, an LW+SW radio antenna and an earphone. It is quite simple, very good for children like 8 years old. It was originally powered from a 4.5 V battery (3 x 1.5V).
Now I try to recover the kit. I realized that diodes are all dead, some transistors are dead; all the other parts seems to be okay (including all those 30 years old capacitors). The original parts from eastern Europe aren't manufactured anymore, but it was easy to find some similar replacements. But the main question now is: Why those parts were damaged and how to protect them from another damage? When children play with this stuff, they can do many stupid circuits, because they are simply curious what will it do. So please tell me if you have got some tips what can be done there to protect those semiconductors from damages. Or at least a little bit.
The problematic parts are:
- BJT transistors, I use BC546A and BC556A now.
- Rectifier diode, I use 1N5817 now - it has 1 A limit, hopefully it helps.
- Signal sensing diode, I use 1N5711 - this one is very sensitive.
Besides the semiconductor parts, I also want to use AC/DC adapter instead of quite expensive 3R12 type 4.5V battery. Of course, I don't know current limit of the original kit - how many amps do I need to replace a battery? I think 0.2 A could be enough. I now use an old Nokia charger. It is rated 3.6V 0.33A 1.3VA, but it is actually unregulated and gives up to 10 volt without load with audible 50 Hz noise when used for an LF amplifier. I think I will add a large capacitor and LM317LZ to regulate it down to 4.5 volt. I hope that LM317LZ will also act as a safe current limiting device which can possibly also protect the semiconductors from future damages.