This Japanese commercial radio with 5 transistors is from the 60s and is powered by 6 V. It is a conventional superheterodyne configuration with good performance.
This circuit monitors extra-low frequency (ELF) fields. We found it in an American documentation from the...
We can use any type of resistive transducer with central resistance in the range of 10 k ohms to 1...
This circuit controls two lamps so that when one increases in brightness the other decreases. The...