This amplifier is old, from a 1973 publication. It uses germanium transistors and transformers that are no longer easy to obtain. However, the pre-amplification stage can be used with BC558 transistors and the output stage can be replaced by a more modern circuit, with the LM386, for example. Note that the phone must be supported on the coil. With some types of modern phones where the signal is digital, this circuit does not work.
