We found this circuit in a 1957 Raytheon transistor publication. The circuit can be assembled with more modern transistors with minor changes. The handset must be high impedance magnetic.
We found this circuit in a 1999 publication. All the components used are still common and the...
This circuit was found in a 1999 English magazine, but can be easily assembled with BC548...
We found this circuit in a 1977 technical documentation. The circuit can use a TIP31 for Q1 and a...