The coils of this circuit will determine the transmission frequency of this device. The circuit is from the 1960 Mullard transistor reference manual and makes use of germanium transistors.
This circuit is from 1977 documentation, but can be assembled with BC548 for Q1, Q2 and Q4, BC558...
Found in American documentation from the 90s, this circuit uses components that are still common...
This high impedance input amplifier is suitable for the use with piezoelectric sources such as...