This circuit was found in Radio Electronics magazine from October 1964. The circuit uses two transistors of the time that require a supply voltage of 9 V. Consumption is 2.5 mA.
This circuit from a Popular Electronics shows how to take the audio signal from a telephone line...
The coil of this transmitter has 4 coils of wire 26 or 28 in the form of 1 cm without core and on it...
In the figure we have another configuration of filter that uses the four Norton amplifiers of the...