This sound effect circuit is from a Radio Electronics magazine from December 1969. The transistors support equivalents and the power is provided by a battery to reduce the possibility of noise.
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...