This circuit was found in a 90s Popular Electronics. It is used for the acoustic transmitters of 40 kHz, as several found in this section. Transistors support current equivalents.
This directed coupled amplifier uses a transformer to drive a low impedance loudspeaker. This...
Found in a 1980s telecommunications documentation, the circuit presented acts as a product...
This circuit converts infrared pulses into audio and can be used in an experimental telegraphic...