This circuit activates an old cassette recorder when the phone is being used, thus making it possible to record the conversation. The circuit is from a Hands On Electronics from the 90s.
This amplifier was found in a Japanese publication in 1972. Transistors are uncommon today, and...
The current of this source is 200 mA at the most, and the output depends on the zener that may...
Found in Mallory documentation from 1968 this circuit uses an integrated circuit from that time. The...