This circuit has a frequency range of 30 Hz to 100 kHz with an output signal of 1 Vrms. We found it in 70s American documentation. The integrated circuits are CA3140.
This receiver with two common JFETs was found in an old English documentation. The phone is...
This TTL circuit with the 7493 makes the binary count of the pulses sent by a flip-flop with the...
This circuit was found in a Popular Electronics from the 90s. The counter circuit is not common...