Found in a 1980’s documentation, this circuit must have its signal applied to an amplifier stage. The unijunction transistors can be 2N2646.
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...