Suitable for operation with high impedance microphones, this circuit was found in American documentation from the 90s. The transistor can be any general-purpose type.
This double-beat oscillator was found in American documentation from the 1970s. FETs admit...
This circuit applies to an old dial phone by detecting light pulses in the dial. The circuit is...
This circuit is from 1970 documentation. The SCRs are types of the era that can be replaced with 106...