This circuit was obtained from an American 1980s documentation. The frequency depends on the crystal and the circuit may be a PNP that reaches the generated frequency.
This circuit uses two Raytheon RC4558 operational amplifiers that are similar to the 741. The...
This audio amplifier circuit is from Ibrape's technical documentation from the 70's. The BC177 can be...
This progressive circuit has a lock allowing coded activation. We found this configuration in...