This circuit from Motorola is from 1968, appearing elsewhere on this site. The transistors admit equivalent and the relay is of the sensitive type for low voltage, according to the power supply.
This circuit is from a Popular Electronics from April 1991. The magazine no longer exists, but the...
We found this circuit in the October 1993 Electronics Now magazine. The 4-channel circuit is...
This amplifier for the experimenter´s bench source 1 W and uses germanium transistors but can be...