This is the typical audio amplifier for a 1967 television. We found it in a magazine from the time. Note the use of the output transformer and the high supply voltage. The circuit is an RCA CTC21.
This circuit can be connected to the output of alarms or sirens with the 555, CMOS or TTL,...
Found in an American leaflet from the 90s, this circuit uses an AM radio out of station to monitor...
Found in the Encyclopedia of Electronic Circuits Volume 5 of 1995 this circuit has the gain...