This 80's Exar circuit has a carrier detector for frequencies up to 500 kHz. The circuit uses a company 567 which is still a common component.
Found in a European magazine from the 90s, this circuit emits beeps that are several seconds apart to...
The figure shows how to add a Darlington stage to an operational amplifier in order to obtain a...
This amplifier has a few Watt output, using old transistors. The speaker is 45 ohms, but with...