This circuit was found in a 90’s Popular Electronics. The power transistors must be equipped with radiators and the transformer has a 2 to 5 A secondary.
This circuit was found in a 1987 magazine. It measures monitors the heartbeat through a...
This crystal-controlled circuit was obtained from a 1980s documentation. The power supply should be 5...
This circuit is from 1957 Raytheon documentation. The phone must be high impedance with 600 ohms...