This interesting sensor for RF signals was found in an article in the June 1989 Radio Electronics magazine. It is a field strength meter with an LED bargraph indicator.
This amplifier is from the Philips Databook of 1990. The circuit is suitable for automotive use...
This is a Japanese commercial radio from the 60s. The circuit is listened to by phone and is...
Found in a 1980s documentation, this amplifier features high common mode rejection. The operating...