Capacitive Relay (T1527E)

Found in Popular Electronics from August 1956 this sensitive two-tube relay is powered directly from the mains power supply.

Symmetric Tracking Type Power Supply 78xx (CB15160E)
This circuit is from the SGS manual of linear integrated circuits of 1982. The L78xx is equivalent to...
Instrumentation amplifier (CB20685E)
This low displacement circuit was found in American documentation from the 90s. Operational...
Liquid Level Control (CB5311E)
The purpose of this circuit is to maintain the liquid level of a reservoir between two values...