This battery-powered 3-valve circuit was found in American documentation from 1947; Two batteries are used, one high voltage and one low voltage for the filaments.
This circuit, from 1999 documentation, prevents the powered device from receiving power when it...
This circuit is intended for monitoring an environment. It fires a relay with a sound, but only if...
Found in a Popular Electronics from the 90's, this circuit uses integrated from that time, today...