Phase selector for remote control (CB9265E)

Found in a 1965 Electronic Design, this circuit makes it possible to select signals with an inverted phase using a relay and a unit gain stage.

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Common collector stage (CB22226E)
This circuit employs an old germanium transistor. The circuit is from a 1950s publication and uses...
5 V zener diode with Transistors (CB20459E)
In the absence of a 5 V zener diode, we can create an equivalent configuration with two...
Operational Multiplier and Divider (CB13812E)
We found this circuit in a publication with experiments with operational amplifiers from 1973. The...