1-tube phono amplifier (T1091E)

This negative feedback circuit was found in a 1946 publication. It can be part of amplifier designs, drawing power from them.

Antenna Impedance Bridge (CB4122E)
Found in an American amateur radio documentation by the name of “antennascope” this circuit is...
0 to 200 nA Current Meter (CB5281E)
This circuit was obtained from a 2005 Linear Technology manual. It is based on company components...
Multisensor Alarm (CB6080S)
This circuit is from a 1968 publication. Here we have several types of resistive sensors with...