Low Voltage Test (CB22158E)

This is a simple voltage tester for voltages from about 2V to about 15V with the indicated resistor and red LEDs.

Ohm to volt converter (CB5102E)
We found this circuit in an American 1980s documentation. The operational ones used are not common...
100 Hz Second Order High Pass Filter (CB25815E)
This filter with the 741 op amp was found in the February 1995 Electronics Now magazine. The power...
Tunnel diode delay (CB21431E)
With two cascading tunnel diodes, this circuit found in a 196 General Electric documentation...