Metal Detector (CB21929E)

This two-transistor metal finder was found in a Raytheon manual from the 1950s. The transistors are germanium from the time.

Notch and Pass Filter LM3900 (CB4041E)
We found this circuit with an operational transconductance amplifier in the Motorola Linear...
XTAL Low Frequency Stable Oscillator (CB14152E)
We found this circuit in the 1994 Linear Applications Handbook by National Semiconductor. The...
LM3900 Differentiator (CB14216E)
In the figure we have a differentiator with the LM3900 transconductance amplifier. The circuit is...