Undervoltage detector with the LM3900 (CB25172E)

The figure shows how to implement an undervoltage detector using a Norton amplifier and a zener diode as the main elements.

Instrumentation High Impedance Stage (CB13413E)
We found this circuit in a 1976 documentation. The FET can be the BF245 and the bipolar transistor a...
15-Channel Remote Control Receiver (CB13998E)
This circuit is the receiver for the CB13997E. The transistor can be the BC548. We also found this...
3 to 20 MHz XTAL Oscillator (CB13870E)
We found this oscillator in a publication for radio amateurs from the 70s. The circuit generates...