Found in a 90s documentation, this circuit makes use of D1, a switching diode that is uncommon today. D3 is an LED. The circuit monitors 12 V batteries.
E) Using a CA3130 this preamp has excellent gain. The power supply does not have to be...
This small experimental transmitter with the CK722 transistors was found in Radio Electronics...
With two cascading tunnel diodes, this circuit found in a 196 General Electric documentation...