This circuit was found in the October 1989 issue of Radio Electronics magazine. It drives an auxiliary relay with the call signal for a possible louder bell.
This circuit uses a LM3900 Norton amplifier and a 2.7 V zener diode to supply a current of 1 mA to...
A 0 V signal initiates sampling on this circuit suggested by documentation from the 1970s. The...
This circuit is from an American publication of 1977. The tunnel diode admits equivalents and the...