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.
The gated oscillator shown here turns on when a “1" Iogic Ievel is applied to the input. The...
Found in Linear Technology documentation, this circuit drains only 70 uA of the monitored circuit....
This good quality audio amplifier with an output of about 10 W with the original transistor was...