Following the American FCC rules, this 90s Radio Electronics circuit shows how to use a transformer to isolate the telephone line from an amplifier circuit.
The trigger element of this circuit is a neon lamp. The SCR admits an equivalent. We found it in...
This bistable with transconductance operational amplifier was found in early National...
This 1965 circuit consists of a small inverter for an ultraviolet lamp. The circuit is from a...