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.
Using a 4046 PLL this circuit generates rectangular signals in three wavebands that depend on the...
The configuration shown was found in an old Poptronics but can be easily assembled using a common...
This circuit, found in a 1977 documentation, indicates when the grid voltage goes through zero....