This high voltage circuit was found in a 1970 documentation. The integrated one is of the time and modern equivalents can be tested. The resistors of the voltage reducing system must be calculated.
This circuit using an operational amplifier was found in old American documentation. It can be...
If the circuit oscillates, emitting sound, it is because the transistor is good. This simple...
Like the previous circuit, this is used in the analog part of the telephone lines. The same...