This high input impedance tone control circuit was found in American documentation from the 1980s. Equivalent operational amplifiers and FTEs can be used.
This small crystal microphone transmitter was indicated in an 80s spy book. The range depends on...
The figure shows how to use an operational amplifier with a low impedance head. The gain is...
Voltage comparators, such as those in the LM139/239/339 series, consist of devices that can be...