We found this circuit in 1969 American documentation. FETs admit equivalents, as do transistors. The circuit can be used as a shield.
This bridge amplifier for the car was found in an American documentation from the 90's. It can be...
This circuit can be made usng the TIP32 transistor but must use carbon microphone (not very common these...
This circuit is from an article that appeared in the June 1974 issue of Radio Electronics...