This circuit was found in Linear Technology documentation from the 90's. The circuit uses components from that time, and can be powered by 5 V. In these conditions, it can function as a shield.
This circuit was found in a Mullard transistor manual from 1960. Note the symmetrical power...
This amplifier step with a transistor has an input impedance of 100k to 10 M. The transistor can be any...
I found this little signaling transmitter in old American documentation. The circuit has a good...