This circuit from a Radio Electronics from October 1965 shows how to obtain the action of an SCR when triggering a relay using two transistors. The relay is according to the circuit supply voltage.
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...