This configuration similar to many of this site was found in 1965 General Electric documentation. Modern equivalent transistors can be used. LEDs can be used.
This circuit with transistors and a crystal microphone appeared in Radio Electronics magazine in...
This small auxiliary amplifier was found in a Radio Electronics from May 1958. Power is supplied with...
The circuit uses a fast Norton amplifier in a configuration that excites a 75 ohms line. The...