This circuit from the 60's uses germanium transistors of the time. Listening is done on high impedance headphones.
This circuit, which uses germanium transistors, is from a 1965 English magazine. The used...
Found in a Popular Electronics from the 90s, this circuit operates up to about 5 MHz input....
The transistors in this circuit can be the BC548 and a small speaker serves as a microphone. The...