This sensitive two-transistor circuit was found in the June 1965 Radio Electronics magazine. The circuit has low drift and uses an analog instrument. The input resistance is high.
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...